Source: UNIVERSITY OF NEVADA submitted to NRP
BIOTIC PROCESSES REGULATING THE CARBON BALANCE OF DESERT ECOSYSTEMS
Sponsoring Institution
State Agricultural Experiment Station
Project Status
COMPLETE
Funding Source
Reporting Frequency
Annual
Accession No.
0187588
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Sep 15, 2000
Project End Date
Sep 14, 2012
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
UNIVERSITY OF NEVADA
(N/A)
RENO,NV 89557
Performing Department
NATURAL RESOURCES & ENVIRONMENTAL SCIENCES
Non Technical Summary
(N/A)
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
20604991060100%
Knowledge Area
206 - Basic Plant Biology;

Subject Of Investigation
0499 - Atmosphere, general/other;

Field Of Science
1060 - Biology (whole systems);
Goals / Objectives
Our overall research program has 3 major objectives:1) study of leaf-to plant-level responses of desert vegetation to elevated atmospheric CO2; 2) study of the ecosystem-level responses; and 3) integration of plant and ecosystem processes to understand carbon balance of deserts.
Project Methods
Determine the effect of elevated CO2 on key phsiological processes that affect primary production in an intact Mojave Deset ecosystem. Determine the effect of elevated CO2 on phenological constraints on primary production in an intact Mojave Desert ecosystem. Determine how elevated CO2 may impact ecosystem water balance, and therefore the water limitation to primary production, in this water-limited system. Determine the effects of elevated CO2 on nitrogen dynamics, including N-fixation, volatization and nitrification rates, and litter decomposition at the NDFF. Determine the effect of elevated CO2 on total belowground respiration in a Mojave Desert ecosystem. Evaluate the impacts of elevated CO2 on plant repoductive patterns in an intact Mojave Desert ecosystem to provide the link between species performance and population reaction to elevated CO2. Assess the impacts of elevated CO2 on fine roots: their occurrence, length, area density, population dynamics and biomass production.

Progress 09/15/00 to 09/14/12

Outputs
OUTPUTS: For additional information, please contact Bob Nowak at 775-784-1656 or nowak@cabnr.unr.edu PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
For additional information, please contact Bob Nowak at 775-784-1656 or nowak@cabnr.unr.edu

Publications

  • No publications reported this period


Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: Summary of activities and actions completed during the last year include: (1) The complete group met at Washington State University in January 2011 to discuss data analysis and manuscript preparation. (2) Derek Sonderegger (Northern Arizona University) has been working closely with Kiona Ogle (Arizona State University) and Dave Evans (Washington State University) on data analyses and modeling. Sonderegger has divided his efforts among three projects corresponding to C and N mass balance of a Mojave Desert ecosystem, effects of elevated atmospheric CO2 on fine root dynamics, and partitioning ecosystem responses to elevated CO2 using stable isotopes. (3) The "fate of C and N" manuscript is in draft form, and the overall carbon budget manuscript is almost complete. (4) Data analyses for the "C turnover" manuscript are nearly complete and an initial draft manuscript has been prepared. (5) The "fine root dynamics" manuscript has been published. In addition, Ogle and Sonderegger used this data set to build a mechanistic Bayesian model of fine root dynamics that incorporates antecedent environmental conditions and feedbacks between root states. Results were presented during an organized oral paper session at the 2010 Annual Meeting of the Ecological Society of America. Modifications were made to the model to incorporate depth-specific effects and to deal with individual, frame-level data (versus using sample means). A manuscript is largely prepared. (6) After much discussion during our September meeting at the University of Nevada Reno, we decided to pool data sets into 3 monographs types of papers: one focused on annuals with Stan Smith & Dene Charlet (University of Nevada Las Vegas) as lead authors, one focused on the temporal dynamic of shoot production over the 10-year study with Beth Newingham (University of Idaho) and Robert Nowak (University of Nevada Reno) as lead authors, and a third focused on detailed analyses of both root and shoot standing crop at the end of the experiments with Newingham and Nowak as lead authors. PARTICIPANTS: Participants in this project include scientists and students from the University of Nevada Reno, University of Nevada Las Vegas, Desert Research Institute, Washington State University, University of Wyoming, University of Idaho, Northern Arizona University, and Arizona State University. TARGET AUDIENCES: Target audiences for this project include scientists interested in global change ecology, scientists interested in desert ecology, and policy makers and land managers concerned about the impacts of global changes on desert ecosystems. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Below we summarize initial results from the NDFF, organized around topics of research: (1) Total ecosystem C and N pools: Final data analysis and modeling were completed in April 2011. Results indicate that significant carbon accumulation has occurred under elevated CO2 and that deserts were a net sink of CO2 during the course of the experiment. Soil carbon is the dominant carbon pool in arid ecosystems and greater carbon content under elevated CO2 is likely due to greater plant production under elevated CO2 during periods of high moisture, and correspondingly greater mortality during drought. Greater root exudation of carbon under elevated CO2 also contributes to the differences between treatments. Results were presented by Dave Evans at the 2011 American Geophysical Union Annual Meeting. (2) Soil C and N pools: Preliminary analysis shows an increased C/N ratio on Larrea leaves under elevated CO2 combined with an increase in δ15N. Analysis of the resin bag data has not shown any treatment effects but there is a strong seasonal component and we are investigating the temporal relationship between the leaf δ15N and resin bags. Carbon isotope ratios are strongly affected by the change in CO2 source and we are examining the length of time necessary to see a significant change after the source change. (3) Belowground biomass, C, and N: Quantifying belowground carbon fluxes and stocks presents one of the greatest challenges to understanding and predicting the terrestrial carbon cycle. Data were analyzed within a Bayesian framework that incorporated a temporally dynamic model of root production, which explicitly included the effects of precipitation history, CO2 level, species identity, depth in the soil, and past root status (e.g. low, medium, or high production / mortality). CO2 treatment interacts significantly with growth "inertia" for each cover class, increasing the magnitude of the high growth and subsequent die-back cycle observed under elevated CO2. These increased inertia effects under elevated CO2 also may be important for sustaining increased assimilation rates for leaves under elevated CO2. (4) Aboveground biomass, C, and N: Our analyses of the extremely large and complex dataset for annual plants are not yet complete, but results indicate that elevated CO2 significantly stimulates plant growth, phenological progression and seed set in annual species, and the exotic grass Bromus rubens is more responsive than are native dicots or grasses, but only in wet winter-spring cycles. Therefore, future projections of how this important community of plants will respond to long-term increases in CO2 will largely be dictated by how precipitation will change in this region in concert with global climate change. For perennial plants, analyses are essentially complete for aboveground biomass for all perennial species harvested at the end of the experiment. Samples were used to calculate standing biomass, biomass allocation, total cover, leaf area index (LAI), carbon to nitrogen ratios and isotopes. Analyses indicate all parameters differed by species; however, only LAI and 13C was affected by elevated CO2.

Publications

  • Ferguson SD, Nowak RS (2011) Transitory effects of elevated atmospheric CO2 on fine root dynamics in an arid ecosystem do not increase long-term soil carbon input from leaf litter. New Phytologist 190:953-967.
  • Jin VL, Schaeffer SM, Ziegler SE, Evans RD (2011) Soil water availability and microsite mediate fungal and bacterial phospholipid fatty acid biomarker abundances in Mojave Desert soils exposed to elevated atmospheric CO2. Journal of Geophysical Research - Biogeosciences doi:10.1029/2010JG001564.
  • Luo Y, Melillo J, Niu S, Beier C, Clark JS, Classen AT, Davidson E, Dukes JS, Evans RD, Field CB, Czimczik CI, Keller M, Kimball BA, Kueppers LM, Norby RJ, Pelini SL, Pendall E, RastetterE , Six J, Smith M, Tjoelker MG, Torn MS (2011) Coordinated approaches to quantify long-term ecosystem dynamics in response to global change. Global Change Biology 17:843-854.
  • Aranjuelo I, Ebbets AL, Evans RD, Tissue DT, Nogues S, van Gestel N, Ebbert V, Adams, WW III, Nowak RS, Smith SD. (2011). Photosynthetic and carbon allocation responses after long-term exposure to elevated [CO2] in two Mojave Desert shrubs. Oecologia 167:339-354.
  • Brinda JC, Fernando C and Stark LR (2011) Ecology of bryophytes in Mojave Desert biological soil crusts: effects of elevated CO2 on sex expression, stress tolerance, and productivity in the moss Syntrichia caninervis Mitt. Pages 169-189 in Tuba Z, Slack N, Stark L (eds.), Bryophyte Ecology and Climate Change. Cambridge University Press.


Progress 01/01/10 to 12/31/10

Outputs
OUTPUTS: Summary of activities and actions completed during the last year: 1. We have pulled together a complete list of data sets, and discussed timelines and goals. Portions of our group had meetings in January 2010 (with appropriate conference calls) to discuss data analysis and outline the mass balance manuscript. Co-PI Evans has also traveled to Laramie to coordinate the modeling and data analysis. 2. Derek Sonderegger, who completed his degree in statistics/modeling, started in our postdoctorate research position in January 2010 and is working closely with Co-PI's Ogle and Evans on data analyses and modeling. 3. We decided to delay preparation of the "fate of C and N" manuscript to focus on the mass balance paper, but analysis of the datasets for this paper is nearly complete. 4. Data analyses for the "C turnover" manuscript is nearly complete and an initial draft manuscript has been prepared. Final manuscript preparation will occur after the "mass balance" manuscript is completed. 5. Data analyses for the "fine root dynamics" manuscript have been completed and a manuscript completed, submitted, and accepted for publication. In addition, Ogle and Sonderegger used this data set to build a simulation model of fine root dynamics, and those results were presented during an organized oral paper session at the 2010 Annual Meeting of the Ecological Society of America. They have also prepared an initial manuscript that describes those results. 6. After much discussion, we decided to break our litter data set into 2 independent manuscripts. The first focuses on nutrient resorption, and this manuscript is nearly complete. Some initial analyses have been completed for the second manuscript that will include the entire 10-year dataset, but additional data analyses need to be completed. 7. The "annuals" data set analyses are almost completed. 8. We moved the "mass balance" manuscript up to high priority because this manuscript is the key synthesis of our experiment. During this process, we identified some areas in our data sets where additional sample analyses were needed and these have been completed. As part of the preparation for this mass balance manuscript, we have also conducted extensive analyses of both the perennial aboveground biomass and root biomass data, with papers presented at the 2010 Annual Meeting of the Ecological Society of America. PARTICIPANTS: Participants in this project include scientists and students from the University of Nevada Reno, University of Nevada Las Vegas, Desert Research Institute, Washington State University, and University of Wyoming. TARGET AUDIENCES: Target audiences for this project include scientists interested in global change ecology, scientists interested in desert ecology, and policy makers and land managers concerned about the impacts of global changes on desert ecosystems. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Summary of preliminary results from the NDFF: 1. Total ecosystem C and N pools: This is the key synthesis of our experiment. Initial results indicate that soil carbon is the dominant carbon pool in arid ecosystems and greater carbon content under elevated CO2 is likely due to greater plant production under elevated CO2 during periods of high moisture, and correspondingly greater mortality during drought. Greater root exudation of carbon under elevated CO2 also contributes to the differences between treatments. 2. Soil C and N pools: A first draft of a manuscript summarizing the data has been completed. However, additional synthesis and modeling efforts are needed to provide a much more informative manuscript. 3. Belowground biomass, C, and N: Results show no significant overall CO2 treatment effect on fine root standing crop, production, loss, turnover, persistence, or depth distribution. Significant treatment effects did occur sporadically for some of these fine root measurements, but differences were transitory and were often in opposite directions during other time periods. Thus, unlike other ecosystems, elevated CO2 does not positively affect fine root dynamics in the Mojave Desert. 4. Aboveground biomass, C, and N: Although our analyses of this extremely large and complex data set on annuals are not yet complete, results indicate that elevated CO2 significantly stimulates plant growth, phenological progression and seed set in annual species, and the exotic grass Bromus rubens is more responsive than are native dicots or grasses, but only in wet winter-spring cycles. Therefore, future projections of how this important community of plants will respond to long-term increases in CO2 will largely be dictated by how precipitation will change in this region in concert with global climate change. Initial results from the final NDFF harvest of all aboveground biomass of all perennial plants in all nine plots indicate CO2 treatments had no effect on total biomass, but individual species had CO2 effects. In addition, total biomass of each species was significantly different, where Larrea comprised nearly 50% of the biomass. A manuscript on foliar nutrient resorption in naturally occurring desert shrubs exposed to CO2 enrichment indicate that nutrient resorption patterns for N were not consistent with respect to CO2 growth environment. While Cu, Mn and Zn all showed some accretion at senescence, resorption of P was extremely proficient in both species, a likely result of low P availability in Mojave Desert soils. The most significant difference appeared to be greater retention of nutrients by these plants in a low rainfall year. The hypothesis that elevated CO2 will result in lower leaf litter quality should not be held as a universal tenet.

Publications

  • Cable JM, Ogle K, Lucas RW, Huxman TE, Loik ME, Smith SD, Tissue DT, Ewers BE, Pendall E, Welker JM, Charlet TN, Cleary M, Griffith A, Nowak RS, Rogers M, Steltzer H, Sullivan PF, van Gestel NC (2011). The temperature responses of soil respiration in deserts: a seven desert synthesis. Biogeochemistry DOI 10.1007/s10533-010-9448-z.
  • Clark NM, Apple ME, Nowak RS (2010) The effects of elevated CO2 on root respiration rates of two Mojave Desert shrubs. Global Change Biology 16:1566-1575.
  • Jin, V.L. and Evans, R.D. 2010. Microbial 13C utilization patterns via stable isotope probing of phospholipid biomarkers in Mojave Desert soils exposed to ambient and elevated atmospheric CO2. Global Change Biology 16:2334-2344.
  • Jin, V.L. and Evans, R.D. 2010. Elevated CO2 increases plant uptake of organic and inorganic N in the desert shrub, Larrea tridentata. Oecologia 163:257-266.


Progress 01/01/09 to 12/31/09

Outputs
OUTPUTS: Our efforts during 2009 on wind-down research and decommissioning of the Nevada Desert FACE Facility (NDFF) primarily involved processing samples, initial data analyses, and site dismantling. In addition, significant progress has been made on dismantling the NDFF this past year. Completed tasks include: FACE rings have been dismantled and components prepared for transport to the NTS landfills. Sensitive equipment has been removed from rings and stored indoors. All soil pits have been closed and leveled. Seed that was collected at NDFF and MGCF from primary plant species was planted within the disturbed ring areas this past winter immediately prior to a series of precipitation events. All micrometeorological data collection has been transferred to the nearby MGCF eddy covariance tower site. All NDFF micrometeorological equipment has been dismantled except for one rain gage. To meet new property removal directives, documentation of specific equipment and material history has been initiated, and a random radiological survey of materials to be removed from the site was recently performed. Several loads of equipment and materials have been processed through NTS Site Monitoring Services on an ad hoc basis and have been transported to the University of Nevada, Las Vegas. The 50-ton CO2 tank was inspected and re-certified for another year. All non-essential experimental infrastructure within the reserve section of the rings was removed to eliminate any potential safety or wildlife hazard. NNSA/NSO has provided verbal approval for all buried lines to remain in place permanently and for all sampling platforms and sheds to remain in the field until final disposition is determined. Facility maintenance was performed as needed to ensure the integrity and safety of sheds and trailers. All NDFF site vehicles that had been acquired from NNSA at the start of the project were transported to Las Vegas and turned over to GSA for auction.   PARTICIPANTS: Participants in this project include scientists and students from the University of Nevada Reno, University of Nevada Las Vegas, Desert Research Institute, Washington State University, and University of Wyoming. TARGET AUDIENCES: Target audiences for this project include scientists interested in global change ecology, scientists interested in desert ecology, and policy makers and land managers concerned about the impacts of global changes on desert ecosystems. PROJECT MODIFICATIONS: No signficant modifications have occurred.

Impacts
Aboveground plant biomass Preliminary ecosystem-based carbon content analysis indicates significantly higher woody biomass accumulation under elevated CO2 in Ambrosia but not in Larrea, no significant CO2 effect on tissue C-contents in either species, and therefore higher landscape-level C content in aboveground biomass in Ambrosia but not in Larrea. Ecosystem-based nitrogen content analysis had similar findings, although in this case leaf tissue %N was reduced at elevated CO2 in Larrea but not in Ambrosia. However, the enhanced biomass effect of Ambrosia woody tissue at elevated CO2 dominated the landscape-N analysis, resulting in more N-storage in aboveground biomass in Ambrosia but not in Larrea. Belowground root biomass Coarse and woody root biomass was significantly different among microsites but the overall CO2 treatment effect was not significant. We also calculated coarse and woody root biomass values for transect excavations that characterized the entire plant community, and again CO2 treatments were not significantly different. Overall, we have little evidence that 10 years of exposure to elevated CO2 results in greater root biomass accumulation in the Mojave Desert. Analyses of seasonal minirhizotron data of fine roots collected from 2003-2007 at the NDFF indicate that distribution of fine roots is seasonally dynamic and differs between microsites, but the treatment main effect is not significant. We also looked at the depth distribution of new roots produced and roots lost between two consecutive sessions and found temporal differences, but no significant treatment or species effects. Root persistence in the soil was not significantly influenced treatment. Soil C and N pools Our objective to investigate soil C and N dynamic under elevated CO2 involved three major questions: (1) Total soil organic C to 1 m soil depth was ca. 10% greater under elevated CO2 with the greatest proportional increase (30%) occurring under plant canopies. Higher organic C was the result of both greater soil C contents under vegetation and higher plant coverage. Greater organic C content under elevated CO2 occurred under all cover types except Pleuraphis. Organic N was greater under elevated CO2 for Ambrosia, Larrea, and Lycium cover types, but total ecosystem soil N was not significantly different between CO2 treatments. (2) Analyses of d13C ratios of bulk soil, soil size and density fractions, and specific compounds were used to investigate the fate of C assimilated under elevated CO2 between 2003 and 2007. Incorporation of the isotopically distinct CO2 was regulated by cover type; differences in d13C were observed only under Larrea and Ambrosia cover types. When present, evidence of carbon incorporation was observed only in surface horizons and overall ecosystem C differences were only 1 ppt. (3) Initial results of bulk soil samples indicate no significant change in d13C over time. In contrast to soils, isotopically labeled C under elevated CO2 in Larrea and litter showed clear C turnover. Overall, C in Larrea live tissues (leaves and wood) has a higher turnover rate than litter, which in turn is greater than that in soil organic matter.

Publications

  • Clark NM, Rillig MC, Nowak RS (2009) Arbuscular mycorrhizal fungal abundance in the Mojave Desert: Seasonal dynamics and impacts of elevated CO2. Journal of Arid Environments 73:834-843.
  • Brinda JC, Fernando C and Stark LR (2009) Ecology of bryophytes in Mojave Desert biological soil crusts: effects of elevated CO2 on sex expression, stress tolerance, and productivity in the moss Syntrichia caninervis Mitt. In Z. Tuba and N. Slack (eds.), Bryophyte Ecology and Climate Change. Cambridge University Press. (in press).
  • Shen W, Jenerette GD, Hui D, Phillips RP, Ren H (2008) Effects of changing precipitation regimes on dryland soil respiration and C pool dynamics at rainfall event, seasonal and interannual scales. Journal of Geophysical Research 113, G03024, doi:10.1029/2008JG000685.


Progress 01/01/08 to 12/31/08

Outputs
OUTPUTS: Progress on wind-down research and decommissioning the Nevada Desert FACE Facility (NDFF): Aboveground plant biomass - Key tasks of aboveground biomass harvests are: 1) Calibrate ten years of production calculations based on biomass regressions. 2) Improve past allometric regression equations. 3) Link canopy spectral properties with area-based production. 4) Coordinate aboveground and belowground biomass harvests for individual plants and thus link processes of C acquisition and storage over the entire plant. 5) Measure tissue [C] and [N] to better define long-term sequestration of fundamental ecosystem pools. Coarse and Woody Roots - We are currently sorting root biomass from target plants to remove roots that are not from the target species to improve our coarse and woody root biomass estimates. Other work that still needs to be completed include determining ash weight of samples, C and N content. Fine roots - Progress has also been made on estimates of fine root biomass. 35% of the fine root samples have been processed and used to make a preliminary regression of root length from minirhizotron images vs. grams of root from soil excavations. Desert soil C dynamics - Total organic and inorganic C content was measured in bulk soils to 1m under six cover types (Ambrosia dumosa, Larrea tridentata, Lycium andersonii, Lycium pallidum, Pleuraphis rigida, and interspace). Rock volume ratio and soil bulk density were measured to calculate total soil C on an area basis. Fate of C under elevated CO2 - Analyses of stable C isotope ratios of bulk soil, soil size and density fractions, and specific compounds were used to investigate the fate of C assimilated under elevated CO2 between 2003 and 2007. Soils were separated into three size fractions and two density fractions. Four classes of compounds were identified with turnover rates ranging from hours to centuries and with different origins. Turnover time of C pools - Analyses of pool size and d13C of bulk soil, soil fractions, and chemical compounds are currently in progress. Soil microfauna - To investigate elevated CO2 effects on soil biota and below-ground herbivores, composite soil samples were collected at 0-0.5 cm and 0-10 cm depths from soil associated with three cover types (shrub, grass, or interspace). N dynamics and soil efflux of reactive N compounds - Since the cessation of the CO2 treatment, major efforts include: (1) soil efflux of reactive N compounds have been monitored; and (2) analyze soil characteristics after ten years of CO2 fumigation. Rapid evolution in Bromus rubens - Long-term global change simulations present a unique opportunity to study contemporary evolution in plants. Our objective was to determine whether red brome (Bromus rubens), an invasive annual grass that is affecting plant community structure in the Mojave desert, is able to evolve over a short ecological time scale in response to global change. NDFF Decommissioning - The first step of the NDFF decommissioning was to provide efficient and cost effective removal and storage of equipment as well as meet National Nuclear Security Administration Nevada Operations site restoration requirements. PARTICIPANTS: Participants in this project include scientists and students from: University of Nevada Las Vegas, Desert Research Institute, Washington State University, US Geological Survey, University of Vermont, Cornell University, and University of California Davis. TARGET AUDIENCES: The target audiences for this project include: scientists interested in global change ecology, scientists interested in desert ecology, and policy makers and land managers concerned about impacts of global changes on desert ecosystems. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Ecosystem C flux - Preliminary results indicate lower NEEs under elevated CO2. Mean daily NEEs were generally positive in both CO2 treatments, indicating net CO2 uptake. Remote Sensing for Whole Plot Assessments - Image analyses being performed include: (1) quantitative assessment of the area harvested; and (2) pre and post multispectral images to assess percent shrub cover. Biological soil crusts - Initial results indicate no significant effect of elevated CO2 on chlorophyll a, UV-protective sunscreen pigments, or quantum yield in S. caninervis, Collema tenax, or the cyanobacteria. There are no biologically significant differences in gross photosynthesis between the two CO2 treatments, although differences at 20% water content indicates less ability to handle drought. Elemental analysis revealed a 20% increase in C content of moss exposed to elevated CO2 but no change in N content. A-ci curves indicated no difference in carboxylation capacity (Vcmax) or maximum rate of electron transport (Jmax). Coarse and Woody Roots - Estimates of root biomass based on transect data (elevated CO2 = 142 g/m2, ambient CO2 = 168 g/m2, non blower control = 151 g/m2) do not support the hypothesis that increased CO2 causes an increase in coarse and woody root biomass. Desert soil C dynamics - Soils in elevated CO2 had greater N content and greater organic C content from 0 to 0.2 m. Values are similar for all variables below 0.2 m. Inorganic C concentration was 10 to 15% lower under elevated CO2. Fate of C under elevated CO2 - C isotope analyses demonstrate incorporation of isotopically labeled C in bulk soils under elevated CO2, but C sink strength was regulated by cover type. Soil microfauna - Total abundance of amoebae, flagellates, ciliates, and nematodes did not differ between elevated and ambient CO2 after ten years of treatment, but the two most striking results observed in soil microfaunal communities were: (1) the interaction between elevated CO2 and cover type for flagellates and depth for ciliates, and (2) the composition of nematode genera between ambient and elevated CO2 plots. N dynamics and soil efflux of reactive N compounds - Significant discoveries include: (1) ~30% of all N losses from this system is through reactive N trace gases and hence significant in terms of the total N budget, and (2) under elevated CO2, the composition of N trace gases changed markedly, with decreased soil NO emission but increased soil ammonia emissions under elevated CO2. Rapid evolution in Bromus rubens - Preliminary results indicate that red brome evolved in response to elevated atmospheric CO2 treatments applied over seven years at the NDFF. NDFF Decommissioning - The first steps of the decommissioning are complete: acquisition of storage containers, organization of storage areas, preparation of the 50-ton CO2 tank for long term empty status, removal of research specific equipment, elimination of materials that will not be used again, repair and maintenance of sheds and other permanent structures, and removal of all field sensors and equipment from the harvested portion of each ring.

Publications

  • Schaeffer, S.M., S.A. Billings and R.D. Evans. 2007. Laboratory incubations reveal potential responses of soil nitrogen cycling to changes in soil C and N availability in Mojave Desert soils exposed to elevated atmospheric CO2. Global Change Biology. 13:854-865.
  • Williams, D.G., R.D. Evans and J.R. Ehleringer. 2007. Applications of stable isotope measurements for early-warning detection of ecological change. In T.E. Dawson and R. Siegwolf (eds), Isotopes as tracers of ecological change.Elsevier Academic Press
  • Smith SD, Charlet TN, Fenstermaker LK, Newingham BA (2008) Effects of global change on Mojave Desert ecosystems. In Webb RH, Andre JM, Fenstermaker LK, Heaton JS, Hughson DL, McDonald EV, Miller DM (eds) The Mojave Desert: Ecosystem Processes and Sustainability. University of Nevada Press, Reno, NV (in press).
  • Smith SD, Tissue DT, Huxman TE, Loik ME (2008) Ecophysiological responses of desert plants to elevated CO2: Environmental determinants and case studies. In De la Barrera E, Smith WK (eds) Perspectives in Biophysical Plant Physiology: A tribute to Park S. Nobel. University of California Press, Los Angeles, CA (in press).
  • Wohlfahrt G, Fenstermaker LF, Arnone III JA (2008) Large annual net ecosystem CO2 uptake of a Mojave Desert ecosystem. Global Change Biology 14:xxx-xxx [available at: http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2486.2008.015 93.x]
  • Evans, R.D. 2007. Soil nitrogen isotope composition. In Michener, R.M. and K. Lajtha, (eds). Stable Isotopes in Ecology and Environmental Science 2nd Edition. Blackwell Scientific, Oxford .
  • Jin, V. and R.D. Evans. 2007. Elevated CO2 affects microbial carbon substrate use and N cycling in Mojave Desert soils. Global Change Biology. 13:1-12.


Progress 01/01/07 to 12/31/07

Outputs
Below is a summary on implementing the wind-down research that precedes decommissioning the Nevada Desert FACE Facility (NDFF). Progress is divided into 2 sections: (1) wind-down research that is funded by TCP; and (2) leveraged research that is funded by other sources. (1) Core, TCP-funded research: (1.a) Aboveground biomass and C harvest protocols were established and implemented for the current field season. Protocols include: (i) detailed allometry and harvests of 15 plants for each of the 8 major species in the ecosystem; and (ii) canopy measurements and corresponding destructive harvest of all perennial plants. We conducted a complete harvest of aboveground biomass for the non-reserve section, which provides an absolute measurement at the end point of the experiment. (1.b) Belowground biomass and C harvest protocols also were established and implemented for the current field season. For belowground systems, a complete harvest analogous to the complete aboveground harvest is not possible. Thus, belowground components of the ecosystem were subsampled. Two techniques were used to estimate belowground biomass and C pools: (i) data collected for specific microsites, then scaled to the whole plot using the canopy coverage data collected during the aboveground harvests; and (ii) systematic sampling throughout the plot to obtain representative data for the plot. (2) Leveraged, externally-funded research: (2.a) An integrated research effort led by Jayne Belnap, USGS, investigated the question "What is the effect of elevated CO2 on biological soil crust cover and function, the composition of soil food webs, and attendant nutrient cycling?" Together, these studies give us mechanisms for any observed differences in the input, retention, and availability of carbon in these soils. (2.b) Jed Sparks, Cornell University and his lab group examined nitrogen cycling. They have three specific research foci: (i) Simultaneous elemental and isotopic assessment of ecosystem pools in terms of nitrogen, (ii) The measurements of gross nitrogen soil fluxes, biological available nitrogen, denitrification and isotopic composition of nitrogen in the soil solution, and (iii) The measurement of the magnitude and isotopic composition of nitrogen trace-gas emissions (N2O, NO, and NH3) following the removal of the elevated CO2 treatment. The results will be fully integrated with the carbon studies ongoing at the site to provide the most complete analysis of carbon and nitrogen cycling in a desert ecosystem under elevated CO2 ever performed. (2.c) Judah Grossman, UC Davis, is investigating if the success of biological invaders like red brome (Bromus rubens) is due, in part, to their ability to evolve rapidly in response to global change (i.e., increasing atmospheric CO2). Preliminary results from their research indicate that red brome populations at the NDFF evolved in response to elevated CO2 treatments applied from 1997-2003. (2.d) Eduardo Robleto, UNLV, and lab will investigate the effects of elevated CO2 on rhizosphere microbial communities for desert plants to determine if elevated CO2 affects the structure of microbial communities in the rhizosphere.

Impacts
Because the NDFF received only ~18 mm of precipitation between Oct 1, 2006 and March 1, 2007, we made a strategic decision to irrigate the entire experiment. About 30 mm of de-ionized water was applied in late March, which brought the soil water content up to ~75% of a normal precipitation year. Plants responded positively to the irrigation, and some additional precipitation events occurred after the irrigation, which continued plant green up. Our decision to irrigate was based on the need for green biomass production, fine root growth, and microbial activity to occur in the current growing season so that the carbon isotope signal could be incorporated into the ecosystem. Following this tracer is critical to accomplishing our goals of quantifying where C is incorporated in the ecosystem and how long that C persists. In addition, the irrigation made it possible for the Net Ecosystem Exchange and biological crust studies to occur. The irrigation treatment provided an excellent opportunity to measure Net Ecosystem Exchange (NEE) and detailed measurements of different biological soil crust respiration under dry and wet conditions.

Publications

  • DeFalco LA, Fernandez GCJ, Nowak RS (2007) Variation in the establishment of a non-native annual grass influences competitive interactions with Mojave Desert perennials. Biological Invasions 9:293-307.
  • Nadeau JA, Quall RG, Nowak RS, Blank RR. (2007). The potential bioavailability of organic C, N, and P through enzyme hydrolysis in soils of the Mojave Desert. Biogeochemistry 52:305-320.
  • Stevenson B, Verburg PSJ (2006) Potential effects of carbonates on soil CO2 efflux in closed-jar incubations. Soil Biology and Biochemistry (in press)
  • Vila M, Corbin JD, Dukes JS, Pino J, Smith SD (2006) Linking plant invasions to environmental global change. Pp 115-124 In Canadell P, Pataki D, Pitelka L (eds) Terrestrial Ecosystems in a Changing World. Springer, Berlin.


Progress 01/01/06 to 12/31/06

Outputs
Increases in atmospheric CO2 concentration during the last 250 years are unequivocal, and CO2 will continue to increase at least for the next several decades. Arid ecosystems are some of the most important biomes globally on a land surface area basis, are increasing in area at an alarming pace, and have a strong coupling with regional climate. These water-limited ecosystems also are predicted to be the most sensitive to elevated CO2, in part because they are stressful environments where plant responses to elevated CO2 may be amplified. To examine responses of arid ecosystems to elevated atmospheric CO2, we established the Nevada Desert FACE (Free Air CO2 Enrichment) Facility in the Mojave Desert of southern Nevada, which is the driest area of North America. Results to date from our research at the Nevada Desert FACE Facility (NDFF) include: (1) Extensive measurements of leaf photosynthesis indicate greater leaf CO2 uptake under elevated CO2 when water availability is high, but only small differences under dry conditions. Thus, Mojave Desert plants have a greater potential to gain C under elevated CO2, especially when precipitation is high. (2) Four independent data sets (aboveground net primary production determined from shoot growth and destructive harvests, litter production, biomass estimated from canopy volume, and canopy spectral characteristics) indicate that the Mojave Desert ecosystem is accumulating aboveground biomass, with greater accumulations under elevated CO2. This CO2 enhancement is greatest when precipitation is high. Other areas in the desert Southwest also show increased cover or biomass over the last few decades. (3) Fine root length measurements show a gradual accumulation of fine roots, regardless of CO2 treatment. During periods of average or low precipitation, slightly lower rates of root loss (mortality and decomposition) under elevated CO2 result in a greater accumulation of fine root length under elevated CO2 through time. However, this relatively greater accumulation of fine roots under elevated CO2 is rapidly lost during periods of high precipitation. Estimates of fine root biomass from the root length data indicate that fine root biomass under elevated CO2 is lower than under ambient CO2, but these calculations use assumptions that need to be quantitatively verified. (4) Net ecosystem exchange (NEE) measurements with a static chamber dome agree very closely with flux tower measurements of NEE in the Mojave Desert. Dome NEE measurements at the NDFF also indicate that the Mojave Desert is accumulating C. However, NEE under elevated CO2 is smaller than NEE under ambient CO2, which suggests that the observed increases in aboveground net primary production under elevated CO2 are overcompensated by increases in ecosystem heterotrophic respiration. (5) Greater soil respiration rates under elevated CO2 help account for the smaller NEE under elevated CO2, but neither the source of C supporting greater soil respiration nor the contribution of soil respiration to heterotrophic respiration are clear.

Impacts
This project will help land managers and ecologists: (1) understand the structure and function of desert ecosystems; (2) how elevated atmospheric atmospheric CO2 will affect the structure and function of desert ecosystems; and (3) provide guidance to land managers and users on actions that will adversely effect deserts in the short- and long-term.

Publications

  • Barker DH, Vanier C, Naumburg E, Charlet TN, Nielsen KM, Newingham BA, Smith SD (2006) Enhanced monsoon precipitation and N deposition affect leaf traits and photosynthesis differently in spring and summer in the desert shrub Larrea tridentata. New Phytologist 169:799-808.
  • Geron, C, Guenther A, Greenberg J, Karl T, and Rasmussen R. 2006. Biogenic volatile organic compound emissions from desert vegetation of the southwestern US. Atmospheric Environment 40:1645-1660.
  • Hartle RT, Fernandez GCJ, Nowak RS (2006) Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs. Journal of Arid Environments 64:586-603.
  • Housman DC, Naumburg E, Huxman TE, Charlet TN, Nowak RS, Smith SD (2006) Increases in desert shrub productivity under elevated CO2 vary with water availability. Ecosystems 9:374-385.
  • Phillips DL, Johnson MG, Tingey DT, Catricala CE, Hoyman TL and Nowak RS (2006) Effects of elevated CO2 on fine root dynamics in a Mojave Desert community: a FACE study. Global Change Biology 12:61-73.


Progress 01/01/05 to 12/31/05

Outputs
Arid ecosystems are predicted to be the most sensitive to elevated CO2, in part because they are stressful environments where plant responses to elevated CO2 may be amplified. Indeed, all C3 species examined at the Nevada Desert FACE Facility (NDFF) have shown increased Anet and WUE under elevated CO2. Furthermore, increased shoot growth for individual species under elevated CO2 was spectacular in a very wet year, although the response in low to average precipitation years has been smaller. Surprisingly, root growth tended to decrease under elevated CO2, and calculations of root biomass for individual species suggest that belowground production may decrease substantially for some species. In addition, our recent measurements of net ecosystem CO2 exchange show 30% lower net ecosystem production under elevated CO2 during an average rainfall year. We suspect that increased respiration from both plants and soil microbes under elevated CO2 may offset increases in Anet and aboveground growth, thus accounting for lower NEP. To form a rigorous understanding of these important component processes, we currently are establishing a multi-faceted, comprehensive approach to quantify NEP and carefully evaluate its component processes in order to create a mechanistic understanding of desert ecosystem carbon balance and its response to elevated CO2.

Impacts
This project will help land managers and ecologists: (1) understand the structure and function of desert ecosystems; (2) how elevated atmospheric atmospheric CO2 will affect the structure and function of desert ecosystems; and (3) provide guidance to land managers and users on actions that will adversely effect deserts in the short- and long-term.

Publications

  • Apple, ME, Thee CI, Smith-Longozo VL, Cogar CR, Wells CE, Nowak RS (2005) Arbuscular mycorrhizal colonization of Larrea tridentata and Ambrosia dumosa roots varies with precipitation and season in the Mojave Desert. Symbiosis (in press).
  • Barker DH, Stark LR, Zimpfer JF, McLetchie DN, Smith SD (2005) Evidence of recent drought-induced stress on biotic crust mosses of the Mojave Desert. Plant, Cell & Environment 28:939-947.
  • Housman DC, Naumburg E, Huxman TE, Charlet TN, Nowak RS, Smith SD (2005) Increases in desert shrub productivity under elevated CO2 vary with seasonal water availability. Ecosystems (in press).
  • Jasoni RL, Smith SD, Arnone JA III (2005) Net ecosystem CO2 exchange in Mojave Desert shrublands during the eighth year of exposure to elevated CO2. Global Change Biology 11:749-756.
  • Vila M, Corbin JD, Dukes JS, Pino J, Smith SD (2005) Linking plant invasions to environmental global change. In Canadell P, Pataki D, Pitelka L (eds) Terrestrial Ecosystems in a Changing World. International Geosphere-Biosphere Synthesis Series, CSIRO, Canberra, Australia (in press).


Progress 01/01/04 to 12/31/04

Outputs
(A) FACE Performance: To further improve the operation of the Nevada Desert FACE Facility (NDFF), we have expanded the local network and added a dedicated server. Three computers form the local network: 1) NDFF control computer that is fully dedicated to controlling the elevated CO2 treatments; 2) a dedicated server that provides on-site data backup, daily reports, daily off-site data backup to Brookhaven National Labs (BNL), and allows remote dial-in access to researchers; and 3) NDRC operations computer that collects and stores the NDFF soil respiration data as well as serves our companion site, the Mojave Global Change Facility. We also updated the NDFF control computer to Windows XP Pro, then installed new FACE control and multiport control programs from BNL. These computer hardware and software changes have improved data backup and transfer, improved remote access and allows access to all on-site computers, and has made the NDFF control computer more stable. As a result, the NDFF control datasets are more complete, with a drop from 79 hours of missing data per year to 12 hours per year. Average CO2 concentration for the elevated CO2 plots during times when the FACE system was operational during January - May 2004 was 550.3 ppm, very close to our target value of 550 ppm. Average CO2 concentration over the entire time period was 509.7 ppm. Average ambient CO2 concentration over this same period was 374.6 ppm. Approximately 800 tons of CO2 have been used to date, with an average use of 7.1 tons per day. We will be posting monthly average FACE performance data on our web site in the near future. (B) System Maintenance: Maintenance and repairs to the following components have been a continuing issue, although the components are replaced or repaired in a timely manner: 1) UV damage to pneumatic lines and the slit-loom that encloses them; 2) MAC valves that stick or leak; 3) pneumatic actuators that leak or fail to turn; 4) rubber tees between the plenum and standpipes that dry out and leak; and 5) leaks in the plenum. (C) NDFF Users and Visitors: During the past year, 4 new projects have been initiated at the NDFF. These new projects include: 1) Arnold Bloom (UC Davis): nitrate assimilation; 2) Kevin Rice (UC Davis): evolutionary changes; 3) Jed Sparks (Cornell University): nitrogen trace gases; and 4) Erika Zavaleta (UC Santa Cruz): evolutionary changes. In addition, the project by BassiriRad has been completed, resulting in a previously reported publication. Visitors to the NDFF include 2 large tour groups plus 17 individuals.

Impacts
This project will help land managers and ecologists: (1) understand the structure and function of desert ecosystems; (2) how elevated atmospheric atmospheric CO2 will affect the structure and function of desert ecosystems; and (3) provide guidance to land managers and users on actions that will adversely effect deserts in the short- and long-term.

Publications

  • Billings S, Schaeffer SM, Evans RD (2004) Soil microbial activity and N availability with elevated CO2 in Mojave Desert soils. Global Biogeochemical Cycles 18 GB1011, 11 p.
  • Ellsworth DS, Reich PB, Naumburg ES, Koch GW, Kubiske ME, Smith SD (2004) Photosynthesis, carboxylation and leaf nitrogen responses of 16 species to elevated pCO2 across four free-air CO2 enrichment (FACE) experiments in forest, grassland and desert. Global Change Biology (in press).
  • Morgan JA, Pataki DE, Korner C, Clark H, Del Grosso SJ, Grunzweig JM, Knapp AK, Mosier AR, Newton PCD, Niklaus PA, Nippert J, Nowak RS, Parton WJ, Polley HW, Shaw MR (2004) Water relations in grassland and desert ecosystems exposed to elevated atmospheric CO2. Oecologia 140:11-25.
  • Nagel JN, Huxman TE, Griffin KL, Smith SD (2004) CO2 enrichment reduces the energetic cost of biomass construction in an invasive desert grass. Ecology 85:100-106.
  • Naumburg E, Loik ME and Smith SD (2004) Photosynthetic responses of Larrea tridentata to seasonal temperature extremes under elevated CO2. New Phytologist 162:323-330.
  • Nowak RS, Ellsworth DS and Smith SD (2004) Tansley Review: Functional responses of plants to elevated atmospheric CO2 - Do photosynthetic and productivity data from FACE experiments support early predictions? New Phytologist 162:253-280.
  • Nowak RS, Zitzer SF, Babcock D, Smith-Longozo V, Charlet TN, Coleman JS, Seemann JR and Smith SD (2004) Elevated atmospheric CO2 does not conserve soil water in the Mojave Desert. Ecology 85:93-99.


Progress 01/01/03 to 12/31/03

Outputs
(1)FACE Performance: For the first 10 months of 2003, the FACE fumigation system operated 87% of the time with an average CO2 concentration of 527 ppm. Daily CO2 usage averaged 7 tons per day. Of greater interest is FACE performance during time periods of potential biological activity, i.e. an air temperature > 4 C. These operations statistics (fumigation for >96% of the time and a CO2 concentration of 543 ppm) are similar to values in previous years. To improve system operations and efficiency, we have made a series of improvements to the FACE system. Extensive multi-port performance tests indicated that we could reset CO2 injections from 1.2 m in height to 1.0 m while still maintaining effective CO2 control to a height of 1.2 m, which resulted in CO2 savings of approximately 16%. Additional savings occurred from: 1) changing the pure CO2 injection point from the leaky blower housing to just downstream of the blower; 2) reset the risers so that they are equidistant from each other; and 3) daily maintenance checks to plug leaks in the plenum, etc. Finally, we have installed an extensive surge-suppression system at the NDFF, which we believe has reduced unscheduled shutdowns due to lightening strikes and other power surges. (2) Facility Use: Currently, 11 different projects are in progress at the NDFF. These projects are focused on nutrient dynamics, net ecosystem exchange of CO2 and water, above- and below-ground physiology and productivity, and biological crust ecology, which in turn are integrated into modeling studies. In addition, 2 projects are focused on remote sensing techniques to assess responses of deserts to global changes. These projects involve 13 PI's/Co-PI's, 5 postdoctorates, 3 Ph.D. students, 7 MS students, 9 undergraduate students, and 6 staff scientists. (3) Data Management: To date, 66 data sets are being prepared for archive by the NDFF. Of these, the micrometeorology and site performance data sets have been released and can be downloaded from http://www.unlv.edu/Climate_Change_Research/Data_Bases/data_index.htm . Efforts this year have focused on helping researchers generate analysis-ready data in order to accelerate the process from data acquisition to publication to data release. The data manager has worked extensively with key data sets to automate many of the labor intensive and error-prone steps in data processing and quality checking. This has resulted in expediting several manuscripts and bringing the concomitant data into near-ready status for data release. The next year will focus on quality assurance and documenting the metadata needed for long-term archival and release of the data sets. (4)Publications: A total of 10 publications on research at the NDFF have been published during 2003 with an additional 5 that are already in press or accepted for 2004.

Impacts
This project will help land managers and ecologists: (1) understand the structure and function of desert ecosystems; (2) how elevated atmospheric atmospheric CO2 will affect the structure and function of desert ecosystems; and (3) provide guidance to land managers and users on actions that will adversely effect deserts in the short- and long-term.

Publications

  • BassiriRad H, Constable JVH, Lussenhop J, Kimball BA, Norby RJ, Oechel WC, Reich PB, Schlesinger WH, Zitzer S, Sehtiya HL, Silim S (2003) Widespread foliage d15N depletion under elevated CO2: inferences for the nitrogen cycle. Global Change Biology 9:1582-1590.
  • Billings S, Schaeffer SM, Evans RD (2003) Nitrogen fixation by biological soil crusts and heterotrophic bacteria in an intact Mojave Desert ecosystem with elevated CO2 and added soil carbon. Soil Biology and Biochemistry, 35:643-649.
  • Billings SA Zitzer SF Weatherley H, Schaeffer SM, Charlet T, Arnone JA Evans RD (2003) Effects of elevated carbon dioxide on green leaf tissue and leaf litter quality in an intact Mojave Desert ecosystem. Global Change Biology 9:729-735.
  • DeFalco LA, Bryla DR, Smith-Longozo V, and Nowak RS (2003) Are Mojave Desert annual species equal? Resource acquisition and allocation for the invasive grass Bromus madritensis subsp. Rubens (Poaceae) and two native species. American Journal of Botany 90(7):1045-1053.
  • Housman, DC, Zitzer SF, Huxman TE, Smith SD (2003) Functional ecology of shrub seedlings after a natural recruitment event at the Nevada Desert FACE Facility. Global Change Biology, 9:718-728.
  • Naumburg E, Housman DC, Huxman TE, Charlet TN, Loik ME, Smith SD (2003) Photosynthetic respones of Mojave Desrt shrubs to Free Air CO2 Enrichment are greatest during wet years. Global Change Biology 9:276-285.
  • Pataki DE, Ellsworth DE, Evans RD, Gonzalez-Meler M, King J, Leavitt SW, Lin G, Matamala R, Pendall E, Siegwolf R, van Kessel C, Ehleringer JR (2003) Tracing changes in ecosystem function under elevated carbon dioxide conditions. BioScience 53:805-818.
  • Reid CD, Maherali H, Johnson HB, Smith SD, Wullschleger SD and Jackson RB (2003) On the relationship between stomatal characters and atmospheric CO2. Geophysical Research Letters 30(19):1-1:1-4.
  • Schaeffer SM, Billings SA, Evans RD (2003) Responses of soil nitrogen dynamics in a Mojave Desert ecosystem to manipulations in soil carbon and nitrogen availability. Oecologia 134:547-553.
  • Weatherly HE, Zitzer SF, Coleman JS, Arnone JA III (2003) In situ litter decomposition and litter quality in a Mojave Desert ecosystem: effects of elevated CO2 and interannual climate variability. Global Change Biology 9:1223-1233.


Progress 01/01/02 to 12/31/02

Outputs
Results from our work at the Nevada Desert FACE Facility (NDFF) provide significant insight into the complex responses of an intact desert ecosystem to elevated CO2. Some key initial results include: 1) Elevated CO2 increases dominance of an exotic annual grass. This could alter the ecology of the Mojave Desert by causing an increase in fire frequency and intensity. 2) The increase in primary production in response to elevated CO2 is greater than that observed in any other ecosystem. However, the magnitude of this increase is strongly and positively related to rainfall inputs to the system. 3) We predicted that reduced transpiration rates at elevated CO2 would result in greater water storage. Reduced stomatal conductance and transpiration have been observed, but soil moisture has not been conserved under elevated CO2. 4) Elevated CO2 has decreased plant-available N and increased gaseous N loss. Isotopic evidence points to altered patterns of microbial activity and plant N acquisition.

Impacts
Deserts are predicted to be the most responsive of all terrestrial ecosystems to global change. Research funded by this grant will test all aspects of this hypothesis.

Publications

  • Billings S, Schaeffer SM, Zitzer S, Charlet T, Smith SD, Evans RD (2002) Alterations of nitrogen dynamics under elevated CO2 in an intact Mojave Desert ecosystem: evidence from d15N. Oecologia 131:463-467.
  • Hamerlynck EP, Huxman TE, Charlet TN, and Smith SD (2002) Effects of elevated CO2 (FACE) on the functional ecology of the drought-deciduous Mojave Desert shrub, Lycium andersonii. Environmental and Experimental Botany 48:93-106.


Progress 01/01/01 to 12/31/01

Outputs
Although the magnitude of the response varies among species, most plants have shown increased biomass production, increased photosynthesis, and decreased stomatal conductance under FACE (Free Air CO2 Enrichment) conditions with an atmospheric CO2 concentration of 550 ppm in an El Nino precipitation year. Under drought conditions, the responses are greatly reduced. The CO2 response of the invasive annual grass Bromus madritensis spp. rubens was especially striking under field conditions. Unlike the aboveground responses of Mojave Desert plants to increased atmospheric CO2 concentration, root responses are generally not significant or transient. For example, root growth under elevated CO2 was initially increased for Larrea tridentata, but root growth for plants under ambient conditions eventually matched that under elevated CO2. Few ecophysiological differences were noted in a detailed greenhouse study, but root growth of a C3 bunchgrass Achnatherum hymenoides was significantly increased under elevated CO2. In contrast, soil respiration was almost doubled by the elevated CO2 treatment.

Impacts
Deserts are predicted to be the most responsive of all terrestrial ecosystems to global change. Research funded by this grant will test all aspects of this hypothesis.

Publications

  • Huxman TE, Hamerlynck EP, Loik ME, Smith SD (1998) Gas exchange and chlorophyll fluorescence responses of three southwestern Yucca species to elevated CO2 and high temperature. Plant, Cell & Environment 21: 1275-1283
  • Huxman TE, Hamerlynck EP, Moore Bd, Smith SD, Jordan DN, Zitzer SF, Nowak RS, Coleman JS, Seemann JR (1998) Photosynthetic down-regulation in Larrea tridentata exposed to elevated atmospheric CO2: Interaction with drought under glasshouse and field (FACE) exposure. Plant, Cell & Environment 21: 1153-1161
  • Smith SD, Huxman TE, Zitzer SF, Charlet TN, Housman DC, Coleman JS, Fenstermaker LK, Seemann JR, Nowak RS (2000) Elevated CO2 increases productivity and invasive species sucess in an arid ecosystem. Nature 408:79-82
  • Evans RD, Lange OL (2001). Biological soil crusts and ecosystem nitrogen and carbon dynamics. In: J. Belnap and O.L. Lange, eds. Biological Soil Crusts: Structure, Function and Management. Ecological Studies Series, Springer Verlag, New York.
  • Evans RD, Belnap J, Garcia-Pichel F, Phillips S (2001). Global change and the future of biological soil crusts. In: J. Belnap and O.L.Lange, eds. Biological Soil Crusts: Structure, Function and Management. Ecological Studies Series, Springer Verlag, New York.
  • Evans RD (2001). Mechanisms controlling plant nitrogen isotope composition. Solicited review. Trends in Plant Sciences 6:121-126.
  • Huxman TE, Smith SD (2001). Photosynthesis in an invasive grass and native forb at elevated CO2 during an El Nino year in the Mojave Desert. Oecologia (in press)
  • Huxman TE, Charlet TN, Grant C, Smith SD (2001). The effects of parental CO2 and offspring nutrient environment on initial growth and photosynthesis in an annual grass. International Journal of Plant Science (in press)
  • Nowak RS, Jordan DN, DeFalco LA, Wilcox CS, Coleman JS, Seemann JR, Smith SD (2001). Effects of elevated atmospheric CO2 on leaf conductance and temperature for three desert perennials at the Nevada Desert FACE Facility. New Phytologist (in press)
  • Hamerlynck EP, Huxman TE, Loik ME, Smith SD (2000). Effects of extreme high temperature, drought and elevated CO2 on photosynthesis of the Mojave Desert evergreen shrub, Larrea tridentata. Plant Ecology 148 (2): 185-195
  • Hamerlynck EP, Huxman TE, Nowak RS, Redar S, Loik ME, Jordan DN, Zitzer SF, Coleman JS,Seemann JR, Smith DS (2000). Photosynthetic responses of Larrea tridentata to a step-increase in atmospheric CO2 at the Nevada Desert FACE Facility. Journal of Arid Environments 44:425-436
  • Loik ME, Huxman TE, Hamerlynck EP, Smith SD (2000) Low temperature tolerance and cold acclimation for seedlings of three Mojave Desert Yucca species exposed to elevated CO2. Journal of Arid Environments 46:43-56
  • Pataki DE, Huxman TE, Jordan DN, Zitzer SF, Coleman JS, Smith SD, Nowak RS, Seemann JR (2000) Water use of two Mojave Desert shrubs under elevated CO2. Global Change Biology 6:889-898
  • Phillips DL, Johnson MG, Tingey DT, Biggart C, Nowak RS, Newsom JC (2000) Minirhizotron Installation in Sandy, Rocky Soils with Minimal Soil Disturbance. Soil Science Society of America Journal 64:761-764
  • Taub DR, Seemann JR, Coleman JS (2000) Growth in elevated CO2 protects against high-temperature damage. Plant, Cell and Environment 23:649-656
  • Yoder C , Vivin P, DeFalco LA, Seemann JR, Nowak RS (2000) Root growth and function of three Mojave Desert grasses in response to elevated atmospheric CO2 concentration. New Phytologist 145: 245-256
  • Huxman KA, Smith SD, Neuman DS (1999) Root hydraulic conductivity of Larrea tridentata and Helianthus annus under elevated CO2. Plant, Cell, & Environment 22: 325-330
  • Huxman TE, Hamerlynck EP, Smith SD (2000) Reproductive allocation and seed production in Bromus madritensis ssp. rubens at elevated atmospheric CO2. Functional Ecology 13:769-777
  • Jordan DN, Zitzer SF, Hendrey GR, Lewin KF, Nagy J, Nowak RS, Smith SD, Coleman JS, Seemann JR (1999) Biotic, Abiotic and Performance Aspects of the Nevada Desert Free-Air CO2 Enrichment (FACE) Facility. Global Change Biology 5: 659-668
  • Smith SD, Jordan DN, Hamerlynck EP (1999) Effects of elevated CO2 and temperature stress on ecosystem processes. Pages 107-137 in Luo Y, Mooney HA (eds) Carbon Dioxide and Environmental Stress. Academic Press, San Diego
  • Huxman TE, Hamerlynck EP, Jordan DN, Salsman KJ, Smith SD (1998) The effects of parental CO2 environment on seed quality and subsequent seedling performance in Bromus rubens. Oecologia 114: 202-208.


Progress 01/01/00 to 12/31/00

Outputs
We have established the Nevada Desert FACE (Free Air CO2 Enrichment) Facility (NDFF) in the most arid region of North America to investigate the effects of increasing atmospheric CO2 on an intact Mojave Desert ecosystem. In continuous operation since April 1997, our results to date have shown productivity increases in wet years that greatly exceeded modeled predictions. For example, growth of the dominant shrub Larrea tridentata was doubled and primary production of annuals increased by 50% with an increase in atmospheric CO2 to 550 micromol mol-1. Although the productivity of native species was greatly enhanced by elevated CO2, productivity and seed rain of an invasive annual Bromus was increased even more, suggesting that elevated CO2 could enhance the long-term success and dominance of this exotic species. This global-change driven shift in species composition, coupled with an observed increase in temporal and spatial variation of production, has the potential to degrade biodiversity and ecosystem functions in the Mojave Desert. This conversion of desert shrublands to annual grasslands would, in turn, likely alter biotic processes regulating the carbon balance of desert ecosystems. The primary goal of this proposal is to continue funding the overall operations of the NDFF. Our current research grants provide most of the resources to collect and analyze data, but we do not have funds for CO2, system maintenance, and personnel needed to run the experiment. The NDFF has been scientifically productive, with 16 journal publications and 13 grants and contracts to date directly attributable to it, and almost 70 scientists at all levels of training have participated in the research at the NDFF. Thus, the impact of the NDFF on knowledge and education has been very large, and continuous operation of the site is critical to understand global change impacts on desert ecosystems. Our overall research program has 3 major objectives: 1) study of leaf- to plant-level responses of desert vegetation to elevated atmospheric CO2; 2) study of the ecosystem-level responses; and 3) integration of plant and ecosystem processes to understand carbon balance of deserts. We focus on the seminal interactions among atmospheric CO2, water, and nitrogen that likely drive desert responses to elevated CO2 and explicitly address processes that occur across scales (biological, spatial, and temporal). We also complement the studies at the NDFF with a field experiment designed to investigate other global changes of altered precipitation patterns and altered nitrogen inputs. Together, these studies provide the most comprehensive understanding, and thus predictive power, of how biotic processes regulate the carbon balance of desert ecosystems.

Impacts
Deserts are predicted to be the most responsive of all terrestrial ecosystems to global change. Research funded by this grant will test all aspects of this hypothesis.

Publications

  • No publications reported this period