PRECIPITATION INTENSITY EFFECTS ON DRYLAND WHEAT AND SAFFLOWER VARIETIES

• Sponsoring Institution: State Agricultural Experiment Station
• Project Status: COMPLETE
• Funding Source: STATE
• Reporting Frequency: Annual
• Accession No.: 1016480
• Project Start Date: Jul 1, 2018
• Project End Date: Jun 30, 2023
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UTAH STATE UNIVERSITY
(N/A)
LOGAN,UT 84322

Performing Department
Wildland Resources

Non Technical Summary
With each degree Celsius increase in temperature, air holds roughly seven percent more water vapor. A consequence of this physical process is that as the air warms, precipitation events become fewer, but larger. This effect has been observed over the past 100 years in many parts of the world including northern Utah. Changes in precipitation intensity are particularly important in semi-arid systems where plant productivity can double in wet years. Many experiments have tested the effects of increasing or decreasing total precipitation, but relatively little is known about the effects of increasing precipitation intensity. The few studies that have examined the effects of precipitation intensity have produced variable results. In some cases, intense events can increase plant productivity by increasing water infiltration into the soil. In other cases, intense events can decrease plant productivity by increasing runoff. Experiments are needed to better parameterize models of water flow and plant productivity under various climate conditions to determine when increased precipitation intensity will increase plant productivity and when it will decrease plant productivity. Results from two current studies in northern Utah highlight this need. One experiment in a rangeland site increased soil water infiltration and shrub growth, while another experiment in a dryland agricultural site increased soil water infiltration but decreased winter wheat growth. The fact that some species in the area increased growth under increased precipitation intensity, while other species decreased growth, suggests that it may be possible to identify dryland crop varieties that respond positively rather than negatively to observed and anticipated precipitation patterns. Here we propose to test the effects of increased precipitation intensity on three varieties of winter wheat and two varieties of safflower to identify plant varieties that can best convert large precipitation events into crop production. Experimental results will be used to parameterize and test predictions of an ecohydrological model that can be used to predict how different crop varieties are likely to respond to anticipated climate conditions.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0199	1070	100%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0199 - Soil and land, general;

Field Of Science
1070 - Ecology;

Keywords

winter wheat

safflower

ecohydrology

precipitation intensity

Goals / Objectives
The overarching goal of the proposed research is to determine how increases in precipitation intensity are likely to affect dryland crop production in northern Utah. In pursuing this objective, we expect to identify crop traits that are likely to improve dryland crop production in the future. The more specific objective is to measure the response of three winter wheat and two safflower varieties to precipitation intensity levels anticipated to occur with -1, 0, 1, 2, 3, 5 and 10° C warming. Results from these experiments will be used to parameterize and test predictions of ecohydrological models of water and energy flow and plant production (i.e., Hydrus 1D; Fig. 6). Rather than attempt to replicate climate conditions that are currently predicted for the study site (e.g., wetter winters, drier summers and higher temperatures throughout the year; Gillies et al. 2012), our goal is to test a wide range of precipitation event sizes on water and energy flows and plant productivity. This data will allow us to parameterize a model that can then be used to explore the effects of different seasonal effects or temperature changes on plant growth and water cycling.Climate and plant growth data in experimental plots will be used to parameterize and test ecohydrological models that can then be used to predict the consequences of a wide range of climate conditions on plant growth. The goal of this research is not necessarily to replicate anticipated climate conditions for this area, but to parameterize and test an ecohydrological model that can be used to predict plant growth responses to a wide range of potential climate conditions. More specifically, we are interested in isolating and testing the effects of precipitation intensity. To accomplish this goal we propose to manipulate only precipitation intensity. So that model simulations can provide inference across a wide range of conditions precipitation intensity will be manipulated across a wide range of values (i.e., associated with increasing atmospheric temperatures of -1 to +10° C). By performing these experiments over several years, and across a range of treatment levels, our experiments will allow us to parameterize and test an ecohydrological model across a wide range of conditions (i.e., wet Fall, dry Fall, intense summer precipitation, less intense summer precipitation). So while constraining treatments to conditions predicted for the local site may provide better inference to our study site, this same approach is likely to limit our inference to conditions at our site. By using a wide range of treatments, applied over several years and using this data to parameterize and test an ecoydrological model, we expect to provide broad inference to the effects of a wider range of potential climate scenarios that may be applicable not only to Cache Valley, but also to ecosystems around the Intermountain West.Objectives will be addressed by answering the following questions:1) How does precipitation intensity affect water cycling and dryland forage production in Cache Valley, Utah?2) How do common dryland crop roots respond to increased precipitation intensity?3) How do common dryland crops adjust gas exchange in response to precipitation intensity?

Project Methods
Broadly, this research will use experimental roofs to collect rain and snow and re-deposit collected precipitation as relatively large, intense events. Treatments collect and redeposit rain at a rate of roughly 1 cm in 10 minutes. Precipitation data collected every 15 minutes on the USU campus over the past 45 years suggests that this rate occurred in 14 of 7375 observed time periods with precipitation (i.e., treatments create 'intense' precipitation events). It is likely that natural events may be more intense over very short time periods than our drip irrigation lines. These very short, intense events are more likely to disturb the soil surface, but are unlikely to produce different infiltration rates except on very steep slopes. In short, treatments redistribute ambient precipitation as fewer, larger events that are very intense relative to historical precipitation recorded in 15-minute intervals.The experimental design will generally follow that of Kulmatiski and Beard (2013) with several important improvements. Control shelters will be used that immediately redeposit collected precipitation. This will allow a test of shelter artifacts. Second, both rain and snow events will be manipulated. Third, rather than comparing plant and soil water responses in one set of treated plots and one set of control plots, a combined ANOVA / regression experimental design will be used. This combined approach will provide inference to a broader range of precipitation intensity conditions. This approach has been recommended because it produces data that is needed by large-scale biosphere-atmosphere models (Smith et al. 2014). Finally, 100% roofing will be used allowing better control of precipitation patterns.Study Site: Our dryland agriculture site is at the Emily Godfrey Fonnesbeck Research Farm in Clarkston, UT (41° 53' 44" N; 112° 2' 39" W; elevation 1485 m). The area has mean annual precipitation of 44 cm (including 45 cm of snow) and mean monthly temperatures from -3.7 °C in January to 23.6 °C in July. The plots and surrounding area are in a crop rotation consisting of alternating years of winter wheat and fallow. The area was historically a shrub steppe ecosystem.Experimental Design: Precipitation manipulations will be achieved using 11, 2.1 m x 2.5 m x 2 m (w x l x h) shelters and three shelter-free control plots. Treatments began spring 2016. Rainwater from roofs is collected in holding tanks adjacent to the plots. For the three sheltered-control plots, water from the tanks is routed onto the plot passively through gravity-fed drip irrigation lines immediately as it is collected. For treatments associated with roughly -1, 1, 2, 3, 5 and 10 °C increases in atmospheric temperature, water is held in the tanks until there was enough water to create 2, 3, 5, 9, and 21 mm rain events at which point floating outlets or 'flouts' in the tanks sink and allow the water to run onto the plots via drip irrigation lines. There are three replicates of the 0 and 3 °C treatments. Remaining treatments have one replicate each. Treatment levels represent a 7% increase in average precipitation event sizes for each 1 °C of warming. For example, if average precipitation event sizes were 10 mm a 1°C treatment would receive precipitation events with an average size of 10.7mm. The -1°C treatments are achieved by routing water from the tanks back onto the plot between rain events, thereby creating additional small (~1 mm) "rain events." To be clear, all plots receive the same total amount of precipitation. As with the rainfall manipulations, snowfall manipulations are used to create fewer, larger precipitation events. Snow treatments are applied by shoveling collected snow 9, 8, 7, 6, 5, 4, and 2 times during the growing season. These snow addition frequencies are roughly based on historical data (1928-2014) of snow events >4 cm. When historical snow event sizes are increased by 7% for each 1 °C of anticipated warming (removing the smallest events so that the yearly totals remains unchanged) then there is a median of 13, 11, 10, 8, 7 and 4 events per year for increases of 0 °C (unchanged), 1 °C, 2 °C, 3 °C, 5 °C and 10 °C, respectively. We used fewer snow additions than this because snow treatments were not applied for the entire winter. As with rain the -1 °C treatment increased the frequency of snow events.Crop plantings will follow the schedule designed by the farm manager. Plots will be seeded at a rate of roughly 125 kg/ha with a row spacing of 15 cm, using a plot seed planting drill. Wheat will be harvested late July each growing season. Herbicide (Roundup PowerMax) will be used once each spring for weed suppression. Safflower will be planted in the Fall of 2019 and 2021.Soil moisture will be measured roughly biweekly during the growing season at six depths in each plot (time domain reflectrometry; Sentek Sensors, Stepney Australia). Hourly measurements of soil water potential (Campbell Scientific 229 heat dissipation sensors; Logan, UT, USA) will be taken at one sheltered-control plot and one 3 °C treatment plot.At the end of each growing season, the target crop will be harvested from a 1 m x 1 m subplot at plot. Wet biomass will be recorded and seed will be collected using a stationary thresher, and wet and dried seed mass measured (oven dried to constant weight at 60 °C). Total crop mass from the remaining plot will be harvested and weighed wet and dry. Wet and dry weed biomass (primarily Lactuca serriola) will also be measured for each plot. Mean plant height will also be recorded prior to harvest. Additional within-season measures of growth will include leaf area index (LAI; AccuPAR LP-80, Meter Group, Inc. Pullman, WA), normalized difference vegetation index measurements (NDVI; Spectral reflectance sensor for NDVI, Meter Group, Inc. Pullman, WA), photochemical reflectance index (PRI; spectral reflectance sensor for PRI, Meter Group, Inc. Pullman, WA), and canopy temperature (infrared radiometer SI-421, Apogee Instruments, Logan, UT).Root growth will be measured using one root observation chamber in each plot (Bartz Technology Co, Carpenteria, CA) and two soil cores (0-15cm) will be taken from each plot during peak growing season.Regressions of above and belowground and seed biomass as a function of treatment (i.e., Fig. 4) will be conducted. The repeated measures data (LAI, NDVI etc.) will be analyzed use a mixed effects model with fixed effects of treatment and time and random effect of plot ("lmer" function in the lme4 package; Bates et al. 2015). Due to the hybrid experimental design, regression analyses, as described above, will be conducted using all treatment levels and mixed models will be run using just the treatments with replicated plots (shelter-less control, sheltered control, and 3°C treatment). Statistical analysis will be done using R (R Core Team 2017).Additional analyses will be performed using the Hydrus 1D model (Šim?nek et al. 1999). This model describes water movement through the soil profile and through plant tissues. Environmental parameters needed by this model (i.e. temperature, relative humidity, precipitation, wind speed and light intensity) will be obtained from a nearby meteorological station and we have soil texture data. Root profiles will be determined from rhizotron samples. LAI will be measured directly as described above. Soil moisture data collected during the experiment will be used to validate Hydrus predictions of soil moisture content (and thus ecohydrological consequences of fewer, larger precipitation events).

Progress 07/01/18 to 06/30/23

Outputs
Target Audience:Extension agents. Dryland wheat farmers. Ecologists, ecohydrologists, rangeland managers. Changes/Problems:Establishing new field sites has become increasingly difficult. Establishing new climate shelters is expected to require a 1-2 year long permitting process on BLM lands in southern Utah. Fortunately, it appears that tracer sampling will require only a 'free-use' permit that is likely to be granted within a couple of months. Graduate students are becoming much more expensive due to inflation, health insurance, and tuition increases. What opportunities for training and professional development has the project provided?A PhD student graduated May 2022. Many undergraduates (Ximena Fuller, Devin Pancake, Cristina Chirvasa, Jacob Pullen, Keslee Green, Dakota Green, Tori Brummer, Finn Christenson, Stephanie Hall, Maria Catalana, Laura Beck, Emily Wilde, Ryan Sandfort, Krishaunna Riggs, Ben Eissler) and graduate students (Julia Aaronson, Ryan Choi, Leslie Forero, Daniella Thiemann) have been involved with this project. Students have gained experience doing field and greenhouse research, stable isotope injections, extractions and analyses, data management and analyses and had the opportunity to work on related projects of their interest including a project that examines the role of silicon on medusahead growth and control, a project that tests subpopulations of common forbs around the western as potential restoration species, and a globally distributed experiment testing the effects of soil disturbance and nutrient deposition on forage production and weed invasion. Between 2018 and 2020, we hosted two Native American students each summer to visit the field site and learn about our research. How have the results been disseminated to communities of interest?Public media: 1) Results from this research were reported at KUER (How a future with less frequent, more intense rain could change Utah's plant landscape KUER ) 2) Results from this research were reported at Utah State Today (Thirsty Roots: Identifying Plant Winners, Losers Under Changing Climate (usu.edu)) University presentations and academic conferences: 1) Holdrege, M.C.,Beard, K.H., Kulmatiski, A. Responses of sagebrush-dominated ecosystems to increased precipitation intensity. Ecological Society of America Meeting, August 2021. 2) Invited to speak about this research at the Cornell Biogeochemistry, Environenmental Science, and Sustainability lecture series (2021). 3) Kulmatiski, A.A new generation of root-based restoration. Society for Ecological Restoration, Great Basin Chapter. May 2021. Invited contribution. 4)Kulmatiski, A. Wildland Stories: Soil Science with Dr. Andrew Kulmatiski. Monthly webinar series. May 2021. Invited contribution. 5) Kulmatiski, A. How plant roots determine plant growth and coexistence: plant-soil feedbacks and resource uptake. University of Granada, Spain. April 2019. 6) Results from this research have been presented to students in USU WILD 3830, and USU WILD/PSC 5350/6350 classes. Publications in Scientific Journals: 1) Kulmatiski, A., Holdrege, M.C.*, Chirvasa, C*.,Beard, K.H.Root distributions predict shrub-steppe responses to precipitation intensity. Biogeochemistry Discussions. In press. 2) Holdrege, M.C*., Beard, K.A., Kulmatiski, A., Palmquist, K. 2023. Precipitation intensification increases shrub dominance in arid, not mesic ecosystems. Ecosystems. 26(3), 568-584. 3) Kulmatiski A., Beard K. 2022. A modern two-layer hypothesis helps resolve the 'savanna problem'. Ecology Letters. 25(9), 1952-1960. 4) Holdrege, M.C*, Beard, K.H. and Kulmatiski, A. Winter wheat resistant to increases in precipitation intensity. Agronomy11(4), 751. 5) Rasmussen, C.R. and Kulmatiski, A., 2021. Improving Inferences from Hydrological Isotope Techniques. Trends in Plant Science26(3), 206-209. 6) Kulmatiski, A. Yu K., Mackay D.S., Staver, C., Parolari, A., Liu Y., Mahumder S., Trugman, A. Forecasting semi-arid biome shifts in the Anthropocene. New Phytologist, 226(2) 351-361. 7) Kulmatiski, A., P.B. Adler, K.M. Foley*. Even weak niche partitioning by active roots can explain plant coexistence. Journal of Ecology. 8) Kulmatiski, A., Beard, K.H., Holdrege, M.C*. and February, E.C., 2020. Small differences in root distributions allow resource niche partitioning. Ecology and Evolution, 10(18), pp.9776-9787. What do you plan to do during the next reporting period to accomplish the goals?This project is now complete. We are now starting a new related project examining water uptake in more arid areas of southern Utah. We have located field sites, submitted permits for field work, collected preliminary site data, secured initial funding to begin new work and submitted a grant to NSF to fund a larger project at the new study site. This research will describe root distributions across an aridity gradient and predict common rangeland species growth across the landscape and in response to climate change. This work will help land managers anticipate changes in forage production and understand how shrub control is likely to change forage production.

Impacts
What was accomplished under these goals? A major accomplishment this year on this project was graduating our PhD student. An important component of graduating this student (Holdrege) was the completion of an 'upscaling' modeling study that has been published in Ecosystems. This work has helped us expand our plot-level studies to provide inference to plant growth across the western US. This work has revealed why some studies have found precipitation intensification to increase plant growth in some sites and decrease it in other. Obviously, it is important for farmers and ranchers to be able to know at least qualitatively whether they can expect forage or crop production to increase or decrease over time as a result of climate change. While our plot-level research found that shrub growth increases and grass (forage) growth decreases, we also found that dryland wheat was very resistant to changes in precipitation intensity. By upscaling our results, we found that productivity is likely to increase in arid and semi-arid regions (aridity index of 0.5) but decrease in more mesic systems (aridity index > 0.5). Working on this upscaling project has also initiated work with new collaborators with whom i am continuing to develop new research ideas. Holdrege was immediately hired as a post-doctoral scientist with the USGS where he is continuing to work on the ecohydrology of the western US. The ecohydrological training received in this research is in high demand and my past students have quickly found employment (water companies, USGS, Native corporations, environmental consulting firms) using the tools learned through my AES projects. The second major accomplishment is that final data analyses were completed and a new paper describing this research is in press at Biogeosciences. This paper demonstrates that it is possible to predict plant community responses to climate change from data on plant root distributions. This paper produced one of the most detailed descriptions of root activity for any system in the world. These types of precise root activity datasets have demonstrated that root biomass does not necessarily correlate with root activity and that by understanding root activity we can predict plant growth, coexistence and response to climate change.

Publications

• Type: Journal Articles Status: Published Year Published: 2023 Citation: Holdrege, M. C., Kulmatiski, A., Beard, K. H., & Palmquist, K. (2023). Precipitation Intensification Increases Shrub Dominance in Arid, Not Mesic, Ecosystems. Ecosystems, 26, 568584.

Progress 10/01/21 to 09/30/22

Outputs
Target Audience:Extension agents. Dryland wheat farmers. Ecologists, ecohydrologists, rangeland managers. Changes/Problems:It has become more difficult in the past 5-10 years to establish new field studies. I have been trying to locate and contact field sites and managers in southern Utah along an elevational gradient. What opportunities for training and professional development has the project provided?A PhD student graduated May 2022. Several undergraduates (Ximena Fuller, Devin Pancake, Cristina Chirvasa, Jacob Pullen, Keslee Green) and graduate students (Julia Aaronson, Daniella Thiemann) have been involved with this project. Students have gained experience doing field and greenhouse research, stable isotope injections, extractions and analyses, data management and analyses and had the opportunity to work on related projects of their interest including a project that examines the role of silicon on medusahead growth and control, a project that tests subpopulations of common forbs around the western as potential restoration species, and a globally distributed experiment testing the effects of soil disturbance and nutrient deposition on forage production and weed invasion. How have the results been disseminated to communities of interest?The PhD working on this paper published a thesis and three related peer-reviewed publications related to this work. The third of these publications was published in 2022 in Ecosystems. An undergraduate student (Chirvasa) has presented results at the USU and Utah undegraduate research conferences. Chirvasa has also applied to present findings at the national undergraduate reserach conference in April 2023. Publications from the PI this past year related to this research include: A modern two?layer hypothesis helps resolve the 'savanna problem' A Kulmatiski, KH Beard Ecology Letters 25 (9), 1952-196012022 Precipitation Intensification Increases Shrub Dominance in Arid, Not Mesic, Ecosystems MC Holdrege, A Kulmatiski, KH Beard, KA Palmquist Ecosystems, 1-17 Plant-soil feedbacks help explain plant community productivity LE Forero, A Kulmatiski, J Grenzer, J Norton Ecology, e3736 What do you plan to do during the next reporting period to accomplish the goals?We have several goals for the remaining six months of this project. First, to complete the publication that is now in review. Second, work with the undergraduate researcher (Chirvasa) on her analyses and presentation for the national undergraduate research conference. Third, to identify a new field site and collaborators for a new project in southern Utah. I plan to visit potential field sites and speak with local land managers (Canyonlands Research Center, USGS, BLM, Forest Service) this winter. Fourth, I plan to inventory and patch 'holes' in basic field research equipment needed to establish new experiments in southern Utah. Fifth, to prepare and submit a new proposal for USDA and / NSF to support the next step of this research in southern Utah.

Impacts
What was accomplished under these goals? A major accomplishment this year on this project was graduating our PhD student. An important component of graduating this student (Holdrege) was the completion of an 'upscaling' modeling study that has been published in Ecosystems. This work has helped us expand our plot-level studies to provide inference to plant growth across the western US. This work has revealed why some studies have found precipitation intensification to increase plant growth in some sites and decrease it in other. Obviously, it is important for farmers and ranchers to be able to know at least qualitatively whether they can expect forage or crop production to increase or decrease over time as a result of climate change. While our plot-level research found that shrub growth increases and grass (forage) growth decreases, we also found that dryland wheat was very resistant to changes in precipitation intensity. By upscaling our results, we found that productivity is likely to increase in arid and semi-arid regions (aridity index of 0.5) but decrease in more mesic systems (aridity index > 0.5). Working on this upscaling project has also initiated work with new collaborators with whom i am continuing to develop new research ideas. Holdrege was immediately hired as a post-doctoral scientist with the USGS where he is continuing to work on the ecohydrology of the western US. The ecohydrological training received in this research is in high demand and my past students have quickly found employment (water companies, USGS, Native corporations, environmental consulting firms) using the tools learned through my AES projects. The second major accomplishment is that final data analyses are being completed and a new paper describing this research is in review at Biogeosciences. This paper demonstrates that it is possible to predict plant community responses to climate change from data on plant root distributions. This paper produced one of the most detailed descriptions of root activity for any system in the world. These types of precise root activity datasets have demonstrated that root biomass does not necessarily correlate with root activity and that by understanding root activity we can predict plant growth, coexistence and response to climate change.

Publications

• Type: Conference Papers and Presentations Status: Other Year Published: 2022 Citation: Presentations Kulmatiski, A., Biogeochemistry, Environmental Science, and Sustainability seminar series., "The two-layer hypothesis is dead. Long live the two-layer hypothesis. New approaches from understanding what plant roots do.," Cornell, Ithaca, NY. (March 25, 2021 - Present)

Progress 10/01/20 to 09/30/21

Outputs
Target Audience:Extension agents. Dryland wheat farmers. Ecologists, ecohydrologists, rangeland managers. Changes/Problems:Last year I had a graduate student leave our planned next step for this research. I am still looking for a student to help setup the next phase of this experiment, which will examine the combined effects of increased precipitation intensity and warming. What opportunities for training and professional development has the project provided?This research has supported one PhD student (Holdrege) who will be graduating spring 2022. In the past year, a PhD student (Thiemann) and master's student (Aaronson) worked on this project, learning about experimental design, soil sampling, plant measurements, isotope tracers and ecohydrology. Two undergraduates (Pullen and Chirvasa) have worked on the project. One undergraduate (Chirvasa) has been working with data from the past two years and presented findings at the USU undergraduate research symposium. Chirvasa continues to work with the data and has been accepted as a undergraduate research presenter at the Utah Undergraduate Research Symposium, St. George, February 2022. How have the results been disseminated to communities of interest?In the past year, I presented results from this research to the following invited talks: Kulmatiski, A.A new generation of root-based restoration. Society for Ecological Restoration, Great Basin Chapter. May 2021. Invited contribution. Kulmatiski, A.Wildland Stories: Soil Science with Dr. Andrew Kulmatiski. Monthly webinar series. May 2021. Invited contribution. Kulmatiski, A.The two-layer hypothesis is dead: long live the two-layer hypothesis. Cornell Biogeochemistry, Environmental Science, and Sustainability seminar series. 25 March 2021. Invited Contribution. What do you plan to do during the next reporting period to accomplish the goals?We have three main goals for the coming year. First, we are completing a manuscript describing our modeling efforts. Second, we are analyzing and will continue to summarize results from the last two growing seasons at Hardware Ranch. This includes data from an isotopic tracer study that revealed the location of shrub, grass and forb roots in treated and control plots. Initial reviews of the data suggest that the experiment was successful. We hope to finish these analyses, write and submit a manuscript from this work during 2022. Finally, we plan to add a warming treatment to our precipitation manipulation shelters. We are beginning to work with collaborators at USU and USGS to potentially expand this experiment to sites in southern Utah.

Impacts
What was accomplished under these goals? This project has produced several important findings in the past year. First, we have finalized analyses from the dryland wheat site. Data (doi:10.5063/0000GQ ) and a published summary (https://www.mdpi.com/2073-4395/11/4/751) from this project are publicly available. Broadly, we found that winter wheat is highly resistant to any anticipated changes in precipitation intensity in this region. We applied a range of precipitation intensity treatments beyond what is expected in the next 50 to 100 years and winter wheat showed no growth response. This is in contrast to plant responses in two related experiments that found that shrubs and trees respond positively and grasses respond neutrally or negatively to bigger precipitation events. We also measured differences between two growing seasons, so we are confident that winter wheat will be resistant to changes in increased precipitation intensity. These results are important because they strongly suggest that winter wheat production will not be affected by anticipated changes in precipitation patterns. Our results also suggest that there may be potential to increase growth or mediate the negative effects of warming by developing winter wheat varieties with slightly deeper rooting patterns that are better able to take advantage of soil water that is 'pushed' deeper into the soil by larger precipitation events. Second, we have finalized analyses from the first three years of precipitation intensity manipulations in a rangeland site. Data ("https://digitalcommons.usu.edu/all_datasets/120/">https://digitalcommons.usu.edu/all_datasets/120/) and a published summary (https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecy.3212) are publicly available. We found that shrubs responded positively to all increases in precipitation intensity. A wide range of precipitation intensity treatments were applied. The largest treatments were larger than anticipated as a result of climate change, so we are confident in our results. Shrub growth increased across all levels of precipitation intensity applied. In contrast, forb and grass growth showed no response to treatments. These results are important because they suggest that the shrub encroachment seen in arid and semi-arid ecosystems around the world in the past 50 years is likely to be caused, at least in part, due to increasing precipitation intensity. Our results strongly suggest that woody plant growth will continue to increase in the coming decades. This has important implications for land managers. While we did not observe a decrease in grass and forb growth during the first three years of our experiment, it is likely that, over time greater shrub growth will lead to shrub canopy closure and competitive suppression of grasses and forbs. This continuing shrub encroachment, therefore, can be expected to increase carbon sequestration and fire return intervals and intensity and decrease forage production for cattle. Finally, we have completed a modeling effort to better understand the effects of precipitation intensity across the western US. These analyses involved simulating water flow and plant growth for 200 sites across the western US using the STEPWAT2 model. We have found that increased precipitation intensity can be expected to increase shrub growth in arid sites but decrease in shrub growth in mesic sites. This transition is expected to occur at aridity values near 0.5 (i.e., when precipitation is 50% of potential evapotranspiration). Similar to our experiment, grasses and forbs showed little response to changes in precipitation intensity. This modeling effort also allowed us to simulate the combined effects of warming and increasing precipitation intensity. Warming decreased all plant growth. Increasing precipitation intensity increased shrub growth with no effect on grasses and forbs, resulting in an anticipated increase in shrub dominance in the coming decades. However, because warming had a larger negative effect than increasing precipitation intensity, total plant productivity is expected to decline across the western US. One notable exception is that C4 grasses, which are now limited to the southern and eastern edges of the sagebrush landscape are expected to increase their growth under warmer and larger precipitation event conditions. Broadly, our findings suggest that woody plant encroachment will continue across the western US, particularly where aridity is less than 0.5. This is likely to increase fire frequency and intensity and decrease forage production.

Publications

• Type: Journal Articles Status: Published Year Published: 2021 Citation: Holdrege, M., Beard, K. H., & Kulmatiski, A. (2021, April). Winter wheat growth resistant to increases in rain and snow intensity. Agronomy, 11(4), 751.
• Type: Conference Papers and Presentations Status: Other Year Published: 2021 Citation: Presentations Kulmatiski, A., Biogeochemistry, Environmental Science, and Sustainability seminar series., "The two-layer hypothesis is dead. Long live the two-layer hypothesis. New approaches from understanding what plant roots do.," Cornell, Ithaca, NY. (March 25, 2021 - Present)

Progress 10/01/19 to 09/30/20

Outputs
Target Audience:Dryland agricultural producers of the Intermountain West. Plant physiologists and ecologists. Changes/Problems:We identified a new site in which to establish plots that test the combined effects of increasing temperature and precipitation intensity. However, the student who began working on this project has decided to pursue different research directions. We are now looking for a new student to establish new plots. What opportunities for training and professional development has the project provided?We have a PhD student (Holdrege) and many undergraduates (see below) working on the project. We have published two papers describing the work in top-tiered journals (New Phytologist and Ecology). Holdrege and Kulmatiski are currently learning the STEPWAT2 program which will allow us to upscale our results. In addition to experimental design, Holdrege has learned data management, root image collection and analysis, plant physiology measurements and interpretation (NDVI, PRI, IR, stomatal conductance, root growth, biomass, seed production, germination), Hydrus soil water flow modeling, stable isotope experimental design and analysis, STEPWAT2 ecohydrologial modeling, and received a master's in statistics. Our PhD student has also begun collaborating with an international research group (IDE: International Drought Experiment) based out of Colorado studying the effects of precipitation on dryland ecosystems. As a part of this group, he is learning to manage and analyze data from a large international group. In the past year, we have had nine undergraduates work extensively on our project. These students have learned about experimental design and fieldwork as well as plant physiology, community ecology, ecohydrology, image analysis, and data collection and preparation. These include Dakota Green, Tori Brummer, Finn Christenson, Stephanie Hall, Maria Catalana, Laura Beck, Ryan Choi, Emily Wilde, Cristana Chirvasa. We have also had additional PhD students, Leslie Forero and Ryan Choi help on the project. How have the results been disseminated to communities of interest?We have a poster describing our research at the Hardware Wildlife Management area. We presented a talk at the Utah Society for Range Management meeting in November, 2020 title: Rangeland responses to increased precipitation intensity. The PhD student and I published a paper including data from this experiment in the top-tiered research journal New Phytologist. This paper describes new approaches to understanding large-scale vegetation changes in semi-arid ecosystems. The PhD student and I have published the first paper from his thesis describing this research at Ecology. Our PhD student has described our research in several meetings to the International Drought Experiment. What do you plan to do during the next reporting period to accomplish the goals?We continue to process isotope samples from our tracer experiment, summer 2020. In the next nine months, we anticipate preparing an additional manuscript describing the six years of the study including the tracer experiment. We continue to learn the STEPWAT2 program, which will allow us to scale-up our results to a landscape / regional level. We anticipate completing these analyses and preparing a manuscript describing these results in the next 12 months. This will allow us to both apply what we have learned to larger scales and conceptually test the effects of temperature and precipitation change. We are beginning to establish a new experiment that will test the effects of increased precipitation intensity and increased temperature on rangeland plants.

Impacts
What was accomplished under these goals? At our agricultural site, we have completed two crop years and two fallow years of treatments and collected all data. We have analyzed data and drafted a manuscript describing the work. We expect to submit this manuscript for review December 2020. Somewhat surprisingly, this research revealed no winter wheat response to a wide range of increasing precipitation intensity. This result was in contrast to results from a paired study in a rangeland site, where shrub growth increased in response to increasing precipitation intensity. There are two important implications from this work. First, winter wheat is highly resistant to changes in precipitation intensity. Inasmuch, producers do not need to worry about negative impacts of expected increases in precipitation intensity. It is important to note that our experiment isolated the effects of increased precipitation intensity. The role of increasing temperatures must be considered separately either through simulation modeling, literature review or additional experiments. The second implication is that there is potential to select winter wheat varieties that can make better use of an increase in soil moisture that is expected with fewer, larger precipitation events. Consistent with theoretical models, treatments increased deep soil moisture but winter wheat at our site was not able to convert this to increased growth or seed production. Varieties with deeper rooting profiles may be better able to respond positively to increased precipitation intensity. At our rangeland site, our first paper describing three years of treatments was recently published in Ecology. In this paper (which will be featured on the cover of Ecology), we report that increased rain and snow intensity 'pushed' water deeper into the soil and that shrub growth increased while grass and forb growth remained unchanged. These results suggest that the increase in precipitation intensity that has been predicted and observed to occur with atmospheric warming is likely to contribute to the shrub encroachment seen around the world. In Utah, this shrub encroachment is reflected in juniper expansion into rangelands and increased sagebrush growth. Our results suggest that increasing precipitation intensity is contributing to and will continue to contribute to juniper and sage growth in Utah. This is an important finding for rangeland managers because juniper and sage are poor forage relative to the grasses and forbs they replace. We have also completed two additional years of treatments at our rangeland site and we have removed our treatment shelters from the site. We are currently monitoring post-treatment responses at the site. This past year we performed an isotope tracer experiment at the site to describe plant rooting distributions in treated and control plots.

Publications

Progress 10/01/18 to 09/30/19

Outputs
Target Audience:Dryland agricultural producers of the Intermountain West. Changes/Problems:We have not encountered problems this year. Things are running smoothly. What opportunities for training and professional development has the project provided?We have a PhD student and several undergraduates working on the project. The PhD has formed their committee, has one paper accepted and a second in review. In the past year he has learned how to use the Hydrus soil water movement model, Random Forest model and is now learning the STEPWAT2 program. Other analyses associated with this research include data management, root image collection and analysis, plant physiology measurements and interpretation (NDVI, PRI, IR, stomatal conductance, root growth, biomass, seed production, germination). Our PhD student has also begun collaborating with an international research group (IDE: International Drought Experiment) based out of Colorado studying the effects of precipitation on dryland ecosystems. As a part of this group, he is learning to manage and analyze data from a large international group. In the past year, we have had three undergraduates work extensively on our project. These students have learned about experimental design and fieldwork as well as plant physiology, community ecology, ecohydrology, image analysis, and data collection and preparation. How have the results been disseminated to communities of interest?We have a poster describing our research at the Hardware Wildlife Management area. The PhD and I have just had a paper accepted in the top-tiered research journal New Phytologist. This paper describes new approaches to understanding large-scale vegetation changes in semi-arid ecosystems. The PhD student has submitted the first paper from his thesis describing this research at Global Change Biology. Our PhD student has described our research in several meetings to the International Drought Experiment. What do you plan to do during the next reporting period to accomplish the goals?This spring is another planned fallow year at the study site. We will use time this winter and spring to prepare manuscripts, maintain our paired experiment in a sagebrush system. We plan to add an isotope tracer study to better describe the rooting distribution of plants in response to precipitation manipulation treatments to be executed spring 2020. Next steps for this research will be to test responses of different varieties and the response of crops to simultaneous increases in precipitation intensity and temperatures.

Impacts
What was accomplished under these goals? We have completed treatments on two winter wheat crops. Data is entered and preliminary analyses performed. We have submitted two manuscripts describing this research (one accepted, one in review). Our PhD student has selected their committee members and we are now working with a colleague to begin to scale our plot-level measurements to landscape scales. Initial results suggest that winter wheat is highly resistant to increases in precipitation intensity. However, results from a paired experiment in a rangeland system suggests that increased precipitation intensity can increase plant productivity by decreasing interception and evaporation and increasing deep soil water infiltration. Together, these results suggest that increasing precipitation intensity is unlikely to decrease dryland production and with appropriate management and variety selection, it may be possible to increase plant productivity under increasing precipitation intensity conditions.

Publications

Progress 07/01/18 to 09/30/18

Outputs
Target Audience:Dryland agricultural producers of the Intermountain West. Changes/Problems:Because snow pack is determined more by wind and topography than by the amount of precipitation, it is difficult to manipulate the snow pack. We have found that our rhizotron tubes produce poor data in the top 10-15 cm due to poor soil contact with the observation tubes . We are now using soil cores to obtain shallow root data. What opportunities for training and professional development has the project provided?The master's student on this project has become a PhD student who will also receive a master's in statistics. This student presented initial results at an international conference and has begun preparing a manuscript describing results from the first winter wheat crop in this experiment. How have the results been disseminated to communities of interest?Results were presented at the Ecological Society of America Conference. We are preparing a manuscript describing results from the first winter wheat crop responses to treatments. What do you plan to do during the next reporting period to accomplish the goals?Treatments will continue this winter and winter wheat responses will be monitored in the spring. Next year will be a fallow season. We expect to prepare and submit a manuscript this spring. We will also begin to contact extension agents with our results.

Impacts
What was accomplished under these goals? Treatment systems are in place and a new winter wheat crop was planted this fall. Treatments continue to be applied.

Publications