Progress 10/01/05 to 09/30/06
Outputs
Activity during the 2005 year focused on (1.) completing the work described in the original proposal and (2.) expanding the work to new species using growth facilities at California State University at Fresno. 1. Completion of work described in the original proposal. At this time all remaining analyses described in the 2004 report have been completed including (a) Tissue N analysis that indicated that while foliar N concentration exceeded fine root N concentration in all species, growth at elevated CO2 had no effect on tissue N concentration. These results agree with those from the nitrate reductase activity measurements performed in the field that indicated growth at elevated CO2 had no influence on the activity of this enzyme that forms the initial step of N assimilation. (b) All statistical analysis of foliar and root carbohydrates for all species have been completed using an two way ANOVA examining effects of tissue differences (foliage and fine roots) and growth
CO2 concentration (ambient and elevated). As with results for tissue N concentration and nitrate reductase activity significant differences were found between tissue types, but growth at elevated CO2 failed to influence the concentration of either soluble sugars or starch. 2. Expansion of work to new species. Activities centered in the laboratory initially centered on a growth chamber experiment to re-examining the response of nitrate reductase to elevated CO2 of Bouteloua and Agropyron. The goal of this experiment was to determine if the observed field variability and the limited sample size of the University of Minnesota field site contributed to the lack of a significant CO2 effect on nitrate reductase activity in these species. These efforts are in the process of being repeated due to changes in student personnel. Additional efforts have expanded the scope of the study. While FACE sites at Duke University and Oak Ridge National Laboratory centered on one primary forest tree
species, the site at the University of Minnesota examined 16 species. Current laboratory work is growing eight additional species found at the Minnesota site (three C4 grasses, three C3 grasses, and one C3 forb) under ambient and elevated CO2 conditions in growth chambers. At this time foliar nitrate reductase activity measurements have been completed and initial statistical analysis indicates that nitrate reductase activity in three species are unaffected by growth CO2 concentration (two C4 grasses and one C3 grass), three species illustrate a 90-140% increase in nitrate reductase activity (one C4 grass, one C3 grass and the C3 forb), and one species (C3 grass) exhibits an ~40% reduction in nitrate reductase activity. This work is continuing with the goal to perform measurements of root nitrate reductase activity and assay changes in foliage and fine root carbohydrate concentration in response to elevated CO2.
Impacts
Additional information of the interaction between elevated CO2 and the changes in plant nitrogen assimilation physiology will assist in developing our understanding of the mechanistic basis for changes in plant competitive relationships in response to an elevation of atmospheric CO2. An understanding of these responses will permit an improved estimation of the responses of ecosystems to changes in atmospheric and climatic conditions.
Publications
- Results were presented at the 100th Annual Meeting of the Botanical Society of America in August 2006 in Chico California as a poster titled: Impact of free air CO2 enrichment (FACE) on assimilatory nitrate reduction.
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Progress 10/01/03 to 09/30/04
Outputs
The 2004 year addressed a number of issues centering on completing the grant including: (i) Measurement and analysis of the tissue N data remains to be completed, although results for Liquidambar styraciflua have been received from Fordham University, the analyses for Pinus, Bouteloua and Agropyron remain outstanding. (ii) Additional laboratory work utilizing a growth chamber experiment to re-examining the activity of nitrate reductase to elevated CO2 of Bouteloua and Agropyron. The goal of this growth chamber based experiment is to determine if the observed lack of effect of CO2 on nitrate reductase activity in the field at the University if Minnesota field site is a true lack of effect or due to the experiment's small sample size (n=2). (iii) Initiation of the statistical analysis of foliar and root carbohydrates for all species.
Impacts
Knowledge regarding how nitrogen assimilation physiology changes under elevated CO2 conditions in the field will assist in enhancing our understanding of the interactions between nitrogen metabolism and carbon metabolism. These studies will contribute to the development of an improved predictive capability for how tree and grassland species of the United States may respond to alterations in global climate.
Publications
- Results to date as of April 2004 were presented at the Central California Research Symposium as a poster during the same month titled "Response of nitrate reductase to elevated CO2 in the field.
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Progress 10/01/02 to 09/30/03
Outputs
Efforts in 2003 centered on tissue sample preparation for analysis of soluble sugars, starch, nitrate and total nitrogen. Grinding of samples from Duke University (Pinus taeda) and Cedar Creek Natural History Area (Agropyron repens (C3 grass) and Bouteloua gracilis (C4 grass)) was performed and once complete, activities centered on two fronts. The first activity was the preparation of samples for total nitrogen analysis at Fordham University. Although completion of the sample preparation was delayed by a non-functional microbalance, once repaired preparation of the 2 mg samples of foliar and fine root tissue proceeded quickly. Samples have been sent to Fordham University for analysis and as of the report date results have not been received. The second activity was the completion of analysis to assess the concentration of soluble sugars (SS) and starch (ST) in the foliar and fine root samples. Initial protocols were discarded after approximately 25% of the samples had
bee measured due to waste disposal and safety concerns. A new protocol utilizing an aqueous extraction of SS and an enzymatic digestion of ST followed by spectrophotometric analysis at 595 nm was adopted and tested. Carbohydrate analysis has been completed for foliage, and certain samples for fine roots are being re-analyzed to reduce between sample variation. Although statistical analysis remain to be performed, preliminary results are that growth at elevated CO2 results in a 13% increase in SS and ST in Liquidambar styraciflua at Oak Ridge National Laboratory, whereas in P. taeda, SS declines 9% and ST increases 31%. In A. repens both SS and ST increase, +12% and +36%, respectively under elevated CO2 conditions; in contrast SS and ST appear to decline, -15% and -23%, respectively, in B. gracilis under elevated CO2 conditions. Statistical analysis of the nitrate reductase activity (NRA) data gathered during the summer of 2002 was also completed. Based on the limited replication at
the FACE sites and variation in NRA of field grown plants few statistically significant effects were apparent. A one-way ANOVA for CO2 effects (ambient vs. elevated) on NRA in L. styraciflua was not significant (p = 0.967), however, a similar analysis testing the effects of tissue type (foliage vs. fine root), indicated that foliage NRA exceeded fine root NRA (p = 0.031). Difference in NRA of P. taeda using a one-way ANOVA detected a marginal reduction in NRA due to growth CO2 (p = 0.123), and a one-way ANOVA testing for tissue differences in NRA demonstrated no significant difference between foliage and fine root tissue (p = 0.499). Measurements of NRA in foliage and fine roots of A. repens and B. gracilis using a two-way ANOVA (CO2 effect and tissue (foliage vs. fine root) effect) were similarly unresponsive to growth CO2 conditions. Growth CO2 effects on foliar and fine root NRA in A. repens and B. gracilis were insignificant, p = 0.385 and p = 0.844 respectively. However, foliar
NRA exceeded that in the fine roots in both A. repens (p = 0.005) and B. gracilis (p = 0.008), but there was no significant interaction with growth CO2 level.
Impacts
Knowledge regarding how nitrogen assimilation physiology changes under elevated CO2 conditions in the field will assist in enhancing our understanding of the interactions between nitrogen metabolism and carbon metabolism. These studies will contribute to the development of an improved predictive capability for how tree and grassland species of the United States may respond to alterations in global climate.
Publications
- No publications reported this period
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