Print PageMean annual temperature for the southwestern, USA is expected to increase 2-4oC by 2100. While this increase may seem modest compared to the annual temperature, even small increases in temperature can negatively affect vegetation in these already warm dryland communities. We tested the hypothesis that a +2oC increases in temperature (applied through infrared heaters) would negatively impact carbon fixation and growth of a dominant C3 bunchgrass -Achanherum hymenoides (Indian Ricegrass)- and that these effects would occur with accompanying changes to carbon cycling. Relative growth rate of these plants were estimated in 2011, as was foliar gas exchange, foliar integrity, foliar and soil carbohydrate concentration and soil CO2 efflux (measured in April, May, June, July and September of 2011).
Results/Conclusions
Elevated temperature significantly reduced net photosynthesis (Anet) during the beginning of the growing season, when plants were most active, but appeared to have no effect later in the growing season when temperatures were highest. In April and May, Anet was regulated by plant water status, while in June and July Anet was regulated by thermal inhibition. Foliar dark respiration was lower in the elevated temperature treatment, suggesting thermal acclimation or substrate limitation. Soil CO2 efflux was also significantly lower, with elevated temperature likely due to substrate limitation. Additionally, there was a strong positive correlation between soil CO2 efflux and Anet. The suppression of Anet in response to increased growth temperature correlated with lower relative growth rates and lower reproductive output, suggesting that warming negatively affected photosynthesis which, in turn, resulted in reduced plant growth and soil respiration. Our findings suggest that a +2oC increase in temperature can substantially negatively affect carbon cycling associated with a common C3 bunchgrass.
phone 202-833-8773