B21F-0537
Effects of warming and elevated CO2 in a semiarid grassland are temporally dynamic due to interactions among water, nitrogen, and plant community composition
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Kevin E Mueller1, Dana M Blumenthal2, Elise Pendall3, Dan R LeCain2, Yolima Carrillo4, Feike A Dijkstra5, David G Williams6, Ron Follett1 and Jack A Morgan2, (1)Agricultural Research Service Headquarters, Boise, ID, United States, (2)United States Department of Agriculture, Agricultural Research Service, Rangeland Resources Research Unit, CO, United States, (3)University of Western Sydney, Penrith, NSW, Australia, (4)University of Sydney, Eveleigh, Australia, (5)University of Sydney, Sydney, Australia, (6)University of Wyoming, Laramie, WY, United States
Abstract:
The effects of environmental change are known to be temporally dynamic and better revealed in long-term studies, partly due to potential feedbacks associated with biogeochemical cycling and plant community composition. Rising air temperatures and atmospheric carbon dioxide (CO2) concentrations are the most pervasive facets of environmental change on land, yet multi-year, factorial studies of warming and elevated CO2 in intact ecosystems are exceedingly rare and the temporal dynamics of such studies have not been thoroughly reported. Here, we report an analysis of how experiment duration and yearly weather variability shaped the impacts of warming and CO2 on plant production, community composition, and biogeochemistry in a semiarid, North American grassland (near Cheyenne, Wyoming, U.S.A.). The experiment was a factorial manipulation of CO2 (ambient and 600 ppmv) and air temperature (ambient and warmed by 1.5°C during the day and 3°C during the night), maintained for 7 consecutive years using mini-FACE (free-air CO2 enrichment) and infrared heaters (T-FACE). We will focus on two particular components of the apparent temporal dynamics. First, we will present how interannual variability in spring precipitation appears to cause related shifts in the effects of elevated CO2 on plant production (above and belowground) and the distribution of nitrogen in plants and soils. The results suggest that the effect of elevated CO2 on plant production could be limited by nitrogen, particularly in wet springs and in the absence of warming. Second, we will show how experiment duration appears to impact the response of various ecosystem attributes to the combined warming and elevated CO2 treatment on related ecosystem attributes. Specifically, we will discuss how potential feedbacks to water and nitrogen availability might be related to the shift from a positive effect of "future conditions" on C4 grasses to a positive effect of future conditions on C3 grasses.
