Response of temperate grasslands at different altitudes to simulated summer drought differed but scaled with annual precipitation

摘要

Water is an important resource for plant life. Since climate scenarios forSwitzerland predict an average reduction of 20% in summer precipitationuntil 2070, understanding ecosystem responses to water shortage, e.g. interms of plant productivity, is of major concern. Thus, we tested theeffects of simulated summer drought on three managed grasslands along analtitudinal gradient in Switzerland from 2005 to 2007, representing typicalmanagement intensities at the respective altitude. We assessed the effectsof experimental drought on above- and below-ground productivity, standstructure (LAI and vegetation height) and resource use (carbon and water).Responses of community above-ground productivity to reduced precipitationinput differed among the three sites but scaled positively with total annualprecipitation at the sites (R2=0.85). Annual community above-groundbiomass productivity was significantly reduced by summer drought at thealpine site receiving the least amount of annual precipitation, while nosignificant decrease (rather an increase) was observed at the pre-alpinesite receiving highest precipitation amounts in all three years. At thelowland site (intermediate precipitation sums), biomass productivitysignificantly decreased in response to drought only in the third year, aftershowing increased abundance of a drought tolerant weed species in the secondyear. No significant change in below-ground biomass productivity wasobserved at any of the sites in response to simulated summer drought.However, vegetation carbon isotope ratios increased under droughtconditions, indicating an increase in water use efficiency. We conclude thatthere is no general drought response of Swiss grasslands, but that siteswith lower annual precipitation seem to be more vulnerable to summer droughtthan sites with higher annual precipitation, and thus site-specificadaptation of management strategies will be needed, especially in regionswith low annual precipitation.