摘要
Aims Rising concentrations of atmospheric carbon dioxide([CO_(2)])may influence forest successional development and species composition of understory plant communities by altering biomass production of plant species of functional groups.Here,we describe how elevated[CO_(2)](eCO_(2))affects aboveground biomass within the understory community of a temperate deciduous forest at the Oak Ridge National Laboratory sweetgum(Liquidambar styraciflua)free-air carbon dioxide enrichment(FACE)facility in eastern Tennessee,USA.We asked if(i)CO_(2)enrichment affected total understory biomass and(ii)whether total biomass responses could be explained by changes in understory species composition or changes in relative abundance of functional groups through time.Materials and methods The FACE experiment started in 1998 with three rings receiving ambient[CO_(2)](aCO_(2))and two rings receiving eCO_(2).From 2001 to 2003,we estimated species-specific,woody versus herbaceous and total aboveground biomass by harvesting four 130.5-m subplots within the established understory plant community in each FACE plot.In 2008,we estimated herbaceous biomass as previously but used allometric relationships to estimate woody biomass across two 535-m quadrats in each FACE plot.Important findings Across years,aboveground biomass of the understory community was on average 25%greater in eCO_(2)than in aCO_(2)plots.We could not detect differences in plant species composition between aCO_(2)and eCO_(2)treatments.However,we did observe shifts in the relative abundance of plant functional groups,which reflect important structural changes in the understory community.In 2001-03,little of the understory biomass was in woody species;herbaceous species made up 94%of the total understory biomass across[CO_(2)]treatments.Through time,woody species increased in importance,mostly in eCO_(2),and in 2008,the contribution of herbaceous species to total understory biomass was 61%in aCO_(2)and only 33%in eCO_(2)treatments.Our results suggest that rising atmospheric[CO_(2)]could accelerate successional development and have longer term impact on forest dynamics.
基金
US Department of Energy Office of Science,Biological and Environmental Research Program,Department of Ecology and Evolutionary Biology,University of Tennessee,Knoxville,Oak Ridge National Laboratory is managed by UT-Battelle,LLC,for the US Department of Energy under contract DE-AC05-00-OR22725.
