Effects Of Soil Warming And Nitrogen Deposition On Soil Respiration Of Chinese Fir Seedling Subplots

Forest soil respiration is the major source for atmospheric CO2,even its minor changes will potentially have strong effects on atmospheric CO2 and soil carbon sequestration.Climatic warming and nitrogen deposition are two major global enverionmental changes and their effects on soil respiration have received many concerns.In order to determine the responses of subtropical forest soil respiration to global warming and nitrogen deposition,a factorial soil warming×nitrogen addition experiment was conducted in Sanming Research Station of Forest Ecosystems and Global Changes in Chengda Town,Sanming City.It included six treatments,i.e.,control(CT),low nitrogen(LN),high nitrogen(HN),warming(W),warming+low nitrogen(WLN),and warming+high nitrogen(WHN),with five replicate 2m×2m subplots.Soil respiration and its heterotrophic and autotrophic components were measured twice a month for one year.The results showed that there were significant seasonal variation in total soil respiration and its components for all treatments,generally with a unimodal pattern.Total soil respiration,soil heterotrophic respiration and autotrophic respiration ranged between 0.54 ?mol·m-2·s-1?2.80 ?mol·m-2·s-1,between 0.08 ?mol·m2·s-1?1.92 ?mol·m-2·s-1,and between 0.1 1 ?mol·m-2·s-1?1.19?mol·m-2·s-1,respectively.15?74%of seasonal variations in total soil respiration and its components could be explained by soil temperature.Although soil water content is positively related to soil respiration rates,soil water content and soil temperature together could only explain seasonal variations of soil respiration in some of these treatments.The two-way ANOVA showed that soil warming had no overall effect,but nitrogen addition had significant effect,on soil respiration and its components.The soil warming and nitrogen addition interaction had significant effects on both heterotrophic and autotrophic respiration but had no effect on total soil respiration.Compared with the control,there was no significant change for all the treatments in mean total soil respiration.Soil warming alone stimulated soil heterotrophic respiration and inhibited autotrophic respiration.Soil warming and nitrogen addition together(WHN and WLN)decreased heterotrophic respiration but enhanced autotrophic respiration(especially the WLN).The annual CO2 effluxes from total soil respiration ranked as W(614.85 gC·m2·a1)>CT(560.80 gC·m2·a1)>HN(549.60 gC·m2·a1)>WLN(547.44 gC·m2·a1)>LN(536.20 gC·m2·a1)>WHN(534.51 gC·m2·a1).The correlative analysis showed that only soil available phosphorus was significantly related to annual fluxes of total soil respiration and its components.It is concluded that nitrogen addition could counteract the stimulation of soil C decomposition induced by soil warming,and thus the warming and nitrogen deposition interation can alleviate the possible positive feedback of global warming.