Effects Of Litter Addition And Removal On Soil Respiration In A Temperate Steppe Of Northern China

Soil respiration,the second largest carbon(C)flux between terrestrial biomes and the atmosphere,responds strongly to changes in substrate supply and microclimate.Elevated carbon dioxide concentration,changing precipitation,and increased nitrogen deposition can greatly alter the quantity of aboveground litter by affecting net primary productivity.Aboveground litter is one of the main sources of C input.Litter input can affect soil respiration by providing plant C substrate for microbial activity and regulating soil microclimate.Although there have been many studies focusing on the effects of litter manipulation on soil respiration in the past,only a few studies have simultaneously explored the effects of aboveground litter addition and removal on soil respiration and the associated underlying mechanism.As part of a long-term field manipulative experiment including control,litter addition,and litter removal since 2005,this work was conducted to examine the effects of changes in litter amount on soil temperature(ST),moisture(SM),soil organic C(SOC),total nitrogen content(TN),microbial biomass C(MBC),aboveground net primary productivity(ANPP),belowground net primary productivity(BNPP),soil respiration,and heterotrophic respiration in a temperate grassland of Northern China from 2017 to 2019.Litter addition had no effects on ST,SM,SOC,TN,MBC,ANPP,or BNPP,but decreased the normalized difference vegetation index(NDVI)by 6.0%.Litter removal did not affect ST,SM,NDVI,or BNPP.However,litter removal reduced SOC,TN,MBC and ANPP by 30.4%,13.2%,26.0%,and 18.9%,respectively.Litter addition had no effect on soil respiration or heterotrophic respiration.Litter removal suppressed soil respiration and heterotrophic respiration by 15.3% and 22.0%,respectively.Both soil respiration and heterotrophic respiration were positively correlated with the SOC,MBC,and ANPP.Litter removal-induced changes in soil respiration were mainly explained by changes in heterotrophic respiration.The reduction of heterotrophic respiration(-0.31 μmol m-2 s-1)caused by litter removal accounted for 85.9%of the reduction of soil respiration(-0.36 μmol m-2 s-1).Under litter removal,the direct decrease in litter C input and indirect decrease in ANPP and the associated reduction in soil C substrate for microbes suppressed heterotrophic respiration and soil respiration.These findings suggest that soil and heterotrophic respiration are more sensitive to litter removal than litter addition.The observations also indicate that the direct decrease in litter input and the associated changes in ANPP under litter removal play important roles in regulating soil respiration.These findings highlight the important implication for accurately predicting terrestrial ecosystem C cycling under global change scenarios in the future.The asymmetric responses of soil respiration to the addition and removal of aboveground litter indicate that simulating impacts of C input changes only by adding litter cannot accurately assess the C budget and C sink potential of the ecosystem in the future global change scenarios.These findings can facilitate accurately predicting the response of terrestrial C cycling to global change.