| Earth system models have predicted that regional and global hydrological cycle will intensify in the future,and thus affect precipitation patterns including precipitation amount,frequency,and intensity.In addition,fossil fuel combustion in industry and excessive nitrogen(N)fertilization in agriculture can also lead to dramatic increase in atmospheric N deposition.Changes in precipitation regimes and atmospheric N deposition have profound influences on terrestrial ecosystems carbon(C)cycling by affecting plant growth,plant community composition,and microbial activities.Forests account for more than 30% of the global land surface and constitute an important C sink,which play an essential role in regulating global terrestrial ecosystem C balance.However,it remains elusive how soil C release responds to changes in altered precipitation regimes and N deposition.Therefore,a field manipulative experiment including control,increased precipitation(+50%),decreased precipitation(-50%),N addition,increased precipitation plus N addition,and decreased precipitation plus N addition was conducted to explore the effects of altered precipitation regimes and N deposition on soil respiration in a deciduous broad-leaved forest ecosystem of the Transition Zone Forest between subtropical and warm temperate regions in Central China.Over the four years(2017-2020),increased precipitation,decreased precipitation or N addition had no effect on soil temperature.Increased precipitation significantly stimulated soil moisture by 1.0V/V%,decreased precipitation reduced it by 1.7 V/V%,but N addition did not alter it.Soil inorganic N content showed no response to increased precipitation or decreased precipitation,but N addition significantly enhanced it by 28.3%.Neither increased nor decreased precipitation had effect on microbial biomass C,whereas N addition suppressed it by 22.9%.Both increased precipitation and N addition significantly elevated belowground net primary production by 19.5% and 13.0%,respectively,but decreased precipitation did not affect it.Increased precipitation and N addition stimulated soil respiration by 14.7% and 11.8%,respectively,but decreased precipitation had no effect on soil respiration.The stimulated soil respiration under increased precipitation could be primarily attributed to enhancing soil moisture and belowground net primary production.In addition,the improved soil inorganic N content and thus enhanced belowground net primary production were primarily responsible for the accelerated soil respiration under N addition.Multiple stepwise regression analysis showed that soil moisture,inorganic N content,and belowground net primary production jointly explained 70.2% of variations in soil respiration.These findings suggest that increased precipitation may be more important in affecting the C cycling in the forest ecosystem than decreased precipitation.Soil microclimate and vegetation growth are the primary factors in regulating forest ecosystem C cycle.These observations will improve the understanding of terrestrial ecosystem C cycling under changes in precipitation regimes and atmospheric N deposition,and the capacity of model prediction of terrestrial ecosystems C cycling under future global change scenarios. |
