Effect Of Changing Precipitation Seasonality On Ecosystem Carbon Fluxes In A Semi-arid Grassland Of Northern China

Earth system models have forecasted an intensification of global hydrological cycles in the future,which is predicted to enhance the inter-and intra-annual variability of precipitation including total amount and temporal distribution pattern.Increasing evidences suggest that seasonal distribution of precipitation may be more important than precipitation amount in regulating ecosystem carbon cycling,especially in arid and semi-arid grasslands.However,irrespective of the well documented influences of changes in precipitation amount,frequency,and intensity on terrestrial ecosystems,how seasonal redistribution of precipitation affects ecosystem carbon cycling remains elusive.A field manipulative experiment that simulates advanced and/or delayed precipitation peaks in the growing season(i.e.shift precipitation peak from July to June and/or from August to September)was conducted to examine the effect of altered precipitation seasonal distribution on soil respiration(SR),net ecosystem CO2 exchange(NEE),ecosystem respiration(ER),and gross ecosystem productivity(GEP)in a semi-arid grassland of the Mongolian Plateau from 2013 to 2016.Over the 4 years,advanced growing-season precipitation peak significantly decreased SR by 6.5%through suppressing microbial biomass carbon(MBC,25.5%)and microbial biomass nitrogen(MBN,44.8%).Delayed growing-season precipitation reduced belowground net primary productivity(BNPP)by 16.7%,and thus leading to 8.5%reduction of SR.Advanced growing-season precipitation peak had no effect on NEE,ER,and GEP,whereas delayed growing-season precipitation peak decreased ER and GEP by 8.8 and 7.8%,respectively.In addition,the decreases of ER and GEP led to neutral change in NEE.Across all the treatments and years,SR,NEE,ER,and GEP showed no relationship with precipitation amount in either the early or late growing season,but increased linearly with precipitation amount in the middle growing season.The study suggests that delayed precipitation peak may have larger effects on ecosystem carbon cycling than advanced precipitation peak.The observations also indicate that precipitation amount in the middle growing season is more crucial than that in early or late growing season,and can determine the inter-and intra-annual variability of carbon cycling.The findings highlight the potential of seasonal redistribution of precipitation in regulating rising atmospheric C02 concentration and consequently feedback to climate change in the future.