Spatial Pattern Distribution And Factors Influencing The Precipitation Pulse Effect Of Forests Soil In Eastern China

As the largest carbon(C)reservoir in terrestrial ecosystems,soil C pool play an important role in the global C cycle,and the stability of soil C pools is related to the development of the global ecosystem C cycle.Global climate change affects the atmospheric circulation and hydrological cycle,triggering changes in precipitation patterns.Changes in rainfall intensity and frequency lead to more precipitation pulses,which stimulate soil microorganisms to rapidly increase the decomposition rate of soil organic matter and release large amounts of CO2 into the atmosphere in a short time,and the annual CO2 emissions caused by precipitation pulses currently account for about 1/5 of the total annual respiration of soil microorganisms.As a major part of terrestrial ecosystems,forests account for 73%of global terrestrial ecosystem C stocks,and the effect of precipitation pulse on forest soils has an important impact on global carbon balance.Currently,related studies are mainly focused on smaller spatial scales,and there are insufficient studies on the large scale of forest soil precipitation pulse effects,which will bring challenges to future scientific simulations and predictions of terrestrial and even biospheric carbon cycles.Based on the above,this thesis selected 22 typical forest sample sites in eastern China,which covered five temperature zones:tropical,subtropical,warm temperate,middle temperate,and cold temperate,and five forest types:evergreen broadleaf,deciduous broadleaf,mixed conifer,evergreen conifer,and deciduous conifer.Forest soils were collected from each site for the study,water was added to 65%WHC(water holding capacity)in the laboratory to simulate natural precipitation pulses,and incubated at a constant temperature of 20°C.The effect of precipitation pulses was tested continuously for 48-h on a time scale of minutes.We found that:Precipitation pulses can cause a dramatic response of soil microorganisms,and producing a precipitation pulse effect.The rate of mineralized decomposing SOM can be rapidly increased by 1.7?38.12 times in a short time(0.28?47.24 h),resulting in a surge of C release from soil C pools.For example,the rate of soil microbial decomposition of SOM in Shennongjia forest increased to 38.12 times of that during drought,and the maximum respiration rate per unit soil microorganism(Rs-soil-max)increased to 14.07?g C g^-1soil h^-1;the rate of microbial mineralization and decomposition of SOM in Changbai Mountain forest soil reached 20 times of that during drought,and R_s-soil-max reached 16.19?g C g^-1 soil h^-1;the peak respiration of Dinghu Mountain forest soil reached after the precipitation pulse was the smallest among these sample sites,also four times higher than during the drought,with Rs-soil-max reaching 1.35?g C g^-1 soil h^-1.(2)The spatial distribution pattern of the precipitation pulse effect in the forest sample zone of eastern China shows a clear pattern:From south to north,the intensity of the precipitation pulse effect increases significantly with increasing latitude.The accumulative emission of CO2(ARs-soil)was33.15?410.15?g C g^-1 soil,increasing with increasing latitude(P<0.05);Time consumed in reaching peak respiration(TRs-soil-max)was 0.28?47.24 h,significantly longer with increasing latitude(P<0.05).The precipitation pulse effect of forest soils differed significantly among the five temperature zones,with the middle temperate forest soils responding most strongly to the precipitation pulse,with Rs-soil-max(11.70?g C g^-1 soil h^-1)and AR_s-soil(300.71?g C g^-1 soil)reaching the maximum.Tropical R_s-soil-max(3.04?g C g^-1soil h^-1)and AR_s-soil(92.07?g C g^-1 soil)were the smallest.From west to east,the precipitation pulse effect increases with increasing longitude.Rs-soil-max,ARs-soil,and TRs-soil-max show an increasing trend.No obvious pattern was found at altitude.The soil precipitation pulse effect differed among different forest types,Rs-soil-max:mixed coniferous forests>deciduous coniferous forests>evergreen coniferous forests>deciduous broadleaf forests>evergreen broadleaf forests;ARs-soil:evergreen coniferous forests>deciduous broadleaf forests>deciduous coniferous forests>mixed coniferous forests>evergreen broadleaf forests;TRs-soil-max:deciduous coniferous forests>evergreen coniferous forests>evergreen broadleaf forests;TRs-soil-max:deciduous coniferous forests>evergreen coniferous forests coniferous forests>mixed coniferous forests>deciduous broad-leaved forests>evergreen broad-leaved forests.(3)Climatic factors(mean annual temperature,annual rainfall,drought index),soil chemical properties(total soil carbon content,total nitrogen content,p H,redox potential),and soil physical properties(silt,sand)were the factors that significantly influenced the pulse effect of precipitation in forest soils.Soil texture>climatic factors>soil redox environment>soil carbon and nitrogen content in order of influence.Besides,microbial communities and biomass(PLFA,G⁺,G^-,fungi,bacteria,actinomycetes,fungi/bacteria,actinomycetes/bacteria)had no significant effect on the precipitation pulse effect.Overall,this study is the first to explore the level,pattern,and influencing factors of the forest soil precipitation pulse effect in four dimensions:latitude,longitude,altitude,and forest type,taking a typical forest ecosystem in the forest sample zone of eastern China as the research object,which is important for understanding the important status and role of the precipitation pulse effect in the context of global change,and estimating the changing trend of soil carbon pool and the global ecosystem carbon cycle.This study provides scientific data support.