Effect Of Plastic Film Mulching On Carbon Balance In Rainfed Spring Maize Croplands

Agro-ecosystem,as the most active and controllable carbon pool in the global carbon pool,play an important role in maintaining global carbon balance.At present,plastic film mulching?PM?is considered to be the most effective way to improve the crop productivity in arid and semi-arid regions.However,its effects on the carbon balance have not been well evaluated.This study investigated the the effect of PM on soil carbon balance in rainfed spring maize croplands.Our results clear the effects and relationship of PM on soil carbon emissions,soil carbon components,soil moisture,soil temperature and CO₂concentration in rainfed spring maize croplands,and reveal the distribution of CO₂-assimilation carbon and the diversity of soil bacteria under elevated CO₂,and clear effects of PM on carbon balance of spring maize ecosystem in rainfed croplands.The main results and conclusions were showed as follow:1.PM increased soil temperature,soil moisture content and soil CO2 concentration in surface soil.Compared with conventional practice without mulch?CK?,PM significantly increased soil temperature of 0-15 cm soil layer by 3.4%,soil water storage of 0-40 cm soil layer by 6.1%and CO₂ concentration in10-30 cm soil layers by 7.3%.The effect of PM on soil carbon composition in different soil layers is different.Compared with CK,PM significantly increased soil organic carbon?SOC?in 5-10 cm and 10-20 cm soil layers by 7.7%and 16.5%and soil microbial biomass carbon?SMBC?in 5-10 cm soil layers by 9.9%.2.PM increased soil respiration?R_s?mainly by promoting soil autotrophic respiration?R_a?during maize growth period.The results showed that PM significantly increased R_s and R_a,but had no significant effect on soil heterotrophic respiration?R_h?during maize growth period.During the fallow period,PM had no significant effect on R_s,R_a and R_h.3.During the growth period of maize,soil total carbon?STC?was the most relevant factor for Rs under PM and SMBC was the most relevant factor for R_s under CK.For PM,the correlation degree of soil temperature and R_s was higher than that of soil moisture and R_s,while in CK,the correlation degree of soil moisture and R_s was higher than that of soil temperature and R_s.4.Under PM,CO₂-assimilation carbon can be immobilized by SOC,SMBC,soil particulate organic carbon?SPOC?and soil inorganic carbon?SIC?.The amount of CO₂ assimilation by SIC in soil was positively correlated with the contents of SPOC and SIC,and significantly positively correlated with the contents of SOC and SMBC.The amount of CO₂ assimilation by SOC was negatively correlated with the contents of SOC and SMBC,and positively correlated with the contents of SPOC and SIC.5.The structure of soil bacterial community were significantly changed by elevated CO₂ under PM.Relative abundance results showed that the unique bacterial genera of elevated CO₂ were Steroidobacter,Gaiella,H16,Nitrospira and RB41.And the RDA results showed that CO₂ concentration was positively correlated with Pseudarthrobacter?Sphingomonas?H16?Steroidobacter?Gaiella?Nitrospira and RB41genera.6.PM significantly increased net primary productivity?NPP?,in which harvested carbon,straw carbon,root carbon and litter carbon increased by 16.9%,14.7%,16.5%and 6.8%,respectively.PM reduced the cumulative annual emissions of R_h by 2.7%,thus increasing the net ecosystem productivity?NEP?of PM by 26.3%.However,because the removal of straw and PM increased carbon emissions from agricultural inputs,the net ecosystem carbon balance?NECB?and net carbon balance?NCB?of PM were negative.