The Effect Of Soil Carbon Forms On Matrix-bound Phosphine Production In Paddy Soils With Elevated Atmospheric Carbon Dioxide/Ozone Concentrations

In recent years,the global climate change caused by the increase of atmospheric concentrations of greenhouse gases,such as CO₂ and O₃,is one of the most important global environmental issues of common concern to humankind.Wetland ecosystems are more sensitive to climate change.Climate change will affect wetland hydrology,biogeochemical processes,plant communities,and wetland ecological functions.It will directly affect the cycling of carbon,nitrogen,and phosphorus in wetlands.However,there is currently a lack of in-depth research in this area,especially the lack of studies on the production of phosphine in paddy fields and the role of carbon morphologies in the phosphorus cycle in the presence of elevated atmospheric carbon dioxide/ozone concentrations.In this study,phosphine in paddy fields was used as the research object,and the method of micro-universe indoor simulation was adopted.Soil pH,oxidation-reduction potential（Eh）,and temperature（Ts）were used as soil basic properties,and total carbon（TC）,total organic carbon（TOC）,total inorganic carbon（TIC）,microbial biomass carbon（MBC）,water-soluble organic carbon（DOC）,HCO₃^-,soil carbon dioxide（SCO₂）,and soil methane（SCH₄）were determined as soil carbon morphological indicators.Total phosphorus（TP）,organic phosphorus（Org-P）,total inorganic phosphorus（IP）,exchangeable phosphorus（EP）,dissolved phosphorus（DP）,phosphorous to Al（Al-P）),phosphorous to Fe（Fe-P）,phosphorous to Ca（Ca-P）,and occluded phosphorus（OP）were determined as soil phosphorus fractions.To explore the effect of carbon morphologies on matrix-bound phosphine（MBP）formation in paddy fields under different CO₂/O₃ concentrations,we analyzed and processed the data obtained from the experiment,the main findings are as follows:（1）MBP concentration did not increase significantly with elevated CO₂ concentrations（400 ppm,550 ppm,700 ppm）over four-week cultivation periods of rice seedlings,regardless of soil layers.MBP had a significant positive correlation withTP,IP,Fe-P and Ca-P,and multiple stepwise linear regression analysis further indicated that MBP preservation in neutral paddy soils with depths of 0-20 cm may have been due to conversion from Fe-P and Ca-P.Based on redundancy analysis,speculated that the formation of MBP in the neutral paddy soils as the response to atmospheric elevated CO₂ concentrations was due to two processes:（i）Fe-P transformation affected by the changes of soil respiration（SCO₂）and TOC was the main precursor for the production of MBP;and（ii）Ca-P transformation resulting from variation in HCO₃^-was the secondary MBP source.The complex combination of these two processes was simultaneously controlled by SCO₂.（2）MBP concentrations had an inconspicuous increase with the elevated O₃concentrations（40±20 ppb,80±20 ppb,120±20 ppb）of 80±20 ppb during the rice cultivation,and showed an unapparent decrease with 120±20 ppb,regardless the type of soil layer.MBP possessed a significant positive correlation with TP,IP and Fe-P,and multiple stepwise linear regression analysis further indicated that MBP preservation in neutral paddy soils with depths of 0-20 cm may have been converted from Fe-P.In the redundancy analysis,it is speculated the MBP formation in the neutral paddy soils as the response to atmospheric elevated O₃ concentrations was determined by the following process:Fe-P transformation affected by the changes of TOC was the main precursor.This complex process was also governed by SCO₂.（3）Three different levels of CO₂/O₃ concentration（400 ppm/40±20 ppb,700 ppm/80±20 ppb,700 ppm/120±20 ppb）in atmosphere were set up to study the formation of MBP caused by different soil basic properties.The elevated CO₂ concentration can relieve the inhibition caused by the increase of O₃ concentration to some extent.The maximum amount of MBP content in 10-20 cm soil appeared at the CO₂/O₃ concentration of 700 ppm/100±20 ppb.Throughout the course of the study,MBP levels increased with a slight decrease in acidity in the neutral test soil environment,and more MBP was easily produced at higher p H,lower redox potential and lower temperature.The results showed that elevated CO₂ and O₃concentrations in the atmosphere could change the soil carbon forms and soil basic properties in paddy fields,which in turn affected the production and distribution of MBP.