Effects Of Straw Returning On The Stability Of Soil Organic Carbon Pool Under Integrated Rice-crayfish System

The straw returning is now a widely valued and effective way of improving soil fertility.At present,studies on the effect of straw returning on soil organic carbon pools are mainly focused on the ratoon rice system and the rice-wheat rotation system,while few studies have been reported on the effect of straw returning on the stability of organic carbon pools under rice-crayfish integrated system.In this study,we analyzed the changes of soil physicochemical properties,organic carbon and its components,organic carbon mineralization,functional diversity of microbial community carbon metabolism,and bacterial community structure and diversity by using a 7-year longterm experiment with three treatments of winter flooded fallow + no straw returning(W),winter flooded fallow + straw returning(WS)and winter flooded fallow + straw returning + crayfish farming(WSC).The main results were as follows.(1)Compared with the W treatment,the WS treatment significantly increased the soil total nutrients contents,but significantly decreased the available N content of the10-20 cm layer.Compared with the WS treatment,the WSC treatment significantly increased the total porosity,total nutrients and available nutrients contents,but significantly decreased the p H and bulk density.Compared with the W treatment,the WS treatment resulted in a significant the total reducing substances in the 0-10 cm layer.Compared with the WS treatment,the WSC treatment resulted in a significant decrease the reducing substances of the 0-20 cm layers,alleviating the soil gleying.(2)Compared with the W treatment,the WS treatment facilitated the transformation of micro-aggregates into larger aggregates and resulted in a significant increase in the organic carbon content of the larger aggregates,but a significant decrease in the organic carbon content of the micro-aggregates,which enhanced the bioavailability of organic carbon in soil.Compared with the WS treatment,on the one hand,the WSC treatment facilitated the transformation of micro-aggregates into larger aggregates in the 0-10 cm layer and the transformation of larger aggregates into microaggregates in the 10-20 cm layer.On the other hand,the WSC treatment increased the organic carbon content of micro-aggregates in 0-20 cm layers which was conducive to the stability of organic carbon in micro-aggregates.(3)Compared with the W treatment,the WS treatment significantly decreased the dissolved organic carbon content in the 0-20 cm layers.The carbon pool management index in the WS treatment showed a decreasing trend in the 0-20 cm layers,which was conducive to carbon fixation and accumulation.Compared with the WS treatment,the WSC treatment significantly increased the microbial biomass carbon and particle organic carbon contents in the 0-10 cm layer.The carbon pool management index in the WSC treatment showed a increasing trend in the 0-20 cm layers,which promoted the transformation of organic carbon.(4)Compared with the W treatment,the WS treatment significantly reduced mineralization of organic carbon in the 10-20 cm layer.Compared with the WS treatment,the WSC treatment enhanced the mineralization of organic carbon in the 0-20 cm layers,which promoted the transformation of organic carbon.(5)Compared with the W treatment,the WS treatment resulted in a significant increase in the microbial activity in the 0-20 cm layers,and the diversity,richness indices of the microbial community and the ability to use carbon sources in the 0-10 cm layer.Compared with the WS treatment,the WSC treatment resulted in a significant increase in the microbial activity in the 10-20 cm layer and the ability of the microbial community in the 0-20 cm layers to use carbon sources,especially the use of phenol acids,which promoted the growth of rice.(6)Compared with the W treatment,the WS treatment significantly increased the relative abundance of the Firmicutes,but made the relative abundance of the Acidobacteriota significantly lower at the phylum level.At the genus level,compared with the W treatment,the WS treatment significantly increased the relative abundance of Thioalkalispira-Sulfurivermis and Gaiella,but decreased the relative abundance of RBG-16-58-14 and Pseudolabrys.Compared with the WS treatment,the WSC treatment significantly increased the relative abundance of Myxococcota and MBNT15 at the phylum level,but decreased the relative abundance of Intrasporangium and MND1 at the genus level.Compared with the WS treatment,the WSC treatment significantly reduced the abundance and diversity of bacterial community.