Effects Of Microplastics And Nitrogen Fertilizer On Microorganism And Rice Straw Decomposition In Paddy Field

Farmland is closely related to human production and life,human beings will leave a lot of straw while harvesting crops,soil microorganisms are the main decomposers of straw and directly participate in the decomposition process of straw,straw can return most of the nutrient elements absorbed by crops to the soil in the process of decomposition,which is an important way for the sustainable development of agriculture.Microplastic are widely distributed in farmland soil,microplastic can affect the composition and activity of soil microbial community,thus affecting the decomposition of rice straw,while microplastic affect the decomposition of rice straw,they will be decomposed into smaller particles by many factors,and further affect the soil microbiological process.Nitrogen fertilizer is also another important environmental factor affecting straw decomposition,studies have shown that the application of nitrogen fertilizer can accelerate the decomposition process of straw cellulose and further affect the soil microbiological process.At present,many studies only focus on the single influence of microplastic or nitrogen fertilizer on the rice straw decomposition process,but seldom study the combined effect of the two factors.At present,microplastic and nitrogen fertilizer are the two main man-made interference factors in farmland,and because microplastic have a certain pore structure,they can provide a stable microenvironment for the growth of microorganisms,and nitrogen is beneficial to the growth of microorganisms,therefore,the existence of the two factors may have an interactive effect on the soil microbiological process,so it is necessary to study the biological effect of this process,this is helpful to deepen the understanding of the biological mechanism of straw returning to the field,and it is also great significance to study the process of soil nutrient cycling under the artificial interference of microplastic and nitrogen fertilizer.In this study,the effect of microplastic and nitrogen fertilizer on decomposition of rice straw were studied by adding microplastic and nitrogen fertilizer to selected field plots,the main experimental results are as follows:(1)first,choose three kinds of microplastic,include polyethylene(PE),polypropylene(PP),polyvinyl chloride(PVC),and set up two kinds of adding level(1%and 5%),and three kinds of particle size(small particle size(S),medium particle size(M),large particle size(L),and control group(no microplastic(Control)).Using rice straw as decomposition substrate,the weight loss rate,microbial activity and particle size distribution of residual microplastic were analyzed.The results show that,microplastic can promote the decomposition of rice straw,the effect of PP and PVC are relatively significantly,while PE had no significant effect,microplastic adding level increase result in the weight loss rate increase,microplastic particle size increase result in the weight loss rate decrease.In the former and later stage of straw decomposition,microplastics mainly promoted CX enzyme,however,microplastic inhibited C1 enzyme,in the former stage of straw decomposition,microplastic promoted the activity of peroxidase;the decomposition range of microplastic with large particle size is larger than that of microplastic with small particle size,the decomposition range of PP was larger than that of PE.(2)after that,set up low-concentration nitrogen(LN)and high-concentration nitrogen(HN),two kinds of microplastic(PE and PP),and processing combination(LN+PE,LN+PP,HN+PE,HN+PP),the control group(without nitrogen fertilizer and microplastic(Control).Using rice straw as decomposition substrate,the weight loss rate,microbial activity and fungal diversity of rice straw were analyzed.Microplastic and low concentration nitrogen fertilizer promoted straw decomposition,in the former stage of straw decomposition,low-concentration nitrogen fertilizer promoted straw decomposition and majority enzyme greatly,in the later stage of decomposition,PP promoted straw decomposition and majority enzyme greatly,the combined effect of PE and nitrogen fertilizer was lower than that of PE and nitrogen fertilizer alone,the combined effect of PP and nitrogen fertilizer was lower than that of PP alone,but higher than that of nitrogen fertilizer alone.Basidiomycota and Ascomycota were the dominant phylum in straw decomposition,both microplastic and nitrogen fertilizer promoted the transformation of dominant fungi from Basidiomycota to Ascomycota to varying degrees,microplastic and low-concentration nitrogen fertilizer can promote the abundance and diversity of fungal,and the fungal diversity under PP treatment is much larger than other treatments,the combined effect of microplastic and nitrogen fertilizer was different on fungal diversity due to the difference of microplastic structural characteristics and nitrogen fertilizer concentration,the combined effect of PE and lowconcentration nitrogen fertilizer is lower than that of low-concentration nitrogen fertilizer and higher than that of PE,the combined effect of PE and high-concentration nitrogen fertilizer is lower than both of treatment alone,the combined effect of PP and nitrogen fertilizer is lower than that of PP and higher than that of nitrogen fertilizer treatment.Microplastic and low-concentration nitrogen fertilizer promoted the decomposition of rice straw,different kinds,concentrations and particle sizes of microplastic have different ecological effects,the main factors affecting the decomposition of microplastic are the structural characteristics of microplastic themselves,microplastic promoted the material energy cycle of farmland ecosystems to some extent,structural difference in microplastic will lead to significant difference in fungal diversity and the combined effect of microplastic and nitrogen fertilizer,and there will be no synergy between microplastic and nitrogen fertilizer.