Effects Of Biochar Persistent Free Radicals On Soil Ecological Behavior

Biochar has been extensively studied in the field of soil improvement and environmental remediation due to its unique physical and chemical properties,large specific surface area,rich functional groups and strong adsorption properties.In recent years,persistent free radicals（PFRs）generated during biomass pyrolysis have attracted more and more attention.On the one hand,biochar PFRs can directly or indirectly regulate and facilitate the removal of environmental pollutants by biochar.On the other hand,recent studies have found that biochar PFRs may also damage biological systems and cause adverse effects on the health of human beings or other environmental organisms.The impacts and risks of biochar PFRs on soil ecological behavior are still poorly understood and unclear.The agronomic effects and ecological response characteristics of soil input of biochar PFRs were explored,and their potential functions and risk mechanisms were systematically revealed,so as to reduce the negative impact of biochar PFRs on the environment and have positive significance for rational utilization of biochar in agriculture.In this study,the types and characteristics of biochar PFRs from different biomass sources and treatments were compared.The effects of biochar with the highest and lowest concentrations of PFRs on the basic physical and chemical indexes of wheat plants,the main enzyme activities of wheat leaves and the relative activity of cells,the effects on soil physical and chemical properties,the main enzyme activities,and the soil microbial diversity and microbial community structure were investigated.The main research conclusions are as follows:（1）Biochar was prepared from cow dung,sheep dung,lotus stalk and egg shell,and the intensity and concentration of PFRs signals in biochar were cow dung biochar>Sheep manure biochar>Lotus stem biochar>Egg shell biochar.The signal intensity and spin concentration of biochar treated by pickling for weathering not only increased,but also changed the type of PFRs.Biochar PFRs are persistent at room temperature.（2）The concentration of biochar PFRs was significantly correlated with the toxicity of biochar.Relatively low biochar PFRs content had limited effect on seed germination,while high biochar content had significant inhibitory effect on seed germination and seedling growth.The toxicity of biochar PFRs to wheat showed a significant dose-effect relationship.With the increase of the concentration of biochar PFRs,the total chlorophyll content in wheat leaves and the activity of antioxidant enzymes first promoted and then inhibited.In addition,the presence of biochar PFRs increased the MDA content in wheat leaves and decreased the relative activity of leaf cells.（3）The effects of biochar PFRs from cow dung and egg shell on soil properties were investigated.On the one hand,in the soil-biochar system,the presence of biochar PFRs changes the concentration and type of free radicals in the soil.On the other hand,soil URE activity and SUC activity increased with the increase of biochar PFRs concentration,while soil N-PHO activity increased at low biochar PFRs concentration(0-20 g·kg^-1)and decreased at high biochar PFRs concentration(40-80g·kg^-1).（4）The effects of biochar PFRs on soil microorganisms in soil-biochar system were investigated.Biochar PFRs indirectly affect soil microbial community by changing soil properties（persistent free radical content and soil enzyme activity,etc.）.The results showed that low biochar supplemental level(20 g·kg^-1)increased the abundance and diversity of functional bacteria,while high biochar supplemental level(80 g·kg^-1)increased the abundance and diversity of functional bacteria,and also changed the distribution of soil bacterial population.At the same time,different biochar gradient levels had different effects on soil microbial community,and different soil treatments had different effects on microbial community.In conclusion,the results for biochar application in agriculture and the environment environmental toxicological mechanism,toxicity and potential ecological risk provides new insights.