The Impact Of Plant Materials And Their Biochars On Nitrogen Transformation In A Subtropical Forest Soil

In recent years,more and more research has focused on the application of biochar and its effect on nitrogen cycle in agricultural ecosystems.Biochar can affect soil nitrogen composition,nitrogen mineralization,nitrification and other nitrogen transformation processes.Unlike farmland soils,the biochar in forest soils mainly derived from the burning of plants in the fire.After the vegetation is restored,both the plant material and biochar will be present in the soil.Therefore,this research focused on the effects of typical plant materials and their biochars on nitrogen transformation in a subtropical forest soil,and explored the influence of plant materials with different C:N ratio and biochars produced under different temperatures and their interactions on soil physicochemical properties and nitrogen transformation processes.The research results can provide scientific evidences for illustrating the mechanism of soil nitrogen cycle in forest ecosystems.The main results were as follows:(1)Plant material was more easily decomposed,which could significantly increase the content of dissolved organic carbon,thereby improved soil respiration.The Phyllostachys heterocycla plant material with low C:N ratio could increase net nitrogen mineralization.In contrast,the Castanopsis sclerophylla plant material with high C:N ratio led to nitrogen immobilization in soil,so the amount of available nitrogen in soil was significantly reduced.The plant materials significantly increased pH and ammonia oxidizing bacteria(AOB)abundance in the soil with larger effect of Castanopsis sclerophylla than Phyllostachys heterocycle.The correlation analysis showed that the ammonia oxidizing bacteria abundance was significantly positively correlated with pH,while the ammonia oxidizing archaea(AOA)abundance was inhibited by higher content of available nitrogen.(2)The addition of biochar significantly increased soil pH and total carbon content and reduced the NI3--N content,which was similar to the soil after fire.With the increase of pyrolysis temperature,the structural stability,C:N ratio and pH of biochar increased.Biochar significantly increased soil pH with larger effect of 700?biochar than 300? biochar.The correlation analysis showed that the ammonia oxidizing bacteria abundance was significantly positively correlated with pH in 3d.The C:N ratio in biochar was relatively high,and it was hard to decompose,which increased soil C:N ratio and reduced soil mineral nitrogen content,the effect of 700?biochar was greater than 300? biochar,too.(3)The plant materials and biochars had significant interactions on both pH and dissolved organic nitrogen,and the Castanopsis sclerophylla plant material and biochar had significant interaction on ammonia oxidizing archaea abundance through changing pH.Soil nitrogen mineralization was dependent on the C:N ratio of organic matter,so the Castanopsis sclerophylla plant material and biochar had significant interaction on soil C:N ratio,and these two had significant interaction on the soil net nitrogen mineralization rate and mineral nitrogen content,too.Therefore,we should pay attention to the interaction of plant material and biochar on soil nitrogen transformation.