Regulation Of Litter On Soil Phosphorus Cycling In Songnen Grassland Under The Background Of Nitrogen Deposition

Soil phosphorus cycling is an important part of ecosystem nutrient cycling,one of the important geochemical cycles,and has a key regulatory role in the structure,process and function of grassland ecosystem.Litter decomposition is a key component of nutrient cycling and phosphorus turnover in terrestrial ecosystems,and Litter accumulation in grasslands can affect soil phosphorus cycling by changing environmental conditions and plant community characteristics.N deposition can affect the quantity and quality of litter in grassland,which in turn can change its decomposition rate and nutrient cycling process.Currently,there are studies on the effects of nitrogen addition and litter on soil phosphorus cycling in grasslands,but the interaction between the two on soil phosphorus cycling in grasslands is not clear.Therefore,it is important to study the regulation of soil phosphorus cycling in grasslands by N addition and litter to understand the mechanism of maintaining grassland function and its response to global changes and human activities.Based on long-term control experiments(for 11 years),we studied the effects of N addition and litter treatment on soil phosphorus pool and phosphorus mineralization rate in Songnen grassland.Through analyzing soil physicochemical properties and plant community characteristics,We explained the mechanism of N addition and litter regulation of soil phosphorus cycling,and obtained the following results:(1)N addition increased above-ground biomass and plant P stock,and litter treatment increased plant P concentration.In July,August and October,N addition significantly increased above-ground biomass,the N:P ratio of plants and plant P stock,but had no significant effect on plant P concentration.The interaction between N addition and litter treatment on above-ground biomass was significant,without N addition,litter addition reduced above-ground biomass;initial litter and litter addition reduced above-ground biomass with N addition.Whether nitrogen is applied or not,Plant P concentration increased with litter treatment,while the N:P ratio of plants and plant P stock were not affected by litter treatment.(2)The effects of N addition and litter treatment on soil P pool varied with time.N addition reduced soil P pool content,while litter addition increased soil P pool content.N addition reduced soil total P in July and August,and soil available P and microbial biomass P in July,August and October;litter addition increased soil total P,soil available P and microbial biomass P in the three months.Soil available P content showed a pattern of decreasing and then increasing between the three months,in contrast,microbial biomass P first increased and then decreased.The variation pattern of soil P pool over time was influenced by the combined effect of plant growth and litter decomposition.(3)N addition increased the rate of soil organic P mineralization,while litter treatment adversely affected P mineralization.N addition significantly increased acid phosphatase activity in July and August,whether N is applied or not,phosphatase activity decreased with litter treatment.N addition increased the rate of organic P mineralization at every litter level;whether N is applied or not,the rate of organic P mineralization decreased with litter treatment.N addition was able to promote the rate of organic P mineralization by increasing plant P stock,which in turn increased acid phosphatase activity.Litter treatment can inhibit the rate of organic P mineralization by inhibiting acid phosphatase activity,and can also promote the rate of organic P mineralization by increasing microbial biomass P.In addition to plant P stock,acid phosphatase activity and microbial biomass P,N addition and litter treatment can also affect the rate of organic P mineralization through other pathways.(4)Plant growth and litter decomposition regulated phosphorus cycling processes together.In July,the rate of organic P mineralization was negatively correlated with soil p H,water content,soil total P and microbial biomass P,and positively correlated with phosphatase activity;in August,the rate of organic P mineralization was negatively correlated with soil total P and microbial biomass P,and positively correlated with phosphatase activity;in October,the rate of organic P mineralization was negatively correlated with soil available P content and microbial biomass P,and positively correlated with soil total P.This indicates that phosphatase activity and microbial biomass P are important regulators of soil organic P mineralization process.N addition increased phosphatase activity,decreased microbial biomass P,and increased the rate of organic P mineralization;litter treatment decreased phosphatase activity,increased microbial biomass P,and decreased the rate of organic P mineralization.Thus,the phosphorus demand of plant growth and litter decomposition can drive the soil phosphorus cycling and soil P pool dynamics in grassland.In summary,N addition can promoted plant growth and increased plant P stock at the early stage of growing,thereby increasing acid phosphatase activity and enhanced the rate of organic P mineralization.At the late stage of growing,the demand for P of plant growth weakened,and the promotion of phosphatase and mineralization rate by N addition led to an increase in soil P pool.Litter treatment increased plant P concerntration and enhanced soil organic P,microbial biomass P,which could alleviate the adverse effects of N addition on soil P pools.This research showed effects of litter on soil P pool and mineralization processes under the background of N deposition,and deeply revealed the mechanism how N addition and litter influenced soil phosphorus cycling through altering environmental conditions and community characteristics.This research deepen the understanding of grassland nutrient cycling in response to N deposition and human activities,but also improves the scientific basis for grassland management under the background of global changes.