| The increase of atmospheric nitrogen deposition and the change of precipitation pattern have effects on litter decomposition and nutrient cycling in grassland ecosystem.However,it is still not clear how nitrogen addition,increased precipitation and interactive processing of nitrogen addition and increased precipitation affect soil characteristics and litter decomposition in grassland ecosystem.In this paper,soil in the Stipa baicalensis meadoe steppe was chosen as the research object and the control experiment of simulation rainfall and increasing nitrogen were carried out in field situ conditions.Increasing nitrogen amount was set to 5 g N m-2 a-1 and 10 g N m-2 a-1 and the rainfall amount was set to 14% and 28% of natural precipitation.The natural precipitation without nitrogen addition as the control and interaction design of two factors nitrogen and precipitation were used to study the effect of simulation rainfall and nitrogen addition on soil physicochemical properties and the litter decomposition percent.The litter decomposition of seasonal dynamic variation was researched to analyze the main environmental factors on litter decomposition.This study is of great significance for understanding the response process and mechanism of litter decomposition in grassland ecosystem to global change.The main results can be summarized as follows:(1)The soil physicochemical properties in the Stipa baicalensis meadoe steppe were significantly affected by nitrogen addition,increased precipitation,seasons and the interaction among the three(P<0.05).Nitrogen addition,increased precipitation and the interaction between the two groups significant(P<0.05)or extremely significant(P<0.01)increased the content of soil available N,soil available P,and decreased the total soil organic carbon(P<0.05).The results showed that nitrogen addition and increased precipitation could promote the utilization and transformation of N and P in grassland soil,but had a certain inhibitory effect on soil C storage.(2)Litter decomposition percent and litter quality showed obvious seasonal variation characteristics.On the whole,litter quality decreased with season.After the decomposition of litter in 2015,the content of cellulose and hemicellulose in litter decreased significantly(P<0.01)in the fall of 2016,while the content of lignin increased significantly(P<0.01).The increase of precipitation,nitrogen addition and two treatments significantly decreased the content of cellulose in litter,increased the N content of litter,decreased the content of C and C/N.Overall,increasing nitrogen promoted litter decomposition(P < 0.05),but the rainfall has negative effects on litter decomposition.Nitrogen and water coupling will promote litter decomposition of the Stipa baicalensis meadoe steppe in a certain extent.(3)The results of correlation analysis showed that soil temperature,soil water content,soil pH and soil nutrient content were the important ecological factors affecting the decomposition of litter.Nitrogen addition made the correlation of litter decomposition percent,soil moisture and soil temperature decreased.Increased precipitation made the correlation between litter decomposition percent and soil temperature increased.Interaction of nitrogen addition and increased precipitation promoted litter decomposition.The results showed that nitrogen addition and increased precipitation had important effects on the microenvironment of litter decomposition,espectially the interaction of nitrogen addition and increased precipitation. |
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