Impact Of Nitrogen Addition On Decomposition Of Leaf Litter And Fresh Leaves In A Semiarid Grassland Ecosystem

Litter decomposition is a critical link in nutrient and carbon cycling in terrestrial ecosystems and plays a key role in arid and semi-arid regions of nitrogen deficiency.Litter generated from natural and human disturbance usually contains a greater proportion of fresh leaves having more nutrients and decomposes more rapidly than typical litter comprised of senescent leaves.Previous studies have focused on the impact of nitrogen deposition or the quality of litter on litter decomposition,but we know litter about the interaction of litter decomposition between nitrogen deposition and litter quality.The study was located in the Semi-arid Loess Plateau Ecosystem Research Station of Lanzhou University on the background of alfalfa land ecosystem of abandoning a decade,using the method of litter bags to compare the decomposition process of fresh leaves and senescent leaves of Stipa capillata Linn?Medicago sativa to explore the response of decomposition rate to nitrogen addition.Additions of N to soils have been performed to apply ammonium nitrate(NH4NO3).N addition treatments include control(N0,without N added)and nitrogen(N1,4.42 g N m-2 per year),each includes MLGREEN?MLLITTER?SLGREEN?SLLITTER.Results indicated:(1)Fresh leaves of Stipa capillata Linn ? Medicago sativa decompose rapidly than senescent leaves,the decomposition of Medicago sativa has significant difference in each sampling date;the decomposition of Stipa capillata Linn has significant differences in April and July of 2015,does not have significant differences under the rest of sampling date.These show the quality of litter has a great influence on the decomposition rate.(2)The decomposition pattern is characterized by using a expolynominal regression equation(Mt=Ae-k1t+B).Compared with control,nitrogen addition accelerates the decomposition rate of MLGREEN ? SLGREEN,inhibits the decomposition rate of MLLITTER? SLLITTER,but does not have significant differences,exclude fresh leaves of Medicago sativa in April and July of 2016 have a significant difference(P<0.05).(3)The correlation between soil moisture content and decomposition rate is weak(? r ? <0.3),the correlation with total nitrogen is negative(0.4<?r?<0.8).The correlation between organic carbon content in soil and fresh leaves of Medicago sativa ? Stipa capillata Linn is positive,the remainning is negative(0.4<?r?<0.8),but all do not have significant difference.In control,the correlation between Stipa capillata Linn and mineralized nitrogen is significantly negative(P<0.05).(4)Impact of nitrogen addition on soil total nitrogen ? soil organic carbon ? soil PH is non-significant.Significantly increasing the content of mineralized nitrogen under the specific sampling date.The content of mineralized nitrogen and microbial carbon have significant differences over time.(5)The impact of the interaction between Nitrogen addition and the quality of litter on decomposition rate do not have significant difference(P>0.05),but the impact is significant over time(P<0.05).