Effects Of Litter On Soil Nitrogen Distribution In Qinling Natural Forest

Litter plays an indispensable role in nutrient cycling of forest ecosystem and has an important influence on nitrogen dynamic changing and recycling.However,the research on litterfall in natural forests of Qinling Mountains,especially the relationship between litterfall input and nitrogen cycle were rarely reported.In this study,the litter manipulation experiments and soil core incubation method were carried out in three natural forests of Qinling Mountains,namely Picea asperata forest,Betula albo-sinensis forest and mixed forest of Picea asperata and Betula albo-sinensis.The difference between the effects of litter removal and non-removal on soil nitrogen distribution,including total nitrogen content,nitrate content,ammonium content,total nitrogen content among soil aggregates with different sizes and soil nitrogen leaching loss were studied.The main conclusions were as follows:The total nitrogen content,soil nitrate content and ammonium content of three natural forests decreased with increasing soil depth.Litter removal for 3 years significantly decreased the soil total nitrogen content,nitrate content,ammonium content and organic carbon content in 0-40 cm soil layer of the three natural forests.Litter removal for 3 years significantly increased the soil bulk density in 0-40 cm soil layer of Picea asperata forest.The soil total nitrogen content,nitrate content and ammonium content had highly significant positive correlation with soil organic matter content in three natural forests.The soil nitrate content and ammonium content of Picea asperata forest and Betula albo-sinensis forest had significant and highly significant correlation with soil water content,the soil nitrogen content of Picea asperata forest had highly significant negative correlation with soil bulk density,and the soil nitrogen content of Betula albo-sinensis forest had highly significant negative correlation with soil bulk density.The DR_0.25?>0.25 mm mechanical stable aggregates?in 0-10 cm soil layer of three natural forests were significantly lower than other soil layers.Among the three stands,,the DR_0.25,WR_0.25?>0.25 mm water stable aggregates?,and MWD?mean weight diameter?in0-40 cm soil layers of Betula albo-sinensis forest were the highest.Litter removal for 3years significantly decreased the soil aggregates stability in 10-40 cm soil layer of Betula albo-sinensis forest and mixed forests,the soil aggregate stability of Betula albo-sinensis forest increased with increasing soil depth.The soil total nitrogen content among soil aggregates with different sizes in three natural forests decreased significantly.The total nitrogen contents among soil aggregates with different sizes in Betula albo-sinensis forest were the highest.Litter removal significantly decreased the total nitrogen content among soil aggregates with different sizes in 0-20 cm soil layers of Betula albo-sinensis forest,and significantly decreased the total nitrogen content among soil aggregates with 0.5-1 mm and0.25-0.5 mm size.In three natural forests,the contributing rates of total nitrogen among soil aggregates with?5 mm size were the highest,followed by 2-5 mm size,and the0.25-0.5 mm size were the lowest.Litter removal significantly increased the contributing rates of total nitrogen among soil aggregates with?5 mm size in 0-10 cm soil layer of three natural forests,and significantly decreased the contributing rates of total nitrogen among soil aggregates with?5 mm size in 0-20 cm soil layers.The lost nitrogen in Picea asperata forest was mainly in the form of nitrate.Different litter treatments have significant effects on soil nitrogen content after leaching at various slope positions.The total nitrogen content of T4 treatment were significantly higher than other treatments at the upper and lower slopes.At the middle slope,the total nitrogen content and ammonium content of T3 treatment were significantly higher than T2treatments.Litter removal and the slope position significantly affected the nitrogen leaching pattern in Qinling forest.The soil nitrogen leaching in the T2 treatment of the lower slopes were significantly higher than that in the T4 treatment,and the total nitrogen leaching in the upper slope position were the highest among the three slope positions.The litter removal and slope position had significant effects on soil total nitrogen leaching,ammonium nitrogen leaching and nitrate nitrogen leaching,and there were significant interaction effects between them.There was a clear linear relationship between the nitrogen input and the leaching output.The T2 and T3 treatments have a significant linear relationship between the total nitrogen input and the leaching output.The T2 treatment regression equation has the highest R²value?0.949?.For soil nitrate and ammonium nitrogen,the leaching input and output of T2 treatment had a significant correlation.The results of this study showed that litter removal significantly decreased the soil total nitrogen content and soil organic carbon content in 0-40 soil layers of three natural forests,significantly increased the soil bulk density in 0-40 cm soil layer of Picea asperata forest.Litter removal significantly decreased the soil aggregates stability in 0-40 soil layers of three natural forests,significantly decreased the contribution of total nitrogen among soil aggregates with?5 mm size in 0-20 cm soil layer.The lost nitrogen in Picea asperata forest was mainly in the form of nitrate.Litter removal significantly increased the nitrogen leaching amount,and the leaching loss of soil nitrogen was the highest in the upper slope.There were significant interaction effects of between the litter removal and slope position on nitrogen leaching loss.The total nitrogen input and leaching output of soil under litter removal have significant linear relationship.