Characteristics Of Precipitation Partitioning And Chemistry In Subtropical Evergreen Broad-leaved Forest

Rainfall plays an important role in water and nutrient cyclings in forest ecosystems,so it is particularly important for the relationship between forest and water.Rainfall passed through the multi-layered canopy caused redistribution of rainfall,and resulted in changes of rainwater chemical characteristics.In this study,as the research object of evergreen broad-leaved forest in Qimen and Shitai,rainfall partitioning（including throughfall and stemflow）and water chemistry were investigated.The results are as follows.（1）Gross rainfall and partitioningThe total rainfall from January 2014 to December 2015 was 3642.5mm in Shitai,and throughfall was 3009.2mm which covered 82.6% of the total rainfall.During this period,the total rainfall was 3974.1mm in Qimen,and throughfall was 2716.4mm.The throughfall covered 68.4% of the total rainfall in Qimen.Rainfall concentrated in summer.In Shitai,the total rainfall from January to December in 2015 was 1975.4mm,in which stemflow was 287.6mm,and covered 14.6% of the total rainfall.Throughfall and stemflow was significant correlation with rainfall（P>0.01）.（2）p H and EC valueIn both Shitai and Qimen,the pH of rain water was neutral with a range of 5.95 to 7.12.The order of pH values in Shitai was: stemflow < throughfall < rainfall,and in Qimen it was ordered as throughfall < rainfall.The pH of rainfall was Qimen <Shitai,while throughfall was Qimen>Shitai.The pH values of rainfall,throughfall and stemflow were high in spring and summer while low in winter and autumn.The pH values was determined by NH4+ and NO3-.The pH values of rain water were correlated with cationand anoinions.The order of EC values in Shitai was: stemflow > throughfall >rainfall,and in Qimen was throughfall > rainfall.With comparison of the two regions,EC values for both rainfall and throughfall were Qimen<Shitai.The seasonal variations were the same in both Qimen and Shitai with low EC in spring and summer and high in winter and autumn for rainfall,throughfall and stemflow.The EC value fluctuated with rainfall intensity in the hydrological processes.In the rainy season,the EC value was relatively lower.（3）Nutrient dynamicsThe nutrient concentrations of rainfall in Shitai ranked as TOC> SO₄^2-> Ca²⁺> Cl^->K⁺> NO3--N > NH4+-N > Mg²⁺>PO₄^3--P.For the throughfall in Shitai,it was ordered as TOC> SO₄^2-> K⁺> Ca²⁺> Cl^-> NO3--N > Mg²⁺ > NH4+-N > PO₄^3--P.The order of the nutrient concentrations was stemflow > throughfall > rainfall in Shitai except for Ca²⁺.In Qimen,the nutrient concentrations of rainfall was ordered by TOC > SO₄^2-> Ca²⁺ > K⁺> Cl^-> NH4+-N > NO3--N > Mg²⁺ > PO₄^3--P and for the throughfall was TOC > SO₄^2-> K⁺> Ca²⁺ > Cl^-> Mg²⁺ > NO3--N > NH4+-N > PO₄^3--P.The nutrient concentrations was higher in throughfall than inrainfall.The correlation analysis of nutrient concentrations showed that high correlation appeared in Shitai andlow in Qimen.