| Dissolved and particulate carbon and nitrogen (DC/DN&PC/PN) fluxes are important components in forest carbon (C) and nitrogen (N) budgets. Quantifying fluxes of DC/DN&PC/PN in forest ecosystems is essential to better understanding the C and N cycling processes and improving the assessment and prediction of C sequestration capacity in the ecosystems. However, DC/DN&PC/PN fluxes were often ignored due to lack of knowledge and difficulties in measuring. This study monitored the precipitation redistribution process of Mongolian oak forest (Dominated by Quercus mongolica Fisch., MO) and mixed deciduous forest (i.e., no dominant tree species, MD), measured the concentrations and fluxes of DC/DN&PC/PN for rainfall, net precipitation (i.e., throughfall plus stemflow) and the stream water, respectively. The main purpose of this study was to quantifying DC/DN&PC/PN flux processes of temperate forest ecosystems, and exploring the relevant influcing factors.During the2012-2013growing seasons, the rainfall was1311.5mm and mostly fell between June to August. The mean throughfall rates (i.e., the ratio of throughfall to rainfall) of MO and MD were73%and80%, respectively, and there were significant difference for two forest stands; the stemflow rates (i.e., the ratio of stemflow to rainfall) were5%both for MO and MD, with no difference between two forest stands either. The rainfall redistribution patterns of these two stands varied as a result of the differences in their canopy structure and responses to various rainfall characteristics (i.e., rainfall amount, rainfall intensity).Total rainfall carbon and nitrogen input fluxes were9.94g C m-2a-1and0.85g N m-2a-1during two growing seasons. DC and DN were major components of the C and N fluxes, which accounted for69.84%and76.34%of the total flux, respectively. Total carbon input fluxes of net precipitation were17.85g C m-2a-1and19.97g C m-2a-1for MO and MD over two growing seasons, respectively, and total nitrogen input fluxes were1.59g N m-2a-1and1.33g N m-2a-1, respectively. Influenced by seasonal distribution of rainfall, DC/DN&PC/PN input fluxes for both rainfall and net precipitation were mainly during June to August every year. The dissolved organic carbon (DOC) concentrations for throughfall of MO were significantly lower than that of MD, however, the DN concentrations and input fluxes for throughfall of MO were significantly higher than that of MD, and so was the DOC concentrations for stemflow. Because of the much higher amount than stemflow, throughfall was the dominated component of C and N fluxes of net precipitation, which accounted for90.12%and92.21%of carbon fluxes for MO and MD respectively, and accounted for95.30%and94.82%of total nitrogen fluxes, respectively. Solute concentrations of rainfall and net precipitation were influenced by the amount of rainfall, throughfall and stemflow, they show non-liner (mostly power function or logarithmic function) relationship with eachother.The streamflow transported6.30g C m-2a-1for carbon and0.44g N m-2a-1for nitrogen on average during the study period, in which DC and DN were the main form of carbon and nitrogen, which accounted for88.5%and81.3%of the total carbon and nitrogen. The C transported by the streamflow in2012was less than that of in2013, but the N was more than that of in2013. DOC, DN concentrations for streamflow show linear relationship against the disharge but there were different manifestations at different periods. DIC concentrations show power function against the temperature of the streamflow.So we can conclude that temperate forest ecosystems was a net sink for DC/DN&PC/PN fluxes during the studied period and the absorption value were3.64g C m-2a-1and0.41g N m-2a-1. DC and DN were the main form of C and N for both the rainfall input and stream water output, while the C and N deposition was strengthened after getting through forest canopy by leaching, pollen deposition and droppings of canopy herbivores. Carbon and nitrogen outputs were mainly driven by the discharge of streamflow in the catchment scale, the DC/DN&PC/PN concentrations were different at different periods for the combined effects of hydrological, biophysical and chemical processes. There were linear relationships between water fluxes and DOC/DN concentrations but with different manifestations in different period. |
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