Effects Of Simulated Warming On Carbon Isotopic Composition Of Forest Litter And Soil In The Northern Slope Of Changbai Mountains

It is important to study the nutrient of carbon and nitrogen and stable carbon isotopic composition in litter and soil organic matter along natural altitudinal forest transect and their responses to the global warming for interpreting forest ecosystem nutrient cycling, value evaluation and simulation ecologicalmodels.Total organic carbon (TOC), total nitrogen (TN) and stable carbon isotopic composition (δ13C values) of litter and soil samples were investigated along a natural altitudinal transect in the north slope of Changbai Mountain, where three forest types existed, i.e, Korean pine forest (Pinus koraiensis) mixed with broadleaf trees (PB, altitude 740 m), Spruce-fir forest (Piceaasperata Mast mixed Abies nephrolepis) (SF, altitude 1,350 m) and Betula ermanii forest (EB, altitude 1,996 m). Responses of TOC, TN and 813C values in litter and soil samples to simulated warming were conducted by relocating intact soil cores (20 cm depth) from high-elevation to low-elevation sites for one year.It was shown that:(1) The litter was significantly depleted in 13C (-29.6～-27.5‰) relative to the soil (-26.4～-24.9‰).δ13C values in both the litter and the soils increased downward through the litter and soil layers in all the three typical forest types.δ13C values increased with decreasing particle size from>63μm to<2μm fractions.(2) The litter showed TOC contents andδ13C values for the three forest types in the same order:SF>PB>EB, and TN contents in another order:EB>PB>SF; Soil TOC and TN contents in Betula ermanii forest (EB) were significantly larger than those in the other two forest types, and soil 813C values showed an order:EB>PB>SF. Pearson correlation analysis demonstrated that both the TOC contents and 813C values in the litter samples were significantly positively related to temperature (r=0.771 and 0.682 respectively,p<0.05), but unrelated to moisture. And litter TN contents were unrelated to both temperature and moisture. TOC and TN contents and 813C values of soil organic matters were significantly negatively related to temperature (r=-0.922,-0.869 and-0.730 respectively, p<0.05), but significantly positively related to moisture (r=0.856,0.949 and 0.789 respectively,p<0.05)(3) As expected, the soil-core relocation caused significant increase in soil temperature but made no significant effect on soil moisture. Over one-year simulated warming, TOC and TN contents of litter and soil samples declined in general, indicating that decomposition of organic matters in the litter and soil samples was accelerated under the warming conditions. Litterδ13C values raised by 0.42‰, while 813C values in the bulk soils reduced by 0.36‰, and there were also corresponding decreases of 813C values in different particle size fractions, after intact soil-core relocation warming incubation. A decrease of 813C values was larger in both 2～63μm and<2μm fractions (0.47‰and 0.48‰) than in the>63μm fractions (0.33‰). The resultes suggest that the older soil organic carbon associated with the fine particle size fraction may be significantly affected by climate warming.