| Larch (Larix gmelinii) plantation was chosen as the concern of this research. One permanent plot (25-years of observation) and 4 chronosequence plot series comprising 159 plots of larch plantations in northeastern China were studied. Soil organic carbon, total nitrogen, alkali-hydrolyzable N, DOC, pH, EC and effective silicon were settled, and the carbon sink of larch plantation ecosystem was estimated. Following conclusions were got:1) Annual NEE(net ecosystem exchange), RE(ecosystem respiration) and GEP(gross ecosystem productivity) of larch plantation ecosystem were 263-264 g C·m-2,718-725 g C·m-2,981-989 g C·m-2, respectively. Environmental factors of different period had different influences on NEE. The afternoon NEE changed more slowly with the VPD(vapor pressure deficit) variation than that in morning. The light use efficiency in the morning was 0.6284 mol.mol-1, which was 14% more than that in afternoon. The NEE increased with the temperature and the increasing rate in the morning was 1.5 times higher than that in the afternoon (air temperature>15℃). These differences in responding environmental changes led to 90% of annual NEE in the morning, and only 10% was attributed from that in afternoon, the annual GEP in the morning took a percentage of 60%, and 40% was from that in afternoon. These findings was supported by the observation in leaf level, i.e., morning photo synthetic capacity on average of whole growing season was over 3-fold higher than that in afternoon.2) Significant SOC accumulation (96.4 g C m-2 yr-1) and soil bulk density decrease (5.7 mg cm-3 yr-1) in the surface soil layer (0-20 cm) during the larch growing, but no consistent changes of soil pH, EC, nitrogen, effective silicon and C/N. Nitrogen depletion (4.1-4.3 g m-2 yr-1), soil acidification (0.007-0.022 pH units yr-1) and C/N ratio increase (0.16-0.46 yr-1) were observed in lessive soil, whereas no significant changes were found in typical dark-brown forest soil. Proper management is therefore important to ensure soil sustainability, especially for the infertile lessive soil. This SOC accumulation rate (96.4 g m-2 yr-1) can take 36% of the total carbon sink capacity (NEE) of larch forests, and 20% of GEP in this region. It's showing the importance of soil carbon accumulation in the ecosystem carbon balance. A much longer duration for observation and research is needed.3) In pedogenesis layers (A, B, C), SOC content increased in A layer () during the larch plantation at the rate of 0.16-0.5 g kg-1 yr-1. While, the SOC storage didn't change at A layer for the decreased bulk density and non-changed thickness of A layer. In lessive soil of Laoshan site, soil nitrogen content decreased 0.014 g.kg-1 yr-1, soil nitrogen storage declined 3 g m"2 yr-1, the soil pH decreased at B and C layer. In three series of polts of dark brown soil, soil nitrogen and pH didn't change obviously with the larch growth. O layer, over the A laer, played an important role in soil carbon accumulation. The process of larch growth accumulated SOC and soil nitrogen in O layer, at the mean rate of 48.5 g m-2 yr-1 and 0.55 g m-2 yr-1, respectively. It was mainly caused by the significant increasing weight of O layer soil (68.55 g.m-2 yr-1). And, the thickness of O layer increased. For the mineral soil, the thickness, bulk density, EC and effective silicon generally didn't significantly correlate with the larch age.4) The relationships between DOC and UV absorption were significant in 20-40cm,40-60cm and 60-80cm soil layers. Functional group compositions were consistent in soil solution of different soil layer. When.coming to more than 400nm wavelength, the functional group compositions didn't change. Soil DOC was significant positively correlated with larch ages, soil nutrient and soil EC. While, which was inversely related with soil pH and bulk density. All the results showed soil DOC changes had important regulating response to soil physical and chemical properties during larch growing.
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