| Active soil organic carbon and nitrogen are important parts of soil carbon and nitrogen pools, which include soluble organic carbon (DOC) and nitrogen (DON), microbial biomass carbon (MBC) and nitrogen (MBN). Based on the activity of DOC, DON, MBC and MBN and its important role in forest ecosystems material cycle, soil active organic carbon and nitrogen become one of the hotspots of global carbon and nitrogen cycling studies. Based on the north subtropical forest vegetation, a complete elevation transects was set up between500to1720m a.s.l. in Dabie mountains in Yaoluoping Nature Reserve, where is extremely sensitive to climate change. The characteristics of organic carbon and nitrogen and their responses to litter decomposition at different altitudes under the evergreen broad-leaved forest (EBF), evergreen broad-leaved and deciduous broad-leaved mixed forests (EDBF), deciduous broad-leaved forests (DBF), broadleaf-conifer mixed forest (CDBF) and coniferous forest (CF) were studied in order to clarify the response of forest soil to different altitudes and climate change at a regional scale and to provide data for a better understanding of the region’s carbon and nitrogen cycle mechanism. In this study, I mainly focus on the following:1) Differences in pool of active soil organic carbon and nitrogen along an elevation gradient;2) Seasonal dynamics of soil dissolved organic carbon and nitrogen of the forest vegetation types along an elevation gradient;3) Characteristics of soil nitrogen mineralization in the forest vegetation types along an elevation gradient;4) Soil microbial characteristics of the forest vegetation types along an elevation gradient and its effect on carbon and nitrogen transformation;5) The impact of litter decomposition on soil carbon and nitrogen cycling processes of the forest vegetation types along an elevation gradient.The main research findings were summarized as follows:(1) Surveys on the community composition of elevation gradient indicated that altitude ranges from500～700m,800～1000m,1100～1300m,1400～1500m and 1600-1700m corresponding to the five kinds of typical forest vegetation types were EBF, EDBF, DBF, CDBF and CF, respectively. Soil organic carbon (SOC), DOC, DON, MBC and MBN content increased with increasing elevation gradient, and total nitrogen content increased with elevation rise first and decreased after. By principal component analysis, soil total organic carbon, soil moisture, soil bulk density and soil pH were main factors of soil active organic carbon and nitrogen content, which makes a contribution to95.5%.(2) Soil DOC and DON content were higher in autumn and winter and relatively lower in spring and summer under five kinds of forest vegetation types. For0-40cm soil layer, DOC content of vegetation EBF, EDBF, DBF, CDBF and CF were16.79-93.69mg·kg-1,20.01-103.77mg·kg-1,30.91-117.29mg·kg-1,20.11-110.23mg·kg-1and18.11～125.11mg·kg-1, respectively. For0-40cm soil layer, DON content of vegetation EBF, EDBF, DBF, CDBF and CF were15.82～65.13mg·kg-1、21.06～58.98mg·kg-1、23.78～80.01mg·kg-1、14.82～50.11mg·kg-1and11.12～40.88mg·kg-1, respectively. The order of absorbance values of five kinds of forest vegetation types were CF> CDBF> DBF> EDBF> EBF. Five kinds of different vegetation types of amino acids in the soil DON components were higher in the autumn and winter, and there was no significant difference (P>0.05) in the spring and summer.(3) There were different types of mineral nitrogen dominant in the five kinds of forest vegetation types. Our study showed that soil NH4+-N content were lower than NO3--N in vegetation EBF, EDBF and DBF, whereas the NH4+-N content were higher than NO3--N in vegetation CDBF and CF. Soil nitrogen mineralization rates with vegetation types, different seasons and soil layers were highly significant differences (P<0.001). Seasonal variation of net ammonification, nitrification and net mineralization rate in the five kinds of vegetation types was consistency. As autumn, soil ammonificaton, nitrification, and nitrogen mineralization rates exhibited varying degrees of negative, indicating that soil inorganic nitrogen transformation to organic nitrogen and the system net consumption of inorganic nitrogen in the five kinds of vegetation types during this season.(4) We have study soil respiration in five kinds of typical forest vegetation along an elevation gradient for one year. For0-20cm soil layer, soil respiration rate of vegetation EDBF were significantly higher than the other four vegetation types throughout the year, and the highest was found in the summer (187.13μg·C·kg-h-1), which was31.56%,43.18%,51.58%and53.98%higher than vegetation EBF, DBF, CDBF and CF, respectively. The lowest soil respiration rate was found in vegetation CF throughout the year, which was34.05μg·C·kg-1h-1(winter). For20-40cm soil layer, soil respiration rate variation between different vegetation types was not. obvious.(5) Soil microbial biomass and soil microbial community composition and C, N turnover rates were significantly (P<0.05) influenced by five kinds of forest vegetation types along an elevation gradient. For0-40cm soil layer, soil MBC content of five forest vegetation was92.04～1225.01mg·kg-1, which were the highest in summer and lowest in winter. It implies that microbial adaptation holding in summer, that assimilation dominant. Soil MBN content of five forest vegetation was15.04-145.02mg·kg-1, and showed the lowest in summer, and highest in winter. However, we observed the highest soil respiration rates in summer. Five kinds of forest vegetations were dominated by the number of bacteria in soil. The total number of microorganisms and bacteria had the same seasonal trends, which were higher in spring and summer and least in winter. Compared with the other four vegetation types, we found that the lowest fungal biomass appeared in vegetation EBF, which could be primarily due to the higher pH value and lower C/N ratio.(6) The order of litter decomposition rates in different forest vegetation types along an elevation gradient was EDBF> DBF> EBF> CDBF> CF. Decomposition rates of five typical vegetation litter were inversely proportional with C, P content and C/N ratio in litter, and proportional with the N/P ratio. Therefore, decomposition rate of leaf litter was influenced not only by the environmental factors, but also by the chemical properties in different forest vegetation types. |
PDF Full Text Request