秦岭南坡红桦林土壤有机碳密度影响因素

以秦岭南坡红桦林为研究对象,利用标准地调查法获得林分、地形、土壤相关数据,分析红桦林土壤有机碳密度(SOCD)分异特征及其与林分因子和地形因子间的关系。结果表明:秦岭南坡红桦林土壤有机碳密度总体均值为(69.02±12.90)t/hm2,原始红桦林土壤有机碳密度均值为(76.21±10.83)t/hm2,次生红桦林为(65.24±12.32)t/hm2,原始红桦林土壤有机碳密度比次生红桦林高16.81%,t-检验结果显示两者存在显著差异;在不同林区间,红桦林土壤有机碳密度亦存在显著差异(P0.05)。从地形因子看,红桦林土壤有机碳密度在不同坡位和坡向间未表现出显著差异,而海拔和坡度对红桦林土壤有机碳密度有较为显著的影响。土壤有机碳密度与海拔、林龄、乔木生物量和草本生物量呈显著正相关,与坡度和林分密度呈显著负相关;主成分分析表明:特征值大于1的四个主成分对土壤有机碳密度的方差累积贡献率为85.62%,海拔、坡度、林分密度和郁闭度是影响秦岭南坡红桦林土壤有机碳密度的主要因子;通过逐步回归分析得到利用海拔、坡度、林龄、林分密度、乔木生物量和草本生物量估算红桦林土壤有机碳密度的模型:SOCD=0.015E-0.332G-0.026FD+0.304SA+0.105BA+21.673BH+36.358。

Factors affecting soil organic carbon density in Betula albo-sinensis forests on the southern slope of the Qinling Mountains

Soil organic carbon, the main part of the terrestrial ecosystem carbon pool, is an essential component of the terrestrial carbon cycle, and one of the most important components of research on global change. Accurate estimation of soil organic carbon storage is important for determining the role that soil organic carbon plays in the terrestrial ecosystem carbon cycle, and thus in changes in the global environment. Forest soil organic carbon storage changes according to topography and forest conditions; therefore, research on forest organic carbon in a variety of such conditions is essential to determine the relationship between soil organic carbon storage, and factors related to topography and forest conditions. Betula albo-sinensis forest is one of the principal forest types in the Qinling Mountains. This study aimed to analyze the distribution patterns of soil organic carbon density (SOCD), and to reveal the relationship between soil organic carbon density and factors influencing Betula albo-sinensis forest on the southern slopes of the Qinling Mountains. We investigated topographical, stand, and soil factors of 122 plots, each of which was 20×30 m. Inventory data (i.e., elevation, gradient, slope position, slope aspect, canopy density, plant cover, biomass, mean height, and mean diameter at breast height) of Betula albo-sinensis individuals in each plot were measured and recorded. Soil samples were tested for SOCD, moisture density, and bulk density. Results indicated that the average SOCD was (69.02±12.90) t/hm². In virgin forest, the average SOCD was (76.21±10.83) t/hm², in secondary forest, (65.24±12.32) t/hm². The difference in average SOCD between them was significant. The average SOCD decreased with soil depth increasing, and the average SOCD for soil layers A-C was (31.52±6.57), (27.18±6.49), and (10.32±2.65) t/hm², respectively. The average SOCD (t/hm²) differed by forest region (Xunyangba=(58.80±10.29), Huoditang=(67.95±10.25), Huangbaiyuan=(69.63±12.78), and Guanyinshan=(75.82±12.30)). One-way ANOVA analysis showed that differences in average SOCD were significant for the four forest regions and soil layers, but not significant for slope positions. Differences in SOCD between shady and sunny slopes were insignificant, based on t-tests. Correlation analysis showed that SOCD was positively correlated with elevation, stand age, arbor biomass, and herb biomass, but negatively correlated with surface gradient and forest density. Principal component analysis showed that elevation and gradient were the first principal components affecting SOCD. Canopy density and forest density were the second principal components, stand age the third, and arbor biomass and herb biomass the fourth. These four principal components accounted for 85.62% of the variance of SOCD. Stepwise regression analysis showed that the effect of different factors on soil organic carbon density was unclear. However, stand age, elevation, gradient, arbor biomass, and herb biomass were the predominant factors affecting SOCD.