| Subtropical evergreen broadleaved forests play an important role in regional carbon (C) balance and sustainable development due to their highest productivity, diverse ecosystem functions and complex habitat for abundant biological diversity in southern China. Spatial heterogeneity of soil nutrients in subtropical forests can provide useful information for understanding the spatial pattern of plants and for explaining to some extent, coexistence mechanism of diverse tree species. To investigate spatial variations in soil nutrients and the causes of the variations, litter and soil samples at0-10cm,10-20cm and20-30cm depth were collected at the center of each10m X10m quadrat within1hectare permanent plot of Lithocarpus glaber-Cyclobalanopsis glauca subtropical evergreen broadleaved forest. Soil organic C and total nitrogen (N) concentrations were determined for all samples. The results showed that:(1) Litter biomass was13.56±0.47t-hm-2in the L. glaber-C. glauca forests, of which decomposed litter layer was greater than the semi-decomposition and litter layer biomass. C concentration of the litter ranged from170.34to387.77g·kg-1and N concentration varied from8.27to15.55g-kg-1. C concentration decreased with the degree of litter decomposition. Litter layer C/N ratio is continuously smaller than the decomposed. Litter C storage was3.71±0.15t-hm-2while litter N storage was162.72±6.25kg·hm-2in the forests. C and N storage among litter different layers had a similar change trend.(2) Based on regional variable theory and spatial analysis functions of GS+Version9, spatial heterogeneity of soil organic C and total N concentrations was examined by using semivariogram of geostatistics. The results showed that averaged soil organic C concentration was18.61g·kg-1, ranging from9.53to39.40g·kg-1, and the average value of total N concentration was1.63g·kg-1with a range between0.73and3.32g·kg-1. Theoretical semivariogram model of soil organic C approached spherical model while the best semivariogram model of total N was close to Gaussian model. The spatial variability of soil nutrient primarily resulted from the structural factors and the spatial heterogeneity degree of those indices was moderate. Fractal dimensions from log-log semivariograms quantitatively described spatial pattern differences and scale dependence of the soil organic C and total N. Fractal dimension was high for soil organic C, so soil organic C spatial structure had strong scale dependence with a complex spatial pattern. (3) Kriging was used to analyze the spatial distribution of soil nutrients. Spatial distribution patterns of soil organic C and total N concentrations similarly revealed an apparent belt-shaped and spot massive gradient change. Within the plot, soil organic C concentration was negatively correlated with topographic factors (i.e. elevation and convexity), but the relationship was not significant. Soil organic C showed very significantly a positive relationship with litter biomass. Total soil N concentration exhibited a significantly negative relationship with topographic factors, however, positive relationship was found between total soil N and litter, indicating leaching characteristics of soil N. Spatial variations in soil organic C and total N highlight the importance of vegetation and litter protection in the hilly area of subtropical China. |
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