| With the aggravation of global climate change, the study of global carbon cycle of terrestrial ecosystem is continuously deepening and expanding. Soil organic carbon of forest is the main component of the terrestrial carbon reservoir, and plays a crucial role in the Earth’s carbon cycle. This study on spatial heterogeneity has guiding significance to analyze deeply the relation between vegetation and soil and to improve the protection of SOC density. The density of soil organic carbon has strongly spatial heterogeneity, and understanding the carbon cycle of terrestrial ecosystem plays an important role in revealing the relationship between the soil and vegetation, biodiversity maintenance and coexistence mechanism. Besides it is an effective method for exploring soil nutrient and the relationship between environmental factors. Tropical forest plays an important role in maintaining global carbon balance. The study was conducted in tropical rain forest of Jianfengling, Hainan Island, China,and use field investigation, laboratory analysis, and geostatistical methods. It aims to find out the spatial heterogeneity of soil organic carbon density and the influence factors in different soil layers and different spatial scale.The main results are as follows:(1) the mean SOC density at different soil profile depths(A [0-10 cm], B [10-30 cm], C [30-60 cm] and D [60-100 cm]) in 60 hm2 plot was 2.699 kg·m-3, 1.391 kg/m3, 0.811 kg/m3 and 0.765 kg/m3, respectively;The differences for A versus B, A versus C, A versus D, B versus C and B versus D layers were statistically significant(P < 0.05).The mean SOC density at different plot scales(Big [164 Km2], Median [83 Km2] and small [64 Km2]) was 5.585 kg·m-2, 5.694 kg·m-2 and 5.004 kg·m-2, respectively; The mean SOC density at different scales(60 hm2、40 hm2、30 hm2、20 hm2、15 hm2、10 hm2、1 hm2) in 60 hm2 plot was 2.779 kg/m2、2.825 kg/m2、2.804 kg/m2、2.865 kg/m2、2.848 kg/m2、2.911 and 3.234 kg/m2, respectively;(2) Cross-validation results shows that the most fitted models for SOC density at different layers in 60 hm2 plot is exponential for A and D layer, Spherical for B and C layer. The Nugget:Sill were 0.512, 0.708, 0.882 and 0.862, respectively. The ranges of different soil layers were 54.2 m, 70.9 m, 97.2 m and 62.0 m for A, B, C and D layer, respectively;The most fitted models for SOC density at different scales in 164 km2 is exponential for big scale, Spherical for median scale, Gauss model for little scale. The Nugget:Sill were 0.469, 0.258, and 0.018, respectively. The ranges of different scales were 449.0 m, 400.0 m, and 230.0m for different scales respectively;The most fitted models for SOC density in 60 hm2 plot is exponential for different scales but Spherical for 1 hm2. The Nugget:Sill ratios were 0.512、0.404、0.578、0.463、0.557 and 0.420, respectively. The ranges of different scales were 54.2 m、21.9 m、38.0 m、24.8 m、35.5 m、22.5 m and 13.6 m for different scales respectively;(3) Ordinary Kriging interpolation shows that A and B soil layers have moderate spatial autocorrelation, while the C and D layer have weak spatial autocorrelation. Meanwhile, the contour maps produced scatter spatial distributions for the A and B layers, but a banded distribution for the C and D layer. In the different study plots and spatial scale,the spatial distribution of soil organic carbon density has a certain similarity and spatial heterogeneity significantly, showed a combination of plaque and banded structure. Sampling density has important influence in computing spatial heterogeneity.(4) Coefficient of variation values shows that moderate variation for both soil organic density values in both different soil layers and scales. Significant correlations and multiple linear regression analysis are detected between soil organic density and these environmental variables, notably with soil available phosphorus, total potassium、nitrogen content in litter(P<0.05); and the soil total nitrogen, soil carbon and nitrogen ratio(C/N); Very significant difference with soil total nitrogen, C/N, soil total phosphorus, soil available nitrogen, soil capillary water holding capacity(P<0.01).(5) Topography-induced water and heat distribution may represent an important factor affecting the spatial distribution patterns of SOC density in different soil layers. The results of ANOVA shows that: the average soil organic carbon density of middle altitude(600-900 m) is significantly lower than the high altitude(> 900 m) and low(< 600 m) altitude(p<0.05), and there is no significant difference between the high and low altitude;The average soil organic carbon density of different slope gradient and position have no significant difference.Different land disturbances have no significant influence on the soil organic carbon density of surface,it may be associated with the recovery period. |
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