喀斯特常绿落叶阔叶混交林土壤磷钾养分空间异质性

在木论国家级自然保护区内喀斯特常绿落叶阔叶混交林内建立500 m×500 m长期监测样地,采用经典统计学和地统计学方法研究喀斯特森林土壤磷钾养分含量及其空间变异特征。结果表明:研究区土壤全磷(TP)、全钾(TK)、速效磷(AP)、速效钾(AK)含量分别为(1.60±0.76)g/kg、(5.42±2.74)g/kg、(5.74±3.63)mg/kg、(5.20±2.96)mg/kg;磷钾养分含量均为中等变异,变异强度为APAKTKTP。研究区土壤TP、TK、AP、AK变异函数值的最佳拟合模型均为指数模型,决定系数均很高(0.671-0.995),TP、AP呈中等强度空间自相关,TK、AK呈弱空间自相关。TP、AP的变程较长,分别为336.00 m和373.50 m,空间连续性较好,TK、AK变程较短(33.30 m、64.50 m),空间依赖性较强。土壤TP表现为坡下(含洼地)含量高,坡上含量较低;AK表现为坡中含量高于洼地含量;AP、TK呈斑块破碎化分布。海拔、坡度和地面凹凸度是土壤磷钾养分空间异质性的主要影响因素。喀斯特常绿落叶阔叶混交林土壤磷钾养分存在不同空间异质性和空间关联性,这为小流域尺度上土壤养分管理、可持续利用策略、喀斯特退化生态系统生态恢复提供理论依据。

Spatial heterogeneity of soil phosphorus and potassium in a mixed evergreen and deciduous broad-leaved forest in karst region of southwest China

The availability of soil nutrients, e.g. phosphorus (P) and potassium (K), and their spatial distribution are key factors controlling plant growth, community development, and ecosystem restoration. Karst is one of the main fragile habitat zones in China. In this study, we examined the soil P and K and their spatial heterogeneity in a 500 m×500 m long-term monitoring forest plot in the Mulun National Nature Reserve, Guangxi, using classical statistics and geostatistics methods. The results showed that the average contents of total phosphorus (TP), total potassium (TK), available phosphorus (AP), and available potassium (AK) in the studied area were (1.60 ±0.76) g/kg, (5.42 ±2.74) g/kg, (5.74 ±3.63) mg/kg, and (5.20 ±2.96) mg/kg, respectively. The variability of soil P and K at a moderate intensity level, and the order of which was AP > AK > TK > TP. Exponential model was best-fitted for the semivariogram of soil TP, TK, AP and AK, and the coefficients of determination are very high, ranging from 0.671 to 0.995. The contents of TP and AP showed moderate spatial autocorrelation, which indicated that the variations were caused by structural variation and random factors, whereas TK and AK had weak spatial autocorrelation. TP and AP had a relatively long autocorrelation distance (336.00 m and 373.50 m, respectively), indicating a relatively good spatial continuity. The autocorrelation distances of TK and AK (33.30 m and 64.50 m, respectively) were shorter than those of TP and AP, suggesting a strong spatial dependence. The distribution of TP in the soil was high on the toe slope (including depressions) and low on the upslope. AK content was higher on the slope than in depression. In addition, both AP and TK had patchy distributions. Elevation, slope, and convex topography were the main factors determining the spatial heterogeneity of soil P and K. Overall, soil P and K showed different patterns for spatial heterogeneity and spatial correlation in karst mixed evergreen and deciduous broad-leaved forest, which provides a reference for site-specific soil nutrients management and designing strategies for ecological restoration of degraded ecosystems in the karst region.