Spatial heterogeneity of soil nutrients and its impact on tree species distribution in a karst forest of Southwest China
喀斯特森林土壤养分的空间异质性及其对树种分布的影响

Aims Studies of spatial variability of soil nutrients are valuable not only to the understanding of formation, structure, and function of soils, but also for understanding soil-plant associations and mechanisms of plant species coexistence. However, little is known about the spatial heterogeneity of soil nutrients in karst forest. Our objectives were to 1) characterize the spatial heterogeneity of soil nutrients in a karst forest, 2) examine correlations between spatial distribution of soil nutrients and local topographic variables and 3) assess the influence of soil nutrients on spatial distributions of tree species. Methods A 100 m × 100 m forest plot was established on a hillside in a karst area in Maolan National Nature Reserve, Guizhou Province, Southwest China. All woody species with a diameter at breast height ≥1 cm were identified and surveyed. Surface soil samples (0–10 cm) were collected from a grid of 10 m × 10 m for the analysis of soil nutrients. The spatial variability of soil nutrients and its impact on distributions of tree species were analyzed by using geo statistic methods (semivariogram and Kriging interpolation) and ordination (canonical correspondence analysis, CCA). Important findings The coefficient of variation for soil nutrients ranges from 10% to 80%, and can be considered relatively moderate. Total phosphorus (TP), total potassium (TK), total magnesium (TMg) and pH show strong spatial autocorrelation, while organic matter (OM), total calcium (TCa), available phosphorus (AP) and available potassium (AK) show moderate spatial autocorrelation. The variation range of soil TCa is the smallest (56.2 m) and those of OM, TP and AK are larger. Spatial distribution of TP, TK, TCa, TMg, AP and pH decreases with increasing elevation and decreasing cover of bare rock, while OM increases with increasing elevation, which indicated that the spatial distributions and variability of soil nutrients were mainly affected by topographic factors and habitat characteristics (especially elevation, slope, slope aspect, slope location and cover of bare rock). CCA indicated that the spatial distribution of soil nutrients, especially TK, TMg, pH, TCa and OM, has an important impact on tree species composition and distribution, and thus showed a prevalence of soil resource-based niche differentiation among tree species. Our results suggested high spatial variability of soil nutrients contributes to promoting maintenance of species diversity and the stability of karst forest communities.