Soil Nutrient Concentrations, Associations and Their Relationships with Canopy Tree Category and Size in the Southwestern China Tropical Rainforests

Soil nutrients and their stoichiometry are important indicators of nutrient biogeochemical cycles and various ecological processes. Soil nutrients are heterogeneously distributed and can be influenced by plants through litterfall and root activity. To explore the associations between soil nutrients and relationships between soil nutrients and plant characteristics, we selected three canopy tree categories based on abundance as dominant, common, and rare, with different plant sizes based on DBH (diameter at breast height, cm) for each species from three 1 ha tropical forest sites (Bu-Beng, P55, and Na-Ban-He forests), and collected the topsoil (0–10 cm) for physiochemical analysis. The results showed that soil nutrient concentrations were significantly different among the three forest sites. For soil total C, N, and P associations, soil total C and N had significant associations at all three sites; however, the associations of soil total C-P and N-P varied among sites. The plant category had significant relationships with soil stoichiometry, whereas plant size had significant relationships with soil nutrient concentrations; these relationships varied among the three sites. The results indicate that soil nutrient heterogeneity is influenced by tree category and size. Future studies should include a larger sample size to further validate these results.