Vegetation and Topographic Factors Affecting SOM, SOC, and N Contents in a Mountainous Watershed in North China

Abstract

This study aimed to reveal the main environmental factors affecting PH, SOM, SOC, TN, and AHN in mountainous areas of Beijing, using the Chaoguan Xigou watershed as the research object. The relationship among pH, SOM, SOC, TN, AHN, topographic factors, and vegetation factors was analyzed by correlation and redundancy analysis (RDA). The results showed that altitude was significantly positively correlated with vegetation types in the study area (p < 0.01). Menhinnick richness index (D), Shannon–Wiener diversity index (H), and Alatalo evenness index (E) ranged from 0.35–0.79, 0.86–1.73, and 0.39–0.7, respectively, indicating moderate variations. E was significantly positively correlated with stand type (p < 0.05), altitude (p < 0.05), and H (p < 0.01). The variation ranges of PH, SOM, SOC, TN, and AHN in soil were 5.78–7.13, 54.73–90.38 g/kg, 23.77–60.25 g/kg, 1.71–4.22 g/kg, and 95.64–223.26 mg/kg, respectively. All soil nutrient indexes had medium variation except for pH (weak variation). In this study, RDA results showed that altitude is the main environmental factor affecting the soil pH, SOM, SOC, TN, and AHN in this area and could explain 25.9% of the total variance. However, the effects of factors associated with altitude on pH, SOM, SOC, TN, and AHN need to be further studied.