Variations in ratio and loads of soil nitrogen and phosphorus explain the coexistence of dominant tree species in a boreal forest of Xinjiang, northwest China

The resource ratio hypothesis (RRH) and the nutrient-load hypothesis (NLH) state that species coexistence is driven by the ratios and loads (contents) of multiple limiting resources, respectively. However, roles of resource ratios and loads to mature forest ecosystems remains unclear. Data were collected within 300 quadrats (20m×20m) spread across a 12 ha plot of boreal forest in the Kanas of Xinjiang, northwest China. We used torus translation tests to analyze the associations of dominant tree species with specific microhabitats. The linear mixed models were used to assess effects of resource ratios and contents on abundance and basal area of specific species, as well as within different life stages. Two shade-tolerant species, Picea obovata and Pinus sibirica, exhibited opposite relationships to the spatial distribution of soil nitrogen (N) content and phosphorus (P) content. Picea. obovata was associated with microhabitats with high N:P ratio, while P. sibirica preferred microhabitat...