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Aims: The response of soil microbial metabolic limitation in forest ecosystems to various factors remains poorly understood. The purpose of the study was to reveal the characteristics of microbial metabolic limitation in soil at the regional scale and the possible influencing factors. Methods: The vector analysis of enzyme activities was used to study the relative soil microbial metabolic limitation characteristics of Quercus aquifolioides forest ecosystems along a mean annual precipitation gradient (MAP, 650 mm–1160 mm). Results: The enzyme activities as well as their partial stoichiometric ratios had negative linear relationships with MAP. Soil microbial metabolism of the study area was limited mainly by carbon (C) and phosphorus (P) and partially by C and nitrogen (N). The C limitation showed a trend of first increasing slightly and then decreasing significantly along the MAP gradient, while N/P limitation did not show an obvious trend. Relative limitation of microbial metabolism was related closely to soil pH and nutrients, where C limitation was affected by soil pH, climatic factors, soil nutrient characteristics and topographic factor, and N/P limitation was affected by soil pH, topographic factor, diameter at breast height of the trees (DBH) and soil nutrient characteristics. In addition, the linear relationship between soil organic matter (SOM) and N limitation was significant, and it was inferred that the degree of N limitation might affect the stability of SOM and C stocks. Conclusions: Microbial C limitation was regulated by MAP, and soil properties were important drivers of both C and N/P limitations. [ABSTRACT FROM AUTHOR]

Soil fungi play an integral and essential role in maintaining soil ecosystem functions. The understanding of altitude variations and their drivers of soil fungal community composition and diversity remains relatively unclear. Mountains provide an open, natural platform for studying how the soil fungal community responds to climatic variability at a short altitude distance. Using the Illumina MiSeq high-throughput sequencing technique, we examined soil fungal community composition and diversity among seven vegetation types (dry valley shrub, valley-mountain ecotone broadleaved mixed forest, subalpine broadleaved mixed forest, subalpine coniferous-broadleaved mixed forest, subalpine coniferous forest, alpine shrub meadow, alpine meadow) along a 2582 m altitude gradient in the alpine–gorge region on the eastern Qinghai–Tibetan Plateau. Ascomycota (47.72%), Basidiomycota (36.58%), and Mortierellomycota (12.14%) were the top three soil fungal dominant phyla in all samples. Soil fungal community composition differed significantly among the seven vegetation types along altitude gradients. The α-diversity of soil total fungi and symbiotic fungi had a distinct hollow pattern, while saprophytic fungi and pathogenic fungi showed no obvious pattern along altitude gradients. The β-diversity of soil total fungi, symbiotic fungi, saprophytic fungi, and pathogenic fungi was derived mainly from species turnover processes and exhibited a significant altitude distance-decay pattern. Soil properties explained 31.27−34.91% of variation in soil fungal (total and trophic modes) community composition along altitude gradients, and the effects of soil nutrients on fungal community composition varied by trophic modes. Soil pH was the main factor affecting α-diversity of soil fungi along altitude gradients. The β-diversity and turnover components of soil total fungi and saprophytic fungi were affected by soil properties and geographic distance, while those of symbiotic fungi and pathogenic fungi were affected only by soil properties. This study deepens our knowledge regarding altitude variations and their drivers of soil fungal community composition and diversity, and confirms that the effects of soil properties on soil fungal community composition and diversity vary by trophic modes along altitude gradients in the alpine–gorge region. [ABSTRACT FROM AUTHOR]

• The soil δ13C showed a moderate spatial heterogeneity in an alpine-gorge region. • The GWR model was a useful tool for mapping the isoscapes of soil δ13C. • Soil C/N and NDVI were the main factors influencing the spatial variation of soil δ13C. Soil stable carbon isotope (soil δ13C) can reflect soil carbon metabolic processes and record environmental and vegetation change information, so mapping the spatial distribution of soil δ13C (isoscapes of soil δ13C) can help us better understand the spatial variability of ecosystem carbon cycles. However, efficient approaches for obtaining the isoscapes of soil δ13C remain challenging, especially in mountainous areas with complex terrain. A total of 150 soil samples were collected and their soil δ13C was measured to investigate the spatial variation of soil δ13C in an alpine-gorge region on the eastern Qinghai-Tibetan Plateau which is characterized by complex terrain. Four prediction methods included ordinary kriging interpolation, multiple linear regression, random forest regression, and geographically weighted regression (GWR) were selected and compared to find the best prediction model for mapping the isoscapes of soil δ13C. The pathways of vegetation, topography, soil, and spatial factors influencing the spatial variability of soil δ13C were explored using variance partitioning analysis and structural equation model. The soil δ13C was significantly different among vegetation types, and ranged from −27.155‰ to −9.647‰. The spatial heterogeneity of soil δ13C showed moderate variation, and was dominated by spatial structural factors. The GWR model had higher prediction accuracy in the modeling soil δ13C in comparison to other models. Soil carbon to nitrogen ratio and normalized difference vegetation index were the main factors determining the spatial variability of soil δ13C, and other topographic and soil factors indirectly regulated the spatial distribution of soil δ13C by influencing these two factors. Our results provided a useful tool (GWR model) for mapping the isoscapes of soil δ13C and explored the factors controlling the spatial variability of soil δ13C in the alpine-gorge region on the eastern Qinghai-Tibetan Plateau, which are important for an in-depth understanding of soil carbon cycling in mountain ecosystems. [ABSTRACT FROM AUTHOR]