Soil microbial biomass, an important nutrient pool for ecosystem nutrient cycling is affected by several factors including climate, edaphic, and land-use change. Himalayan soils are young and unstable and prone to erosion and degradation due to its topography, bioclimatic conditions and anthropogenic activities such as frequent land-use change. Through this study, we tried to assess how soil parameters and microbial biomass carbon (MBC) of Eastern Himalayan soils originated from gneissic rock change with land-use type, soil depth and season. Chloroform fumigation extraction method was employed to determine MBC from different land-use types. Soil physical and chemical properties varied significantly with season, land-use and soil depth (p < 0.001). The maximum values of soil properties were observed in the rainy season followed by summer and winter season in all the study sites. Annual mean microbial biomass carbon was highest in the forest (455.03 μg g− 1) followed by cardamom agroforestry (392.86 μg g− 1) and paddy cropland (317.47 μg g− 1). Microbial biomass carbon exhibited strong significant seasonal difference (p < 0.001) in all the land-use types with a peak value in the rainy season (forest-592.78 μg g− 1; agroforestry- 499.84 μg g− 1 and cropland- 365.21 μg g− 1) and lowest in the winter season (forest − 338.46 μg g− 1; agroforestry – 320.28 μg g− 1 and cropland − 265.70 μg g− 1). The value of microbial biomass carbon decreased significantly with soil depth (p < 0.001) but showed an insignificant increase in the second year which corresponds to a change in rainfall pattern. Besides, land-use type, season and soil depth, soil properties also strongly influenced microbial biomass carbon (p < 0.001). Microbial quotient was highest in the agroforestry system (2.16%) and least in the subtropical forest (1.91%). Our results indicate that land-use, soil depth and season significantly influenced soil properties and microbial biomass carbon. The physical and chemical properties of soil and MBC exhibit strong seasonality while the type of land-use influenced the microbial activity and biomass of different soil layers in the study sites. Higher soil organic carbon content in cardamom agroforestry and forest in the present study indicates that restoration of the litter layer through retrogressive land-use change accelerates microbial C immobilization which further helps in the maintenance of soil fertility and soil organic carbon sequestration.

中文翻译：

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土地利用，季节和土壤深度对喜马拉雅东部土壤微生物生物量碳的影响

土壤微生物生物量是生态系统养分循环的重要养分库，受多种因素的影响，包括气候，土壤环境和土地利用变化。喜马拉雅土壤年轻且不稳定，由于其地形，生物气候条件和人为活动（例如频繁的土地用途变化）而易于侵蚀和退化。通过这项研究，我们试图评估东部喜马拉雅土壤的土壤参数和微生物生物量碳（MBC）是如何从源于片麻质岩的土地利用类型，土壤深度和季节变化而变化的。采用氯仿熏蒸提取法测定不同土地利用类型的MBC。土壤的理化性质随季节，土地利用和土壤深度的不同而有很大差异（p <0.001）。在所有研究地点，在雨季，夏季和冬季均观察到土壤特性的最大值。森林中的年平均微生物生物量碳最高（455.03μgg-1），其次是豆蔻农林业（392.86μgg-1）和稻田（317.47μgg-1）。在所有土地利用类型中，微生物生物量碳均表现出明显的季节性差异（p <0.001），并在雨季达到峰值（森林-592.78μgg-1；农林业-499.84μgg-1和耕地-365.21μgg）。 − 1），冬季最低（森林− 338.46μgg-1；农林业– 320.28μgg-1和耕地− 265.70μgg-1）。微生物生物量碳的值随土壤深度的增加而显着降低（p <0.001），但第二年却没有明显增加，这与降雨模式的变化相对应。此外，土地利用类型，季节和土壤深度，土壤性质也对微生物生物量碳有很大影响（p <0.001）。在农林业系统中，微生物商最高（2.16％），在亚热带森林中则最低（1.91％）。我们的结果表明，土地利用，土壤深度和季节显着影响土壤性质和微生物生物量碳。土壤和MBC的理化性质表现出强烈的季节性，而土地利用的类型影响研究地点不同土壤层的微生物活性和生物量。