Abstract

Studies during last decade have established that soil microbial biomass, enzyme activity and nutrient pools in some cold regions often keep relatively high level in winter and drop rapidly when soil temperatures approach and exceed 0°C during winter-spring transitional period. However, the inconsistent results were observed in different ecosystems due to various temperature dynamics. Based on previous observations on nutrient dynamics, soil microbial biomass, enzyme activity and soluble carbon and nitrogen were investigated in the highly humified soils of subalpine and alpine fir (Abies faxoniana) forests along an altitude gradient in the Eastern Qinghai–Tibet Plateau every 10 days from 5 March until 25 April, 2009, including the winter-spring transitional period. Soil temperature significantly changed during the soil thawing period with frequent soil temperature fluctuations around 0°C. Microbial biomass sharply increased as soil thawing proceeded until an obvious peak when soil temperatures rise to 0°C. Thereafter, microbial biomass declined during the thawing period when soil temperatures exceeded 0°C. Likewise, the rapid crashed in the soluble organic nutrient pools occurred shortly before or coincident with the microbial biomass dropped as soil temperature fluctuated close to 0°C. Meanwhile, the sudden decline in enzyme activity occurred just before the soluble organic nutrient pools collapsed. Additionally, the dynamic patterns of microbial biomass, enzyme activity and soluble organic substrate varied with altitudes due to different temperature fluctuations. The results indicate that the release of nutrients as microbial biomass decline might represent an important pulse of carbon and nutrients pools for vegetation growth in the early stage of growing season.

Key words: Subalpine and alpine forest, temperature dynamics, soil microbial biomass, soil enzyme activity, soluble organic substrate, soil thawing period.