Effects of warming on the stoichiometry of soil microbial biomass and extracellular enzymes in an alpine shrubland

Abstract

The alpine shrublands on the Qinghai-Tibetan Plateau are experiencing significant warming. Revealing the effects of warming on the soil microbial metabolism will provide insights into the dynamics of soil carbon (C) and nutrient cycling in these alpine ecosystems. A five-year warming experiment (+1.3 °C, using open-top chambers) was conducted in a Sibiraea angustata-dominated alpine shrubland on the eastern Qinghai-Tibetan Plateau. We examined the effects of warming on the stoichiometry of topsoil (0–15 cm) microbial biomass, extracellular enzyme activity and their relationships with soil physicochemical properties. The results showed that the effects of warming on the soil microbial biomass C, nitrogen (N) and phosphorus (P) varied with the growing season. Warming increased the activity levels of C-acquiring enzymes (β-glucosidase, BG) by 7.5 %-15.1 % throughout the growing season (P < 0.01) and the activity of polyphenol oxidase (PPO) by 6.5 % during the early growing season (P < 0.05), indicating that warming would strengthen microbial C limitation and increase degradation of soil labile and recalcitrant C components. Warming increased the activity of P-acquiring enzyme (acid phosphatase, AP) by 14.6 % (P < 0.01) and triggered microbial P limitation during the late growing season, which might be a result of an increasing alpine shrub P uptake. Warming did not affect the total activity levels of N-acquiring enzymes throughout the growing season (P > 0.05), mainly due to higher soil N availability. Warming did not affect the stoichiometry of soil extracellular enzymes throughout the growing season (P > 0.05), except for a decreasing in the enzyme N:P ratio during the early growing season (P < 0.05). Moreover, the microclimate (air and soil temperature), available soil nutrients (soil dissolved organic C and available P) and soil pH accounted for most of the variation in soil microbial biomass, extracellular enzyme activity and their stoichiometry in response to warming. Our results suggest that warming may trigger and strengthen soil microbial C and P limitation during the growing season, accelerating soil C loss and nutrient cycling in alpine shrublands on the Qinghai-Tibetan Plateau.