Symmetric responses of microbial carbon and nutrient limitations to warming and cooling in boreal forests: Insights from a transplant experiment

Abstract

Soil extracellular enzymes in boreal forests are considered more susceptible to climate change, which might result in potential changes in carbon (C) stocks and available nutrients. Despite mounting evidence has proven that warming (duration and magnitude) has a profound effect on extracellular enzyme activities (EEAs), little consideration has been given to the symmetric and asymmetric effects of warming and cooling on EEAs, as well as the limitations posed by microbial metabolism. Here, we reciprocally transplanted field soil monoliths from warm and cold sites with a short-term manipulated experiment (15 months) in boreal forests to stimulate climate change (varied 2.09 °C). This study aims to unravel divergent responses of EEAs to cooling and warming, and evaluate the metabolic limitation of soil microbes via ecoenzymatic stoichiometry. The results showed that the activities of 1,4-β-glucosidase, 1,4-β-N-acetyl-glucosaminidase and acid phosphatase were increased by 36.4 %, 77.9 % and 29.3 % under the warming regime, respectively. The symmetric variations of EEAs (excluding leucine aminopeptidase) were detected between cooling and warming regimes. In addition, warming had a slight alleviation of soil C limitation on microbial metabolism, whereas nutrient limitations were not changed by any stimulated climate change regimes. The variations in C limitations induced by warming/cooling were mainly driven by the microbial biomass, C- and phosphorus- acquiring enzyme activities, which were mediated by soil pH, macronutrients and dissolved organic nutrients, respectively. Collectively, our findings highlight the symmetric effects of stimulated warming and cooling on C limitation of soil microbial metabolism.