Potential effect of warming on soil microbial nutrient limitations as determined by enzymatic stoichiometry in the farmland from different climate zones

Abstract

The decomposition of organic matter mediated by soil enzymes is the key process that transports carbon from the soil into the atmosphere. To better understand the effect of global warming on organic matter decomposition, we evaluated the temperature sensitivity (Q₁₀) of invertase (EC3.2.1.26), β-glucosidase (EC3.2.1.21), urease (EC3.1.1.5), acid phosphatase (EC3.1.3.2), and arylsulfatase (EC3.1.6.1) activities in red soil from the subtropical region and black soil from the mid-temperate region at 5, 15, 25, 35, and 45 °C. Further, the in-situ stoichiometry of the products released by enzymes was modelled. All of the enzyme activities in the tested soils increased with the increasing temperature (1.1-8.9 fold per 10 °C), indicating an enhanced degradation of the organic substrate with warming. In the lower temperature range (5-25 °C), Q₁₀ of the enzyme activities in the red soil evaluated in terms of total enzyme activity index were more prominent than that in black soil (1.53 and 3.46 vs 1.16 and 3.19). Changes in the in-situ stoichiometry of enzyme products with warming indicated that, in colder months (Jan. to Apr. and Oct. to Dec.), the microbial nutrient demand in the red soil exhibited the following order, N > P > S > C. While in the black soil, it suggested that there is increasing microbial demand for only N and S. In the warmer months (May to Sep.), the microbial nutrient demands in the two soils were opposite to the colder months. The results suggested differential changes in microbial nutrient limitation with warming, which has significant implications for the carbon stocks management in farmlands under the changing global climate.

Keywords: In situ model; Stoichiometry; Temperature sensitivity; Total enzyme activity index.