Temperature dependence of nitrogen mineralization and microbial status in O_H horizon of a temperate forest ecosystem

Abstract

It was hypothesized that increasing air and/or soil temperature would increase rates of microbial processes including litter decomposition and net N mineralization, resulting in greater sequestration of carbon and nitrogen in humus, and consequently development in O_H horizon (humus horizon). To quantify the effect of temperature on biochemical processes controlling the rate of O_H layer development three adjacent forest floors under beech, Norway spruce and mixed species stands were investigated at Solling forest, Germany by an incubation experiment of O_H layer for three months. Comparing the fitted curves for temperature sensitivity of O_H layers in relation to net N mineralization revealed positive correlation across all sites. For the whole data set of all stands, a Q10 (temperature sensitivity index) value of 2.35–2.44 dependent on the measured units was found to be adequate for describing the temperature dependency of net N mineralization at experimental site. Species-specific differences of substrate quality did not result in changes in biochemical properties of O_H horizon of the forest floors. Temperature elevation increased net N mineralization without significant changes in microbial status in the range of 1 to 15°C. A low C_mic/C_org (microbial carbon/organic carbon) ratio at 20°C indicated that the resource availability for decomposers has been restricted as reflected in significant decrease of microbial biomass.

Keywords

beech / spruce / nitrogen mineralization / forest floor / temperature / temperature sensitivity index (Q₁₀)