The temperature sensitivity (Q10) of soil heterotrophic respiration (Rh) is an important ecological model parameter and may vary with temperature and moisture. While Q10 generally decreases with increasing temperature, the moisture effects on Q10 have been controversial. To address this, we conducted a 90-day laboratory incubation experiment using a subtropical forest soil with a full factorial combination of five moisture levels (20%, 40%, 60%, 80%, and 100 % water holding capacity-WHC) and five temperature levels (10, 17, 24, 31, and 38uC). Under each moisture treatment, Rh was measured several times for each temperature treatment to derive Q10 based on the exponential relationships between Rh and temperature. Microbial biomass carbon (MBC), microbial community structure and soil nutrients were also measured several times to detect their potential contributions to the moisture-induced Q10 variation. We found that Q10 was significantly lower at lower moisture levels (60%, 40 % and 20 % WHC) than at higher moisture level (80 % WHC) during the early stage of the incubation, but became significantly higher at 20%WHC than at 60 % WHC and not significantly different from the other three moisture levels during the late stage of incubation. In contrast, soil Rh had the highest value at 60 % WHC and the lowest at 20 % WHC throughout the whole incubation period. Variations of Q10 were significantly associated with MBC during the early stages of incubation, but with the fungi-to-bacteria ratio during the later stages, suggesting that changes in microbial biomass and community structure are related to the moisture-induced Q10 changes. This study implies that global

[1] Plant productivity in upland tundra and boreal forest is demonstrably limited by nitrogen (N) and indirect evidence from field studies suggests that decomposition by soil microbes may be similarly limited. As climate warms at high latitudes, understanding the response of soil organic matter (SOM) decomposition to increased soil temperature may be crucial for determining the net effect of warming on ecosystem carbon (C) balance because temperature directly affects decomposition but also because it has an indirect effect on C balance via nutrient mineralization. We incubated northern Alaskan soils at two temperatures (5°C and 15°C) and two levels of N addition (with and without) to directly test for N limitation of SOM decomposition and to explore the interaction between temperature and N limitation. Over the entire 924 day incubation of organic and mineral soils from two ecosystem types, we measured microbial respiration; over the initial 90 days of the incubation, we measured microbial biomass N, net N mineralization, and the isotopic signatures (d 13 C and D 14 C) of microbial respiration. Across soil layers and ecosystem types, temperature always had a strong positive effect on SOM decomposition rates, whereas N addition had positive, negative, and neutral effects.

Copyright © 2014 Gang Fu et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Alpine meadows are onemajor type of pastureland on the Tibetan Plateau. However, few studies have evaluated the response of soil respiration (

Regulatory mechanisms of soil respiratory carbon (C) release induced by substrates (i.e., plant derived substrates) are critical for predicting ecosystem responses to climate change, but the mechanisms are not well understood. In this study, we sampled soils from a long-term field manipulative experiment and conducted a laboratory incubation to explore the role of substrate supply in regulating the differences in soil C release among the experimental treatments, including control, warming, clipping, and warming plus clipping. Three types of substrates (glucose, C3 and C4 plant materials) were added with an amount equal to 1 % of soil dry weight under the four treatments. We found that the addition of all three substrates significantly stimulated soil respiratory C release in all four warming and clipping treatments. In soils without substrate addition, warming significantly stimulated soil C release but clipping decreased it. However, additions of glucose and C3 plant materials (C3 addition) offset the warming effects, whereas C4 addition still showed the warming-induced stimulation of soil C release. Our