Abstract
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 38°C). 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 warming’s impacts on soil CO2 emission may depend upon soil moisture conditions. With the same temperature rise, wetter soils may emit more CO2 into the atmosphere via heterotrophic respiration.
Highlights
Temperature sensitivity of soil respiration, usually termed as Q10, is defined as the increase of soil respiration rate by a 10uC rise in temperature [1]
Throughout the whole incubation period, soil Rh was highest at 60% water holding capacity (WHC), lowest at 20% WHC, and intermediate at the other moisture levels (Fig. 1)
Among the three measurement days, soil Rh had the highest values on day 7, especially at 60% and 80% WHC, compared to those on days 30 and 90
Summary
Temperature sensitivity of soil respiration, usually termed as Q10, is defined as the increase of soil respiration rate by a 10uC rise in temperature [1]. In the past several decades, Q10 has been investigated extensively, through fieldobserved soil respiration and environmental factor data [3,4]. It has been found that Q10 is not a constant of 2, but varies with vegetation and edaphic conditions such as temperature, moisture, and substrate availability [2]. As global temperature continues to rise [5], it is of paramount importance to understand how Q10 is influenced by these factors individually and interactively. Effects of soil temperature and moisture on Q10 are often confounded with each other and with other factors, laboratory incubation has the advantage of deriving the primary and interactive effects of the environmental factors on Q10
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