Abstract
Soil microbial carbon-use efficiency (CUE), which is defined as the ratio of growth over C uptake, is commonly assumed as a constant or estimated by a temperature-dependent function in current microbial-explicit soil carbon (C) models. The temperature-dependent function (i.e., CUE = CUE0 + m × (T − 20)) simulates the dynamic CUE based on the specific CUE at a given reference temperature (i.e., CUE0) and a temperature response coefficient (i.e., m). Here, based on 780 observations from 98 sites, we showed a divergent spatial distribution of the soil microbial CUE (0.5 ± 0.25; mean ± SD) at the global scale. Then, the key parameters CUE0 and m in the above equation were estimated as 0.475 and −0.016, respectively, based on the observations with the Markov chain Monte Carlo technique. We also found a strong dependence of microbial CUE on the type of C substrate. The multiple regression analysis showed that glucose influences the variation of measured CUE associated with the environmental factors. Overall, this study confirms the global divergence of soil microbial CUE and calls for the incorporation of C substrate beside temperature in estimating the microbial CUE in different biomes.
Highlights
Soil microbial dynamic is a key regulator of ecosystem carbon (C) cycling because of its important role in decomposition and stabilization of soil organic carbon (SOC)[1,2,3]
Substrates consist of more degradable compounds such as carbohydrates and protein could result in higher carbon-use efficiency (CUE) than those contains more recalcitrant compounds, e.g., aliphatic, aromatic and lignin[11,22,23,24,25]
The global mean CUE in our analysis (0.5) is comparable to the result of a former data-analysis across the world, where soil CUE was about 0.5511. These values are close to the thermodynamic www.nature.com/scientificreports maximum of metabolic efficiency (0.6)[26,27], but is much higher than the CUE value of 0.3, which has been recommended for large-scale models by Sinsabaugh et al.[30]
Summary
Soil microbial dynamic is a key regulator of ecosystem carbon (C) cycling because of its important role in decomposition and stabilization of soil organic carbon (SOC)[1,2,3]. The simulated global SOC by the Community Land Model (CLM) has been more accurate with the implementation of microbial dynamics[7,8,9] In those microbial-explicit SOC models, the soil microbial carbon-use efficiency (CUE; i.e., the ratio of growth over C uptake) is a key parameter. Respiration increases more than growth as a function of temperature, so CUE tends to decrease with temperature in both soil and aquatic systems[6,12,13,14,15,16,17] This pattern has already been represented in many microbial-explicit SOC models as a linear temperature sensitivity function[5,9,10,18,19,20]: CUE = CUE0 + m(T – T0). Microbial growth is strongly related to the substrate accessibility which is collectively affected by environmental and soil conditions such as water availability[28] and aggregates[29]
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