Soil contains large amounts of organic carbon (C). Priming and exogenous C incorporation caused by fresh C inputs are two critical biogeochemical processes that regulate soil organic C content. However, the ecological predictors of soil priming and exogenous C incorporation remain unclear, especially for soils spanning a wide range of climates and soil conditions.
To identify the controlling factors on soil priming and exogenous C incorporation, researchers led by Prof. LIU Feng from the Wuhan Botanical Garden (WBG) of the Chinese Academy of Sciences (CAS) presented a study based on 51 soils (belonging to 15 soil profiles in five forest types) along an elevation gradient in the Taibai Mountain. The magnitudes of priming and exogenous C incorporation were determined using a 30-day soil incubation coupled with 13C-labeled glucose.
Significant elevational and vertical patterns of soil priming and exogenous C incorporation were observed. The priming effect showed hump-shaped trends with elevation, and the proportion of glucose-C retained decreased significantly with elevation. Surface soils had significantly lower priming and exogenous C incorporation than deep soils. The incorporated glucose-C could offset the primed C, and further led to a positive net C balance.
Among the various soil properties (including soil C availability, soil C fractions, soil nitrogen availability, soil C saturation deficit, pH, microbial biomass C, soil metabolic quotient (qCO2) and soil bacterial composition), relative priming was negatively driven by qCO2 through microbial energy demand, and exogenous C incorporation was mainly explained by bacterial community composition due to the different life strategies of specific microbial taxa, and qCO2 was a proxy for C utilization efficiency and soil C saturation deficit.
These results emphasized that microbial properties play a critical role in regulating soil C cycling under exogenous C input, and considering their effects would improve our understanding in soil organic C dynamics under climate change and the performance of global C models.
This work was supported by the National Natural Science Foundation of China, and the Youth Innovation Promotion Association of CAS.
Spearman's correlation (a) and partial correlation (b) matrix between the variables of soil properties and absolute priming, relative priming, the proportion of glucose-C retained. (Image by WBG)
Conceptual diagram about microbial properties controlling soil priming and exogenous carbon incorporation, and consequently net carbon balance. (Image by WBG)
