Scaling soil organic matter formation with microbial physiology

Abstract:

Soil organic matter (SOM) regulates multiple ecosystem processes, including the exchange of trace gases and primary productivity. Recently, there has been vigorous debate over the role that microbial products play in forming stable soil organic matter, with increasing analytical evidence using isotopes, molecular chemistry, and microcopy all showing that SOM possesses a strong microbial signature. However, scaling these observations – typically made at the molecular to nano or micron scales – to ecosystems or larger scales remains challenging. Here we show that microbial physiological processes such as growth efficiency and growth rate regulate the accumulation of microbial products. These processes are also strongly regulated by ecosystem disturbance and can be readily incorporated into microbial-explicit global C cycling models.

 In our experiments with model artificial soils accruing SOM and field soils with varying soil C concentrations, the accumulation of SOM is closely related to microbial physiology. Further, the rate and efficiency that isotopically labelled C is converted to soil C depends strongly on microbial physiological characteristics. Given the sensitivity of microbial physiological characteristics to disturbance, these physiological traits can help explain ecosystem-scale SOM responses to environmental changes.

Variation in microbial physiology can also be directly incorporated into models, allowing us to scale microbial processes that regulate SOM formation to regional and global scales. Here we demonstrate the incorporation of microbial processes into MIMICS, the MIcrobial MIneral Carbon Stabilization model. Moving from ecosystem to larger scales, we demonstrate that MIMICS, a microbial-explicit model with output strongly dependent on microbial physiology is able to predict large-scale soil C dynamics as well as or better than conventional models. Microbial physiology, which varies among microbial groups and is highly sensitive disturbance, can be used to scale from the smallest processes regulating SOM formation to global C cycling.