Modeling Global Soil Carbon and Soil Microbial Carbon by Integrating Microbial Processes into the Ecosystem Process Model TRIPLEX‐GHG

Abstract

Microbial physiology plays a critical role in the biogeochemical cycles of the Earth system. However, most traditional soil carbon models are lacking in terms of the representation of key microbial processes that control the soil carbon response to global climate change. In this study, the improved process‐based model TRIPLEX‐GHG was developed by coupling it with the new MEND (Microbial‐ENzyme‐mediated Decomposition) model to estimate total global soil organic carbon (SOC) and global soil microbial carbon. The new model (TRIPLEX‐MICROBE) shows considerable improvement over the previous version (TRIPLEX‐GHG) in simulating SOC. We estimated the global soil carbon stock to be approximately 1195 Pg C, with 348 Pg C located in the high northern latitudes, which is in good agreement with the well‐regarded Harmonized World Soil Database (HWSD) and the Northern Circumpolar Soil Carbon Database (NCSCD). We also estimated the global soil microbial carbon to be 21 Pg C, similar to the 23 Pg C estimated by Xu et al. (2014). We found that the microbial carbon quantity in the latitudinal direction showed reversions at approximately 30°N, near the equator and at 25°S. A sensitivity analysis suggested that the tundra ecosystem exhibited the highest sensitivity to a 1°C increase or decrease in temperature in terms of dissolved organic carbon (DOC), microbial biomass carbon (MBC), and mineral‐associated organic carbon (MOC). However, our work represents the first step toward a new generation of ecosystem process models capable of integrating key microbial processes into soil carbon cycles.

Dominant regions and drivers of the variability of the global land carbon sink across timescales

“…TRENDY DGVMs shows higher (lower) turnover rates in temperate and boreal ecosystems (tropical rainforests) than CARDAMOM. The bias in turnover rates reflects uncertainties of representations within DGVMs’ ecosystem carbon cycle processes, such as photosynthesis parameterization, plant carbon allocation, nutrient limitation effect, and simple soil carbon decomposition schemes (Wang et al., , Wieder, Bonan, & Allison, ). Since carbon turnover time of ecosystems in boreal regions is much longer than 100 years (Bloom et al., ; Erb et al., ), the contribution of variability of NBP in boreal regions to global NBP at timescales longer than 100 years may stand out from other regions.…”

Niche differentiation is spatially and temporally regulated in the rhizosphere

“…Rhizodeposits also stimulate depolymerization by cellulases, chitinases, and proteases (15,16) leading to higher rates of decomposition, and thus nutrient availability, in the region surrounding both living roots and decaying root detritus (17). However, the ecological controls of rhizosphere carbohydrate depolymerization are not well understood, which limits our ability to accurately model soil C dynamics (18) and plant-microbe interactions.…”

Stoichiometrically coupled carbon and nitrogen cycling in the MIcrobial-MIneral Carbon Stabilization model (MIMICS-CN)

“…and others (Abramoff et al, 2017;Allison, 2014;Fatichi et al, 2019;Hararuk et al, 2015;Robertson et al, 2018;Sulman et al, 2014;Wang et al, 2013Wang et al, , 2014aWang et al, , 2017. These models are as good as or better than models without explicit microbial pools at simulating global soil C stocks and the response of soil C to environmental perturbations (Wieder et al, 2013(Wieder et al, , 2015b, and they also predict very different long-term responses of soil C to global change (Wieder et al, 2013(Wieder et al, , 2018.…”