Incorporating microbial dormancy dynamics into soil decomposition models to improve quantification of soil carbon dynamics of northern temperate forests

Abstract

Soil carbon dynamics of terrestrial ecosystems play a significant role in the global carbon cycle.Microbial-based decomposition models have seen much growth recently for quantifying this role, yet dormancy as a common strategy used by microorganisms has not usually been represented and tested in these models against field observations. Here we developed an explicit microbial-enzyme decomposition model and examined model performance with and without representation of microbial dormancy at six temperate forest sites of different forest types. We then extrapolated the model to global temperate forest ecosystems to investigate biogeochemical controls on soil heterotrophic respiration and microbial dormancy dynamics at different temporal-spatial scales. The dormancy model consistently produced better match with field-observed heterotrophic soil CO 2 efflux (R H ) than the no dormancy model. Our regional modeling results further indicated that models with dormancy were able to produce more realistic magnitude of microbial biomass (<2% of soil organic carbon) and soil R H (7.5 ± 2.4 Pg C yr À1 ). Spatial correlation analysis showed that soil organic carbon content was the dominating factor (correlation coefficient = 0.4-0.6) in the simulated spatial pattern of soil R H with both models. In contrast to strong temporal and local controls of soil temperature and moisture on microbial dormancy, our modeling results showed that soil carbon-to-nitrogen ratio (C:N) was a major regulating factor at regional scales (correlation coefficient = À0.43 to À0.58), indicating scale-dependent biogeochemical controls on microbial dynamics. Our findings suggest that incorporating microbial dormancy could improve the realism of microbial-based decomposition models and enhance the integration of soil experiments and mechanistically based modeling.Recent comprehensive analyses have shown that there are notable limitations of traditional first-order decomposition algorithms in current Earth system models. Those decomposition models are not able to capture the spatial distributions of SOC stocks and primary drivers of SOC dynamics [Todd-Brown et al., 2013], while microbial-based soil organic matter decomposition models have been increasingly used at both site-and global-scale studies [Allison et al., 2010;He et al., 2014b;Wieder et al., 2013], although more rigorous examination of these models is still needed [Li et al., 2014]. The current generation of microbial-based decomposition models usually features a common framework where enzyme production and microbial physiology are associated with total microbial biomass (MIC), which has a direct coupling with SOC enzymatic decomposition. HE ET AL. MODELING MICROBIAL DORMANCY IN GLOBAL TEMPERATE FOREST ECOSYSTEMS 2596 PUBLICATIONS

ORCHIMIC (v1.0), a microbe-driven model for soil organic matter decomposition designed for large-scale applications

“…Dormant microbes still need a minimum of energy for maintenance, albeit at a much lower rate compared that of active microbes (Lennon and 20 Jones, 2011). The maintenance respiration coefficient of dormant microbes is set to be a ratio b (between 0 and 1) of that of active microbes (Wang et al, 2014;He et al, 2015). The maintenance respiration thus can be described by Eq.…”

“…The maintenance respiration of MFTs (bacteria and fungi) is modelled as a fixed ratio (maintenance respiration coefficient) of their biomass (Schimel & Weintraub, 2003;Lawrence et al, 2009;Allison et al, 2010;Wang et al, 2014;He et al, 2015) modulated by temperature using an Arrhenius equation following Tang and Riley (2015) (Eq. 36).…”

“…For 10 instance, only active microbes are involved in decomposing SOC (Blagodatskaya and Kuzyakov, 2013) and in producing enzymes (He et al, 2015). However, with 80 % of microbial cells typically being dormant in soils, dormancy is the most common state of microbial communities (Lennon and Jones, 2011).…”

“…Recently, new models have included the effects of microbial dynamics on SOC decomposition, but not always with an explicit representation of microbial processes (Schimel and Weintraub, 2003;Moorhead and Sinsabaugh, 2006;Lawrence et al, 2009;Wang et al, 2013;Wieder et al, 2014;Kaiser et al, 2014Kaiser et al, , 2015He et al, 2015). In those models, SOC decomposition is mediated by 30 soil enzymes released by microorganisms (Allison et al, 2010;Schimel and Weintraub, 2003;Lawrence et al, 2009;).…”

“…CC BY 4.0 License. the production of enzymes in models is typically modelled as a fixed fraction of total microbial biomass (Allison et al, 2010;He et al, 2015) or as a fixed fraction of the uptake of C or N (Schimel and Weintraub, 2003;Kaiser et al, 2014Kaiser et al, , 2015.…”