Abstract
Abstract. Climate change has the potential to destabilize the Earth's massive terrestrial carbon (C) stocks, but the degree to which models project this destabilization to occur depends on the kinds and complexities of microbial processes they simulate. Of particular note is carbon use efficiency (CUE), which determines the fraction of C processed by microbes that is anabolized into microbial biomass rather than lost to the atmosphere and soil as carbon dioxide and extracellular products. The temperature sensitivity of CUE is often modeled as an intrinsically fixed (homogeneous) property of the community, which contrasts with empirical data and has unknown impacts on projected changes to the soil C cycle under global warming. We used the Decomposition Model of Enzymatic Traits (DEMENT) – which simulates taxon-level litter decomposition dynamics – to explore the effects of introducing organism-level heterogeneity into the CUE response to temperature for decomposition of leaf litter under 5 ∘C of warming. We found that allowing the CUE temperature response to differ between taxa facilitated increased loss of litter C, unless fungal taxa were specifically restricted to decreasing CUE with temperature. Litter C loss was exacerbated by variable and elevated CUE at higher temperature, which effectively lowered costs for extracellular enzyme production. Together these results implicate a role for diversity of taxon-level CUE responses in driving the fate of litter C in a warmer world within DEMENT, which should be explored within the framework of additional model structures and validated with empirical studies.
Highlights
Soil heterotrophs are central to the cycling and recycling of the 60 Gt of organic carbon (C) that plants deposit onto and into the ground each year
litter organic matter (LOM) and microbial biomass carbon (MBC) values were within the range previously observed for simulations using Decomposition Model of Enzymatic Traits (DEMENT) with daily litter inputs (Allison et al, 2014) but greater than those with just a single litter pulse (Allison, 2012; Allison and Goulden, 2017; Evans et al, 2017), indicating that these high biomass and litter C values can be attributed to these substrate inputs
The communities characterized by heterogeneous Ct maintained a higher median microbial biomass – driving 2.5 times more LOM loss – than the communities characterized by a homogeneous Ct (Fig. 3)
Summary
Soil heterotrophs are central to the cycling and recycling of the 60 Gt of organic carbon (C) that plants deposit onto and into the ground each year. How well these inputs are converted into relatively stable soil organic matter depends on temperature, moisture, chemical composition, and soil mineralogy, which interact to influence microbial physiology (Manzoni et al, 2012; Kallenbach et al, 2016; Oldfield et al, 2018).
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