A Theoretical Model of Litter Decay and Microbial Interaction

Abstract

Despite the central role of microorganisms in the decomposition of dead organic matter, few models have integrated the dynamics of litter chemistry with microbial interactions. Here we propose a functional resolution of the microbial community that parallels the commonly used chemical characterization of plant litter, i.e., a guild of opportunist microorganisms that grows quickly and has high affinity for soluble substrates, a guild of decomposer specialists that grows more slowly and has high affinity for holocellulose substrates, and a guild of miners that grows very slowly and is specialized for degrading lignin. This guild‐based decomposition model (GDM) includes the interactions of holocellulose and lignin, manifest as mutual feedback controls on microbial‐based activities. It also includes N limitations on early stages of litter decay resulting from nutritional demands of microorganisms and N inhibition on late stages of litter decay resulting from reduced lignin degradation. Competitive interactions between microbial guilds result from different growth rates and substrate affinities, given limits on microbial colonization of litter. Simulations are consistent with commonly reported and proposed patterns of microbial community succession during litter decay, changes in and controls imposed by litter chemistry, and system responses to N availability. Modest impacts of litter chemistry and N effects on patterns of decay can yield substantial impacts on the relative amount of litter remaining through time, the time required to stabilize litter carbon (i.e., as the lignin content approaches Ìf70% of the total litter carbon), the relative contributions of different guilds to decay, and the net amount of microbial production. Moreover, seemingly inconsistent patterns in system responses to N regimes can be explained by interactions between litter chemistry and microbial guilds. A validation exercise demonstrated general correspondence of model behavior to field observations. However, relationships among mass loss, litter chemistry, and N availability were more variable in field studies than in simulations. Also, observed changes in litter quality indicated the progressive accumulation of microbial products. Hence, field studies suggest expanding GDM to include dynamics of microbial products and also suggest the utility of GDM in exploring site effects on decomposition as a result of differences in microbial community composition.

Microbial community structure mediates response of soil C decomposition to litter addition and warming

“…However, the addition of N did not cause the priming response in this experiment, as (a) the two litters caused different directions of priming, and (b) the substrate with the lowest C:N ratio (Table 1) and highest inorganic N concentrations (Table 3) had the strongest soil-priming response (Fig. 2), inconsistent with a mechanism of priming driven by microbial 'mining' of the soil for N after the addition of C (Fontaine et al, 2003;Moorhead and Sinsabaugh, 2006;Craine et al, 2007). However, the litter additions may have impacted the increase in priming in response to soil temperature, as the higher N content of the soil-litter mixtures may have allowed for the production of a larger number of hydrolytic enzymes Cusack et al, 2011), or a suite of more efficient enzymes (Stone et al, 2012), that were capable of degrading more soil-C as the temperature increased.…”

Forest harvesting reduces the soil metagenomic potential for biomass decomposition

“…At 11 years after harvesting, total carbon, the C/N ratio and manganese remained depleted in the organic layer of harvested treatments versus the reference (Figure 1b). Soil carbon reflects the amount of organic matter, whereas C/N reflects the bioavailability and nutrient content of organic matter, both key selective factors for heterotrophic communities (Paul and Clark, 1996;Moorhead and Sinsabaugh, 2006). Manganese is an important cofactor for oxidative enzymes, especially ones involved in lignin degradation.…”

“…Soil microbial communities mediate key processes, such as nutrient cycling, transport of water and nutrients as well as maintenance of soil structure. Decomposition of biomass is an essential role of soil communities that enables cycling of carbon and other nutrients sequestered in biomass, making those nutrients available for primary productivity (Moorhead and Sinsabaugh, 2006). Enzymes involved in decomposition are additionally important for the conversion of biomass to commercial products, such as fuels, aromatic compounds and animal feed (Tuck et al, 2012).…”

Responses of peat carbon at different depths to simulated warming and oxidizing

“…The main factors in Rs include soil microbial communities, enzyme diversity and nutrient condition (Lawrence et al, 2009;Moorhead and Sinsabaugh, 2006) which all vary with temperature and O 2 conditions (Kim et al, 2012). Most microbes and enzymes are sensitive to temperature and O 2 change, and so is soil nutrient determined by vegetation that varies with climate (Mikan et al, 2002).…”