Influence of litter chemistry and stoichiometry on glucan depolymerization during decomposition of beech (Fagus sylvatica L.) litter

Abstract

Glucans like cellulose and starch are a major source of carbon for decomposer food webs, especially during early- and intermediate-stages of decomposition. Litter quality has previously been suggested to notably influence decomposition processes as it determines the decomposability of organic material and the nutrient availability to the decomposer community. To study the impact of chemical and elemental composition of resources on glucan decomposition, a laboratory experiment was carried out using beech (Fagus sylvatica, L.) litter from four different locations in Austria, differing in composition (concentration of starch, cellulose and acid unhydrolyzable residue or AUR fraction) and elemental stoichiometry (C:N:P ratio). Leaf litter was incubated in mesocosms for six months in the laboratory under controlled conditions. To investigate the process of glucan decomposition and its controls, we developed an isotope pool dilution (IPD) assay using 13C-glucose to label the pool of free glucose in the litter, and subsequently measured the dilution of label over time. This enabled us to calculate gross rates of glucose production through glucan depolymerization, and glucose consumption by the microbial community. In addition, potential activities of extracellular cellulases and ligninases (peroxidases and phenoloxidases) were measured to identify effects of resource chemistry and stoichiometry on microbial enzyme production. Gross rates of glucan depolymerization and glucose consumption were highly correlated, indicating that both processes are co-regulated and intrinsically linked by the microbial demand for C and energy and thereby to resource allocation to enzymes that depolymerize glucans. At early stages of decomposition, glucan depolymerization rates were correlated with starch content, indicating that starch was the primary source for glucose. With progressing litter decomposition, the correlation with starch diminished and glucan depolymerization rates were highly correlated to cellulase activities, suggesting that cellulose was the primary substrate for glucan depolymerization at this stage of decomposition. Litter stoichiometry did not affect glucan depolymerization or glucose consumption rates early in decomposition. At later stages, however, we found significant negative relationships between glucan depolymerization and litter C:N and AUR:N ratio and a positive relationship between glucan depolymerization and litter N concentration. Litter C:N and C:P ratios were negatively related to cellulase, peroxidase and phenoloxidase activities three and six months after incubation, further corroborating the importance of resource stoichiometry for glucan depolymerization after the initial pulse of starch degradation.

C/N Ratio Drives Soil Actinobacterial Cellobiohydrolase Gene Diversity

“…However, it is interesting that the Bogo pasture had the lowest overall C/N ratio and the highest overall GH48 abundance; likewise, the Bogo woodlands had the lowest C/N ratio and the highest GH48 abundance among woodlands (46). This pattern agrees with data from studies showing that higher C/N ratios are negatively correlated with extracellular hydrolytic enzyme activity during litter decomposition (69).…”

“…2A). The C/N ratio is thought to influence litter C availability, and a high C/N ratio has a negative effect on extracellular hydrolytic enzymes during litter decomposition (69,70). It is not surprising, therefore, that the C/N ratio was one of the vectors with the strongest correlations to the main PCO axis and was more important than the levels of the organic soil carbon fractions themselves.…”

Impact of fine litter chemistry on lignocellulolytic enzyme efficiency during decomposition of maize leaf and root in soil

“…Data represents two replicates at each sampling date i.e. days 8, 14, 21, 28, 35 and 43 LSD states for least significant differences, nd for not determined levels of glucan, suggesting that soil microorganisms use glucan (cellulose) as the preferred substrate irrespective of the type of residue (Leitner et al 2012) (Fig. 5a), and that enzyme production was responsive to substrate availability (Leinweber et al 2008).…”

Effect of contrasting crop rotation systems on soil chemical, biochemical properties and plant root growth in organic farming: first results

“…In accordance with other studies (Bongiovanni and Lobartini, 2006), the cultivation of wheat had an overall detrimental effect on all of the organic C pools examined. The major depletion observed at 0-10 cm of the P-C soil was likely due to higher microbial biomass content and activity coupled with greater availability of N (Leitner et al, 2012;Zotarelli et al, 2012).…”

“…In the P-C soil, the presence of perennial legume may have favoured the continuous supply of the more accessible pools of organic carbon, i.e., LFOM and WSOC which, coupled with a higher availability of N, might have preferentially led soil microorganisms to degrade the more labile carbon instead of ligneous recalcitrant carbon, thus enhancing soil in humic fraction (Leitner et al, 2012). Indeed, in our study, the P-C soil always showed lower o-DPO activity than that in the A-C soil (Table 3).…”