Field and lab conditions alter microbial enzyme and biomass dynamics driving decomposition of the same leaf litter

Abstract

Fluctuations in climate and edaphic factors influence field decomposition rates and preclude a complete understanding of how microbial communities respond to plant litter quality. In contrast, laboratory microcosms isolate the intrinsic effects of litter chemistry and microbial community from extrinsic effects of environmental variation. Used together, these paired approaches provide mechanistic insights to decomposition processes. In order to elucidate the microbial mechanisms underlying how environmental conditions alter the trajectory of decay, we characterized microbial biomass, respiration, enzyme activities, and nutrient dynamics during early (<10% mass loss), mid- (10–40% mass loss), and late (>40% mass loss) decay in parallel field and laboratory litter bag incubations for deciduous tree litters with varying recalcitrance (dogwood < maple < maple-oak mixture < oak). In the field, mass loss was minimal (<10%) over the first 50 days (January–February), even for labile litter types, despite above-freezing soil temperatures and adequate moisture during these winter months. In contrast, microcosms displayed high C mineralization rates in the first week. During mid-decay, the labile dogwood and maple litters in the field had higher mass loss per unit enzyme activity than the lab, possibly due to leaching of soluble compounds. Microbial biomass to litter mass (B:C) ratios peaked in the field during late decay, but B:C ratios declined between mid- and late decay in the lab. Thus, microbial biomass did not have a consistent relationship with litter quality between studies. Higher oxidative enzyme activities in oak litters in the field, and higher nitrogen (N) accumulation in the lab microcosms occurred in late decay. We speculate that elevated N suppressed fungal activity and/or biomass in microcosms. Our results suggest that differences in microbial biomass and enzyme dynamics alter the decay trajectory of the same leaf litter under field and lab conditions.

Microbial physiology and necromass regulate agricultural soil carbon accumulation

“…4). Given the central role of enzymes in decomposition, and close relationships between enzyme activities and decomposition rates (Sinsabaugh et al, 1991;Rinkes et al, 2013), how can these differences in microbial physiology and activity enhance the persistence of new C inputs in soil? One answer rests with our knowledge that under most temperate and tropical systems plant litter will eventually decompose, and even lignin-rich materials can decompose within a year .…”

Land‐use legacies regulate decomposition dynamics following bioenergy crop conversion

“…To more fully understand decomposition following bioenergy crop conversion, we need to examine decomposer community processes and functions. For instance, shifts in litter and soil microbial biomass may indicate changes in potential biological activity and decomposition rates (Rinkes et al ., ), while changes in enzyme activities (the catalysts for litter breakdown) can reflect altered microbial nutrient demands (Sinsabaugh et al ., ). Further, differences in decomposer community composition or changes in nutrient and energy availability may lead to distinct chemistries of decomposed litter (e.g.…”

Eleven years of crop diversification alters decomposition dynamics of litter mixtures incubated with soil

“…, Rinkes et al. ). The agricultural studies we summarized measured residue mixture responses between 18‐ and 500‐d incubations, which may account for the highly variable mixture effect indices.…”