Decomposition of organic matter (OM) contributes to structure and function of terrestrial ecosystems. It provides energy and carbon (C) for microbial functioning and recycling essential nutrients for plants and microorganisms. Several studies have suggested that microorganisms cope with C:N imbalance between organic matters and their biomass through regulating their C- and N-use efficiencies. However, it remains unknown how microbial decomposition of heterogeneous OMs with wide C:N ratios responds to varying ratios of labile C and N inputs along OM decay continuum.

Dr. QIAO Na of Xishuangbanna Tropical Botanical Garden (XTBG) and her collaborators explored effects of labile C and N inputs on decomposition of plant litter and soil OM along the decay continuum over a wide range of C:N ratios in labile inputs. They collected four organic substrates (i.e. organic soil horizon, mineral soil horizon, leaf litter, and wood litter) from a subtropical broad-leaved evergreen forest in the Ailao Mountains Nature Reserve (24°32′N, 101°01′E), Yunnan.

The researchers measured decomposition rates of wood, leaf litter, and OM in both organic and mineral soil horizons along the decay continuum, adding labile C and N inputs over potential global ranges of C:N ratios. They assessed decomposition as cumulative CO2 production, with isotopically labeled C to distinguish OM substrate C from labile-C inputs. They aimed to clarify how OM decomposition responded to labile C and N inputs and what controlled OM decomposition along the decay continuum. They further demonstrated priming stoichiometry in three dimensions (C:N ratios in OM, C:N ratios in labile inputs, and priming intensity).

The study found that decomposition of the four heterogeneous OM decreased along the decay continuum. Proceeding from leaf to wood, organic soil, and mineral soil, the contribution of labile C inputs to priming substantially increased, while that of labile N inputs and C:N ratios decreased. With low labile C:N input ratios (less than 55), priming had relatively minor differences among the four OM forms. Conversely, with high labile C:N input ratios, priming was strongly negative for the OM with high C:N ratios and strongly positive for those with lower C:N ratios.

Their study provided a basis for incorporating stoichiometric responses of microbial decomposition and energy demand into conceptual and mathematical models. 

The study entitled “Carbon and nitrogen additions induce distinct priming effects along an organic-matter decay continuum” has been published in Scientific Reports.