Stoichiometric controls on carbon, nitrogen, and phosphorus dynamics in decomposing litter

Abstract

The mineralization of nitrogen and phosphorus from plant residues provides an important input of inorganic nutrients to the soil, which can be taken up by plants. The dynamics of nutrient mineralization or immobilization during decomposition are controlled by different biological and physical factors. Decomposers sequester carbon and nutrients from organic substrates and exchange inorganic nutrients with the environment to maintain their stoichiometric balance. Additionally, physical losses of organic compounds from leaching and other processes may alter the nutrient content of litter. In this work, we extend a stoichiometric model of litter nitrogen mineralization to include (1) phosphorus mineralization, (2) physical losses of organic nutrients, and (3) chemical heterogeneity of litter substrates. The enhanced model provides analytical mineralization curves for nitrogen and phosphorus as well as critical litter carbon : nutrient ratios (the carbon : nutrient ratios below which net nutrient release occurs) as a function of the elemental composition of the decomposers, their carbon-use efficiency, and the rate of physical loss of organic compounds. The model is used to infer the critical litter carbon : nutrient ratios from observed nitrogen and phosphorus dynamics in about 2600 litterbag samplings from 21 decomposition data sets spanning artic to tropical ecosystems. At the beginning of decomposition, nitrogen and phosphorus tend to be immobilized in boreal and temperate climates (i.e., both C:N and C:P critical ratios are lower than the initial ratios), while in tropical areas nitrogen is generally released and phosphorus may be either immobilized or released, regardless of the typically low phosphorus concentrations. The critical carbon : nutrient ratios we observed were found to increase with initial litter carbon : nutrient ratios, indicating that decomposers adapt to low-nutrient conditions by reducing their carbon-use efficiency. This stoichiometric control on nutrient dynamics appears ubiquitous across climatic regions and ecosystems, although other biological and physical processes also play important roles in litter decomposition. In tropical humid conditions, we found high critical C:P ratios likely due to high leaching and low decomposer phosphorus concentrations. In general, the compound effects of stoichiometric constraints and physical losses explain most of the variability in critical carbon : nutrient ratios and dynamics of nutrient immobilization and release at the global scale.

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

“…If driven solely by C:N ratios, then the CUE should have increased from the soil < fresh litter < pre-incubated litter. The pre-incubated litter, with a C:N ratio nearing the ratios required for microbial biomass (Cleveland and Liptzin, 2007;Manzoni et al, 2010), did have the highest CUE (lowest qCO 2 ) (Table 4). Similarly, the higher CUE of the soils with litter addition relative to the control soil may have been driven by more available N resulting from the litter addition (Table 3).…”

The decomposition of ectomycorrhizal fungal necromass

“…C, N, P) and the recalcitrance, or the resistance to decomposition, of the molecules comprising the litter. Decomposition is generally favored by relatively low litter C:N ratios (Cleveland and Liptzin, 2007), which presumably helps to maintain the low C:N ratio of microbial cells (Sinsabaugh et al, 2009;Manzoni et al, 2010), yet, there is increasing evidence that additional aspects of quality beyond basic stoichiometry also can play a role determining decomposition rates. Koide and Malcolm (2009) tested the role of C and N concentrations on the decomposition rate of EM fungal necromass in a litterbag study and found that initial N concentration was a good predictor of the decomposition rate of these tissues.…”

Management practices amplify the effects of N deposition on leaf litter decomposition of the Moso bamboo forest

“…The accumulation or release of nutrients from decomposing litter is predominantly regulated by the initial N content and the stoichiometric requirements of the microbial decomposers (Xu and Hirata 2005;Parton et al 2007;Manzoni et al 2010). N release takes place generally when the initial N content is between 0.6 and 2.8 % (Berg and Staff 1981) or the C:N ratio drops below a critical threshold of 5 to 15 (Parton et al 2007;Manzoni et al 2008).…”

“…The critical C:P ratio, with a typical range between 200 and 480 (Gosz et al 1973;Manzoni et al 2010), varies across climatic regions and ecosystems. Tropical regions generally have a higher C:P ratio due to the compound effects of increased decomposer respiration, a high decomposer C:P ratio, and strong leaching (Manzoni et al 2010). In the current study, the litter C:P ratio was far less than 480 and showed net P release from the beginning of the decomposition experiment under all treatments.…”

“…In the current study, the litter C:P ratio was far less than 480 and showed net P release from the beginning of the decomposition experiment under all treatments. The accumulation or release of P and N generally occur simultaneously (Manzoni et al 2008(Manzoni et al , 2010. Unlike the effects on N loss in the later stage, management practices strengthened both the positive effects of N addition on P loss in the early stage and the negative effects in the later stage.…”