The Carbon Transfer From Plant to Soil Is More Efficient in Less Productive Ecosystems

The organic carbon (C) in soil is mainly from plants via litter decomposition. Here, we developed a new litter decomposition submodel incorporating the microbial biomass effect on the decomposition rate based on the Michaelis-Menten kinetics. This new submodel was coupled with the existing plant and soil submodels to simulate C cycling in natural ecosystems in the continental United States. The C transfer efficiency (EFF), defined as the percentage of C transferred to the next layer in the plant-litter-soil continuum, was quantified in different types of natural ecosystems. We estimated that on average 48.1% of gross primary productivity (GPP) was transferred from plant to litter and 15.1% of litterfall was transferred from litter to soil, meaning that the C that finally enters soil was on average approximately 7.3% of GPP. Ecosystems with a drier climate and lower GPP had higher EFF from plant to soil. The EFF concept we proposed provides an empirical proxy for diagnosing ecosystem C cycling and a framework for projecting the change of C fluxes and C pool sizes in response to climate change. If C transfer can represent energy transfer analogous to Lindeman Efficiency, our results suggest a pattern of resource and energy transfer in nature: higher resource or energy availability usually means lower resource or energy transfer efficiency.

Automated summary

Soil organic carbon mainly comes from plants through litter decomposition. A new submodel for litter decomposition incorporating the microbial biomass effect was developed based on the Michaelis-Menten kinetics. The submodel was coupled with plant and soil submodels to simulate carbon cycling in US ecosystems. The transfer efficiency of carbon from plants to soil was quantified, providing an empirical proxy for diagnosing ecosystem carbon cycling and projecting carbon fluxes and pool sizes in response to climate change.