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. Plain Language Summary Carbon sequestration by ecosystems is important for mitigating global warming. During the transfer of carbon from atmospheric CO2 to plants, then to litter, and then to soil, carbon is continuously lost to the atmosphere via CO2. Here, we adopted the idea of Lindeman Efficiency to express this efficiency of carbon transfer between different layers in the plant‐litter‐soil systems in the continental US. We found that ecosystems with higher productivity have lower carbon transfer efficiency, indicating the tradeoff between the two. Therefore, it is hard to find an ecosystem with both high productivity and high carbon transfer efficiency to soil for carbon sequestration. Our attempt to understand carbon transfer efficiency provides an intuitive proxy of C cycling and a framework for future research on ecosystem carbon sequestration and global warming. Key Points The transfer of carbon from plant to litter than to soil is more efficient in ecosystems with higher productivity Our litter submodel can directly simulate carbon input fluxes into soil, has intermediate complexity, and shows good performance Th