The Litter Decomposition and Leaching (LIDEL) model: modeling plant litter decomposition to CO2, dissolved organic matter and microbial products through nitrogen and lignin controls on microbial carbon use efficiency

Abstract:

Litter decomposition links terrestrial primary productivity to soil organic matter (OM) dynamics, by determining the quantity and chemical characteristics of plant-derived material entering the soil system. The controls on and products of litter decomposition form a foundation for the role of terrestrial ecosystems in global C cycling (i.e. as sinks or sources), by determining the contribution of plant productivity to atmospheric CO₂ through respiration versus to soil OM as direct plant or biologically processed material. We identified two areas in need of theoretical development in litter decomposition models. First, current litter decomposition models are generally based on litter mass loss and CO₂ flux, an approach which does not consider leaching and the generation of dissolved organic matter (DOM) from litter decomposition. Second, new hypotheses for the role of variable microbial carbon use efficiency (CUE) have important implications for the form and quantity of litter decomposition products- specifically, respiration of CO₂ versus the formation of microbes, microbial products, and DOM. We propose the Litter Decomposition and Leaching (LIDEL) model as a new theoretical approach to litter decomposition that 1) includes explicit modeling of DOM as a litter decomposition product, and 2) dynamically links substrate chemistry with variable CUE and the generation of DOM and other litter decomposition products. We parameterized the model using Bayesian calibration, based on a random-walk Metropolis Hastings within Gibbs Sampling Markov Chain-Monte Carlo algorithm. This Bayesian analysis uses litter decomposition and leaching experimental data for five litter types that vary by lignin and nitrogen content. By separating the dynamics of lignin versus microbial products as well as CO₂ versus DOM partitioning during litter decomposition, the LIDEL model clarifies the linkage between litter chemistry, microbial CUE, and SOM inputs from litter. We suggest the LIDEL model can be implemented in ecosystem models such as DAYCENT, as a better representation of above and below ground litter decomposition.