Common structure in the heterogeneity of plant-matter decay.
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Here, we pose and solve an inverse problem to find the rate distributions corresponding to the decomposition of plant matter throughout North America.These findings probably result from the interplay of stochastic processes and biochemical kinetics, suggesting that the intrinsic variability of decomposers, substrate and environment results in a predictable distribution of rates.Within this framework, turnover times increase exponentially with the kinetic heterogeneity of rates, thereby providing a theoretical expression for the persistence of recalcitrant organic carbon in the natural environment.
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Affiliation: Lorenz Center and Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. dforney@mit.edu
ABSTRACT
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Carbon removed from the atmosphere by photosynthesis is released back by respiration. Although some organic carbon is degraded quickly, older carbon persists; consequently carbon stocks are much larger than predicted by initial decomposition rates. This disparity can be traced to a wide range of first-order decay-rate constants, but the rate distributions and the mechanisms that determine them are unknown. Here, we pose and solve an inverse problem to find the rate distributions corresponding to the decomposition of plant matter throughout North America. We find that rate distributions are lognormal, with a mean and variance that depend on climatic conditions and substrate. Changes in temperature and precipitation scale all rates similarly, whereas the initial substrate composition sets the time scale of faster rates. These findings probably result from the interplay of stochastic processes and biochemical kinetics, suggesting that the intrinsic variability of decomposers, substrate and environment results in a predictable distribution of rates. Within this framework, turnover times increase exponentially with the kinetic heterogeneity of rates, thereby providing a theoretical expression for the persistence of recalcitrant organic carbon in the natural environment. Related in: MedlinePlus |
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Mentions: We apply this procedure to litter decomposition data from the LIDET study. An example of decay from an LIDET dataset is shown in figure 1a. The corresponding estimate of the rate distribution in logarithmic space, expressed as , where x = ln k, is shown in figure 1b. The rate k is rescaled by the period of seasonal forcing (1 year) and is therefore non-dimensional. The good fit of ρ(ln k) to a Gaussian indicates that the distribution of rates is lognormal, characterized by the parameters μ and σ, where μ is the mean of ln k and σ2 is the variance of ln k.Figure 1. |
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Affiliation: Lorenz Center and Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. dforney@mit.edu