Soil microbial loop and nutrient uptake by plants: a test using a coupled C:N model of plant–microbial interactions

Abstract

We have developed a spatially explicit model of plant root and soil bacteria interactions in the rhizosphere in order to formalise and study the microbial loop hypothesis that postulates that plants can stimulate the release of mineral N from the soil organic matter by providing low molecular weight C molecules to C-limited microorganisms able to liberate into the soil enzymes that degrade the organic matter. The model is based on a mechanistic description of diffusion of solutes in the soil, nutrient uptake by plants, bacterial activity and bacterial predation. Modelled soil bacterial populations grow, mediate transformations among several forms of nitrogen (mineral and organic) and compete for nitrogen with plants. Our objectives were to see if we could simulate the stimulation of turnover of the microbial loop by exudates and to study the effects of diffusion of C and N in the rhizosphere on these different processes. The model qualitatively mimics most of the characteristics of the microbial loop hypothesis. In particular, (1) plant exudates increase the growth of bacteria in the soil and (2) increase the degradation of soil organic matter and N mineralisation. (3) The increased bacterial biomass induces an increase in predator biomass and, as a result, (4) plant mineral N uptake is increased threefold compared with scenarios without exudation. However, the temporal dynamics simulated by the model are much slower than observed dynamics (the increase in uptake appears after a few months). Taking into consideration the diffusion of C and N containing molecules in soil has large effects on the spatial structure of the bacterial and predator biomass. However, the average biomass of bacteria and predators, N mineralisation and plant N uptake were not affected by these properties. The model provides a quantitative and mechanistic explanation of how plants could benefit from liberating low molecular organic matter and the subsequent stimulation of the microbial loop and increases N mineralisation

Multiple soil nutrient competition between plants, microbes, and mineral surfaces: model development, parameterization, and example applications in several tropical forests

“…Terrestrial ecosystem growth and function are continuously altered by climate (e.g., warming, drought; Chaves et al, Springate and Kover, 2014), external nutrient inputs (e.g., N deposition; Matson et al, 1999Matson et al, , 2002, and atmospheric composition (e.g., CO 2 concentration; Norby et al, 2010;Oren et al, 2001;Reich et al, 2006). Improved understanding of the underlying mechanisms regulating ecosystem responses to environmental changes has been obtained through in situ level to large-scale and long-term manipulation experiments.…”

Colimitation of decomposition by substrate and decomposers – a comparison of model formulations

“…10. The same equation has been used by other studies as well (Garnier et al, 2003;Raynaud et al, 2006). The formulation is structurally opposite to the formulation of Monod (Eq.…”

“…We propose to challenge models by observations of patterns of several variables, which is used in multiple constraint model identification (Raupach et al, 2005;Reichstein et al, 2003) or pattern oriented modelling (Wiegand et al, 2003). The inclusion of the isotopic ratio in addition to the amount of respiration clearly improved the identifiability of model formulations in the artificial model discrimination experiment.…”

When microbes and consumers determine the limiting nutrient of autotrophs: a theoretical analysis

“…They can also be responsible for the remineralization of the nutrients immobilized in decomposer biomass (Andersen et al 1986;Raynaud et al 2006).…”