Soil microbial loop and nutrient uptake by plants: a test using a coupled C:N model of plant–microbial interactions
- 546 Downloads
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.
KeywordsPlant–bacteria interactions Exudates Microbial loop hypothesis Barber–Cushman model Competition Mutualism Nitrogen Carbon
Unable to display preview. Download preview PDF.
We gratefully thank three anonymous referees and the editor for valuable comments on a prior version of this manuscript. Computer source code of the model is available from X. Raynaud upon requests.
- Adamowicz S, Le Bot J (1999) Trends in modelling nitrate uptake. Acta Hort 507:231–239Google Scholar
- Barber SA, Silberbush M (1984) Plant root morphology and nutrient uptake. In: Barber S, Bouldin D (eds) Roots, nutrients and water influx, and plant growth. American Society of Agronomy, Madison, WI, USA, pp 65–87. Special publication 49Google Scholar
- Clarholm M (1985b) Possible roles for roots, bacteria, protozoa and fungi in supplying nitrogen to plants. Ecol Interact Soil 4:355–365Google Scholar
- Coleman DC, Ingham RE, McClellan JF, Trofymow JA (1984) Soil nutrient transformations in the rhizosphere via animal–microbial interactions. In: Anderson JH, Raynew ADM, Walton DHW (eds) Invertebrate–microbial interactions. Cambridge University Press, Cambridge, pp 35–58Google Scholar
- Gee CS, Pfeffer JT, Suidan MT (1990) Nitrosomonas and Nitrobacter interactions in biological nitrification. J␣Environ Eng 116(1):4–17Google Scholar
- Jones TH, Thompson LJ, Lawton JH, Bezemer TM, Bardgett RD, Blackburn TM, Bruce KD, Cannon PF, Hall GS, Hartley SE, Howson G, Jones CG, Kampichler C, Kandeler E, Ritchie DA (1998) Impacts of rising atmospheric carbon dioxide on model terrestrial ecosystems. Science 280(5362):441–443PubMedCrossRefGoogle Scholar
- Killham K (1994) Soil ecology. Cambridge University Press, Cambridge, UKGoogle Scholar
- Nye PH, Tinker PB (1977) Solute movement in the soil–root system. Blackwell Scientific, Oxford, UKGoogle Scholar
- Paul EA, Clark FE (1989) Soil microbiology and biochemistry. Academic Press, San Diego, CA, pp 275Google Scholar
- Pelmont J (1993) Bactéries et environement: adaptations physiologiques. Presses universitaires de Grenoble, Grenoble, FranceGoogle Scholar
- Prescott L, Harley J, Klein D (1999) Microbiologie, 2nd edn. De Boeck Université, BruxellesGoogle Scholar
- Tinker PB, Nye PH (2000) Solute movement in the rhizosphere. Oxford University Press, Oxford, UKGoogle Scholar