Tuesday, November 14, 2006 - 10:00 AM

From Microbial Activities to Root Uptake Kinetics: The Role of Rhizospheric Biology in Plant Nitrogen Uptake.

Hormoz BassiriRad, Univ of Illinois at Chicago, Dept of Biological Sciences, 845 West Taylor Street, Chicago, IL 60607 and Vincent Gutschick, New Mexico State Univ, Dept of Biology, 3AF, Las Cruces, NM 88003.

Models of plant nitrogen uptake often lack parameters that account for either the release or immoblization of N in the soil by microbes. In addition, the role of mycorrhizal association with the plant root system and how such a symbiosis affects N acquisition is poorly integrated into models of plant N uptake. Here we suggest that development of robust models of N uptake require effective integration of microbial parameters. This will be true even in cases when the target systems are heavily fertilized. Furthermore, we argue that plant roots show a remarkable degree of adjustment in kinetics of N uptake under different environmental conditions. These adjustments must be characterized and then effectively incorporated into models of N uptake. We will also present evidence that in most agricultural as well as native systems, a substantial proportion of soil available N is present as dissolved organic N (DON) such as amino acids. These, relatively small organic N compound, can be directly acquired as an N source hence, affect plant demand for N, or alternatively, they can alter kinetic properties of root ammonium and nitrate transporters. Therefore, the reliability of N uptake models can be significantly improved if the role of DON is addressed. Lastly, we must consider how these different forms of N aretransported in soil among organic matter pools, microbes, roots, and mycorrhizae. Diffusion heavily dominates over mass flow in all cases, but the various forms of N differ significantly in diffusion kinetics.