title: Direct estimation of mass flow and diffusion of nitrogen compounds in solution and soil.
abstract: Plant nutrient uptake from soil is mainly governed by diffusion and transpirationally induced mass flow, but the current methods for assessing the relative importance of these processes are indirect. We developed a microdialysis method using solutions of different osmotic potentials as perfusates to simulate diffusion and mass flow processes, and assessed how induced mass flow affected fluxes of nitrogen (N) compounds in solution and in boreal forest soil. Varying the osmotic potential of perfusates induced vertical fluxes in the direction of the dialysis membranes at rates of between 1 × 10(-8) and 3 × 10(-7)  m s(-1) , thus covering the estimated range of water velocities perpendicular to root surfaces and induced by transpiration. Mass flow increased N fluxes in solution but even more so in soil. This effect was explained by an indirect effect of mass flow on rates of diffusive fluxes, possibly caused by the formation of steeper gradients in concentrations of N compounds from membrane surfaces out in the soil. Our results suggest that transpiration may be an essential driver of plant N acquisition.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
authors.forename: Olusegun Ayodeji
authors.initials: OA
authors.lastname: Oyewole
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
authors.forename: Erich
authors.initials: E
authors.lastname: Inselsbacher
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.|Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
authors.forename: Torgny
authors.initials: T
authors.lastname: Näsholm
mesh_terms: D004058:Diffusion; D017551:Microdialysis / Q000379:methods*; D017672:Nitrogen Compounds / Q000032:analysis*; D009995:Osmosis; D010477:Perfusion; D012212:Rheology; D012987:Soil / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D014197:Trees / Q000737:chemistry
chemical_list: D017672:Nitrogen Compounds; D012987:Soil; D012996:Solutions
keywords: Dextran 40; amino acids; diffusion; mass flow; microdialysis; nutrient availability; osmotic potential; transpiration