The rhizosphere: some conventions Root Rhizoplane Inner rhizosphere Outer rhizosphere 0-10pm 10-500pm 500-5000pm But defined phases may not be helpful because of Padients(no sharp boundaries)
The rhizosphere: some conventions Outer rhizosphere 500-5000 µm Inner rhizosphere 10-500 µm Rhizoplane 0-10 µm Root But defined ‘phases’ may not be helpful because of gradients (no sharp boundaries)
Gradients in the rhizosphere Longitudinal lateral gradients important for plant nutrition: Nutrient concentration H Redox potential -especially in waterlogged soils Exudates concentrations composition 2 Microbial activity]-population density composition Non-infecting rhizosphere microorganisms -especially soil bacteria Infecting rhizosphere microorganisms:-especially mycorrhizal fungi
Gradients in the rhizosphere Longitudinal & lateral gradients important for plant nutrition: - concentrations & composition - population density & composition - especially in waterlogged soils - especially soil bacteria - especially mycorrhizal fungi
Gradients in the rhizosphere Longitudinal lateral gradients: Nutrient concentration *Depends on balance between soil supply and plant uptake; depending in turn on Concentrations in bulk soil mobility in soil solution mass flow rate water content of soil rate of uptake into roots interactions with microorganisms
Gradients in the rhizosphere Longitudinal & lateral gradients: Mycorrhizal & other fungi - concentrations & composition - population density & composition Nutrient concentration Depends on balance between soil supply and plant uptake; depending in turn on: • Concentrations in bulk soil • mobility in soil solution • mass flow rate • water content of soil • rate of uptake into roots • interactions with microorganisms
lon mobilities and rhizosphere depletion Distance moved by diffusion(mm in 6 days) Soil volumetric water content Diffusion rate depends on 0.3 0.1 on NO3 >K*>H2PO4 NO 30 3 · Water content: 0.3 High >low H2PO4 0.3 0.03 Rhizosphere depletion of p is common in many soils
Ion mobilities and rhizosphere depletion Distance moved by diffusion (mm in 6 days) Soil volumetric water content NO3 - K + H2PO4 - 0.3 30 3 0.3 0.1 3 0.3 0.03 Diffusion rate depends on • Ion: NO3 ->K+>H2PO4 - • Water content: High > low Rhizosphere depletion of P is common in many soils
P depletion zones in the rhizosphere of maize and rape: influence of root hairs 150 Bulk soil Isotopical exchangeable p (ug ml 100 Canola 50 Mean root hair length Distance from root surface(mm) Hendriks et al. 1981
P depletion zones in the rhizosphere of maize and rape: influence of root hairs Hendriks et al. 1981 Distance from root surface (mm) Isotopically exchangeable P (µg ml -1 ) 150 100 50 1 2 3 Mean root hair length Canola Maize Bulk soil