Chapter 4 The rhizosphere
The rhizosphere Chapter 4
Aims of this lecture Summarize properties of the rhizosphere, especially Gradients in Nutrient concentration Redox potential Exudates Microbial activi Non-infecting rhizosphere mIcroorganIsms necting rhizosphere mIcroorganisms that are relevant to plant mineral nutrition T/d from H Marschner: Fig 15.1
Aims of this lecture Summarize properties of the rhizosphere, especially: Modified from H. Marschner: Fig. 15.1 …that are relevant to plant mineral nutrition
The rhizosphere(根际) Width not to scale Layer of soil surrounding the -Root- growing root that is affected by the root(concept) pidermal and cortical cells Usually a few mm wide, up to lysed and invaded say 1 cm(no sharp boundary) by bacteria Extent depends on plant properties; e.g 20 CIm Root hair length density Micro-organisms Rhizodeposition(exudates etc) with microbial and plant mucilages spreading into the sd Nutrient uptake versus supply Sloughed root cap celis Root cap Mycorrhizospheres'(菌根际)can extend many cm Rovira
The rhizosphere(根际) Rovira 1960? • Layer of soil surrounding the growing root that is affected by the root (concept) • Usually a few mm wide, up to say 1 cm (no sharp boundary)* • Extent depends on plant properties; e.g. - Root hair length & density - Rhizodeposition (exudates etc) - Nutrient uptake versus supply Width not to scale * ‘Mycorrhizospheres’ (菌根际)can extend many cm c
The rhizosphere: soil factors Width not to scale Layer of soil surrounding the Root→·tSol growing root that is affected B the root Epidermal and cortical cells lysed and invaded Usually a few mm, up to say 1 bacteria cm (no sharp boundary EXtent depends on soil properties, e. g 鬆- Micro-organisms with microbial an d pH buffering plant mucilages spreading into the soi-Sorption capacity Nutrient supply rate Sloughed root cap cells Microbial populations Root cap Decomposition of exudates Rovira
The rhizosphere: soil factors Rovira 1960? • Layer of soil surrounding the growing root that is affected by the root • Usually a few mm, up to say 1 cm (no sharp boundary) • Extent depends on soil properties; e.g. - pH & buffering - Sorption capacity - Nutrient supply rate - Microbial populations - Decomposition of exudates Width not to scale
The rhizosphere: some conventions Root Rhizoplane Inner rhizosphere Outer 0-10um 10-500pm rhizosphere 根土界面 内根际 500-5000pm
The rhizosphere: some conventions Outer rhizosphere 500-5000 µm 外根际 Inner rhizosphere 10-500 µm 内根际 Rhizoplane 0-10 µm 根土界面 Root
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
