西北农林科技大学：《植物营养学》课程教学资源（PPT课件讲稿，英文版）Chapter 10 Nitrogen nutrition of plant and Nitrogen fertilizers

Chapter 10 Nitrogen nutrition of plant and Nitrogen fertilizers

Nitrogen nutrition of plant and Nitrogen fertilizers Chapter 10

Plant nitrogen 1.1 Uptake of N 1. N is required by plants in large amounts Most plant material contains 2-4%N and 40%C. 2. N is usually the limiting nutrient in unfertilized systems 3. Most N is taken up from the soil in the form of nhat or no a small amount of NH can be absorbed through the leaves N2 can be used by legume plant via biological nitrogen fixation

I Plant nitrogen 1.1 Uptake of N 1. N is required by plants in large amounts. Most plant material contains 2-4% N and 40% C. 2. N is usually the limiting nutrient in unfertilized systems. 3. Most N is taken up from the soil in the form of NH4 + or NO3 - . A small amount of NH3 can be absorbed through the leaves. N2 can be used by legume plant via biological nitrogen fixation

Plant nitrogen Most plants grow best with a combination of NO3 and NH4 Some plants are specialists: e.g. use NH4 amino acids( e.g. mature forests, arctic tundra北极冻塬,rice) Some take up more Nhat than noa when both supplied together in equal amounts, but NO3 is prime form of N in soil solution Over-supply of Nhat can be toxic to plants

▪ Most plants grow best with a combination of NO3 - and NH4 + . ▪ Some plants are specialists: e.g. use NH4 + & amino acids (e.g. mature forests, arctic tundra北极冻塬, rice) ▪ Some take up more NH4 + than NO3 - when both supplied together in equal amounts, but NO3 - is prime form of N in soil solution ▪ Over-supply of NH4 + can be toxic to plants I Plant nitrogen

I Plant nitrogen Uptake of NH4 may be brought about by the facilitated diffusion(by the electropotential difference and cation selective channels). With Nhat nutrition recycling of ht back into the cytosol is restricted and the ht/pumped out of the cell and remain mainly outside and hence the pH is depressed

Uptake of NH4 + may be brought about by the facilitated diffusion (by the electropotential difference and cation selective channels). With NH4 + nutrition recycling of H+ back into the cytosol is restricted and the H+ /pumped out of the cell and remain mainly outside and hence the pH is depressed. I Plant nitrogen

Mechanism of uptake NO3 The uptake of NO3 is mainly a H#/NO 3 cotransport with the pumped out of the cell by the PM proton pump being recycled back into the cytosol Hence the nitrate uptake is associated with an pH increase in the outer medium

▪ The uptake of NO3 - is mainly a H+ / NO3 - cotransport with the pumped out of the cell by the PM proton pump being recycled back into the cytosol. ▪ Hence the nitrate uptake is associated with an pH increase in the outer medium. Mechanism of uptake NO3 -

1.2 Uptake of N and rhizosphere pH changes NH4+ assimilation: pH(acicl)-often whole root surface NO3 assimilation; pH often alkaline-sometimes in patches, may be also be pH patches elsewhere on same root Maize(in soil agar indicator) NO NH+ low no Marschner Romheld (1983) 60 1D

1.2 Uptake of N and Rhizosphere pH changes ▪ NH4 + assimilation: pH  (acid) - often whole root surface ▪ NO3 - assimilation: pH often  (alkaline) - sometimes in patches; may be also be pH  patches elsewhere on same root Maize (in soil & agar + indicator) NO3 - NH4 + low NO3 - Marschner & Römheld (1983)

NH4 assimilation in roots (and pH regulation) protein etc light sucrose cO2 shoot Xylem phloem root Excess cation uptake amino-N NH4 Raven& Smith (1976); modified pH protein etc

NH4 + assimilation in roots (and pH regulation) amino-N NH4 + H+ protein etc protein etc sucrose CO2 shoot root xylem phloem pH  light ‘Excess’ cation uptake Raven & Smith (1976); modified

NHy assimilation in roois (and pH regulation) protein etc light sucrose cO2 shoot xylem phloem root amino-N H protein etc

NH4 + assimilation in roots (and pH regulation) amino-N NH4 + H+ protein etc protein etc sucrose CO2 shoot root xylem phloem pH  light ‘pH non￾perturbing’ amino acids & amides

Ammonium cytoplasm outside High Affinity Trans port ve PD Systems: Km=20 NH4 40mmol/m As well as net efflux some ' re-cycles' by co transport NH transport with NH IIIEIIEIEIEE NH4+[& Kti Low Affinity TS channel NH4+ [&K+1? NH3?(Diffusion at high concentrations?) Energetics, kinetics, regulation, genes: Forde Clarkson(1999); Glass et al. (2002)

Ammonium cytoplasm outside -ve PD  NH4 +  H+ )  NH4 + ) H+ →  NH4 + [& K+ ]  NH4 + [& K+ ]? NH3? High Affinity Transport Systems; Km=20- 40mmol/m3 Low Affinity TS (Diffusion at high concentrations?) channel H+ co￾transport As well as net H+ efflux, some H+ ‘re-cycles’ by co￾transport with NH4 + Energetics, kinetics, regulation, genes : Forde & Clarkson (1999); Glass et al. (2002) pH 

pH regulation during NO3 assimilation in roots protein etc light sucrose cO2 shoot xylem phloem root amino-N 2H+pH T protein etc

pH regulation during NO3 - assimilation in roots amino-N NO3 - 2H+ protein etc protein etc sucrose CO2 shoot root xylem phloem pH  light ‘Excess’ anion uptake