Chapter 11 Plant p nutrition and p fertilizers
Chapter 11 Plant P nutrition and P fertilizers
Phosphorus in plant physiology P content of plants Approximately 0.2%of plant dry weight is P Plants require a relatively large amount of P. The phosphate concentration in the cytosol is maintained at fairly constant concentrations in the 5 to 8 mol/ms regardless of the external phosphate concentration except under severe P deficiency. By contrast is the vacuolar phosphate concentration
P content of plants • Approximately 0.2% of plant dry weight is P • Plants require a relatively large amount of P. The phosphate concentration in the cytosol is maintained at fairly constant concentrations in the 5 to 8 mol/m3 regardless of the external phosphate concentration except under severe P deficiency. By contrast is the vacuolar phosphate concentration. Phosphorus in plant physiology
Forms of P taken up Most P is taken up by roots as inorganic orthophosphate ions(H2 PO4 and HPO42) Roots may absorb some organic p but the amount is very small The polyphosphate(聚磷酸) was only taken up by young barley plants after hydrolysis to the orthophosphate(正磷酸) form
Forms of P taken up • Most P is taken up by roots as inorganic orthophosphate ions (H2PO4 - and HPO4 2- ) • Roots may absorb some organic P, but the amount is very small. • The polyphosphate(聚磷酸) was only taken up by young barley plants after hydrolysis to the orthophosphate(正磷酸) form
P uptake by plant H PO concentration in the root and Xylem sap is 100-1000 times greater than in the soil solution Active uptake is used to overcome this concentration gradient It is likely that inorganic P is co-transported across the plasma membrane with positively charged ions(Hf) The transport across the membrane requires energy. Wet or cold soils that reduce plant metabolic activity are likely to reduce P uptake
P uptake by plant H2PO4 - concentration in the root and xylem sap is 100-1000 times greater than in the soil solution Active uptake is used to overcome this concentration gradient. • It is likely that inorganic P is co-transported across the plasma membrane with positively charged ions (H+ ) • The transport across the membrane requires energy. Wet or cold soils that reduce plant metabolic activity are likely to reduce P uptake
P uptake by plant There are two types of transporters with different affinities for pi, one with a high affinity with a Km of 3-5 mmo/m and the other a low affinity system with a Km of 50 to 330 mmol/m3 Molecular studies have confirmed the presence of multiple genes encoding phosphate transporters that are differentially expressed
There are two types of transporters with different affinities for Pi, one with a high affinity with a Km of 3-5 mmol/m3 and the other a low affinity system with a Km of 50 to 330 mmol/m3 Molecular studies have confirmed the presence of multiple genes encoding phosphate transporters that are differentially expressed. P uptake by plant
P uptake by plant Some are strongly upregulated when phosphate supply is inadequate. Other phosphate systems are constitutive which are not affected by changes in phosphate concentration in the nutrient medium The ph in the apoplast controls the H2PO4 the uptake rate
• Some are strongly upregulated when phosphate supply is inadequate. Other phosphate systems are constitutive which are not affected by changes in phosphate concentration in the nutrient medium. • The pH in the apoplast controls the H2PO4 - the uptake rate. P uptake by plant
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Role of mycorrhizae in P uptake Many plants have associations have a symbiotic relationship with mycorrhizae The plants supply mycorrhizae with C and the mycorrhizae supply the plant with nutrients 2. Mycorrhizae may increase P uptake by 3-5 times No mycorrhizae With mycorrhizae
1. Many plants have associations have a symbiotic relationship with mycorrhizae The plants supply mycorrhizae with C and the mycorrhizae supply the plant with nutrients. 2. Mycorrhizae may increase P uptake by 3-5 times. Role of mycorrhizae in P uptake
Transport of phosphorus in plant P adsorbed from the roots is transported in the xylem to young leaves. The xylem contains mostly inorganic P P can also be transported from older leaves to younger leaves - and from the shoots to the roots-in the phloem. The process is known as re-translocation The phloem can contain both organic and inorganic P So the P is remobilization in plant
– P adsorbed from the roots is transported in the xylem to young leaves. The xylem contains mostly inorganic P. – P can also be transported from older leaves to younger leaves – and from the shoots to the roots – in the phloem. The process is known as re-translocation. – The phloem can contain both organic and inorganic P. – So the P is remobilization in plant. Transport of phosphorus in plant
Regulation of P uptake The concentration of phosphate cycled in phloem from shoot to root acts as a feedback signal to regulate P uptake(Drew and Saker 1984) High concentrations of phosphate in the phloem induced by low demand in shoot repress uptake Conversely low concentration associated with high shoot demand stimulate uptake
Regulation of P uptake • The concentration of phosphate cycled in phloem from shoot to root acts as a feedback signal to regulate P uptake (Drew and Saker 1984). • High concentrations of phosphate in the phloem induced by low demand in shoot repress uptake. Conversely low concentration associated with high shoot demand stimulate uptake
