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Phosphorus availability, root exudates, and microbial activity in the rhizosphere
Author(s) -
Schilling Günther,
Gransee Andreas,
Deuhel Annette,
Ležoviž Grit,
Ruppel Silke
Publication year - 1998
Publication title -
zeitschrift für pflanzenernährung und bodenkunde
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 0044-3263
DOI - 10.1002/jpln.1998.3581610413
Subject(s) - rhizosphere , exudate , chemistry , phosphorus , sativum , nutrient , brassica , fructose , pisum , sugar , phosphate , agronomy , horticulture , botany , food science , biology , biochemistry , bacteria , organic chemistry , genetics
Field and pot experiments showed that the P demand of wheat is highest in early stages of growth (up to 1.67 μg P per cm 2 root surface and day). The needed orthophosphate ions H 2 PO 4 − and HPO 4 2 ‐move from soil to the root by diffusion. This process is controlled by the concentration gradient of the diffusible phosphate and the effective diffusion coefficient according to Pick's first law. Root excretions (rhizodeposition) are able to affect both characteristics. The water soluble portion of rhizodeposition contains more than 50% of up to 8 different sugars, 10–40% carboxylic acids and 10–15 amino acids and amides. The composition varies in dependence on the age of the root parts and on nutrition ( Zea mays L., Brassica napus L., Pisum sativum L.). Diffusion experiments using small soil blocks showed that 50–75% of the root exudates were decomposed by respiration within 3 days. The rest was largely chemically converted. Originally present sugars disappeared. Due to the biosynthesis of different organic acids from the individual sugars the mobilisation of Ca 3 (PO 4 ) 2 by Pantoea agglomerans increased when the sugar mixture was derived from the rhizodeposition of P deficient plants with more pentoses instead of glucose and fructose (mainly effect of anions). In the rhizosphere therefore a mixture of rhizodeposition and its conversion products exists which affects the binding of phosphorus in soil and the P transport to the root. This should be considered both for the development of new soil extractants and for modelling the P supply to plants.