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Phosphorus efficiency of plants ii. significance of root radius root hairs and cation anion balance for phosphorus influx in seven plant species

Foehse, D.; Claassen, N.; Jungk, A.

Plant and Soil 132(2): 261-272

1991


ISSN/ISBN: 0032-079X
Accession: 007652066

Fohse et al. (1988) have shown that P influx per unit root length in seven plant species growing in a low-P soil varied from 0.6 .times. 10-14 to 4.8 .times. 10-14 mol cm-1s-1. The objective of this work was to investigate the reasons for these differences. No correlation was found between P influx and root radius, roots hairs, cation-anion balance and Ca uptake. However, when root hairs were included in mathematical model calculations, the differences of P influx could be accounted for. These calculations have shown that in soils low in available P, contribution to P uptake by root hairs was up to 90% of total uptake. The large contribution of root hairs to P uptake was partly due to their surface area, which was similar to that of the root cylinder. However, the main reason for the high P uptake efficiency of root hairs was their small radius (approx. 5 .times. 10-4 cm) and their perpendicular growth into the soil from the root axis. Because of the small radius compared to root axes, P concentration at root hair surfaces decreased at a slower pace and therefore P influx remained higher. Under these conditions higher Imax (maximum influx) or smaller Km values (Michaelis constant) increased P influx. The main reasons for differences found in P influx among species were the size of Imax and the number and length of root hairs. In a soil low in available P, plant species having more root hairs were able to satisfy a higher proportion of their P demand required for maximum growth.

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