The Significance of the Root Cell Wall in Phosphorus Uptake

Summary

Groundnut grew well on an extremely phosphorus (P) deficient soil in which soybean and sorghum did not survive. This ability could not be attributed to differences in root development, C _min , or root exudates that are capable of solubilizing sparingly soluble iron- and aluminum-bound P in soils. Since plants acquire P by diffusion, poor survival of soybean and sorghum indicated that P diffusion to their roots was negligible. Because P solubilization must occur in the contact zone between root and soil, the “contact reaction” between root epidermal cell walls and P-fixing minerals was examined in detail. Upon treatment with naturally-occurring P minerals such as strengite and variscite, root cell walls of groundnut solubilized twice as much P than those of sorghum and soybean. Such activity partly explains the superior growth of groundnut on P-deficient soils. The ability of pigeonpea to take up P from a low-P soil was associated with its production of root exudates. However, since exudation is high mainly during reproductive growth, its ability to take up P from P-deficient soils in earlier growth stages is worth examining. Tests on pigeonpea root cell walls indicated that its P solubilization activity was as high as that of groundnut. The findings from both crops suggest that “contact reaction” may contribute to P uptake by plants.