Comparative phosphorus responses in plants to a range of available phosphorus situations

Abstract

The ranking in productivity of four species against a gradient of phosphorus availability in four soil situations was buckwheat > rye > crimson clover ≥ subterranean clover. Relative performance seemed to be a characteristic of the plant. Ranking between species changed little over the soil situations. Buckwhelt obtained more phosphorus and used it more efficiently in dry matter production than the other species. Differences in efficiency or use were associated with productivity rankings in the other species. Greater phosphorus uptake by buckwheat was associated with its ability to acidify the rooting medium. This did not result from exuded organic acids, but ions exchanged for cations taken up by the plant, particularly the calcium ion, seemed to be implicated. Productivity and eficiency of phosphorus use were associated with greater root weights, root volumes and root hair production. Root respiration and exocellular phosphatase activity were lower for high performance than for low performance species. The importance of root development seemed to be associated with absorptive area rather than metabolic activity. Phosphatase appeared to be an adaptive enzyme. Its activity could be used to distinguish species better adapted to use the existing phosphorus in low fertility situations.