PHYSIOLOGICAL DISTURBANCES CAUSED BY HIGH RHIZOSPHERIC CALCIUM IN THECALCIFUGE LUPINUS-LUTEUS

A detailed study of the calcifuge Lupinus luteus L. (yellow lupin) has been carried out in an attempt to explain its poor performance in the presence of high concentrations of rhizospheric calcium. Plants were grown on two different calcium regimes, 1 or 15 mol m(-3) Ca and, afte r an establishment period, measurements were made of the rate of leaf extension, final length of the leaflets and the leaf gas exchange. In addition, the distribution of calcium within the leaf tissue was inves tigated. At 15 mol m(-3) Ca, leaflet length at full expansion was redu ced as a consequence of reduced extension rate and a decline in cell w all extensibility. Transpiration in excised leaves, assayed gravimetri cally, was significantly reduced in plants grown in high calcium. Simi lar results were also obtained from gas exchange measurements. Analysi s of A/C-i curves indicated that in plants grown in high [Ca] there wa s a substantial reduction in net assimilation over a range of concentr ations of CO2. X-ray microanalysis revealed that a large amount of cal cium delivered in the xylem sap is retained in the mesophyll tissue, a nd most of that reaching the epidermal tissue is not found in the guar d cells but in the cells adjacent to them, which in this species are n ot anatomically distinct as 'subsidiary' cells.