The influence of alkalinity and water stress on the stomatal conductance, photosynthetic rate and growth of Lupinus angustifolius L. and Lupinus pilosus Murr.

A glasshouse experiment examined the effect of water stress on the growth of Lupinus angustifolius L. and Lupinus pilosus Murr. grown on an acid sandy soil, a limed sandy soil and an alkaline clay soil. Decreasing soil water content decreased the stomatal conductance and photosynthetic rate, and reduced plant growth. The responses of both species to water stress were generally similar in the sand and limed soils, but in the alkaline soil, L. angustifolius grown with limited water had markedly lower conductances and photosynthetic rates than the plants in the other soils at equivalent soil water contents. In adequately watered plants, the lupin species differed substantially in their growth response to soil types. Whereas the growth of L. pilosus was unaffected, the shoot dry weight of L. angustifolius grown on the limed and alkaline soils for 25-44 days was reduced by 32-54 and 44-86%, respectively, compared with the growth in the acid soil. The poor growth of L. angustifolius appeared to be primarily due to its poor root growth. In the alkaline soil, water stress reduced rather than stimulated root growth. The results suggest that, in the field, the limited root growth of L. angustifolius on alkaline soils will exacerbate water deficits when the topsoil dries out in the latter part of the season.