The response of Primula species to soil waterlogging and soil drought.

The distributions of Primula vulgaris, P. elatior and P. veris in the British Isles are partly dependent on differences in waterlogging and drought tolerance. Comparison of biomass production and root length on soils with different water tables ranked the species in order of increasing waterlogging-tolerance: P. veris < P. vulgaris < P. elatior. P. veris and P. vulgaris were most sensitive to waterlogging during the first three months of growth. Waterloggingtolerance in P. elatior was associated with the ability to maintain an oxygen flux from the roots in anoxic media, which was not present in the other species. Solution culture experiments indicated that poor growth of P. vulgaris on saturated soils was a consequence of anoxia but gave no explanation for the waterlogging-intolerance of P. veris.Maximum photosynthetic rate recovered rapidly in P. vulgaris and P. veris following drought. In P. elatior, however, recovery was slower and associated with the production of new leaf area. Older, wilted leaves senesced rapidly and reduced the overall photosynthetic performance of the plant. Comparison of cumulative water loss on a leaf area basis against the proportion of maximum photosynthetic rate prior to soil drought, ranked the species in order of increasing drought tolerance; P. veris>vulgaris>elatior.The habitats of P. vulgaris and P. elatior are recognisably distinct where the species occur together as a consequence of differences in their drought and waterloggingtolerances. Amongst other factors, the more developed drought tolerance of P. veris enables it to exploit drier, more open, situations.