Seasonal progressions of tissue and cell water relations parameters in evergreen and deciduous perennials

Abstract. Tissue and cell water relations parameters were followed for Heteromeles arbutifolia, Cercis occidentalis and Aesculus californica , in an environment exhibiting seasonally increasing drought. The extensive seasonal osmotic adjustment of evergreen H. arbutifolia and the moderate adjustment in C. occidentalis closely matched their respective seasonal decreases in minimum daily water potential. Summer deciduous A. californica exhibited only small drops in osmotic potential and water potential. Experiments with irrigated plants indicated that drought was not required for the osmotic adjustment of H. arbutifolia and C. occidentalis. However, in H. arbutifolia drought treatment enhanced osmotic adjustment. In irrigated H. arbutifolia , osmotic adjustment was mainly the result of an accumulation of osmotica. In drought-stressed plants, the same change in osmotic potential resulted from a combination of accumulation of osmotica and a decrease in symplast volume.