Effects of Water and Nutrient Availability on Water Relations, Gas Exchange and Growth Rate of Mature Plants and Resprouts of Arbutus unedo L.

Abstract

This study examines the effects of water supply and nutrition on the water status, gas exchange and growth of mature plants and resprouts of Arbutus unedo, a Mediterranean evergreen shrub adapted to drought and poor nutrition. Mature plants of A. unedo respond to irrigation with increased leaf water potential during summer drought, but they show a very conservative use of water and they do not increase leaf conductance. There is also a very small increase in net photosynthesis and growth, which does not significantly increase productivity.Resprouts of A. unedo increase water potential, leaf conductance, transpiration rate, net photosynthesis and growth rate in response to watering, showing a less conservative use of water than mature plants. Increased growth rates, both in mature plants and resprouts, are likely to be due to the higher cell turgor caused by improved leaf water potential, rather than to increased photosynthesis.The only effect of nutrient addition on mature plants is an increase in leaf nutrient content, and other aspects of the physiology and growth of resprouts were unaffected. We therefore conclude that water is a more limiting factor than nutrients for mature plants and resprouts of A. unedo growing in the study area. These results support previous data which indicate that higher growth rates in resprouts than in mature plants of A. unedo are mainly the result of a higher water availability.