Canopy dynamics and carbon gain in response to soil water availability in Encelia frutescens gray, a...

The production and longevity of leaves of Encelia frutescens Gray, a drought-deciduous subshrub of the Mohave and Sonoran Deserts, were followed during the summer and fall of 1983 in an experimental field garden. The relationships between seasonally changing plant water status, extent of canopy development, and photosynthetic capacity per unit leaf area were determined. Maximum leaf life spans during a summer activity period were between 3 and 4 months, with the great majority living between 1 and 3 months. Leaf production occurred synchronously in well defined cohorts triggered by precipitation events. Extensive leaf turnover occurred during the summer period even though the plants remained in continuous leaf. Turnover was most pronounced when precipitation triggered the production of new leaf cohorts.Five weeks were required for plants to reach maximum canopy development when renewed soil-water availability followed a prolonged drought. Photosynthetic capacity per unit leaf area recovered much sooner than total leaf area, and submaximal leaf area development was the major factor limiting whole-plant carbon gain during a leaf-flushing period lasting several weeks. As the soil began to dry out, physiological capacity declined more rapidly than leaf area, and became the primary limiting factor to whole plant carbon gain.