Water Relations of Flowering of Agave deserti

Abstract

The water budget during flowering for the leaves, inflorescence and lateral floral branches of the monocarpic perennial A. deserti Engelm. (Agavaceae) was investigated in the western Colorado [USA] desert. During the 159 days from the emergence of the inflorescence until the fruit could be removed from the plant without affecting seed viability, the approximately 68 leaves on a plant decreased 24.9 kg in wet wt (7.1 kg attributable to leaf transpiration) and 1.84 kg in dry wt. The decrease of water in the leaves, which accompanied their death, was balanced by water storage in the inflorescence (3.1 kg), transpirational water loss from its surface (4.3 kg) and water loss from the lateral floral branches (10.8 kg), most of which came from the fruit. The final dry weight of the inflorescence (1.25 kg) approximately equaled the total annual photosynthetic productivity of a mature plant; such a large demand on its reserves is consistent with the single blooming period for this perennial. Due to seed predation, stringent germination conditions, and seedling fatalities, only about 1 seed in 1.2 .times. 106 will lead to a mature flowering plant. Most A. deserti plants are produced vegetatively.