Water Relations of Flowering of Agave deserti

The water budget during flowering for the leaves, inflorescence, and lateral floral branches of the monocarpic perennial Agave deserti Engelm. (Agavaceae) was investigated in the western Colorado 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 weight (7.1 kg attributable to leaf transpiration) and 1.84 kg in dry weight. 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 one seed in 1.2 x 106 will lead to a mature flowering plant. In fact, most A. deserti plants are produced vegetatively.