Parent-ramet connections in Agave deserti: influences of carbohydrates on growth.

Agave deserti, a monocarpic perennial occurring in the northwestern Sonoran Desert, produces ramets on rhizomes that extend from the base of a parent plant. Shading ramtes to light compensation for two years did not decrease their relative growth rate (RGR) compared with unshaded ramets. However, the parents experienced a 30% decrease in total nonstructural carbohydrate (TNC) level, suggesting that carbohydrates were translocated from parents to ramets. Shaded parents had RGR's similar to unshaded parents, due in large part to consumption of 50% of the TNC reserves of shaded parents, but about 10% of the growth of the shaded parents was attributed to TNC received from their attached ramets. Estimates of parent and ramet growth separately, based on changes in TNC levels (converted to dry weight using a measured production value), net CO2 uptake of unfolded leaves, and respiration of roots, stems, and folded leaves, were similar to measured growth of parents and ramets combined, suggesting that parents and ramets are physiologically integrated and grow as a unit. Large TNC reserves, which were also shown to support growth during conditions of water limitation in the field, enhance the growth of ramets in an environment where seedling establishment is rare.