Growth and Survivorship of Ramets and Seedlings of Agave deserti: Influences of Parent-Ramet Connections

Abstract

Parent-ramet connections for Agave deserti, a common perennial of the Sonoran Desert, greatly enhanced ramet growth and survivorship compared with its seedling. One year after ramets had been severed from their parents, 27% of the ramets had died, while all unsevered ramets remained alive; survivorship of severed ramets increased from 38% at 2 g dry weight (DW) to 100% at 60 g DW. Ages of ramets and seedlings were estimated with the component interest law, using the observed decreasing monthly relative growth rate (RGR) with increasing size and an RGR of zero in dry months. Ramets appear to achieve independence from their parent at 14 yr, i.e, at up to 35% of the rosette lifetime. Prior to that, ramets apparently depend on their parent for water, because water potentials of severed ramets averaged 0.26 MPa lower than those of unsevered ramets 9 mo after severing. Movement of water from parent to ramet may explain the increased growth and survivorship of ramets in an environment where water is limiting and successful seedling establishment is rare.