Phenology of Growth and Resource Deployment in Alexgeorgea nitens (Nees) Johnson and Briggs (Restionaceae), a Clonal Species From South-Western Western Australia

Abstract

Seasonal patterns are described for growth and partitioning of dry matter and selected nutrients between different age classes and types of plant organs of ramets of non-reproductive, presumed female clones of Alexgeorgea nitens in native sandplain habitat at Eneabba, south-western Western Australia. New rhizome extension and associated production of new culms and nodal roots are initiated following onset of rain in autumn. Rate of growth of these parts remains slow through winter, peaks in spring and early summer and then becomes much reduced in the hot, dry summer. The bulk (87%) of the season's dry matter increment of new ramet parts is estimated to be derived from current photosynthesis, the remaining 13% by mobilisation of dry matter from older parts of the ramet, especially from 1- and 2-yearold culms. Growth of new organs is severely reduced by removal or shading of culms at the beginning of the season. Older culms and rhizomes carry substantial starch reserves, but mobilisation of this reserve accounts for 2% at most of the dry matter gain of new organs of intact ramets, 19% of that of shaded and 65% of detopped ramets. A substantial fraction of the starch pool of a rhizome segment normally remains until its senescence, possibly as a long-term energy reserve, utilisable after destruction of above-ground parts by fire or grazing. Concentrations of N, P, K, Ca and Mg in organ dry matter of A. nitens are generally very low in comparison with species other than those Cyperaceae or Restionaceae from similar habitats. There is no evidence of preferential storage in below-ground parts, and efficiencies of emptying of nutrient reserves from senescing ramet parts are not high. Mobilisation from older source organs of ramets of intact, unstressed clones is estimated to provide 14% of the new organ's seasonal gain of P, 16% of Mg, 21% of Ca, 22% of N and 58% of K. Annual factorial increases of a ramet in the studied nutrient elements range from 1.3 (for K) to 2.4 (for P), indicating flexibility in exploiting sources of different nutrients as their respective availabilities change from season to season.