Survival strategies of the root tuberous geophyte Chamaescilla corymbosa in a Mediterranean-climate rock-outcrop environment

Abstract

This field-based study aimed to identify adaptive traits that operate interactively and sequentially towards survival and growth of the perennial geophyte Chamaescilla corymbosa when inhabiting shallow soils on exposed granite outcrops in south-western Australia. During an annual cycle of growth and dormancy, we measured changes in biomass partitioning, mineral nutrient concentrations in root tubers, leaves, roots and seed. Anatomical and histochemical analyses of fleshy-root tubers included identification and quantification of key carbohydrate and free amino acid reserves. During the course of the growing season, developing root tubers accumulated fructans, raffinose and sucrose to maximal concentration at the onset of summer dormancy. Water content of root tubers was similar in summer or winter (79% or 84%, respectively). Accumulation of carbohydrates and development of a lignified and suberised hypodermis are likely to protect aestivating root tubers from desiccation during hot, dry summer. Assimilates and mineral resources acquired in the winter growing season were shown to be preferentially allocated for new tuber production, as opposed to sexual reproduction. Accumulation of key nitrogenous solutes and phosphorus in root tubers before dormancy suggested an adaptive response of the species to soils with inherently low concentrations of available nutrients. Experiments on field-grown populations showed the species to be responsive to delayed commencement of seasonal growth by reducing size and number of root tubers; however, plants still survived until the next growing season. Results are discussed against previous studies of other geophytes on rock outcrops and other similarly testing environments.