Search

Here, we tested the alternation of root summer dormancy and winter growth as a critical survival strategy for a long-lived monocotyledon (Restionaceae) adapted to harsh seasonal extremes of Mediterranean southwest Western Australia. Measurements of growth and the results of comparative studies of the physiology, water content, metabolites, osmotic adjustments, and proteomics of the dormant and growing perennial roots of Lyginia barbata (Restionaceae) were assessed in field-grown plants. Formation of dormant roots occurred before the onset of summer extremes. They resumed growth (average 2.3 mm d(-1)) the following winter to eventually reach depths of 2-4 m. Compared with winter-growing roots, summer dormant roots had decreased respiration and protein concentration and c. 70% water content, sustained by sand-sheaths, osmotic adjustment and presumably hydraulic redistribution. Concentrations of compatible solutes (e.g. sucrose and proline) were significantly greater during dormancy, presumably mitigating the effects of heat and drought. Fifteen root proteins showed differential abundance and were correlated with either winter growth or summer dormancy. None matched currently available libraries. The specific features of the root dormancy strategy of L. barbata revealed in this study are likely to be important to understanding similar behaviour in roots of many long-lived monocotyledons, including overwintering and oversummering crop species.

* The incidence of species that develop specialised 'dauciform' lateral roots, which are hypothesised to be important for phosphorus (P) acquisition, is uncertain. We investigated their occurrence in Australian reed, rush and sedge species, grown at low P concentration in nutrient solution, and studied the response of Schoenus unispiculatus (Cyperaceae) to a range of P concentrations. * We assessed the fraction of root biomass invested in dauciform roots, their respiration and net P-uptake rate, and the P status of roots and leaves. * Dauciform-root development occurred only in particular genera of Cyperaceae when grown at low P supply. Increased P supply was associated with increased growth of S. unispiculatus and increased leaf [P]. Dauciform-root growth was reduced by increased P supply, and reduced P uptake co-occurred with the complete suppression of dauciform roots. * The P-induced suppression of dauciform roots in Cyperaceae is similar to that observed for proteoid roots in members of Proteaceae and Lupinus albus. The response of dauciform roots to altered P supply and their absence from root systems of some sedge species are discussed in terms of managed and natural systems.