Contrasting Growth and Morphological Characteristics of Fire-Sensitive (Obligate Seeder) and Fire-Resistant (Resprouter) Species of Restionaceae (S Hemisphere Restiads) From South-Western Western-Australia

Abstract

Populations of south-western Australian members of the Restionaceae were examined in a wide range of wetland, seasonally inundated and dryland habitats over 4 years and the behaviour of 82 of the species authenticated according to whether they survived (resprouter strategy) or were killed (obligate seeder strategy) by fire. Material of the same seeder and resprouter species collected during summer or early autumn from habitats not burnt for at least 5 years was then used for morphometric measurements, observations on rhizome morphology, determinations of culm: rhizome dry weight (DW) ratios and assays of starch and sugars in rhizomes. Rhizome diameters of all 37 resprouters exceeded 2.3 mm while 28 of the 45 seeder species had narrow rhizomes in the range 0.2-2.1 mm. Culm : rhizome DW ratios of seeders (mean 12.3 ± s.e. 1.2) were much higher than those of resprouters (mean 2.9 ± s.e. 0.4). Mean ± position of perennating buds of seeders was mostly at or close to soil surface (-0.6 ± 0.2 cm), while that of resprouters was more deeply buried ( 2.8 ± s.e. 0.5 cm), Seven categories of rhizome morphology were recognised. Three of these (essentially tufted habit, rhizome growth ascending or erect) were much more typical of seeders (n = 37) than resprouters (n = 5). The other four categories included rhizomes of basically horizontal growth and a loosely tufted or widely spreading habit, and were collectively associated more with resprouters (n = 32) than seeders (n = 8). Starch was present at detectable levels in rhizomes of 23 species of resprouters (mean concentration ± s.e. DW for these positive species was 7.13 ± 1.62%) and only 3 seeders (0.16 ± 0.11%). Levels of total soluble sugars (mean ± s.e. DW) (predominantly sucrose, fructose and glucose) were 3.39 ± 0.59% in resprouters compared with 1.06 ± 0.19% in seeders. Data are discussed in relation to previous studies on seeder and resprouter representatives from other plant families.