Growth, reproductive performance and resource allocation of the herbaceous obligate seeder Gompholobium marginatum R. Br. (Fabaceae)

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Abstract
Perennial species have evolved several strategies to survive fire, with resprouters and seeders forming two major categories. Gompholobium marginatum is a herbaceous seeder legume occurring in the Western Australian jarrah (Eucalyptus marginata) forest which since 1961 has been subjected to burns every sixth year. Such frequent fires potentially endanger the survival of seeder species like G. marginatum, whose establishment and reproductive achievement is, therefore, the subject of this study. Sexual reproduction commenced in the second growing season and reached peak reproductive capacity (136 ovules per plant) and success (38 seeds per plant) in the 3rd year of growth. This ovule production represented more than 30% of the total reproductive potential (455 ovules per plant) recorded during the normally observed 6-year life span. Maturation of several generations of reproductive units occurred consecutively over 5 months with approximately 75% of initiated flowers setting fruit. Almost 30% of all initiated ovules, i.e. 132, matured to seeds during 6 years of undisturbed growth. P and N emerged as elements most limiting to plant growth and reproduction and proved to be the best indicators of reproductive costs. In contrast to many other seeder species, the phenorythmics of G. marginatum is compatible with a high fire frequency. While its intrinsically low growth rate may be viewed as a factor responsible for poor competitiveness with cohabiting understorey species, the high investment in early reproduction at the expense of vegetative growth can be interpreted as an evolved response to the opening of the habitat after fire. Whether the tendency to senescence of plants older than 3 years has its origin mainly in unfavorable environmental conditions (e.g. canopy closure, water or nutrient competition) or in a genetically induced decline in fecundity remains to be determined.