Life histories and reproductive strategies of plants in the desert and halophytic genus Frankenia in Australia

Summary of final report on the Australian Flora Foundation funded project:

Dr Lyndlee C. Easton
School of Biological Sciences, Flinders University
1 February 2009   

Grant Details    Final Report

The aim of this project was to investigate basic germination requirements for Australian species of Frankenia in relation to seed age, light requirements, temperature preferences, salinity tolerance, and soil properties. Germination strategies play a major role in the persistence of all plant taxa, particularly in arid zone halophyte species. The evolution of germination strategies is a consequence of plant taxa responses to environmental cues. Arid zone halophytes have evolved germination strategies under selective pressures – notably in relation to seed age, light requirements, temperature preferences, salinity tolerance, and soil properties – whereby they respond to a sequence of environmental cues that indicate periods of relatively high probability of subsequent seedling survival. Elucidating these strategies is of fundamental importance to the understanding of halophyte life histories. Frankenia in particular has several rare and little known species, and the vulnerability of these species cannot be assessed without basic life history data. This data is also a prerequisite for the consideration of Frankenia in salinity remediation, mine-site remediation, and coastal revegetation projects.

The underpinning aim of this study was to investigate reproductive strategies, and in particular the large-seeded versus small-seeded strategies in relation to environmental variables that are commonly experienced by arid zone halophyte plant taxa. Previous research has shown that larger-seededness arose several times in Australian Frankenia as a result of evolution towards fewer ovule numbers per fruit, although both the larger- and smaller-seeded species still co-occur in biogeographical proximity. By restricting the analysis of seed packaging strategy variations to similar habitats and within a genus, it was possible to uncover ecological correlates that would otherwise have been masked by the strong effects of habitat differences and phylogenetic constraints on seed mass. I could thus test the hypothesis that large-seededness is favoured over small-seededness in drought and/or saline stressed environments.

The key finding was that overall, larger-seedness is advantageous for rapid germination after transitory water availability, and for providing resources to seedlings if resources become limiting before their successful establishment. Smaller-seeded species delay germination until both soil-water availability and cooler temperatures persist over a long time period, improving the chances of successful establishment for the more slowly growing seedlings that are reliant on their surroundings for resources.