1. Demographic recruitment processes, such as seed germination and seedling emergence, are critical transitional phases to the re-establishment of degraded plant populations, but often fail due to rainfall not supporting plant requirements. Using species from the widespread arid Australian perennial grass genus Triodia, we investigated the interactions of seeds in different dormancy states and their functional germination envelope in response to water stress after simulated pulse rainfall events. 2. Seed dormancy was alleviated in Triodia species to varying degrees by wet/ dry cycling or by removing floret structures from seeds. The seeds were then exposed to different rainfall frequency and quantity events mimicking the 25th, median, 75th and 95th percentile rainfall events found in natural habitats for the study species in the north-west Australian arid zone. 3. Under 95th percentile rainfall conditions recruitment was highest, but still limited to 35% germination and 10% emergence of cleaned seeds (i.e. the least dormant state evaluated). This was related to the functional germination envelope as indicated by more negative base water potential thresholds (Ψb50) for cleaned seeds (≥ -0.33 MPa) compared to intact florets (≥ -0.26 MPa). As a result the maximum cumulative time where soil water potentials were optimal for germination (Ψsoil ≥ Ψb50) were 1.6–2.6 times longer for cleaned seeds in large frequent rainfall events when compared to intact florets. Furthermore, seed dormancy, that usually prolongs seed survival, was linked to a short-term reduction in seed viability, which may further reduce recruitment rates. 4. Synthesis and applications. Our findings indicate that large frequent rainfall events raised soil water potentials above critical thresholds for germination and are important for successful plant establishment. If recruitment bottlenecks are a result of seed dormancy and variable rainfall for arid grass species, then this study shows benefits for alleviating seed dormancy prior to seeding in restoration sites, as this increases the environmental envelope for germination.

Lewandrowski et al. JAPPL2016-00640This data file contains five spreadsheets of the data described in Lewandrowski et al. JAPPL2016-00640.R1. The first worksheet contains the validation experiment for the different seed treatments tested in Triodia epactia and Triodia wiseana under optimal germination conditions. The second worksheet is the data used to quantify b50-thresholds under water stress of the different seed treatments using three parameter nonlinear functions.The third worksheet comprises the field recruitment data under the various rainfall events tested, along with the fourth spreadsheet containing the average soil water potential and temperature for the trial period. The last worksheet contains the modelled cumulative mean time parameters according to the b50 water potential thresholds. All methods and materials are described in the manuscript. For further information, please contact the authors, or wolfgang.lewandrowski@bgpa.wa.gov.au for assistance.