Predicting the seed germination response of four rare Grevillea species (Proteaceae) to current and future temperatures

Nathan J. Emery; Ruby Paroissien; Stefanie Carusi; Graeme Errington; Samuel Padgett; Katherine Thomson; Laura Watts

doi:10.1071/BT25024

RESEARCH ARTICLE (Open Access)

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Predicting the seed germination response of four rare Grevillea species (Proteaceae) to current and future temperatures

Nathan J. Emery

^A ^* , Ruby Paroissien

^A , Stefanie Carusi ^A , Graeme Errington ^A , Samuel Padgett

^A , Katherine Thomson

^A and Laura Watts ^A

+ Author Affiliations

- Author Affiliations

^A The Australian PlantBank, Botanic Gardens of Sydney, Mount Annan, NSW, Australia.

^* Correspondence to: nathan.emery@botanicgardens.nsw.gov.au

Handling Editor: Susanna Venn

Australian Journal of Botany 73, BT25024 https://doi.org/10.1071/BT25024

Submitted: 2 April 2025 Accepted: 26 August 2025 Published: 9 September 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Grevillea is one of Australia’s largest plant genera, with 15% of species being federally listed as threatened. Although seed germination studies have largely focused on common species, knowledge of germination in threatened species remains limited. This gap is critical to address effective conservation actions, including translocations.

Aims

This study used a bi-directional thermogradient plate (TGP) to examine the germination responses of four threatened Grevillea species from New South Wales to varying temperatures.

Methods

Generalised additive models were used to predict monthly final germination proportions and time to 50% germination (t₅₀) across 36 TGP temperature regimes, representing current and two future climate scenarios (SSP2-4.5 and SSP5-8.5).

Results

Three species exhibited high germination across most temperatures, whereas G. iaspicula had a narrow range, preferring cooler conditions (≤15–20°C). For G. masonii and G. rivularis, t₅₀ was under 5 days at all but the most extreme temperatures. G. wilkinsonii and G. iaspicula showed longer germination periods, with t₅₀ exceeding 15 days for most temperatures. All species except G. iaspicula were predicted to maintain consistent germination across current and future climates, whereas G. iaspicula and G. wilkinsonii showed stable t₅₀, and G. masonii and G. rivularis predicted longer t₅₀ in winter.

Conclusions

Modelling seed germination under current and future temperatures highlights potential climate change risks and helps predict impacts on regeneration.

Implications

Germination in G. masonii, G. rivularis, and G. wilkinsonii may be resilient to temperature rises, whereas a cooler temperature preference for G. iaspicula may indicate a sensitivity to future temperature changes.

Keywords: Australia, climate change, ex situ conservation, germination niche, germplasm, seed dormancy, thermogradient plate, threatened species.

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