Dormancy, germination and desiccation sensitivity in the seeds of <i>Podocarpus drouynianus</i> , a species growing in a seasonally hot and dry Mediterranean environment

Background: Podocarpus drouynianus is an ecologically unique, taxonomically distinct range-restricted gymnosperm that occurs exclusively within Mediterranean woodlands in the south-west of Western Australia. Limited information is known about this species regarding seed dormancy, germination, and seed desiccation sensitivity. Aims: This study aimed to determine whether P. drouynianus seeds possess dormancy, quantify the responses of seeds to a range of incubation temperatures and examine seed desiccation sensitivity (i.e. recalcitrance) after exposure to different conditions to understand recruitment dynamics in a seasonally dry environment and ex situ seed storage. Methods: Fresh diaspores (seeds enclosed within an indehiscent epimatium) were collected upon maturity for experimentation. Diaspores and extracted seeds were assessed for viability, moisture content and embryo size with a subset of diaspores placed at various incubation temperatures to investigate germination response. Additional diaspores were placed under a range of storage conditions and assessed regularly for viability, moisture content and germination. Results: Upon hydration, fresh diaspore germination commenced rapidly (~5 days) at several temperatures with maximum germination (0.88 germination proportion) achieved at 15°C or 20°C. Seeds were found to have morphological dormancy as embryos grew prior to radicle emergence. Fresh diaspores and seeds had a high moisture content (&gt; 56% - fresh weight basis) and viability (0.96 viability proportion) which declined to 45% MC and 0.75 viability proportion following storage for 42 days at 5°C and 10% eRH. Conclusions: Podocarpus drouynianus diaspores germinate readily over a broad range of temperatures but were found to lose viability due to desiccation sensitivity when placed in either a cool (5°C) dry environment (~10% eRH) for 42 days or in warm (25°C) ambient (~40% eRH) conditions for 60 to 90 days. These findings are crucial for informing potential management strategies for P. drouynianus, particularly as the climate warms and dries across the south-west Australian biodiversity hotspot.