Abstract
Seed banking of rainforest species is hindered by lack of knowledge as to which species are tolerant of desiccation and freezing. We assessed 313 Australian rainforest species for seed banking suitability by comparing the germination percentage of fresh seeds to seeds dried at 15% RH and seeds stored at −20 °C after drying. We then compared desiccation responses to environmental, habit, fruit and seed characteristics to identify the most useful predictors of desiccation sensitivity. Of 162 species with ≥ 50% initial germination, 22% were sensitive to desiccation, 64% were tolerant and 10% were partially tolerant; the responses of 4% were uncertain. Of 107 desiccation tolerant species tested for response to freezing, 24% were freezing sensitive or short-lived in storage at −20 °C. Median values for fresh seed moisture content (SMC), oven dry weight (DW) and the likelihood of desiccation sensitivity (PD-S) were significantly greater for desiccation sensitive than desiccation tolerant seeds. Ninety-four to 97% of seeds with SMC < 29%, DW < 20 mg or PD-S < 0.01 were desiccation tolerant. Ordinal logistic regression of desiccation response against environmental, habit, fruit and seed characteristics indicated that the likelihood of desiccation sensitivity was significantly increased by a tree habit, fleshy fruit, increasing fresh SMC and increasing PD-S. The responses observed in this study were combined with earlier studies to develop a simple decision key to aid prediction of desiccation responses in untested rainforest species.
Highlights
Rainforests are highly diverse plant communities (Corlett and Primack 2008; Sommerville et al 2018) that provide habitat for a wide range of fauna, essential goods such as food, medicines, and clean water, and essential services such as maintenance of soil fertility, regulation of air quality and sequestration of carbon (Nahuelhual et al 2007; Golden et al 2012; Brandt et al 2014; Alamgir et al 2016; Delgado-Aguilar et al 2017)
Similar results were obtained by Hamilton et al (2013) for Australian rainforests (43% of 69 woody species), while Lan et al (2014) found the proportion to be much higher in tropical rainforest in Southern China (68% of 41 wild woody species)
Where the initial germination test was conducted on water agar and subsequent tests were on agar containing 250 ppm G A3, any reduction in germination in the latter was assumed to be due to the storage treatment given that GA3 is a germination promoter and has not been observed to be toxic in this lab at the concentration used
Summary
Rainforests are highly diverse plant communities (Corlett and Primack 2008; Sommerville et al 2018) that provide habitat for a wide range of fauna, essential goods such as food, medicines, and clean water, and essential services such as maintenance of soil fertility, regulation of air quality and sequestration of carbon (Nahuelhual et al 2007; Golden et al 2012; Brandt et al 2014; Alamgir et al 2016; Delgado-Aguilar et al 2017). Seedbanking is the most efficient and cost-effective method for conserving seed-bearing species ex situ (Offord and Meagher 2009) and protocols for conserving seed from relatively dry habitats have been well-honed over the past few decades. Species in these habitats tend to produce seeds with characteristics essential to surviving storage in a seedbank (Tweddle et al 2003; Wyse and Dickie 2017), i.e. tolerance of drying to low moisture content and tolerance of storage at cold temperatures (Roberts 1973). Herbaceous species often have desiccation tolerant seeds and recent modelling by Wyse and Dickie (2017) indicated that the proportion of species with desiccation sensitive seeds in evergreen rainforest may be as low as 18.5% when herbaceous species are included
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