Exploring seed longevity of UK native trees: implications for ex situ conservation

Abstract

UK trees require increased conservation efforts due to sparse and fragmented populations. Ex situ conservation, including seed banking, can be used to better manage these issues. We conducted accelerated ageing tests on seeds of 22 UK native woody species, in order to assess their likely longevity and optimize their conservation in a seed bank. Germination at four ageing time points was determined to construct survival curves, and it was concluded that multiple samples within a species showed comparable responses for most species tested, except for Fraxinus excelsior. Of all species studied, one could be classified as very short-lived, four as short-lived and 17 as medium, with none exceeding the medium category. The most important finding of this manuscript is that although some taxonomic trends were observed, the results indicate the need for caution when making broad conclusions on potential seed storage life at a species, genus or family level. Longevity predictions were compared to actual performance of older collections held in long-term storage at the Millennium Seed Bank, Kew. Although most collections remain high in viability in storage after more than 20 years, for short-lived species at least, there is some indication that accelerated ageing predicts longevity in seed bank conditions. For species with reduced potential longevity, such as Fagus sylvatica and Ulmus glabra, additional storage options are recommended for long-term gene banking.

Seed Longevity—The Evolution of Knowledge and a Conceptual Framework

“…For example, seeds that exhibit orthodox behaviour can be stored using refrigerators (medium-term) or freezers (long-term) [ 14 ] ( Figure 1 ). However, we might wish to cryopreserve orthodox seeds to prolong the shelf life of accessions that are difficult to regenerate (e.g., tree species) or that are relatively short lived [ 76 , 77 ] ( Figure 1 , purple arrow in “short-lived” seeds). In contrast to the range of options available for orthodox seeds, most seeds exhibiting intermediate or recalcitrant traits require cryogenic storage [ 36 , 78 , 79 ] ( Figure 1 , purple arrow for “recalcitrant” and intermediate” seeds).…”

“…are extremely short-lived, with a greater than 50% loss in viability over four decades reported by conventional seed banks ([ 76 ] and references therein). Similarly, seeds of some tree species, such as Fagus sylvatica and Ulmus glabra , and some species within Poaceae, Apiaceae, Asteraceae and Brassicaceae families have also been reported to show greater than 50% viability loss over four decades [ 37 , 77 , 121 ]. Cryogenic storage using liquid nitrogen as the cryogen (storage temperature between −170 °C and −196 °C) is recommended [ 36 ] and routinely implemented at some seed banks [ 57 , 101 , 125 ] ( Figure 1 , purple arrows for “short-lived” seeds).…”

Can seed banking assist in conserving the highly endemic New Zealand indigenous flora?

“…Information on seed longevity in an ex situ seed bank is critical for effective collection management, as it will set the seed viability re-test intervals for the collections, determine re-collection strategies (Liu et al 2020), and inform any adaptation of current conventional protocols that may be required to suit short-lived seeds. Accelerated ageing tests have been found to correlate with real time data of seed survival in storage, and can augment the real time data to aid understanding of potential seed lifespan in storage (Davies et al 2020). Data suggest that there is considerable variability among, and within, orthodox species in their longevity in an ex situ seed bank, with indications that species from hot dry environments may store longer than those from cool, wet habitats (Probert et al 2009;Davies et al 2020;Liu et al 2020).…”

“…Accelerated ageing tests have been found to correlate with real time data of seed survival in storage, and can augment the real time data to aid understanding of potential seed lifespan in storage (Davies et al 2020). Data suggest that there is considerable variability among, and within, orthodox species in their longevity in an ex situ seed bank, with indications that species from hot dry environments may store longer than those from cool, wet habitats (Probert et al 2009;Davies et al 2020;Liu et al 2020). For example, among the Hawaiian indigenous flora, 63% of 295 species examined by Chau et al (2019) retained at least 70% viability after 10 years in storage, while 23% declined to less than 70% of the initial viability within 5 years of storage.…”

Plant Diversity Conservation Challenges and Prospects—The Perspective of Botanic Gardens and the Millennium Seed Bank

“…For a significant proportion of the MSB's seed accessions made since 2000, there are not yet sufficient viability test data points to permit fitting of survival curves, from which to estimate likely regeneration/recollection intervals. The relatively sparse, usable real-time survival data have been supplemented by an on-going programme of comparative accelerated ageing experiments across diverse species (see [65,66]). While the possibility that the causes of death of individual seeds are different under accelerated ageing conditions from those in long-term storage in a seed bank, the data provide a relative ranking of species' likely storage longevity.…”