The potential impacts of climate change on ex situ conservation options for recalcitrant-seeded species

Abstract

Recalcitrant seeds are characterized by desiccation and freezing sensitivity, and short storage longevity. These physiological attributes obviate their ex situ conservation in conventional seed banks, where seeds are stored dry at sub-zero temperatures (typically, 15% relative humidity and –20°C) for extended periods of time. Propagation of plants for field collections (e.g., botanical gardens, nurseries, and arboretums) is a valuable ex situ conservation option. However, these collections are relatively costly, require high maintenance, preserve limited genetic diversity and/or are directly exposed to biotic (e.g., pests) and abiotic (e.g., climatic) threats. Therefore, recalcitrant-seeded (RS) species are dependent on cryopreservation for their safe and long-term ex situ conservation. Different explant sources such as whole seeds, zygotic embryos, dormant buds, shoot tips, and pollen, can be used for plant propagation of RS species in field collections as well as for their cryopreservation. The success of the propagation or the cryopreservation of these explants often depends on their developmental status, vigor, and/or tolerance to desiccation and chilling/freezing. These attributes are modulated by the environment where the donor plant grows and we hypothesize that climate change, by affecting these biological attributes, would impact the success of explant propagation and cryopreservation. To support this hypothesis, we have reviewed how temperature changes and drought, the two main climate change scenarios, affect the main biological attributes that are directly involved in the success of ex situ conservation of tropical and temperate RS species. In general, increases in temperature and drought will negatively affect plant development in field collections and the quality of the explants used in cryopreservation. Consequently, field collections of RS species may need to be moved to more suitable places (e.g., higher latitudes/altitudes). Additionally, we may find a reduction in the success of cryopreservation of RS species germplasm directly harvested from field collections. However, we cannot always generalize these effects for all species since they often depend on the origin of the species (e.g., tropical and temperate species tend to respond to climate change differently), the genotype, the adaptive genetic potential of each population, and the severity of the environmental change. On the other hand, the increase in temperatures and water stress in donor plants at high-latitude areas and also some tropical environments may favor the production of seeds and seedlings better adapted to drying, and hence, increase the success of plant propagation and zygotic embryo cryopreservation.

Climate Change Impacts on Species Composition and Floristic Regions in Thailand

“…In addition, studies suggest tropical lowland species may contract their distribution or shift in phenotypes (plasticity) as mean or extreme temperatures increase above their heat tolerance, but this scenario could also lead to novel communities of heat-tolerant species [26,33,34]. The impacts of climate change are projected to be greater for Dipterocarpaceae, Meliaceae, and Moraceae families that are dominant in tropics [35,36] as these families are characterized by recalcitrant seeds or short storage longevity [37].…”

“…The population dynamic processes of tree growth, mortality, and regeneration are leading to changes in species composition and ecosystem structure and function. The impact of climate change on tropical tree distributions has been substantially studied [35,[37][38][39][40]. However, studies on the consequences of species shifts may have on species composition and floristic regions are lacking for tropical forests compared with temperate forests [41] and grassland [18].…”

Investigating experimental storage methodologies for the understudied intermediate recalcitrant seed of Northern Wild Rice (Zizania palustrisL.)

“…As plant diversity is eroding on a global scale at alarming rates, concerted efforts to maintain and conserve that diversity have focused on the ex-situ storage of germplasm outside of species' native habitats (Parmesan and Hanley 2015;Wyse et al 2018;Breman et al 2021;Pence et al 2022). Today, over 100,000 species are conserved via ex-situ methods (Breman et al 2021), including a variety of sociologically and economically important species as well as those threatened by habitat alterations, new diseases and pests, and extinction (Liu et al 2018;Wyse et al 2018;Walters and Pence 2021;Pence et al 2022;Fernández et al 2023). This germplasm can be preserved, while also allowing for its use in agriculture, restoration projects, species reintroduction, biological control, breeding, and research (Liu et al 2018;Walters and Pence 2021).…”

“…Species vary in their ability to be stored, particularly as seed, and estimates suggest that close to half of all plant species may not be storable by these conventional methods (Li and Pritchard 2009;Wyse et al 2018;Hay and Sershen 2021;Walters and Pence 2021;Fernández et al 2023). Orthodox seed, which is desiccation tolerant, for example, can be dried and frozen, halting metabolic functions.…”

Advances in cryopreservation of Syzygium maire (swamp maire, maire tawake) zygotic embryos, a critically endangered tree species endemic to New Zealand

“…Despite the ecological (van der Walt et al, 2021b), commercial (Nair, 2017) and pharmaceutical (Chua et al, 2019) values of Syzygium species, their conservation is largely limited to in situ conservation such as nature reserves and living collections. Living trees are vulnerable to climate change (Fernandez et al, 2023) and invasive plant pathogens such as Austropuccinia psidii (Myrtle Rust) (Beresford et al, 2020), making ex situ conservation using techniques such as seed banking essential. Seed banking is an effective ex situ method for the long-term preservation of plant genetic resources and an efficient form of conservation for plant genetic diversity (Nadarajan et al, 2023).…”