Climate change leads to global drought-induced stress and increased plant mortality. Tree species living in rapidly changing climate conditions are exposed to danger and must adapt to new climate conditions to survive. Trees respond to changes in the environment in numerous ways. Physiological modulation at the seed stage, germination strategy and further development are influenced by many different factors. We review forest abiotic threats (such as drought and heat), including biochemical responses of plants to stress, and biotic threats (pathogens and insects) related to global warming. We then discus the varied adaptations of tree species to changing climate conditions such as seed resistance to environmental stress, improved by an increase in temperature, affinity to specific fungal symbionts, a wide range of tolerance to abiotic environmental conditions in the offspring of populations occurring in continental climate, and germination strategies closely linked to the ecological niche of the species. The existing studies do not clearly indicate whether tree adaptations are shaped by epigenetics or phenology and do not define the role of phenotypic plasticity in tree development. We have created a juxtaposition of literature that is useful in identifying the factors that play key roles in these processes. We compare scientific evidence that species distribution and survival are possible due to phenotypic plasticity and thermal memory with studies that testify that trees’ phenology depends on phylogenesis, but this issue is still open. It is possible that studies in the near future will bring us closer to understanding the mechanisms through which trees adapt to stressful conditions, especially in the context of epigenetic memory in long-lived organisms, and allow us to minimize the harmful effects of climatic events by predicting tree species’ responses or by developing solutions such as assisted migration to mitigate the consequences of these phenomena.

Somatic embryogenesis (SE) is an important method for the vegetative propagation of trees. SE is the developmental in vitro process in which embryos are produced from somatic cells. This method can be integrated with other biotechnological techniques, genomic breeding and cryopreservation, which enables commercial-scale sapling production of selected high-yielding genotypes in wood production combined with fast breeding cycles. The SE is potential tool to improve plant stock in comparison with seed orchards. It can be useful for ecologically and economically important species, such as Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), ensuring stable production in the era of climate change and biodiversity crisis. In this review, we summarize the current state of research on problems associated with somatic embryogenesis in P. abies and P. sylvestris.

Key message: Environmental stress resulting from rapid climate changes leads to the initiation of the seed aging process in mitochondria and peroxisomes. Seed storage methods limiting germinability loss are fundamental for forest future. Seed aging is a natural process. It decreases the seed germination rate, i.e. the process is essential for the plant’s life cycle. Aging involves a progressive accumulation of oxidative damage over time. One of the main plant responses to stress is an excessive production of reactive oxygen species (ROS), such as O ₂ ^−• , H₂O₂ and ^•OH. If the concentration of ROS is too high, it causes damage of the structure of lipid membranes, proteins, carbohydrates, and DNA. Climate changes affect tree reproduction and may have long-term consequences in the form of reduced species dispersal and acquisition of new habitats. High temperatures accelerate the aging of seeds and decrease their viability. There is, therefore, an indisputable need to store forest reproductive material to maintain continuity of regeneration in farm forests. The quality of seeds subjected to long-term storage correlates negatively with ROS concentration, as ROS accumulation typically occurs in tissues experiencing oxidative stress. Therefore, to preserve forest genetic resources, it is particularly important to know the causes and sites of initiation of the aging process in seed cells, as well as to prevent the germination rate decrease by developing appropriate storage methods. The main organelles responsible for intracellular ROS production are mitochondria and peroxisomes. This article aims at verifying the causes of seed aging and determining its consequences for future forest regeneration due to climate changes. We review the literature on oxidative stress, as well as the sites where the tree seed aging process originates, such as mitochondria and peroxisomes.

Proline accumulation represents one of mechanisms used by plants to prevent the adverse consequences of water stress. The effects of increased proline levels in response to drought differ among species. Trees are exposed to the long-term effects of climate change. The reproductive success of species in a specific environment depends on the functional trait of tree seeds. We conducted a meta-analysis to evaluate the effects of drought stress on the proline concentrations in seedling leaf tissues of woody plant species and their relationships to drought duration, seed mass, seed category and coniferous/deciduous classification. Drought duration exhibited a nonlinear effect on proline accumulations. The drought effect on proline accumulations is greater for deciduous than for coniferous species and is higher for orthodox seed species than for recalcitrant. The seedlings of large-seeded species showed greater effect sizes than those of small-seeded species. Our results suggest that there is an optimum level at which proline accumulations under the influence of drought are the highest. A link between seed functional traits, as well as the coniferous/deciduous classification, and proline concentrations in tree seedlings during water stress were determined for the first time. Proline may help to identify high-quality seeds of trees used for reforestation.

In the present study, we examined the utility of proline usage as a biochemical indicator of metabolic changes caused by climate change (mean temperature and precipitation) during seed development of two Acer species differing in desiccation tolerance: Norway maple (Acer platanoides L.—desiccation tolerant—orthodox) and sycamore (Acer pseudoplatanus L.—desiccation sensitive—recalcitrant). In plants, proline is an element of the antioxidant system, which has a role in response to water loss and high temperatures. Our study considered whether proline could be treated as an indicator of tree seed viability, crucial for genetic resources conservation. Proline content was measured biweekly in developing seeds (between 11 and 23 weeks after flowering) collected in consecutive years (2017, 2018, and 2019). We showed that proline concentrations in recalcitrant seeds were positively correlated with mean two-week temperature. In contrast, in orthodox seeds no such relationship was found. Proline content proved to be sensitive to thermal-moisture conditions changes, which makes it a promising biochemical marker of seed desiccation tolerance in different climatic conditions.

Instytut Dendrologii PAN w Kórniku - Institute of Dendrology PAS (Kórnik, Poland)