Riparian tree species are thought to be sensitive to the more frequent and intensive drought and heat events that are projected to occur in the future. However, compared to waterlogging, information about the responses of these tree species to water limitation and heat is still scare. Black alder (Alnus glutinosa L.) is a riparian tree species with significant ecological and economic importance in Europe. In the present study, we investigated the physiological responses of black alder (Alnus glutinosa L.) to different water availabilities growing at neighboring sites. Compared to trees with unlimited water source, trees with a limited water source had 20% lower leaf hydration, 39% less H₂O₂ contents, and 34% lower dehydroascorbate reductase activities. Concurrent with dramatically accumulated glutathione and phenolic compounds, leaf glutathione contents were two times higher in trees with limited water than in trees with sufficient water. Limited water availability also resulted in increased abundances of sugars, sugar acids, and polyols. Serine, alanine, as well as soluble protein related to nitrogen metabolism were also accumulated under limited water conditions. In contrast to sulfate, leaf phosphate contents were significantly increased under limited water. No significant effects of water conditions on malondialdehyde and ascorbate contents and fatty acid abundances were observed. The present study improves our understanding of the physiological responses of black alder to different water conditions. Our findings highlight this riparian species is at least to some extent resistant to future drought with a well-regulated system including antioxidative and metabolic processes and its potential as an admixture candidate for afforestation in either water-logged or dry areas, particularly in nitrogen limited habitats.

In recent years, afforestation has been conducted in China’s hot and dry valleys. However, there is still a paucity of knowledge regarding the performance of tree species in these semi-arid regions, particularly with regard to interspecies differences. The present study compares the growth and metabolome characteristics of two widely used cypress species, namely Cupressus chengiana and Platycladus orientalis, grown at two sites with distinct climate conditions in the hot and dry Minjiang Valley in southwestern China. The findings indicate that C. chengiana trees exhibit superior growth rates compared to P. orientalis trees at both study sites. In comparison to P. orientalis trees, C. chengiana trees demonstrated a greater tendency to close their stomata in order to prevent water loss at the hotter and drier site, Llianghekou (LHK). Additionally, C. chengiana trees exhibited significantly lower hydrogen peroxide levels than P. orientalis trees, either due to lower production and/or higher scavenging of reactive oxygen species. C. chengiana trees accumulated soluble sugars as well as sugar derivatives, particularly those involved in sucrose and galactose metabolisms under stressful conditions. The species-specific differences were also reflected in metabolites involved in the tricarboxylic acid cycle, nitrogen, and secondary metabolisms. The metabolome profiles of the two species appeared to be influenced by the prevailing climatic conditions. It appeared that the trees at the drier and hotter site, LHK, were capable of efficient nitrogen uptake from the soil despite the low soil nitrogen concentration. This study is the first to compare the growth performance and metabolic profiles of two widely used tree species with high resistance to adverse conditions. In addition to the species-specific differences and adaptations to different sites, the present study also provides insights into potential management strategies to alleviate abiotic stress, particularly with regard to nitrogen nutrients, in the context of climate change.

Drylands cover more than 40% of global land surface and will continue to expand by 10% at the end of this century. Understanding the resistance mechanisms of native species is of particular importance for vegetation restoration and management in drylands. In the present study, metabolome of a dominant shrub Campylotropis polyantha in a dry-hot valley were investigated. Compared to plants grown at the wetter site, C. polyantha tended to slow down carbon (C) assimilation to prevent water loss concurrent with low foliar reactive oxygen species and sugar concentrations at the drier and hotter site. Nitrogen (N) assimilation and turn over were stimulated under stressful conditions and higher leaf N content was kept at the expense of root N pools. At the drier site, roots contained more water but less N compounds derived from the citric acid cycle. The site had little effect on metabolites partitioning between leaves and roots. Generally, roots contained more C but less N. Aromatic compounds were differently impacted by site conditions. The present study, for the first time, uncovers the apparent metabolic adaptations of C. polyantha to hostile dryland conditions. However, due to the limited number of samples, we are cautious about drawing general conclusions regarding the resistance mechanisms. Further studies with a broader spatial range and larger time scale are therefore recommended to provide more robust information for vegetation restoration and management in dryland areas under a changing climate.