The objective of this study was to illustrate the photosynthetic characteristics of current twigs of Salix matsudana Koidz., and clarify the effect of stem photosynthesis on the new organ development in cutting seedlings. Excised twigs were taken as the experimental samples. The response of the stem photosynthesis rate to increasing light intensity and the effective photochemical efficiency of the cross section of the twig were determined. Then, twigs were used as cuttings and exposed to 0, 20, and 100 μmol m⁻² s⁻¹ light intensities, respectively, to achieve distinctive stem photosynthetic rates. After 14 days of treatment, stem water and non-structural carbohydrate (NSC) content, as well as the biomass and carbon isotopic composition, of new organs in the cutting seedlings under different light treatments were examined. The results showed that the gross photosynthetic rate significantly increased within 400 μmol m⁻² s⁻¹ of light intensity, and the maximum rate was approximately 1.27 μmol m⁻² s⁻¹. The effective photochemical efficiency of the PSⅡ of the cortex was significantly higher than the inner tissues in the cross section of the twig. When twig cuttings were exposed to different light intensities, stem water and starch content, as well as bud and root biomass, were significantly higher in the cutting seedling subjected to 100 μmol m⁻² s⁻¹ than the case treated in darkness; however, the bud δ¹³C trend was the opposite. Stem photosynthesis played a positive role in the maintenance of stem water and starch supply for the cutting seedlings, and ¹³C depleted assimilates produced by stem photosynthesis contributed to bud biomass, revealing that stem photosynthesis promotes organ development in cutting seedlings of Salix matsudana.

As a short-rotation woody plant, Salix viminalis has the potential for phytoremediation of cadmium (Cd), but it has poor tolerance to high Cd concentrations. Melatonin (MEL), a candidate bio-promoter, was considered to play an active role in plant responses to Cd. However, the molecular mechanism by which MEL regulates metabolic processes in plants to defend against Cd stress remain unclear. Transcriptomics and global untargeted metabolomic sequencing were used to investigate the rapid response of S. viminalis to high Cd concentrations during initial growth stage after foliar application of MEL. Four treatments were set up in a pot experiment involving foliar application of MEL on the first day, followed by irrigation with a Cd solution the next day. Significant variations in the relevant defence genes and metabolites in leaves exposed to Cd were observed between willows treated with and without MEL. Foliar application of MEL upregulated sulphur metabolism-related genes such as methionine and S-adenosylmethionine synthases in leaves exposed to Cd; glutamine content, which is the key point of nitrogen assimilation, also increased. Additionally, glycolysis and sucrose metabolic genes, including hexokinase, sucrose synthase, invertase, and the inositol phosphate metabolic gene myo-inositol-1-phosphate synthase were also upregulated in leaves. Moreover, MEL also upregulated genes related to the synthesis of flavonoids, anthocyanins, and proanthocyanins in the leaves. These results demonstrated that MEL improved amino acid and saccharide metabolism in the leaves of S. viminalis in response to Cd. It also improved the antioxidant capacity and Cd tolerance in S. viminalis leaves by enhancing synthetic capacity of polyphenol compounds. MEL may be involved in processes of photorespiration, ethylene metabolism, GABA shunt, nitric oxide metabolism, osmotic adjustment, and the synthesis of glutathione and ascorbate in S. viminalis under Cd stress. This series of metabolic changes in S. viminalis occurred within 24 h of the foliar application of MEL, which provided a sufficient substrate for subsequent defence reactions to cope with Cd stress. Our findings will help elucidate the molecular mechanism by which MEL regulates metabolic processes in plants in response to Cd challenges and guide the application of MEL to improve Cd phytoremediation efficiency.

Polycyclic aromatic hydrocarbons (PAHs) are widely prevalent harmful organic pollutants. Enzymatic activities (such as those of dehydrogenases, catalase, protease and urease), as well as the microbial community structure and assembly (through 16S and ITS amplicon sequencing), were evaluated 90 days after PAH contamination and compared to those in normal soils. Microbial activity, as indicated by soil urease, catalase, and protease activities, was inhibited under PAH stress. Furthermore, PAH stress exerted significant impacts on the soil microbial community structure. Notably, PAH stress reduced soil bacterial and fungal biomass and inhibited the abundance of microbial taxa involved in soil carbon and nitrogen cycling (e.g., Marmoricola, Pedobacter, and Streptomyces), along with the majority of predicted responsive metabolic functions, particularly those related to amino acid and carbohydrate metabolism. PAH stress enriched PAH-degrading microorganisms, including Pseudomonas, Mycobacterium, Bacillus, Cycloclasticus, and Flavobacterium. The niche breadth of bacterial and fungal communities decreased significantly under PAH stress (51.5 and 14.1, respectively) compared to that in normal soil (63.7 and 22.3), which was further supported by Beta Nearest Taxon Index and co-occurrence network analysis. PAH stress increased the contribution of heterogeneous selection to soil microbial assembly (100%) compared to that in normal soil (80%). Thus, the majority of microbial community responses to PAH stress were adversely affected. These results suggest that PAH contamination may profoundly affect the soil quality by restricting the survival space of bacteria and fungi.

Bamboos, as imperative vegetations in Chinese traditional gardens, also significantly influenced the recently originated Neo-Chinese-style landscape in China, and their habitat ranges have been profoundly impacted by global climate warming. Current studies on the distribution dynamics of bamboo reveal existent gaps in assessing the suitable distribution area of Neo-Chinese-style landscapes. In this study, we calculated the habitat ranges of two widely distributed bamboo genera (Phyllostachys and Bambusa) based on the optimal MaxEnt model, predicted their future (2050s, 2070s and 2090s) distributions under different climate scenarios (SSP1-2.6 and SSP5-8.5), and assessed the suitable distribution area of the Neo-Chinese-style landscape according to the distribution union of two bamboo genera. The results showed that the optimal MaxEnt model exhibited high evaluation indices (AUC > 0.90) for the two bamboo genera. The habitat ranges of bamboo genera were significantly influenced by the minimum temperature of the coldest month and would expand northwardly in the future. The suitable distribution area of Neo-Chinese-style landscapes covered about 71.3% cities of China, which would expand 5.9%–8.7% of cities and 10%–18.7% of cities under the SSP1-2.6 climate scenario and the SSP5-8.5 climate scenario, respectively. The suitable distributions are mainly located in the southeast part of China. This study advanced our understanding of the restriction of bamboo to the distribution of the Neo-Chinese-style landscape and provided valuable insights and a scientific basis for landscape construction in different areas of China.