Salix spp. Bark Hot Water Extracts Show Antiviral, Antibacterial, and Antioxidant Activities—The Bioactive Properties of 16 Clones

Earlier studies have shown that the bark of Salix L. species (Salicaceae family) is rich in extractives, such as diverse bioactive phenolic compounds. However, we lack knowledge on the bioactive properties of the bark of willow species and clones adapted to the harsh climate conditions of the cool temperate zone. Therefore, the present study aimed to obtain information on the functional profiles of northern willow clones for the use of value-added bioactive solutions. Of the 16 willow clones studied here, 12 were examples of widely distributed native Finnish willow species, including dark-leaved willow (S. myrsinifolia Salisb.) and tea-leaved willow (S. phylicifolia L.) (3 + 4 clones, respectively) and their natural and artificial hybrids (3 + 2 clones, respectively). The four remaining clones were commercial willow varieties from the Swedish willow breeding program. Hot water extraction of bark under mild conditions was carried out. Bioactivity assays were used to screen antiviral, antibacterial, antifungal, yeasticidal, and antioxidant activities, as well as the total phenolic content of the extracts. Additionally, we introduce a fast and less labor-intensive steam-debarking method for Salix spp. feedstocks. Clonal variation was observed in the antioxidant properties of the bark extracts of the 16 Salix spp. clones. High antiviral activity against a non-enveloped enterovirus, coxsackievirus A9, was found, with no marked differences in efficacy between the native clones. All the clones also showed antibacterial activity against Staphylococcus aureus and Escherichia coli, whereas no antifungal (Aspergillus brasiliensis) or yeasticidal (Candida albicans) efficacy was detected. When grouping the clone extract results into Salix myrsinifolia, Salix phylicifolia, native hybrid, artificial hybrid, and commercial clones, there was a significant difference in the activities between S. phylicifolia clone extracts and commercial clone extracts in the favor of S. phylicifolia in the antibacterial and antioxidant tests. In some antioxidant tests, S. phylicifolia clone extracts were also significantly more active than artificial clone extracts. Additionally, S. myrsinifolia clone extracts showed significantly higher activities in some antioxidant tests than commercial clone extracts and artificial clone extracts. Nevertheless, the bark extracts of native Finnish willow clones showed high bioactivity. The obtained knowledge paves the way towards developing high value-added biochemicals and other functional solutions based on willow biorefinery approaches.

Phenological response to temperature variability and orography in Central Italy

Even if the sensitivity of vegetation phenology to climate change has been accepted on global and continental scales, the correlation between global warming and phenotypic variability shows a modulated answer depending on altitude, latitude, and the local seasonal thermal trend. To connect global patterns of change with local effects, we investigated the impact of the observed signal of warming found in Central Italy on two different willow species, Salix acutifolia and Salix smithiana, growing in three phenological gardens of the International Phenological Gardens’ network (IPG) located in different orographic positions. The time series of temperatures and phenological data for the period 2005–2018 were analysed first to find trends over time in the three gardens and then to correlate the recent local warming and the change in the two species phenology. The results confirmed the correlation between phenological trends and local trend of temperatures. In particular: budburst showed a trend of advancement of 1.4 days/year on average in all three gardens; flowering showed a divergent pattern between the gardens of either advancement of 1.0 days/year on average or delay of 1.1 days/year on average; while senescence showed a delay reaching even 3.3 days/year, although significant in only two gardens for both species. These trends were found to be correlated mainly with the temperatures of the months preceding the occurrence of the phase, with a shift in terms of days of the year (DOY) of the two species. Our conclusion is that the observed warming in Central Italy played a key role in controlling the phenophases occurrences of the two willow species, and that the orographic forcing leads to the different shift in DOY of phenophases (from 5 to 20 days) due to the local thermal forcing of the three phenological gardens.

Willows in the farming landscape: a forgotten eco-cultural icon

Recent studies have revealed a largely forgotten rural landscape in which Salix (willow) species were a characteristic, iconic, and utilitarian feature. In former wetlands, now largely removed by massive drainage schemes since the 1600s various willow species were distinctive features of the landscape and of major value to agricultural communities that inhabited those places. From lowlands to uplands across the British countryside willows dominated much wetter and more extensive landscapes. Remnant upland willow woods (now present as ‘shadow woods’) exist as isolated remnants in small wet habitats in an often desiccated landscape fragmented and drained. In the lowlands, especially former fenland areas, willows were present in extensive wet (carr) woodlands and in cultivated beds of withies or osier holts, and as coppices and pollards on boundaries and in field edges across the countryside. The economic driver of withy beds survived in the main English fenlands until the mid-twentieth century. Today these once extensive and important landscapes are mostly forgotten and derelict; and furthermore, the eco-cultural resource of the willows is currently under threat with unrecorded veteran trees being actively removed by farmers. This paper introduces the significance of the willow landscapes, the history of the eco-cultural resource, and the implications of neglect for future conservation.

Plant growth and nutrient composition in shrub and arbor willows grown in Cu contaminated soil as affected by flooding

Flooding can adversely worsen the metal contaminated soil and plant growth thus, it is crucial to explore the ecophysiological responses of plants upon co-exposure to heavy metals and flooding. Here, the plant growth, photosynthesis, and nutrient elements composition in arbor willow (Salix jiangsuensis ‘J172’) and shrub willow (Salix integra ‘Yizhibi’) were studied using a pot experiment with Cu contaminated soil (239.51 mg∙kg-1) under flooded versus non flooded condition. Salix integra showed larger BCFs than Salix jiangsuensis in both treatments, soil flooding significantly decreased the Cu contents and BCF while obviously increased TF values in both willow species (p < 0.05). Soil flooding markedly enhanced the leaf C:P and N:P ratios, while significantly decreased root C:P and N:P ratios, as compared to non flooded condition. The shrub willow exhibited better tolerance to soil flooding with little alteration in biomass and photosynthetic rate, and showed greater potential of Cu accumulation capacity, even though its total biomass was significantly lower than arbor willow. Our study also helps further understanding the nutrient balance and stoichiometry of willows in Cu contaminated soil and their response to soil flooding, helping the management of Cu-contaminated flooded soils.

The interactions between habitat, sex, biomass and leaf traits of different willow (Salix) genotypes

Knowledge of the impacts of sex on plant mortality and biomass production has scientific and practical importance. In the case of willows, we know relatively little about such effects. The main objective of this study was to evaluate whether the sex of individuals of different willow species determines their biomass and mortality. An additional goal was to determine whether the secondary sex characteristics, such as leaf traits, depend on sex. The experiment was conducted from 2011 to 2014 with 8100 plants comprising 150 willow genotypes, including 8 species, 16 interspecies hybrids, cultivars, and specimens differentiated by sex. Statistical analysis of the leaf traits revealed their relationship to sex. On average, male specimens have longer and wider leaves. They also have longer petioles. Males of the studied Salix genotypes were characterized by higher biomass and showed a greater survival rate than females but only under better site conditions; when the site conditions were poorer, males had higher mortality than females.

Could the Content of Soluble Carbohydrates in the Young Shoots of Selected Willow Cultivars Be a Determinant of the Plants’ Attractiveness to Cervids (Cervidae, Mammalia)?

Ten willow cultivars grown in experimental plots were evaluated for performance, attractiveness to foragers, and the content and composition of soluble carbohydrates. The survival of willow cuttings in a thicket and in browse plots differed subject to cultivar, soil quality, and soil moisture content. The number of stump sprouts varied considerably, from 1.1 shoots in the weakest soils in Słonin, Poland, to 3.43 in the plot in Czempin, Poland. Browse plots were established in 2017. They were cut, and fencing was removed in early spring of 2019. Young shoots (10 cm shoot tip with buds, preferably eaten by animals) were sampled for analyses of soluble carbohydrates as potential attractors for foraging cervids. All willow cultivars contained the same soluble carbohydrates: glucose, fructose, galactose, sucrose, myo-inositol, galactinol, and raffinose. Total carbohydrate content ranged from 21.31 (S. amygdalina 1045) to 69.37 mg/g−1 DM (dry matter) (S. purpurea). Glucose was the predominant soluble sugar in the shoots of all willow cultivars, excluding S. viminalis. The fructose content of the shoots was approximately twice lower than their glucose content in all willow cultivars. Smaller differences were observed in the content of myo-inositol, which ranged from 4.61 (S. amygdalina 1045) to 8.26 mg/g−1 DM (S. fragilis cv. Kamon/Resko). The phloem of all willow species contained small quantities of galactinol and trace amounts of raffinose. Weak negative correlations were noted between total carbohydrate content, the content of glucose, fructose, and galactose vs. the attractiveness of willow shoots to foraging cervids. The remaining carbohydrates that occurred in smaller quantities in willow shoots were not correlated with their attractiveness to cervids.

Genome sequencing and phylogenetic analysis of allotetraploid Salix matsudana Koidz

Polyploidy is a common phenomenon among willow species. In this study, genome sequencing was conducted for Salix matsudana Koidz (also named Chinese willow), an important greening and arbor tree species, and the genome of this species was compared with those of four other tree species in Salicaceae. The total genome sequence of S. matsudana was 655.72 Mb in size, with repeated sequences accounting for 45.97% of the total length. In total, 531.43 Mb of the genome sequence could be mapped onto 38 chromosomes using the published genetic map as a reference. The genome of S. matsudana could be divided into two groups, the A and B genomes, through homology analysis with the genome of Populus trichocarpa, and the A and B genomes contained 23,985 and 25,107 genes, respectively. 4DTv combined transposon analysis predicted that allotetraploidy in S. matsudana appeared ~4 million years ago. The results from this study will help reveal the evolutionary history of S. matsudana and lay a genetic basis for its breeding.

Willow phenological modelling at different altitudes in central Italy

In order to estimate the impact of climate change on the phenological parameters and to compare them with the historical record, a decision support system (DSS) has been applied employing a Phenological Modelling Platform. Biological observations of two willow species (Salix acutifolia and smithiana Willd) in 3 gardens at different altitudes located in Central Italy were utilized to identify suitable phenological models related to four main vegetative phase timings (BBCH11, BBCH91, BBCH 94, BBCH95), and male full flowering (BBCH 65) clearly identifiable in these species. The present investigation identifies the best phenological models for the main phenophases allowing their practical application as real-time monitoring and plant development prediction tools. Sigmoid model revealed high performances in simulating spring vegetative phases, BBCH11 (First leaves unfolded), and BBCH91 (Shoot and foliage growth completed). Salix acutifolia Willd. development appeared to be more related to temperature amount interpreted by phenological models in comparison to Salix smithiana Willd. above all during spring (BBCH11 and 91), probably due to a different grade of phenotypic plasticity between the 2 considered species.

Morphological and physiological responses of two willow species from different habitats to salt stress

Plant salt tolerance is a complex mechanism, and different plant species have different strategies for surviving salt stress. In the present study, we analyzed and compared the morphological and physiological responses of two willow species (Salix linearistipularis and Salix matsudana) from different habitats to salt stress. S. linearistipularis exhibited higher seed germination rates and seedling root Na+ efflux than S. matsudana under salt stress. After salt treatment, S. linearistipularis leaves exhibited less Na+ accumulation, loss of water and chlorophyll, reduction in photosynthetic capacity, and damage to leaf cell structure than leaves of S. matsudana. Scanning electron microscopy combined with gas chromatography mass spectrometry showed that S. linearistipularis leaves had higher cuticular wax loads than S. matsudana leaves. Overall, our results showed that S. linearistipularis had higher salt tolerance than S. matsudana, which was associated with different morphological and physiological responses to salt stress. Furthermore, our study suggested that S. linearistipularis could be a promising tree species for saline-alkali land greening and improvement.