The Effect of Mycorrhizal Fungi on the Fate of PCBs in Two Vegetated Systems

The objective of this study was to investigate the effects of mycorrhizal infection on vegetative uptake of polychlorinated biphenyls. Feltleaf willow (Salix alaxensis) and balsam poplar (Populus balsamifera) were grown in soil spiked with 6 mg/kg 3,3′,4,4′-tetrachlorobiphenyl-(UL-¹⁴C). The fungicide Daconil₂₇₈₇® was employed to suppress indigenous mycorrhizal infection. After 100 days of greenhouse incubation in semienclosed phytoreactors, mycorrhizal infection was found to be approximately threefold higher in the untreated willows vs. the fungicide-amended willows. Radio-label uptake was found to correlate most highly with mycorrhizal infection in the willow roots (R = 0.83). Over the same time period, mycorrhizal infection in the poplars was not significantly affected by fungicide addition. In the poplar phytoreactors, radiolabel uptake was most highly correlated with water use (R = 0.70). The overall vegetative radiolabel uptake was low (≈ 1%), but the limited uptake was attributed to soil sorption processes rather than vegetative limitations.     

Effects of above-ground browsing by mammals on mycorrhizal infection in an early successional taiga ecosystem

Using an exclosure experiment in the willow stage of primary succession on the floodplain of the Tanana River, we tested the hypothesis that browsing can reduce mycorrhizal infection. We measured the effects winter browsing by moose (Alcesalces) and snowshoe hare (Lepusamericanus) had on mycorrhizal infection and fine root biomass of willow (Salix spp.) and balsam poplar (Populusbalsamifera). We found that protection from winter browsing increased ectomycorrhizal infection by 10% in the top 5 cm of the soil profile, by 23% at 5–10 cm, and by 42% at the 10–15 cm depth. Mammal browsing in taiga forests is now recognized as a major cause of the shift from palatable deciduous species such as willow and balsam poplar to less palatable species such as alder and spruce. We suggest that browsing-induced reduction in ectomycorrhizal infection of salicaceous species plays a central role in this shift in plant community composition. Received: 26 March 1996 / Accepted: 26 September 1996     

Alignment of a <Emphasis Type="Italic">Salix</Emphasis> linkage map to the <Emphasis Type="Italic">Populus</Emphasis> genomic sequence reveals macrosynteny between willow and poplar genomes

Poplars (genus Populus) and willows (genus Salix) are members of the Salicaceae, a family of catkin-bearing trees, shrubs and sub-shrubs. Poplar is considered the model system for biological studies in trees and considerable genetic and genomic resources have become available in recent years. The transfer of information to research studies in willow, for which fewer resources are currently available, would be highly beneficial. However, the extent of conservation between poplar and willow genomes has not yet been extensively studied. To address this, we have constructed a linkage map of willow based on a large mapping population derived from a cross between two Salix viminalis × (S. viminalis × S. schwerinii) hybrid sibs, and aligned this to the publicly available poplar genome sequence. A set of genome-wide, expressed poplar sequences was selected and used to design primer sets that efficiently amplified homeologous regions in willow. Direct sequencing of the willow products confirmed homology with the poplar target in the majority of instances and allowed identification of single nucleotide polymorphisms (SNPs) that were used to map these loci. In total, 202 amplified fragment length polymorphisms (AFLPs), 75 microsatellites and 79 SNPs were used to construct a willow consensus map that spanned 1,856.7 cM with an average interval between markers of 6.3 cM. Poplar sequences homologous to those of the mapped willow microsatellite loci were identified and used in addition to the SNP markers to putatively align all but two minor linkage groups to the poplar genome sequence. A high degree of macrosynteny was revealed.     

Vegetation influence on ectomycorrhizal inoculum Available to sub-arctic willow (Salix lapponum L.) planted in an upland Site

Summary

Restoration of scrub and woodland in deforested upland sites is an important conservation activity. However, little is known about the mycorrhizal colonisation potential of upland soils or the factors that influence the distribution of mycorrhizal inoculum. We investigated the effect of existing vegetation on mycorrhizal colonisation potential for a sub-arctic willow (Salix lapponum) by planting uninoculated cuttings into plotsrepresenting two upland habitats with either grassand herbs (‘grass’) or Vaccinium myrtillus (‘vaccinium’) and assessing mycorrhizal colonisation after 14 months using morphological and molecular techniques. From 40 willow cuttings (20 in each habitat), DNA sequences of rive ectomycorrhizal (EcM) fungal taxa were recovered: Laccaria proxima, Thelephora terrestris, Hebeloma sp., ‘Thelephoraceae sp.’ and ‘Pezizales sp.’. Cuttings in the ‘grass’ habitat were dominated by Laccaria proxima and ‘Pezizales sp.’ and in the ‘vaccinium’ habitat by Thelephora terrestris which was absent from the ‘grass’ habitat. There were no significant differences between habitats in frequency of EcM inoculum (overall percentage of cuttings colonised = 70%) or colonisation potential (overall mean percentage of root tips colonised per cutting = 20 %). These data suggest that the mycorrhizal colonisation potential and diversity of fungi available to willow in these upland soils are low and planted willow may benefit from inoculum enhancement.     

METAL UPTAKE AND ALLOCATION IN TREES GROWN ON CONTAMINATED LAND: IMPLICATIONS FOR BIOMASS PRODUCTION

Phytostabilization aims to reduce environmental and health risks arising from contaminated soil. To be economically attractive, plants used for phytostabilization should produce valuable biomass. This study investigated the biomass production and metal allocation to foliage and wood of willow (Salix viminalis L.), poplar (Populus monviso), birch (Betula pendula), and oak (Quercus robur) on five different soils contaminated with trace elements (TE), with varying high concentrations of Cu, Zn, Cd, and Pb as well as an uncontaminated control soil. In the treatment soils, the biomass was reduced in all species except oak. There was a significant negative correlation between biomass and foliar Cd and Zn concentrations, reaching up to 15 mg Cd kg^?1 and 2000 mg Zn kg ^?1 in willow leaves. Lead was the only TE with higher wood than foliage concentrations. The highest Pb accumulation occurred in birch with up to 135 mg kg ^?1 in wood and 78 mg kg ^?1 in foliage. Birch could be suitable for phytostabilization of soils with high Cd and Zn but low Pb concentrations, while poplars and willows could be used to stabilise soils with high Cu and Pb and low Zn and Cd concentrations.     

Variation in the uptake of Arsenic, Cadmium, Lead, and Zinc by different species of willows Salix spp. grown in contaminated soils

The experiment assessed the variability of in seven clones of willow plants of high biomass production (Salix smithiana S-218, Salix smithiana S-150, Salix viminalis S-519, Salix alba S-464, Salix ’Pyramidalis’ S-141, Salix dasyclados S-406, Salix rubens S-391). They were planted in a pots for three vegetation periods in three soils differing in the total content of risk elements. Comparing the calculated relative decrease of total metal contents in soils, the phytoextraction potential of willows was obtained for cadmium (Cd) and zinc (Zn), moderately contaminated Cambisol and uncontaminated Chernozem, where aboveground biomass removed about 30% Cd and 5% Zn of the total element content, respectively. The clones showed variability in removing Cd and Zn, depending on soil type and contamination level: S. smithiana (S-150) and S. rubens (S-391) demonstrated the highest phytoextraction effect for Cd and Zn. For lead (Pb) and arsenic (As), the ability to accumulate the aboveground biomass of willows was found to be negligible in both soils. The results confirmed that willow plants show promising results for several elements, mainly for mobile ones like cadmium and zinc in moderate levels of contamination. The differences in accumulation among the clones seemed to be affected more by the properties of clones, not by the soil element concentrations or soil properties. However, confirmation and verification of the results in field conditions as well as more detailed investigation of the mechanisms of cadmium uptake in rhizosphere of willow plants will be determined by further research.     

Natural and induced cadmium-accumulation in poplar and willow: Implications for phytoremediation

Potentially poplars and willows may be used for the in situ decontamination of soils polluted with Cd, such as pasturelands fertilised with Cd-rich superphosphate fertiliser. Poplar (Kawa and Argyle) and willow (Tangoio) clones were grown in soils containing a range (0.6–60.6 μg g⁻¹ dry soil) of Cd concentrations. The willow clone accumulated significantly more Cd (9–167 μg g⁻¹ dry matter) than the two poplar clones (6–75 μg g⁻¹), which themselves were not significantly different. Poplar trees (Beaupré) sampled in situ from a contaminated site near the town of Auby, Northern France, were also found to accumulate significant quantities (up to 209 μg g⁻¹) of Cd. The addition of chelating agents (0.5 and 2 g kg⁻¹ EDTA, 0.5 g kg⁻¹ DTPA and 0.5 g kg⁻¹NTA) to poplar (Kawa) clones caused a temporary increase in uptake of Cd. However, two of the chelating agents (2 g kg⁻¹ EDTA and 0.5 g kg⁻¹ NTA) also resulted in a significant reduction in growth, as well as abscission of leaves. If the results obtained in these pot experiments can be realised in the field, then a single crop of willows could remove over 100 years worth of fertiliser-induced Cd contamination from pasturelands. This revised version was published online in June 2006 with corrections to the Cover Date.     

Genotypic variability and stability of poplars and willows grown onnitrate-contaminated soils

Abstract

Phyto-recurrent selection is an established method for selecting tree genotypes for phytoremediation. To identify promising Populus (poplar) and Salix (willow) genotypes for phytotechnologies, our objectives were to (1) evaluate the genotypic variability in survival, height, and diameter of poplar and willow clones established on soils heavily contaminated with nitrates; and (2) assess the genotypic stability in survival and diameter of selected poplar clones after one and eleven growing seasons. We tested 27 poplar and 10 willow clones planted as unrooted cuttings, along with 15 poplar genotypes planted as rooted cuttings. The trees were tested at an agricultural production facility in the Midwestern, United States. After 11 growing seasons, using phyto-recurrent selection, we surveyed survival and measured the diameter of 27 poplar clones (14 unrooted, 13 rooted) that were selected based on superior survival and growth throughout plantation development. Overall, willow exhibited the greatest survival, while poplar had the greatest height and diameter. At 11 years after planting, superior clones were identified that exhibited above-average diameter growth at the establishment- and rotation-age, most of which had stable genotypic performance over time. Selection of specific clones was favorable to genomic groups, based on the geographic location and soil conditions of the site.     

Soil trace element changes during a phytoremediation trial with willows in southern Québec,Canada

This study determined the changes in trace elements (TE) (As, Cd, Cu, Ni, Pb, Zn) chemistry in the soils of a willow (“Fish Creek” – Salix purpurea, SV1 – Salix x dasyclados and SX67 – Salix miyabeana) plantation growing under a cold climate during a three-year trial. The soil HNO₃-extractable and H₂O-soluble TE concentrations and pools significantly decreased under most cultivars (Fish, SX67). Yet, TE changes showed inconsistent patterns and localized soil TE increases (Ni, Pb) were measured. Temporal changes in soil TE were also detected in control plots and sometimes exceeded changes in planted plots. Discrepancies existed between the amount of soil TE change and the amount of TE uptake by willows, except for Cd and Zn. Phytoremediation with willows could reduce soil Cd and Zn within a decadal timeframe indicating that they can be remediated by willows in moderately contaminated soils. However, the time needed to reduce soil As, Cu, Ni and Pb was too long to be efficient. We submit that soil leaching contributed to the TE decrease in controls and the TE discrepancies, and that the plantation could have secondary effects such as the accelerated leaching of soil TE.     

Establishment of Moose Browse on Four Growth Media on a Proposed Mine Site in Southcentral Alaska

The objective of this study was to evaluate seven woody plant species on four growth media for their potential contribution to moose habitat and establishment of viable plant communities on a proposed mine site in southcentral Alaska. Populus balsamifera (balsam poplar), Salix alaxensis (feltleaf willow), S. barclayi (Barclay willow), S. bebbiana (Bebb willow), Alnus tenuifolia (thinleaf alder), Betula papyrifera (paper birch), and Picea glauca (white spruce) were selected for their functions in moose habitat, ease of propagation, and presence in the existing native vegetation. Three native soils were selected for biological characteristics such as different potential to form mycorrhizae and to regenerate local plant species, both of which are governed partly by existing vegetation. The fourth growth medium, glacial till or overburden, was expected to have little or no biological activity. A mining disturbance was simulated on three sites by removing existing vegetation from the plots, stripping the native soils, and then spreading these soil materials over the respective study plots. Rooted cuttings of the Salicaceae and nursery seedlings of the other species were planted in each of the four growth media. Height and survival of all plant species were greater on the three soil media than on the glacial till during the second and third years. Percentage of ectomycorrhizal infection on transplants was similar among growth media, although lower ectomycorrhizal infection occurred on volunteers in grassland soils than in the other growth media. Browsable plants were produced within three years on the disturbed native soils but not on the glacial till.     

The giant willow aphid (Tuberolachnus salignus) and its effects on the survival and growth of willows

1. The giant willow aphid (Tuberolachnus salignus) is an invasive pest that can attain large populations on willows (Salix spp.). This has the potential to have a negative impact on the extensive use of willows for soil conservation, and as a source of pollen and nectar for honey bees in New Zealand.
2. A willow nursery field trial was established to evaluate the aphid populations, and the survival and growth of young plants of several willow species and hybrids, during two growing seasons from planting.
3. The willow species and hybrids varied widely in their susceptibility to the aphid, with large aphid populations and plant mortality in the most susceptible willows, and reductions in plant growth in all but aphid-resistant willows. The effects on the plants were not seen in the first season, but occurred during the second season.
4. The aphid can be expected to have some negative impacts in New Zealand, with reductions in growth of some willows commonly used for soil conservation, and for pollen and nectar for honey bees.

     

ASSOCIATED BACTERIA INCREASE THE PHYTOEXTRACTION OF CADMIUM AND ZINC FROM A METAL-CONTAMINATED SOIL BY MYCORRHIZAL WILLOWS

In order to enhance phytoremediation efficiency, we investigated the effects of dual inoculation with ectomycorrhizal fungi and the ectomycorrhiza associated bacteria Micrococcus luteus and Sphingomonas sp. on the growth and metal accumulation of willows (Salix viminalis x caprea) on contaminated soil. The bacterial strains were previously collected from sporocarps of ectomycorrhizal fungi. The bacteria increased plant growth and the mycorrhizal dependency of willows colonized with the ectomycorrhizal fungus Hebeloma crustuliniforme. The total cadmium (Cd) and zinc (Zn) accumulation in the shoot biomass was increased after inoculation with the fungal strain Hebeloma crustuliniforme in combination with Micrococcus luteus up to 53% and in combination with Sphingomonas sp. up to 62%, respectively. The dual inoculation in combination with Laccaria laccata did not increase the accumulation of Cd and Zn in the willows. We conclude that associated bacteria can enhance the ectomyorrhiza formation and growth of willows and, thereby, the Cd and Zn accumulation in the plant biomass. The results suggest that bacterial support of root growth promoting ectomycorrhizal fungi may be a promising approach to improve the remediation of metal-contaminated soils by using willows.     

Growth Response of Coyote Willow (Salix exigua) Cuttings in Relation to Alluvial Soil Texture and Water Availability

A common approach to re‐establishing cottonwood–willow habitat along regulated rivers is through installing dormant, rootless cuttings, yet there is little published information exploring floodplain characteristics that optimize growth of southwestern riparian willows planted in this manner. The goal of this project was to evaluate relationships between growth attributes of Salix exigua and soil texture and soil water availability. Monitoring plots were established in five willow swales planted with dormant S. exigua cuttings along the banks of the Middle Rio Grande in central New Mexico. Data analysis revealed significantly higher aerial cover, height, and stem density for S. exigua plants installed in plots with intermediate levels (15–25%) of fine textured soils distributed through the soil profile. Similar relationships were found in relation to soil water availability. Regression analysis of percent fines and available water at different depth increments provided limited explanation of variability in willow growth attributes at different plots. Findings indicate that S. exigua plants established from cuttings can achieve heights and aerial cover values similar to naturally established willow bars if the floodplain soil profile contains intermediate levels of fine textured soils and the maximum depth to groundwater is within 1.5 m of the ground surface. Where sites are dominated by coarse sand, S. exigua growth may be improved if maximum depth to groundwater is within 1 m of the ground surface.     

Biomass Harvest from Natural Willow Rings around Prairie Wetlands

The study followed the harvest of natural willow from three wetlands using a prototype modified agricultural round baler nicknamed a Bio-Baler. The study reports fuel characteristics and combustion testing of biomass harvested from natural willow rings. Composition of native willow species in the harvested willow rings was determined. We specifically measured regrowth of the biomass and number of regenerated stems per stump 1 year after harvest to determine how different willow species responded to mechanical biomass cutting with the Bio-Baler. The results of combustion testing for the natural willow were essentially similar to those with “conventional” wood chips or planted willows. The ash content was approximately 1.65%, slightly lower than for planted willow plantations. The calorific value of the natural willow was 19.6 MJ kg^?1 (dry basis) similar to what is expected for wood and planted willow. Four Salix species (Salix bebbiana Sarg., Salix petiolaris Sm., Salix eriocephala Michx., and Salix discolor Muhl) were identified in the willow rings. Stem biomass increased for all species except S. bebbiana after willow was harvested with the Bio-Baler. Overall, willow regeneration was not affected by mechanical harvesting compared to hand cutting. Regenerated stem density was 93 stems per square meter for mechanically harvested stumps compared to 105 stems per square meter for hand-pruned stumps. Based on the results, biomass harvested from natural willow rings has acceptable fuel characteristics when compared to purpose-grown willows and mechanical harvest with a Bio-Baler does not have a negative effect on willow regeneration.     

Cadmium accumulation and tolerance in Populus nigra and Salix alba

Rooted cuttings of Populus nigra L. clone Poli and Salix alba L. clone SS5 were treated for three weeks with 50 μM CdSO₄ in nutrient solution. The willow showed a far higher Cd tolerance, expressed as tolerance index (Ti), than the poplar in both roots and leaves. The root Cd content was higher in poplar than in willow, whereas in leaves the opposite was found. As a consequence, the translocation factor (Tf) revealed a greater ability of Cd transport in willow than in poplar. Cd treatment enhanced cysteine, γ-glutamylcysteine and reduced glutathione contents in roots of both species, whereas in leaves they were only enhanced in poplar. Furthermore, only poplar leaves showed an enhanced content of phytochelatins, whereas malic and citric acids rose in response to Cd only in the willow leaves. Cd treatment increased putrescine, spermidine and spermine contents in both roots and leaves of the willow, whereas in poplar only the putrescine content was enhanced in roots.     

Brenneria salicis, the bacterium causing watermark disease in willow, resides as an endophyte in wood

Brenneria salicis has been studied in willow wood only in relation to watermark disease. In this pathogenic condition, the bacterium occurs at high concentrations. Pathogenicity of B. salicis is still uncontrollable and the disease unpredictable because the plant–bacteria interaction is not understood. Thanks to molecular techniques B. salicis can be detected at low concentrations, which are found in most non-pathogenic interactions. Brenneria salicis was identified and traced with a new specific three-primer polymerase chain reaction and its identity and relative concentration in biological samples confirmed through denaturing gradient gel electrophoresis profiling. Brenneria salicis was found in symptomless willows sampled randomly in Flanders agricultural areas, in young nursery willows, and also in poplar ( Populus ) and alder ( Alnus ). It harboured the nitrogenase reductase gene NifH and promoted growth and chlorophyll in willow. Inoculated luminescence-marked B. salicis circulated through the whole plant without inducing disease and exuded at the leaf margins. Other willow endophytes identified were Rahnella , Sphingomonas and Methylobacterium . In conclusion, because endophytic B. salicis is generally observed in willow, disease must not be dependent on infection. Leaf-to-leaf spread is proposed as an important mechanism for spread of B. salicis .     

Effects of Propagule Phenology (Non-Dormant Versus Dormant) and Planting System (Vertical Versus Horizontal) on Growth Performance of Willow Clones Grown Under Different Weeding Regimes

To assess the effects of propagule phenology and planting system on growth performance of three willow clones grown under different weeding regimes, a field experiment was performed in central Sweden 2014–2016. Freshly harvested (non-dormant) and cold-stored (dormant) cuttings (planted vertically) and billets (planted horizontally) from willow clones Tordis, Tora, and Jorr were planted in weeded and in unweeded plots. Sprouting was significantly higher for willows grown from non-dormant (74%) than dormant (58%) propagules and for cuttings (84%) compared with billets (42%). Survival was higher for willows from non-dormant propagules in weeded (71%) compared with unweeded (63%) plots, willows from dormant propagules in weeded (72%) compared with unweeded (60%) plots, and for willows from cuttings (93%) compared with billets (39%). During 2014–2016, aboveground biomass production was significantly higher for willows from cuttings (11.71 t DW ha^?1) than from billets (6.13 t DW ha^?1), grown in weeded (15.29 t DW ha^?1) than in unweeded (2.55 t DW ha^?1) plots, and differed significantly among willow clones (11.48, 9.27, and 6.01 t DW ha^?1 for Tordis, Tora, and Jorr, respectively). In this study, (i) planting with cold-stored and freshly harvested willow propagules was equally successful and therefore cold storage could be potentially avoided and replaced with planting of freshly harvested propagules in early spring; however, (ii) in terms of measured growth performance parameters, willows grown from cuttings performed better than grown from billets; and (iii) weed competition significantly reduced survival and aboveground biomass production, confirming that weed control during establishment of willow is crucial.     

Evidence for host race formation in the leaf beetle Galerucella lineola

We examined preference and performance of four Finnish Galerucella lineola F. populations on alder and willow. In standardized two‐choice laboratory feeding trials with alder and willow, only two naturally alder‐associated G. lineola populations accepted alder. Two conspecific willow‐associated populations preferred willow. These preferences seem to be unstable, however, because they can be modified by the beetles’ experience. Thus, there probably is not a complete host preference‐based isolation of alder‐ and willow‐associated G. lineola beetles in nature. In performance experiments, larvae of all four populations survived better on willow than on alder. This may indicate that willows are the ancestral hosts for G. lineola. Nevertheless, larvae of the two alder‐associated G. lineola populations survived better on alder than larvae of the two willow‐associated populations. On the other hand, larvae of the two willow‐associated populations survived better on willow than larvae of the two alder‐associated populations. This performance trade‐off suggests that G. lineola encounters different selective pressures on alders and willows. On both of them, selection probably disfavours those G. lineola genotypes that are the most successful and abundant on alternative hosts. This may reduce the effects of gene flow that is likely to occur as a consequence of incomplete host preference‐based isolation of alder‐ and willow‐associated G. lineola populations. Data from pupal weights support the idea that alder‐ and willow‐associated G. lineola populations may be genetically differentiated. Pupae of the two alder‐associated populations were heavier than those of the willow‐associated populations irrespective of whether larvae had fed on alder or on willow. Overall, our results indicate host race formation in G. lineola. This process may be enforced by the variable abundance of alders and willows in local communities.     

Size class structure and tree dispersion patterns in old-growth cedar-hemlock forests of the northern Rocky Mountains (USA)

Summary The relationship between the food selection of four leaf beetle species (Phratora vitellinae, Plagiodera versicolora, Lochmaea capreae, Galerucella lineola) and the phenolic glycosides of willow (Salix spp.) leaves was tested in laboratory food choice experiments. Four willow species native to the study area (Eastern Finland) and four introduced, cultivated willows were tested.The willow species exhibited profound differences in their phenolic glycoside composition and total concentration. The food selection patterns of the leaf beetles followed closely the phenolic glycoside spectra of the willow species. Both the total amount and the composition of phenolic glycosides affected the feeding by the beetles. Phenolic glycosides apparently have both stimulatory and inhibitory influences on leaf beetle feeding depending on the degree of adaptation of a particular insect. Very rare glycosides or exceptional combination of several glycoside types seem to provide certain willow species with high level of resistance against most herbivorous insects. Analogously the average absolute amount of leaf beetle feeding was lower on the introduced willows than on the native species to which the local herbivores have a good opportunity to become adapted.     

Phenolic compounds of willow bark as deterrents against feeding by mountain hare

Summary Overwintering mountain hares (Lepus timidus) fed selectively on the shoots of a number of northern willow (Salix spp.) species. The hares preferred certain species over others and mature shoots over juvenile ones. There was a negative correlation between the phenolic glycoside concentration in the twigs and the hares' feeding. This correlation was substantiated by feeding experiments in which oat grains treated with purified phenoglycoside and catechin fractions of willow bark were offered along with untreated control oat grains to free-ranging mountain hares. Both fractions in concentrations normally found in willow twigs inhibited hare feeding. The results suggest that these phenolic compounds play a crucial role in the building up of resistance patterns among the willows. The decline in resistance in mature shoots of tall willows indicates that the juvenile resistance can be, perhaps secondarily, an adaptation against mammals browsing from ground level. Accordingly, low willow species retain a high level of resistance also in maturity.