Salix Miyabeana Research Articles

Soil carbon dynamics in perennial biomass crops on marginally productive cropland in southern Canada

Predicting changes in soil organic carbon (SOC) in perennial biomass crops using process-based models provides a greater understanding of land management impacts on climate mitigation through long-term soil carbon sequestration. The objective of this study was to predict long-term SOC dynamics in different perennial biomass crops [miscanthus (Miscanthus giganteus L.), switchgrass (Panicum virgatum L.), willow (Salix miyabeana L.)] as compared to secondary regrowth vegetation (successional site) and a row crop system. The Century model accurately predicted SOC when simulated values were compared to measured field data. Average SOC stocks over the 162-year simulation period to 20 cm, were highest in miscanthus (8521 g C m−2), followed by the successional site (6877 g C m−2), switchgrass (6480 g C m−2), willow (5448 g C m−2) and lowest in the row crop system (3995 g C m−2). Higher SOC stocks in the miscanthus than the successional site indicates that, despite frequent biomass harvest, perennial biomass crops can accumulate higher carbon in soil than when a marginally productive cropland is left to undergo secondary regrowth. However, this depends on the crop species, since the miscanthus was the only biomass crop that reached pre-cultivation (1911) SOC stock of 8288 g C m−2. Moreover, the perennial biomass crops enhanced SOC in the slow fraction, whereas row crops depleted SOC in this fraction. This indicates the vital contribution of perennial biomass crops in long-term SOC sequestration and their role in climate change mitigation, especially when grown on marginally productive croplands.

Irrigation with primary wastewater alters wood anatomy and composition in willow Salix miyabeana SX67.

Traditional treatment of wastewaters is a burden for local governments. Using short rotation coppice willow (SRCW) as vegetal filter has several environmental and economic benefits. Here, we investigated the effect of primary wastewater irrigation on wood structure and composition of the willow cultivar Salix miyabeana 'SX67' following two years of growth. Compared to unirrigated plants (UI), stem sections of plants irrigated with primary wastewater (WWD) showed an unexpected decrease of hydraulic conductance (KS) associated with a decrease in vessel density but not vessel diameter. The majority (86%) of vessels had diameters range groups [20-30[, [30-40[and [40-50[µm and contributed to > 75% of theoretical KS, while the group class [50-60[µm (less than 10% of vessels) still accounted for > 20% of total KS regardless irrigation treatments. WWD significantly alters the chemical composition of wood with an increase of glucan content by 9 to 16.4% and a decrease of extractives by 35.3 to 36.4% when compared to UI or to plants irrigated with potable water (PW). The fertigation did also increase the proportion of the tension wood which highly correlated with glucan content. In the context of energetic transition and mitigation of climate change, such results are of high interest since WWD effectively permit the phytofiltration of large amounts of organic contaminated effluents without impairing SRCW physiology.

Willow and Herbaceous Species' Phytoremediation Potential in Zn-Contaminated Farm Field Soil in Eastern Québec, Canada: A Greenhouse Feasibility Study.

Phytoremediation shows great promise as a plant-based alternative to conventional clean-up methods that are prohibitively expensive. As part of an integrated strategy, the selection of well-adapted plant species as well as planting and management techniques could determine the success of a long-term program. Herein, we conducted an experiment under semi-controlled conditions to screen different plants species with respect to their ability to phytoremediate Zn-contaminated soil excavated from a contaminated site following a train derailment and spillage. The effect of nitrilotriacetic acid (NTA) application on the plants and soil was also comprehensively evaluated, albeit we did not find its use relevant for field application. In less than 100 days, substantial Zn removal occurred in the soil zone proximal to the roots of all the tested plant species. Three perennial herbaceous species were tested, namely, Festuca arundinacea, Medicago sativa, and a commercial mix purposely designed for revegetation; they all showed strong capacity for phytostabilization at the root level but not for phytoextraction. The Zn content in the aboveground biomass of willows was much higher. Furthermore, the degree of growth, physiological measurements, and the Zn extraction yield indicated Salix purpurea ‘Fish Creek’ could perform better than Salix miyabeana, ‘SX67’, in situ. Therefore, we suggest implementing an S. purpurea—perennial herbaceous co-cropping strategy at this decade-long-abandoned contaminated site or at similar disrupted landscapes.

Impact of stem age and winter outdoor storage on willow chip chemical composition and physicochemical properties

Willow (Salix) biomass production has been expanding dramatically in recent years with the development of phytoremediation and wastewater treatment projects and plans to build bio-refineries are increasing the future options for valorizing this biomass. In this context, winter storage of biomass after harvesting is unavoidable, due to limited shelter capacity. Questions about the impact of outdoor storage during winter and stem age at harvest time led to the establishment of an experiment on the site of Ramo®, a biomass-based products producer. Two- and three-year-old Salix miyabeana ‘SX67′ stems were chipped and piled after leaf fall in November 2018. Temperature was measured during the experiment, while physicochemical parameters and biomass composition were analyzed at the beginning and the end. The experiment showed that stem age influenced the initial biomass composition, with the two-year-old stems containing more extractives and the three-year-old stems containing more structural sugars. Heat production varied with stem age, which was reflected in the final biomass composition. A loss of extractives and an increase in lignin was measured in both stem types, while an increase in glucan, xylan and mannan was also measured in the two-year-old chips. This new information complements existing data on mass loss during wood chip storage and provides essential knowledge for future decision-making related to the development of lignocellulose value chains from bioenergy crops.

Ectomycorrhizal Fungi Dominated the Root and Rhizosphere Microbial Communities of Two Willow Cultivars Grown for Six-Years in a Mixed-Contaminated Environment.

There is a growing interest in plant microbiome’s engineering to optimize desired functions such as improved phytoremediation. This study is aimed at examining the microbial communities inhabiting the roots and rhizospheres of two Salix miyabeana cultivars that had been grown in a short-rotation intensive culture (SRIC) system for six years in a soil contaminated with the discharge from a petrochemical factory. DNA was extracted from roots and rhizospheric soils, and fungal ITS and bacterial and archaeal 16S rDNA regions were amplified and sequenced using Illumina MiSeq technology. Cultivars ‘SX61’ and ‘SX64’ were found to harbor a similar diversity of fungal, bacterial, and archaeal amplicon sequence variants (ASVs). As expected, a greater microbial diversity was found in the rhizosphere biotope than in the roots of both cultivars, except for cultivar ‘SX64’, where a similar fungal diversity was observed in both biotopes. However, we found that microbial community structures were cultivar- and biotope-specific. Although the implication of some identified taxa for plant adaptability and biomass production capacity remains to be explored, this study provides valuable and useful information regarding microbes that could potentially favor the implantation and phytoremediation efficiency of Salix miyabeana in mixed contamination sites in similar climatic environments.

Nutrient Availability for Lactuca sativa Cultivated in an Amended Peatland: An Ionic Exchange Study

Few conservation strategies have been applied to cultivated peatland. This field study over one growth cycle of Lactuca sativa examined the effect of plant-based, high-C/N-ratio amendments in a real farming situation on peatland. Plant Root Simulator (PRS®) probes were used directly in the field to assess the impacts of incorporating Miscanthus x giganteus straw and Salix miyabeana chips on nutrient availability for lettuce. The results showed that lettuce yield decreased by 35% in the miscanthus straw treatment and by 14% in the willow chip treatment. In addition, the nitrogen flux rate was severely reduced during crop growth (75% reduction) and the plant N uptake index was much lower in the amended treatments than in the control. The phosphorus supply rate was also significantly lower (24% reduction) in the willow treatment. The influence of sampling zone was significant as well, with most macro-nutrients being depleted in the root zone and most micro-nutrients being mobilized. Additional work is needed to optimize the proposed conservation strategy and investigate the effects of consecutive years of soil amendment on different vegetable crops and in different types of cultivated peatlands to confirm and generalize the findings of this study. Future field studies should also explore the long-term carbon dynamics under plant-based, high-C/N-ratio amendments to determine if they can offset annual C losses.

The Effects of Agronomic Herbaceous Plants on the Soil Structure of Gold Mine Tailings and the Establishment of Boreal Forest Tree Seedlings

In Canada, low-grade ore mines generate large amounts of mineral waste, such as mine tailings. To control erosion of the fine-grained tailings particles as quickly as possible, it is common practice for the mining industry to revegetate the mine tailings with agronomic herbaceous plants. However, it is unclear whether this practice is consequential to the natural establishment of boreal species. The first objective of this study was to evaluate which families of agronomic herbaceous plants (legumes or grasses) result in the most favorable physical and chemical soil properties for the establishment of boreal species. The second objective was to determine the effect of the agronomic herbaceous plants on the growth and foliar nutrient concentration on three indigenous boreal forest seedlings; jack pine (Pinus banksiana Lambert), tamarack (Larix laricina Du Roi), paper birch (Betula papyrifera Marshall), and a willow cultivar (Salix miyabeana Seemen). In 2013, a 1-ha in situ experimental surface of mine tailings was set up on the gold mine site in Malartic, Abitibi-Témiscamingue, Quebec. The experimental site was subdivided into three blocks, each further divided in 5 plots. Each plot was randomly seeded as follows: 100% grass, 100% legumes, a mixture of both, topsoil, and a control (tailings only, no seeding). In the 2015 spring season, thirty seedlings of the three boreal tree species and cuttings of the willow cultivars were planted in each treatment plot. Seedling height and root biomass were measured at the end of the 2016 growing season. Soil sample analyses indicated significant differences for bulk density, wilting point, and organic matter content between the topsoil and the different agronomic herbaceous and control treatments; however, no significant differences were found between the different herbaceous treatments and the control for soil pH, bulk density, wilting point, macroporosity, and organic matter content. The mortality rate of jack pine, tamarack, and paper birch seedlings was higher in the control plots compared to all other treatments. Root biomass and height of the willow cultivar were significantly higher in the legumes compared with topsoil treatment. Among the four pioneer tree seedlings studied, this research indicates that the combination of the willow cultivar with the legumes treatment produces the best seedling growth and survival in the highly abiotic and stressful environments inherent to mine tailings.

Nonadditive gene expression is correlated with nonadditive phenotypic expression in interspecific triploid hybrids of willow (Salix spp.).

Many studies have highlighted the complex and diverse basis for heterosis in inbred crops. Despite the lack of a consensus model, it is vital that we turn our attention to understanding heterosis in undomesticated, heterozygous, and polyploid species, such as willow (Salix spp.). Shrub willow is a dedicated energy crop bred to be fast-growing and high yielding on marginal land without competing with food crops. A trend in willow breeding is the consistent pattern of heterosis in triploids produced from crosses between diploid and tetraploid species. Here, we test whether differentially expressed genes are associated with heterosis in triploid families derived from diploid Salix purpurea, diploid Salix viminalis, and tetraploid Salix miyabeana parents. Three biological replicates of shoot tips from all family progeny and parents were collected after 12 weeks in the greenhouse and RNA extracted for RNA-Seq analysis. This study provides evidence that nonadditive patterns of gene expression are correlated with nonadditive phenotypic expression in interspecific triploid hybrids of willow. Expression-level dominance was most correlated with heterosis for biomass yield traits and was highly enriched for processes involved in starch and sucrose metabolism. In addition, there was a global dosage effect of parent alleles in triploid hybrids, with expression proportional to copy number variation. Importantly, differentially expressed genes between family parents were most predictive of heterosis for both field and greenhouse collected traits. Altogether, these data will be used to progress models of heterosis to complement the growing genomic resources available for the improvement of heterozygous perennial bioenergy crops.

Willows Used for Phytoremediation Increased Organic Contaminant Concentrations in Soil Surface

The Salix genus includes shrub species that are widely used in phytoremediation and various other phytotechnologies due to their advantageous characteristics, such as a high evapotranspiration (ET) rate, in particular when cultivated in short rotation intensive culture (SRIC). Observations made in past field studies suggest that ET and its impact on soil hydrology can also lead to increases in soil pollutant concentrations near shrubs. To investigate this, sections of a mature willow plantation (seven years old) were cut to eliminate transpiration (Cut treatment). Soil concentrations of polychlorinated biphenyls (PCBs), aliphatic compounds C10–C50, polycyclic aromatic hydrocarbons (PAHs) and five trace elements (Cd, Cr, Cu, Ni and Zn) were compared between the Cut and the uncut plots (Salix miyabeana ‘SX61’). Over 24 months, the results clearly show that removal of the willow shrubs limited the contaminants’ increase in the soil surface, as observed for C10–C50 and of 10 PAHs under the Salix treatment. This finding strongly reinforces a hypothesis that SRIC of willows may facilitate the migration of contaminants towards their roots, thus increasing their concentration in the surrounding soil. Such a “pumping effect” in a high-density willow crop is a prominent characteristic specific to field studies that can lead to counterintuitive results. Although apparent increases of contaminant concentrations contradict the purification benefits usually pursued in phytoremediation, the possibility of active phytoextraction and rhizodegradation is not excluded. Moreover, increases of pollutant concentrations under shrubs following migration suggest that decreases would consequently occur at the source points. Some reflections on interpreting field work results are provided.

Optimization of the wastewater treatment capacity of a short rotation willow coppice vegetation filter

The objective of this study was to determine the conditions to optimize the wastewater treatment efficiency of a short rotation willow coppice (SRWC) plantation (Salix miyabeana ‘SX67’) used as a vegetation filter to treat small municipal primary effluents (with less than 800 population equivalent). With the aim of maximizing the annual amount of wastewater treated, the effect of adjusting the hydraulic loading rate (HLR) according to the estimated evapotranspiration was tested at demonstration scale under humid continental climate conditions. We proposed a new method to calculate the evapotranspiration rate from plant physiological data, introducing an α factor based on direct transpiration measurements. This method increased the accuracy of the water balance, with a prediction of the crop coefficient (kc) based on either an seasonal approach (R2 of 0.88) or a monthly approach (R2 of 0.94). This led to a more precise estimation of the pollutant loading reaching the groundwater and could be used after plantation establishment as a fine-tuning tool. Adjusting the HLR to that of evapotranspiration between May and October led to an annual increase of 2 mm/d (around 0.35 m3/m2 per growing season) in HLR, while maintaining a pollutant loading removal efficiency of at least 96% for organic matter, 99% for total phosphorus and 93% for total nitrogen. A high HLR at the end of the season caused nitrogen leaching into groundwater, indicating that the HLR should be decreased in October, when willow growth is greatly reduced.

High biomass yield increases in a primary effluent wastewater phytofiltration are associated to altered leaf morphology and stomatal size in Salix miyabeana

Municipal wastewater treatment using willow ‘phyto’-filtration has the potential for reduced environmental impact compared to conventional treatment practices. However, the physiological adaptations underpinning tolerance to high wastewater irrigation in willow are unknown. A one-hectare phytofiltration plantation established using the Salix miyabeana cultivar ‘SX67’ in Saint-Roch-de-l'Achigan, Quebec, Canada, tested the impact of unirrigated, potable water or two loads of primary effluent wastewater 19 and 30 ML ha−1 yr−1. A nitrogen load of 817 kg N ha−1 from wastewater did not increase soil pore water nitrogen concentrations beyond Quebec drinking water standards. The willow phytofiltration phenotype had increased leaf area (+106–142%) and leaf nitrogen (+94%) which were accompanied by significant increases in chlorophyll a + b content. Wastewater irrigated trees had higher stomatal sizes and a higher stomatal pore index, despite lower stomatal density, resulting in increased stomatal conductance (+42–78%). These developmental responses led to substantial increases in biomass yields of 56–207% and potable water controls revealed the nitrogen load to be necessary for the high productivity of 28–40 t ha−1 yr−1 in wastewater irrigated trees. Collectively, this study suggests phytofiltration plantations could treat primary effluent municipal wastewater at volumes of at least 19 million litres per hectare and benefit from increased yields of sustainable biomass over a two-year coppice cycle. Added-value cultivation practices, such as phytofiltration, have the potential to mitigate negative local and global environmental impact of wastewater treatment while providing valuable services and sustainable bioproducts.

Two-year performance of single-stage vertical flow treatment wetlands planted with willows under cold-climate conditions

Climate-related issues constitute an important obstacle for the development of treatment wetland (TW) applications in regions with freezing winter temperatures. The aim of the present study was to evaluate the efficiency of a new configuration of TWs based on the vertical flow (VF) configuration. The proposed TWs system is planted with a willow species (Salix miyabeana SX67) and including design adaptations for cold climate operation. Two different flow modes for winter-time operation were proposed: percolated and saturated with continuous artificial aeration. The pilot-scale systems were tested with municipal wastewater, at an organic loading ranging from 5 to 20 g CBOD5 m−2 d−1.The pilot TWs were successfully operated for 22 months despite freezing winter temperatures reaching as low as −32 °C. Willow development was normal, with evapotranspiration ranging from 19 to 23 mm/d in July 2017 for the pilot TWs at an organic loading of 10 g CBOD5 m−2 d−1. Organic matter removal efficiency was high for all pilot TWs, with an average 91% COD and 81% TSS removal. Nitrification was essentially complete during the summer period and remained high for pilot TWs operated under percolating flow mode in winter but was lower for the saturated flow mode, probably due to insufficient air supply. Our study confirms the successful application of a modified version of VF TW in regions with freezing air temperatures.

Long-Term Monitoring of Soil Carbon Sequestration in Woody and Herbaceous Bioenergy Crop Production Systems on Marginal Lands in Southern Ontario, Canada

Enhancement of terrestrial carbon (C) sequestration on marginal lands in Canada using bioenergy crops has been proposed. However, factors influencing system-level C gain (SLCG) potentials of maturing bioenergy cropping systems, including belowground biomass C and soil organic carbon (SOC) accumulation, are not well documented. This study, therefore, quantified the long-term C sequestration potentials at the system-level in nine-year-old (2009–2018) woody (poplar clone 2293–29 (Populus spp.), hybrid willow clone SX-67 (Salix miyabeana)), and herbaceous (miscanthus (Miscanthus giganteus var. Nagara), switchgrass (Panicum virgatum)) bioenergy crop production systems on marginal lands in Southern Ontario, Canada. Results showed that woody cropping systems had significantly higher aboveground biomass C stock of 10.02 compared to 7.65 Mg C ha−1 in herbaceous cropping systems, although their belowground biomass C was not significantly different. Woody crops and switchgrass were able to increase SOC significantly over the tested period. However, when long term soil organic carbon (∆SOC) gains were compared, woody and herbaceous biomass crops gained 11.0 and 9.8 Mg C ha−1, respectively, which were not statistically different. Results also indicate a significantly higher total C pool [aboveground + belowground + soil organic carbon] in the willow (103 Mg ha−1) biomass system compared to other bioenergy crops. In the nine-year study period, woody crops had only 1.35 Mg C ha−1 more SLCG, suggesting that the influence of woody and herbaceous biomass crops on SLCG and ∆SOC sequestrations were similar. Further, among all tested biomass crops, willow had the highest annual SLCG of 1.66 Mg C ha−1 y−1.

Biomass crops as a soil amendment in cultivated histosols: Can we reach carbon equilibrium?

AbstractPeatlands are known to perform essential economical, societal and regulating functions. Once they are drained to provide optimal crop growth conditions, however, a series of degradation processes is generated. Wind and water erosion, subsidence and soil organic matter oxidation are the main causes of degradation observed in cultivated histosols. This study evaluated the decomposition dynamics and chemical changes of three biomass crops during an in‐situ incubation in a cultivated histosol. The decomposition dynamics characterized in the field study were then used in a simulation to determine if sustainability could be reached by using biomass crops as a soil amendment. The results showed that an exponential decay fitting curve best represented the weight loss of sorghum [Sorghum bicolor (L.) Moench] in the in‐situ bags over time, while a logistic fitting curve best represented that of miscanthus (Miscanthus X giganteus) and willow (Salix miyabeana). The quality of the crop determined the initial and overall decomposition dynamics observed. The loss of carbon from the crushed biomass crop was much more important in sorghum than in miscanthus and willow. The long‐term simulation of histosol amendment revealed that using miscanthus and willow at input rates of 7.5 and 10 T of carbon per year, respectively, would be sufficient to ensure sustainability. Improving knowledge on carbon loss in cultivated histosols as related to soil and crop management would help in developing a soil amendment program at the farm scale. In addition, more knowledge is needed to determine the impact of long‐term and successive amendment with biomass crops on the physical and biochemical properties of histosols.

Effects of different foliar nitrogen fertilizers on cellular nitrogen metabolism and biomass of two shrub willow cultivars

We examined the effects of foliar supplementation of different nitrogen sources (urea, Nitamin, NH4NO3, and arginine) to study their efficacy as fertilizers for growth of two clonally propagated shrub willow cultivars; namely, ‘Fish Creek’ (Salix purpurea L.) and ‘Preble’ (Salix viminalis L. × (Salix sachalinensis F. Schmidt × Salix miyabeana Seemen)). Our objectives were to determine (i) if foliar nitrogen application is an effective method of fertilization for the two shrub willows and (ii) if different nitrogen sources are metabolized similarly by the plants. The analyses involved soluble leaf polyamines, amino acids, total protein, total nitrogen and carbon, and plant biomass in response to short-term treatments with four sources of nitrogen. The effects of foliar nitrogen application on leaf chemistry, biomass, and foliar nitrogen content varied according to the form of nitrogen used. The data indicate that (i) urea is the most suitable nitrogen source for foliar spray (29% higher N accumulation vs. Nitamin), whereas arginine is the least suitable, and (ii) different nitrogen sources are metabolized differently by the plant. While the foliar nitrogen application method could become a practical and sustainable way to fertilize shrub willows and other short-rotation biofuel crops, it may also help reduce nitrogen loss to the environment.

Co-cropping with three phytoremediation crops influences rhizosphere microbiome community in contaminated soil

Human industrial activities have left millions of hectares of land polluted with trace element metals and persistent organic pollutants (POPs) around the world. Although contaminated sites are environmentally damaging, high economic costs often discourage soil remediation efforts. Phytoremediation is a potential green technology solution but can be challenging due to the diversity of anthropogenic contaminants. Co-cropping could provide improved tolerance to diverse soil challenges by taking advantage of distinct crop capabilities. Co-cropping of three species with potentially complementary functions, Festuca arundinacea, Salix miyabeana and Medicago sativa, perform well on diversely contaminated soils. Here, rhizosphere microbiomes of each crop in monoculture and in all co-cropping combinations were compared using 16S rRNA gene amplification, sequencing and differential abundance analysis. The hyperaccumulating F. arundinacea rhizosphere microbiome included putative plant growth promoting bacteria (PGPB) and metal tolerance species, such as Rhizorhapis suberifaciens, Cellvibrio fibrivorans and Pseudomonas lini. The rhizosphere microbiome of the fast-growing tree S. miyabeana included diverse taxa involved in POP degradation, including the species Phenylobacterium panacis. The well-characterised nitrogen-fixing M. sativa microbiome species, Sinorhizobium meliloti, was identified alongside others involved in nutrient acquisition and putative yet-to-be-cultured Candidatus saccharibacteria (TM7-1 group). The majority of differentially abundant rhizosphere-associated bacterial species were maintained in co-cropping pairs, with pairs having higher numbers of differentially abundant taxa than monocultures in all cases. This was not the case when all three crops were co-cropped, where most host-specific bacterial species were not detected as differentially abundant, indicating the potential for reduced rhizosphere functionality. The crops cultivated in pairs here retained rhizosphere microbiome bacteria involved in these monoculture ecosystem services of plant growth promotion, POP tolerance and degradation, and improved nutrient acquisition. These findings provide a promising outlook of the potential for complementary co-cropping strategies for phytoremediation of the multifaceted anthropogenic pollution which can disastrously affect soils around the world.

Establishment and potential use of woody species in treatment wetlands

Plant species selection is an important criterion for improving treatment wetland performance. The aim of this work was to evaluate removal efficiency and potential uses of woody species in treatment wetlands during the establishment year. Plant development, removal efficiency and evapotranspiration rate of five woody species (Salix interior, Salix miyabeana, Sambucus canadensis, Myrica gale, Acer saccharinum) and four herbaceous taxa typically used in treatment wetlands (Typha angustifolia, Phragmites australis australis, Phragmites australis americanus, Phalaris arundinacea) were compared in a mesocosm-scale study during one growing season. Woody species showed significantly slower growth, but displayed several characteristics of interest for treatment wetland applications: good adaptation to wetlands conditions; high organic matter removal (76–88%); high nutrient accumulation in tissues and high evapotranspiration capacity. During the establishment year, herbaceous species showed greater biomass development (above- and belowground parts), higher evapotranspiration rate (>3.84 L m−2 d−1 compared to <3.23 L m−2 d−1 for woody species) and overall pollutant removal efficiency. These characteristics confirm the high efficiency of treatment wetlands planted with herbaceous species even in the first growing season. However, given their greater potential biomass development, woody species could represent an excellent alternative for improving treatment wetlands long-term performance.

Ecophysiological Responses of a Willow Cultivar (Salix miyabeana ‘SX67’) Irrigated with Treated Wood Leachate

As wood preservatives leach from exposed treated wood, they contaminate soil and water, creating an environmental problem that needs to be addressed. Treating this contamination is particularly challenging since it includes mixed compounds, such as heavy metals and trace elements, as well as xenobiotic organic pollutants like polychlorinated dibenzo-dioxin/furan congeners (PCDD/Fs) that are very toxic and are under very strict discharge regulations. Cultivating fast-growing willow shrubs, either in soil or in treatment wetlands, offers a flexible and inexpensive treatment option. The main objective of this study was to evaluate the tolerance of a frequently used willow cultivar (Salix miyabeana ‘SX67’) to irrigation with leachate contaminated with pentachlorophenol (PCP) and chromated chromium arsenate (CCA), two important wood preservatives. We designed a mesocosms experiment with willow grown in three different substrates and irrigated over 12 weeks with three different leachate concentrations. Willow proved to be tolerant to irrigation with the raw leachate, with only leaf area decreasing with increasing leachate concentration. However, the type of growing substrate influenced willow ecophysiological responses and overall performance, and seemed to affect contaminant dynamics in the plant-soil system. All contaminants accumulated in willow roots, and Cu and PCDD/Fs were also translocated to aerial parts. Overall, this study suggests that Salix miyabeana ‘SX67’ could be a good candidate for treating water or soil contaminated with wood preservatives.

Evapotranspiration of a willow cultivar (Salix miyabeana SX67) grown in a full-scale treatment wetland

Since woody plants like willow are used increasingly in treatment wetlands, there is a growing need to characterize their ecophysiology in these specific growing conditions. For instance, evapotranspiration (ET) can be greatly increased in wetlands, due to factors like high water availability as well as oasis and clothesline effects. Few studies report willow ET rates measured in full-scale constructed wetland conditions, and fewer still in a temperate North-American climate. The objective of this study was to measure and model evapotranspiration of a commonly used willow cultivar, Salix miyabeana (SX67), to provide the ET rates and crop coefficient for this species. During two growing seasons, we studied a 48 m2 horizontal subsurface flow willow wetland located in eastern Canada, irrigated with pretreated wood preservative leachate. Over two seasons, from May to October, we measured a mean monthly evapotranspiration rate of 22.7 mm/day (16.5 mm/d modelled), for a seasonal cumulative ET of 3954 mm (2897 mm modelled) and a mean crop coefficient of 6.4 (4.2 modelled). Both the evapotranspiration results and leaf area index (LAI) were greater than most results reported for open field willow plantations. Maximal stomatal conductance (G¯s) was higher than that expected for deciduous trees and even for wetland plants, and mean values correlated well with temperature, solar radiation, relative humidity and day of the year. We demonstrated that an ET model using G¯s, LAI and water vapor pressure deficit (VPD) as parameters could predict the evapotranspiration rate of our wetland. This simplification of traditional ET models illustrates the absence of evapotranspiration limitations in wetlands. Furthermore, this study also highlights some factors that can enhance ET in treatment wetlands. Our results should both improve the design of treatment wetlands using willows, and provide a simple ET predictive model based on major evapotranspiration drivers in wetlands.

Assessing the impact of fertilizer application on net soil-derived emission budgets from a temperate willow (Salix miyabeana) short rotation coppice system

Willow (Salix spp.) short-rotation coppice (SRC) systems are productive bioenergy feedstocks that can be cultivated on marginal land and generate high yields when amended with nitrogen (N) fertilizers. However, fertilizer application results in greater N2O emissions and negates the potential carbon (C) neutrality of willow bioenergy systems. We evaluated 1) the effect of N fertilizer application on the soil-atmosphere exchange of CO2-C and (N2O-N emissions, soil NH4+-N and NO3−-N); 2) emissions generated during winter and freeze-thaw cycles (FTCs); and 3) the net annual emission (CO2-equivalents [CO2-eq]) from willow SRC systems. CO2-C emissions followed seasonal trends with elevated emissions occurring in the spring and summer. Significantly greater (p < 0.05) CO2-C emissions were observed during the growing season, whereas only 7.2%–13.4% of the total CO2-C emissions occurred during the winter. Freeze-thaw cycles (FTCs) did not significantly (p < 0.05) increase CO2-C emissions. Nitrogen fertilizer application increased soil NH4+ and NO3− availability resulting in an N2O-N hot moment following fertilizer application in the spring. There was a N2O-N hot moment following FTC events, and winter N2O-N emissions were minimal. Overall, N2O-N emissions accounted for 2.2–3.4% of the total annual emissions. Willow SRC systems were a C sink in fertilized treatments with a C sequestration potential of 10.79 Mg CO2-eq ha−1 yr−1. Unfertilized treatments were a slight C source, with net emissions of 1.19 Mg CO2-eq ha−1 yr−1. We recommend a low rate of fertilizer application to willow SRC systems to maintain these systems as a long-term C sink.