Ken C. J. Van Rees

Coupling the use of computer chemical speciation models and culture techniques in laboratory investigations of trace metal toxicity

Abstract The bioavailability and toxicity of a dissolved metal are closely linked to the metal’s chemical speciation in solution. A variety of inorganic and organic ligands are often used in laboratory toxicity tests to control the concentration of labile trace metal in solution. Computerised chemical speciation models based on thermodynamic principles can be used to estimate metal speciation under such experimental conditions. However, these models are sensitive to the quality of their thermodynamic databases. Detailed protocols for the incorporation of reliable equilibrium formation constants into widely available computer chemical speciation programs (e.g., MINEQL+ and MINTEQ) are provided. The examples demonstrate both the benefits and the potential pitfalls involved in the use of chemical speciation models. The application of chemical speciation modelling to metal toxicity studies is discussed and guidelines are proposed for its proper use. Both defined media and chemical speciation programs have co-existed for two decades but the combined use of these techniques has been reserved for those possessing in-depth knowledge of both chemistry and biology. The techniques presented should enable an investigator with basic biological, chemical and computing skills to design an aqueous medium and incorporate correct thermodynamic constants into a computer chemical speciation program, starting from a standardised database, thereby providing a sound framework for critically assessing the biological response of a particular test organism to a given metal.

The carbon implications of large-scale afforestation of agriculturally marginal land with short-rotation willow in Saskatchewan.

Afforestation with short‐rotation coppice (SRC) willow plantations for the purpose of producing bioenergy feedstock was contemplated as one potential climate change mitigation option. The objectives of this study were to assess the magnitude of this mitigation potential by addressing: (i) the land area potentially available for SRC systems in the province of Saskatchewan, Canada; (ii) the potential biomass yields of SRC plantations; and (iii) the carbon implications from such a large‐scale afforestation program. Digital soils and land‐use data were used to identify, map, and group into clusters of similar polygons 2.12 million hectares (Mha) of agriculturally marginal land that was potentially suitable for willow in the Boreal Plains and Prairies ecozones in Saskatchewan. The Physiological Principles in Predicting Growth (3PG) model was calibrated with data from SRC experiments in Saskatchewan, to quantify potential willow biomass yields, and the Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3), was used to simulate stand and landscape‐level C fluxes and stocks. Short‐rotation willow plantations managed in 3 year rotations for seven consecutive harvests (21 years) after coppicing at Year 1 produced about 12 Mg ha−1 yr−1 biomass. The more significant contribution to the C cycle was the cumulative harvest. After 44 years, the potential average cumulative harvested biomass C in the Prairies was 244 Mg C ha−1 (5.5 Mg C ha−1 yr−1) about 20% higher than the average for the Boreal Plains, 203 Mg C ha−1 (4.6 Mg C ha−1 yr−1). This analysis did not consider afforestation costs, rate of establishment of willow plantations, and other constraints, such as drought and disease effects on biomass yield. The results must therefore be interpreted as a biophysical mitigation potential with the technical and economic potential being both lower than our estimates. Nevertheless, short‐rotation bioenergy plantations offer one potential mitigation option to reduce the rate of CO2 accumulation in the earths atmosphere and further research is needed to operationalise such a mitigation effort.

Genotype × environment interaction analysis of North American shrub willow yield trials confirms superior performance of triploid hybrids

Development of dedicated bioenergy crop production systems will require accurate yield estimates, which will be important for determining many of the associated environmental and economic impacts of their production. Shrub willow (Salix spp) is being promoted in areas of the USA and Canada due to its adaption to cool climates and wide genetic diversity available for breeding improvement. Willow breeding in North America is in an early stage, and selection of elite genotypes for commercialization will require testing across broad geographic regions to gain an understanding of how shrub willow interacts with the environment. We analyzed a dataset of first‐rotation shrub willow yields of 16 genotypes across 10 trial environments in the USA and Canada for genotype‐by‐environment interactions using the additive main effects and multiplicative interactions (AMMI) model. Mean genotype yields ranged from 5.22 to 8.58 oven‐dry Mg ha−1 yr−1. Analysis of the main effect of genotype showed that one round of breeding improved yields by as much as 20% over check cultivars and that triploid hybrids, most notably Salix viminalis × S. miyabeana, exhibited superior yields. We also found important variability in genotypic response to environments, which suggests specific adaptability could be exploited among 16 genotypes for yield gains. Strong positive correlations were found between environment main effects and AMMI parameters and growing environment temperatures. These findings demonstrate yield improvements are possible in one generation and will be important for developing cultivar recommendations and for future breeding efforts.

Fine root dynamics of trembling aspen in boreal forest and aspen parkland in central Canada

Abstract• Fine root responses to potential climate change are relatively unknown in spite of their central role in ecosystem functioning.• We quantified fine root length, production, and turnover in boreal forest and aspen parkland of central Canada because the future climate of the boreal site is expected to be similar to the current climate of the parkland site.• Root depth distribution and turnover were similar between sites. Fine root mass was 4× greater at the parkland site and root length was 10× greater. Accordingly, the ecosystem level fine root: leaf mass ratio was 1.6 in the boreal site compared to 4.3 in the parkland site. On a per tree basis, however, fine root biomass was similar between sites due to the higher stem density of the parkland site.• The parkland site had a greater proportion of very fine roots (62% of the fine roots were < 0.1 mm in diameter) compared with the boreal site (82% of the fine roots were between 0.1–0.5 mm in diameter).• These differences indicate a large-scale shift towards increased root allocation at the parkland site associated with decreasing water availability and earlier successional stage.

Agroforestry Research and Development in Canada: The Way Forward

The purpose of this chapter is to describe the history and current status of agroforestry research and practices across Canada and provide recommendations as “the way forward.” Each of the five regions (the Atlantic Region, Quebec, Ontario, the Prairies, and British Columbia) has unique climates, soils, landforms, and natural resource management systems. The influence of these factors has resulted in different agroforestry practices and approaches to their application in each region. For example, the riparian buffer systems are promoted for the Atlantic Region; tree-based intercropping and windbreak systems in Quebec, Ontario, and in the Prairies; and silvopastoral systems in British Columbia. European settlement, beginning in the late 1700s, initiated the conversion of much of eastern Canada from native forest into agricultural land. As farming practices modernized across the country, new environmental problems (e.g., soil erosion and loss of wildlife habitat) and new socioeconomic issues (e.g., loss of income diversity) emerged. Recently, Canadian citizens have become increasingly concerned with potential ecological impacts of agricultural production, and the policy has moved toward fostering stewardship initiatives that address not only environmental goods and services but also climate change issues with a special emphasis on carbon sequestration. Agroforestry is perceived to be able to provide benefits in these areas; however, the problems and their potential solutions are different in different regions. Each region faces a unique set of challenges and constraints related to lack of knowledge, high initial capital and labor costs, farm operational issues, resource tenure, lack of niche markets, and lack of incentives.

Nutrient uptake of hybrid poplar in competition with weeds using the soil supply and nutrient demand (SSAND) model

Mechanistic nutrient uptake models can help gain a quantitative understanding of nutrient uptake by plants under weed-competing conditions. The objectives of this study were to check the applicability of the soil supply and nutrient demand (SSAND) model to predict N, P and K uptake by hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) grown with and without competition with dandelion (Taraxacum officinale) and quackgrass (Elymus repens) in a controlled environment, and to determine if incorporating N mineralization into the model would improve N uptake predictions. Simulation results showed that N uptake was underestimated for hybrid poplar by 58 to 73%, depending upon soil type and weed treatment. Incorporation of N mineralization as a model input improved the hybrid poplar N uptake predictions by 24 and 67% in the pasture and alfalfa soil, respectively, when grown without weeds. The SSAND model underestimated P uptake by 84 to 89% and overestimated K uptake by 28 to 59% for hybrid po...

Soil organic carbon sequestration by shelterbelt agroforestry systems in Saskatchewan1

Abstract: Carbon (C) sequestration through the implementation of agroforestry practices is identified as one of the major strategies in the reduction of carbon dioxide (CO2) emissions from the agricultural sector. The objective of this study was to examine the soil organic carbon (SOC) sequestration potential of major shelterbelt species, including green ash (Fraxinus pennsylvanica), hybrid poplar (Populus spp.), Manitoba maple (Acer negundo), white spruce (Picea glauca), Scots pine (Pinus sylvestris), and caragana (Caragana arborescens), ranging in age from 5 to 63 yr. Soil samples (0–50 cm) were collected for six major shelterbelt species and adjacent agricultural fields, and SOC concentration was determined. Shelterbelts had a significantly higher amount of SOC compared with adjacent agricultural fields, with an average difference of 18.6 Mg C ha-1 in the top 50 cm soil. An additional 3–8 Mg C ha-1 was contained in the tree litter layer. Younger shelterbelts (age less than 20 yr) tended to lose SOC in the early years of shelterbelt establishment. However, the SOC accrual was positively related to shelterbelt stand age. Besides stand age, other shelterbelt stand characteristics, including tree height and diameter, crown width, and amount of surface litter, were also positively correlated with the increase in SOC concentration. The findings of this study support the hypothesis that shelterbelts can lead to a significant amount of SOC sequestration in agroecosystems.

Accurate and Precise Measurement of Organic Carbon Content in Carbonate-Rich Soils

Accurate measurement of soil organic carbon (SOC) is dependent on precise and fast methods for the separation of organic and inorganic carbon. The widely used methods involving thermal decomposition of soil samples at a specific temperature in an automated carbon (C) analyzer are susceptible to interference by carbonates and overestimation of organic C, and thus removal of carbonates by acid pretreatment of samples is recommended. Two carbonate-removal pretreatments including hydrochloric (HCl) acid addition and HCl fumigation are compared using the calcium carbonate (CaCO3) standard and soil samples of varying SOC contents. Both pretreatment methods provided similar measurements of organic C, indicating that both methods are efficient in removal of carbonates present in the soil. However, the HCl fumigation method exhibited greater accuracy and precision compared to the HCl addition method. Hence, SOC measurement procedure involving HCl fumigation as a pretreatment for the removal of carbonates is recommended for carbonate-rich soils.

Preventing unwanted spread of invasive fungal species in willow (Salix spp.) plantations

Abstract In North America, biomass production of fast-growing trees represents an important forestry and agroforestry practice for bioenergy, bioproducts and phytoremediation. In Canada, imported cuttings are used as the propagation material to establish Short Rotation Intensive Culture (SRIC) of willow. Profiling the mycodiversity of willow cuttings is vital for early diagnosis, prevention or control of exotic diseases. It also helps to identify disease tolerant willow genotypes to increase the survival rate of cuttings and the establishment of high-density tree plantations, free of introduction of alien pathogenic species to the Canadian ecosystems. In this study, a total of 82 fungal taxa were isolated and identified from asymptomatic willow cuttings imported in Canada. The most abundant phylum was Ascomycota, although some Basidiomycota (Agaricales and Tremellales) were also detected. The most abundant fungal taxa belonged to Hypocreales, while the most abundant species belonged to Kabatiella in Dothideales. In vitro and in planta bioassays results, combined with polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) analyses, revealed that potentially pathogenic species belonging to Glomeraceae, Dermateaceae, Diaporthaceae and Venturiaceae may originate from the willow cuttings, which could be transmitted to tree plantations and spread via standard management and coppice practices. A newly discovered Lecythophora–Coneochaeta complex was the most frequently observed. Pathogenic Cadophora spp. were also detected; they are a potential threat to the health of willow during long cold-storage of cuttings. Among cultivars, SV1 (Salix dasyclados) showed low infection rates and demonstrates the possibility of risk stratification according to willow genotypes.

Gas chromatographic analysis of low molecular weight organic acids in roots and shoots of durum wheat plants

Low molecular weight organic acids (LMWOAs) in plant tissue have been shown to play a role in plant response to metals. Therefore, there is a need for effective analytical methods capable of quantitating LMWOAs in plants. Several solvents were examined for the efficiency of the LMWOA extraction from plant tissue of durum wheat (Triticum turgidum var. durum) and for the suitability of the resulting extracts for the gas chromatographic (GC) analysis. Water, 1 N HCl, 0.5 N KCl, 0.5 N HCl in MeOH at room temperature, and water and 1 N HCl at 100°C were tested. Increased temperature and use of 1 N HCl improved the recovery of most of the LMWOAs as compared to water or KCl extractions at room temperature. However, recovery of fumaric and t-aconitic acids was lowered by the addition of HCl and/or increased temperature of extraction probably because of the instability of the double bond. The highest efficiency for oxalic acid was obtained with HCl/MeOH extraction; however, the chromatograms contained many peaks interfering with those of other LMWOAs, rendering this extractant unsuitable for the GC analysis. Thus the extraction with 1 N HCl at room temperature was found to be the most suitable; 1 N HCl removed the majority of the acids studied without artifacts appearing in the chromatograms. Non-volatile LMWOAs were analyzed by GC after sample trimethylsilylation (TMS) and after sample methylation, while volatile LMWOAs were injected directly into the GC without sample derivatization. The combination of the three chromatographic separations allowed for the determination of oxalic, malonic, succinic, fumaric, malic, t-aconitic, citric, acetic, and propionic acids in roots and shoots of wheat plants. This method was applied to two durum wheat cultivars, i.e., Kyle and Arcola grown hydroponically for two weeks. LMWOA concentrations were greater in shoots than in roots for both cultivars. Individual and total LMWOA concentrations in roots and shoots did not differ significantly between cultivars. Further studies are needed to identify the factors controlling LMWOA production in plant tissue and its significance in processes occurring in plants and at the root/soil interface.