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.

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Riparian zones provide multiple benefits, including streambank stabilization and nutrient abatement. However, there is a knowledge gap on how the type of vegetation and environmental factors (e.g., soil temperature, moisture) within the riparian zone influence CO 2 and CH 4 emissions. Our objective was to quantify and compare CO 2 and CH 4 emissions from a herbaceous (grass) riparian zone (GRS), a rehabilitated riparian zone composed of deciduous trees, an undisturbed natural forested riparian zone with deciduous trees (UNF-D) or coniferous trees (UNF-C), and an agricultural field. Cumulative soil CO 2 emission ranged from 23 to 105 g CO 2 -C m -2 . Carbon dioxide emissions were greatest (p < .05) in the GRS zone and lowest (p < .05) in the UNF-C riparian zone. The best predictors for CO 2 emissions were soil temperature and soil organic carbon (SOC) content. Cumulative CH 4 emission ranged from -23 to 253 g CH 4 -C m -2 . Methane emissions were greatest (p < .05) in the UNF-D and lowest (p < .05) in the GRS riparian zone. The best predictors for CH 4 emissions were soil moisture, SOC, and photosynthetic photon flux density. The total CO 2 -C equivalent (i.e., CH 4 + CO 2 ) was greatest (p < .05) for the GRS and lowest (p < .05) for the UNF-C riparian zone. The environmental factors controlling CO 2 and CH 4 emissions within the various riparian zones did not change; instead, changes were due to how vegetation within riparian zones influenced these controls. INTRODUCTIONRiparian zones play a crucial role in regulating nutrient dynamics between terrestrial and aquatic environments in agricultural landscapes (Cole et al., 2020). Although ripar-Abbreviations: AGR, agricultural field; GHG, greenhouse gas; GRS, herbaceous (grassed) riparian zone; PPFD, photosynthetic photon flux density; RH, rehabilitated riparian zone composed of deciduous trees; SOC, soil organic carbon; UNF-C, undisturbed natural forested riparian zone composed of coniferous trees; UNF-D, undisturbed natural forested riparian zone composed of deciduous trees.

The sustainability of purpose-grown biomass production on marginal lands in Canada is uncertain. In this study, an assessment of biomass yield and sustainability was performed for two poplar clones (Poplus deltoides × P. nigra, DN-34-PDN, and P. nigra × P. maximowiczii, NM-6-PNM) and two switchgrass cultivars (Panicum virgatum 'Cave-in-Rock'-SGC, and P. virgatum 'Nebraska'-SGN) on three marginal lands in Guelph (ON), Kemptville (ON), and Nappan (NS) in Canada. The differences in stem biomass across sites were not significant; however, differences in stem biomass among plants were statistically significant between poplar and switchgrass (p < 0.0001) and between poplar clones (p < 0.0001). The 2-yr stem biomass yield in PNM (15.27 ± 1.28 t ha −1 ) was significantly higher than those in PDN (7.02 ± 0.54 t ha −1 ), SGC (2.57 ± 0.28 t ha −1 ), and SGN (1.45 ± 0.22 t ha −1 ). Two sustainability indices based on macronutrients (MBSI) and nitrogen (NBSI), were developed to assess sustainability. Both indices show that the biomass production system of high-yielding poplar clone PNM depicts nutrient loss and may require external nutrient inputs via fertilization during the establishment phase. Higher index values for switchgrass SGC (1.47 ± 0.22, 1.11 ± 0.15) and SGN (1.37 ± 0.16, 1.17 ± 0.12) for MBSI and NBSI, respectively, indicate that despite low stem biomass yields, switchgrass biomass production is sustainable. These findings suggest that, from a nutrient perspective, sustainable biomass production systems can be established on marginal lands in Canada; however, there is a trade-off between high yield and long-term sustainability in purpose-grown biomass production systems.Key words: marginal lands, nutrient, poplar, sustainability, switchgrass.Résumé : On ignore dans quelle mesure la production de biomasse sur les terres marginales du Canada serait une activité durable. La présente étude évalue le rendement de la biomasse et la pérennité de deux clones de peuplier (Poplus deltoides × P. nigra, DN-34 -PDN, et P. nigra × P. maximowiczii, NM-6 -PNM) ainsi que de deux cultivars de panic raide (Panicum virgatum cv. Cave-in-Rock -SGC et Panicum virgatum cv. Nebraska -SGN) sur trois terres peu productives situées à Guelph (ON), à Kemptville (ON) et à Nappan (NS), au Canada. La biomasse des tiges n'a pas varié de façon significative aux trois endroits, cependant, l'écart entre la biomasse des peupliers et celle du panic raide est statistiquement significatif (p < 0,0001), de même que l'écart entre la biomasse des deux clones de peuplier (p < 0,0001). Le rendement en biomasse de PNM au cours des deux années de l'étude (15,27 ± 1,28 t par hectare) était sensiblement plus important que celui de PDN (7,02 ± 0,54 t par hectare), de SGC (2,57 ± 0,28 t par hectare) et de SGN (1,45 ± 0,22 t par hectare). Les auteurs ont élaboré deux indices pour évaluer la pérennité d'après la concentration de macronutriments (MBSI) et celle d'azote (NBSI). Les deux indices révèlent que la production de For personal use only.biomasse ...