The forest floor of boreal forest stores large amounts of organic C that may react to a warming climate and increased N deposition. It is therefore crucial to assess the impact of these factors on the temperature sensitivity of this C pool to help predict future soil CO₂ emissions from boreal forest soils to the atmosphere. In this study, soil warming (+2–4°C) and canopy N addition (CNA; +0.30–0.35 kg·N·ha^-1·yr^-1) were replicated along a topographic gradient (upper, back and lower slope) in a boreal forest in Quebec, Canada. After nine years of treatment, the forest floor was collected in each plot, and its organic C composition was characterized through solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy. Forest floor samples were incubated at four temperatures (16, 24, 32 and 40°C) and respiration rates (RR) measured to assess the temperature sensitivity of forest floor RR (Q₁₀ = e^10k) and basal RR (B). Both soil warming and CNA had no significant effect on forest floor chemistry (e.g., C, N, Ca and Mg content, amount of soil organic matter, pH, chemical functional groups). The NMR analyses did not show evidence of significant changes in the forest floor organic C quality. Nonetheless, a significant effect of soil warming on both the Q₁₀ of RR and B was observed. On average, B was 72% lower and Q₁₀ 45% higher in the warmed, versus the control plots. This result implies that forest floor respiration will more strongly react to changes in soil temperature in a future warmer climate. CNA had no significant effect on the measured soil and respiration parameters, and no interaction effects with warming. In contrast, slope position had a significant effect on forest floor organic C quality. Upper slope plots had higher soil alkyl C:O-alkyl C ratios and lower B values than those in the lower slope, across all different treatments. This result likely resulted from a relative decrease in the labile C fraction in the upper slope, characterized by lower moisture levels. Our results point towards higher temperature sensitivity of RR under warmer conditions, accompanied by an overall down-regulation of RR at low temperatures (lower B). Since soil C quantity and quality were unaffected by the nine years of warming, the observed patterns could result from microbial adaptations to warming.

Allometric equations use easily measurable biometric variables to determine the aboveground and belowground biomasses of trees. Equations produced for estimating the biomass within Canadian forests at a large scale have not yet been validated for eastern Canadian boreal open woodlands (OWs), where trees experience particular environmental conditions. In this study, we harvested 167 trees from seven boreal OWs in Quebec, Canada for biomass and allometric measurements. These data show that Canadian national equations accurately predict the whole aboveground biomass for both black spruce and jack pine trees, but underestimated branches biomass, possibly owing to a particular tree morphology in OWs relative to closed-canopy stands. We therefore developed ad hoc allometric equations based on three power models including diameter at breast height (DBH) alone or in combination with tree height (H) as allometric variables. Our results show that although the inclusion of H in the model yields better fits for most tree compartments in both species, the difference is minor and does not markedly affect biomass C stocks at the stand level. Using these newly developed equations, we found that carbon stocks in afforested OWs varied markedly among sites owing to differences in tree growth and species. Nine years after afforestation, jack pine plantations had accumulated about five times more carbon than black spruce plantations (0.14 vs. 0.80 t C·ha⁻¹), highlighting the much larger potential of jack pine for OW afforestation projects in this environment.

Canada is one of the world’s largest producers of oat (Avena sativa L.) grains and their derivatives, such as oat flakes. During oat flake production, considerable amounts of residue are generated, which constitutes a major issue for producers. We applied life cycle assessment (LCA): (1) to quantify the environmental impacts of oat flakes production in northeastern Canada and (2) to compare two agro-industrial symbiosis scenarios applied to agricultural residues (transformation of residues into feed for farm animals vs. composting). LCA results indicated that the environmental impacts of oat flake production are largely dominated by the production and use of synthetic fertilisers (contributing to at least 50% of the impact of each evaluated category). Regarding end-of-life scenarios, an environmental advantage is observed for the scenario of residue transformation into animal feed in the provinces of Quebec and Manitoba. However, this recommendation may change depending on the electricity mix used and the assumptions made for the avoided products. The choice of industrial symbiosis chains must take into consideration the economic characteristics of the region where they will be implemented and the methodological parameters that can influence the decision-making process.