Paludification reduces black spruce growth rate but does not alter tree water use efficiency in Canadian boreal forested peatlands

Abstract

Background Black spruce (Picea mariana (Mill.) BSP)-forested peatlands are widespread ecosystems in boreal North America in which peat accumulation, known as the paludification process, has been shown to induce forest growth decline. The continuously evolving environmental conditions (e.g., water table rise, increasing peat thickness) in paludified forests may require tree growth mechanism adjustments over time. In this study, we investigate tree ecophysiological mechanisms along a paludification gradient in a boreal forested peatland of eastern Canada by combining peat-based and tree-ring analyses. Carbon and oxygen stable isotopes in tree rings are used to document changes in carbon assimilation rates, stomatal conductance, and water use efficiency. In addition, paleohydrological analyses are performed to evaluate the dynamical ecophysiological adjustments of black spruce trees to site-specific water table variations. Results Increasing peat accumulation considerably impacts forest growth, but no significant differences in tree water use efficiency (iWUE) are found between the study sites. Tree-ring isotopic analysis indicates no iWUE decrease over the last 100 years, but rather an important increase at each site up to the 1980s, before iWUE stabilized. Surprisingly, inferred basal area increments do not reflect such trends. Therefore, iWUE variations do not reflect tree ecophysiological adjustments required by changes in growing conditions. Local water table variations induce no changes in ecophysiological mechanisms, but a synchronous shift in iWUE is observed at all sites in the mid-1980s. Conclusions Our study shows that paludification induces black spruce growth decline without altering tree water use efficiency in boreal forested peatlands. These findings highlight that failing to account for paludification-related carbon use and allocation could result in the overestimation of aboveground biomass production in paludified sites. Further research on carbon allocation strategies is of utmost importance to understand the carbon sink capacity of these widespread ecosystems in the context of climate change, and to make appropriate forest management decisions in the boreal biome.

Estimation of carbon stock and emission of community forests in Eastern Amhara, Ethiopia

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Nonlinear Growth and Physiological Responses of White Spruce at North American Arctic Treeline

“…After 1970, white spruce trees shifted their gas exchange strategy and exhibited an active stomatal regulation by maintaining a constant c i / c a ratio that translated to an increase in i WUE of ∼11%–12% at both sites. This limited increase in i WUE of ∼11%–12% over the period 1901–2003/2004 contrasts with the average increase of 26% in i WUE found for conifers over the 20th century in Europe (Saurer et al., 2014) and the ∼30%–40% increases reported for white and black spruce in North American boreal forests (Beaulne et al., 2021; Sullivan et al., 2017).…”

Root adaptations of black spruce growing in water-saturated soil

“…Black spruce (Picea mariana (Mill.) BSP) is the main tree species growing in Canadian peatlands (Beaulne et al 2021;Zoltai et al 1988). Black spruce generally exhibits its best growth on welldrained and mesic soils, but it can also grow well on both dry and wet sites (Klinka et al 2002).…”