Facilitation of Balsam Fir by Trembling Aspen in the Boreal Forest: Do Ectomycorrhizal Communities Matter?

Abstract

Succession is generally well described above-ground in the boreal forest, and several studies have demonstrated the role of interspecific facilitation in tree species establishment. However, the role of mycorrhizal communities for tree establishment and interspecific facilitation, has been little explored. At the ecotone between the mixed boreal forest, dominated by balsam fir and hardwood species, and the boreal forest, dominated by black spruce, several stands of trembling aspen can be found, surrounded by black spruce forest. Regeneration of balsam fir seems to have increased in the recent decades within the boreal forest, and it seems better adapted to grow in trembling aspen stands than in black spruce stands, even when located in similar abiotic conditions. As black spruce stands are also covered by ericaceous shrubs, we investigated if differences in soil fungal communities and ericaceous shrubs abundance could explain the differences observed in balsam fir growth and nutrition. We conducted a study centered on individual saplings to link growth and foliar nutrient concentrations to local vegetation cover, mycorrhization rate, and mycorrhizal communities associated with balsam fir roots. We found that foliar nutrient concentrations and ramification indices (colonization by mycorrhiza per length of root) were greater in trembling aspen stands and were positively correlated to apical and lateral growth of balsam fir saplings. In black spruce stands, the presence of ericaceous shrubs near balsam fir saplings affected ectomycorrhizal communities associated with tree roots which in turn negatively correlated with N foliar concentrations. Our results reveal that fungal communities observed under aspen are drivers of balsam fir early growth and nutrition in boreal forest stands and may facilitate ecotone migration in a context of climate change.

Role of Mixed-Species Stands in Attenuating the Vulnerability of Boreal Forests to Climate Change and Insect Epidemics

“…Two potential explanations may be proposed for this unexpected result. First, within the study area, Nagati et al (2019) found a spatial association between balsam fir and trembling aspen linked to higher litter nutrient availability, which supports mycorrhizal communities associated with balsam fir. In our plots, we noticed the presence of balsam fir regeneration mainly in aspen dominated stands and we hypothesized that this presence may have contributed to the concentration of SBW on the nearby available spruce trees.…”

Responses of Soil Fungal Communities to Lime Application in Wheat Fields in the Pacific Northwest

“…Helotiaceae is a small group of fungicolous, lichenicolous, and discomycetes members (Zhuang, 2000) and was reported to be positively correlated with soil carbon accumulation (Zhang et al, 2017). Nagati et al (2019) found that higher abundance of Helotiaceae was associated with the lower N nutrition of balsam fir near ericaceous shrubs. Moreover, previous studies reported that soil C:N ratio significantly increased with liming and the effect of liming on soil fungal community was closely tied to the way liming affected the C:N ratio (Melvin et al, 2013;Suz et al, 2014).…”

Factors explaining the composition and diversity of vascular plant understories along a transcontinental gradient in the Canadian boreal forest

“…In North America, an increase in aspen‐dominated boreal forests is expected in response to global changes in climate and associated natural (fires) and anthropic (forestry) disturbance regimes (Laquerre et al, 2009; Johnstone et al, 2010). Because it exerts a strong impact on its environment, aspen might contribute to changing ecosystem attributes and favour migration of species better adapted to climate change (Nagati et al, 2019; Barbé et al, 2020). Improving our understanding of how deterministic processes and adaptation to disturbance and climatic conditions structure understorey community composition is therefore important to adapt forest conservation and management.…”