Ecological responses to forest age, habitat, and host vary by mycorrhizal type in boreal peatlands

Abstract

Despite covering vast areas of boreal North America, the ecological factors structuring mycorrhizal fungal communities in peatland forests are relatively poorly understood. To assess how these communities vary by age (younger vs. mature), habitat (fen vs. bog), and host (conifer trees vs. ericaceous shrub), we sampled the roots of two canopy trees (Larix laricina and Picea mariana) and an ericaceous shrub (Ledum groenlandicum) at four sites in northern Minnesota, USA. To characterize the specific influence of host co-occurrence on mycorrhizal fungal community structure, we also conducted a greenhouse bioassay using the same three hosts. Root samples were assessed using Illumina-based high-throughput sequencing (HTS) of the ITS1 rRNA gene region. As expected, we found that the relative abundance of ectomycorrhizal fungi was high on both Larix and Picea, whereas ericoid mycorrhizal fungi had high relative abundance only on Ledum. Ericoid mycorrhizal fungal richness was significantly higher in mature forests, in bogs, and on Ledum hosts, while ectomycorrhizal fungal richness did not differ significantly across any of these three variables. In terms of community composition, ericoid mycorrhizal fungi were more strongly influenced by host while ectomycorrhizal fungi were more influenced by habitat. In the greenhouse bioassay, the presence of Ledum had consistently stronger effects on the composition of ectomycorrhizal, ericoid, and ericoid-ectomycorrhizal fungal communities than either Larix or Picea. Collectively, these results suggest that partitioning HTS-based datasets by mycorrhizal type in boreal peatland forests is important, as their responses to rapidly changing environmental conditions are not likely to be uniform.

Arbuscular Mycorrhizal Fungal Communities Are Influenced by Host Tree Species on the Loess Plateau, Northwest China

“…Mycorrhizal colonization rate, species richness, and spore density were dependent on the identity of tree species'. This finding concurs with other studies reporting that the host plant affects the composition and diversity of AM fungal communities across various ecosystems, including deserts, tropical zones, and peatlands [11,16,44]. Such effects may arise from differences in fundamental traits of host plants, such as the root morphology and structure of tree species [45,46], which could have affected the likelihood of mycorrhizal formation among fungal taxa.…”

Melanin mitigates the accelerated decay of mycorrhizal necromass with peatland warming

“…in this peatland (Kennedy et al . ), it is plausible to expect increased non‐melanised necromass inputs that are highly labile compared to the recalcitrant inputs produced by Cenococcum geophilum . These host‐mediated responses to warming, along with those of the ericaceous shrubs, may also play a key role in determining the amount of necromass C that is quickly mineralised versus the amount entering stable belowground C pools.…”

“…and Larix laricina (Du Roi) K. Koch, both of which are well‐colonised by EM fungi at the site (Kennedy et al . ). The understory shrub communities are primarily composed of ericaceous shrubs such as Rhododendron groenlandicum Oeder and Chamaedaphne calyculata (L.) Moench that all host ERM fungi (Kennedy et al .…”

“…The understory shrub communities are primarily composed of ericaceous shrubs such as Rhododendron groenlandicum Oeder and Chamaedaphne calyculata (L.) Moench that all host ERM fungi (Kennedy et al . ). The bryophyte layer is dominated by Sphagnum angustifolium (C.E.O.…”

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

“…In our study, the presence of ericaceous shrubs (associated with ericoid fungi) close to fir saplings rather affected their root EMF communities than reduced the ramification index. Numerous studies have already shown how ericaceous shrubs affect EMF communities associated with trees, such as red oak ( Quercus rubra L.), hemlock (Walker et al, 1999), pine ( Pinus strobus L., P. sylvestris L.) (Kohout et al, 2011), and black spruce (Yamasaki et al, 1998; Kennedy et al, 2018). In the boreal forest, ericaceous shrubs not only compete with fir growth and nutrition, but also modify forest dynamics and lead to thick accumulation of soil organic matter and soil acidification.…”