Phosphorus Mobilizing Enzymes of Alnus-Associated Ectomycorrhizal Fungi in an Alaskan Boreal Floodplain

Effect of an Ectomycorrhizal Fungus on the Growth of Castanea henryi Seedlings and the Seasonal Variation of Root Tips’ Structure and Physiology

Castanea henryi is a ubiquitous hardwood chestnut species in southern China and is important both ecologically and economically. It is mainly cultivated for nut production, just like other chestnut species. However, the establishment of C. henryi seedlings in a new orchard has proven to be difficult because few seedlings survive transplanting due to the incompatibility of their coarse root architecture with nutrient-depleted red acid soils in southern China. Root architecture can be profoundly modified and nutrient can be stress alleviated due to the association of roots with ectomycorrhizal (ECM) fungi. Boletus edulis is an ECM fungus with edible and medicinal fruiting bodies. However, its impact on plant growth varies with the plant species it is associated with. In order to elucidate the role of B. edulis in C. henryi afforestation, we evaluated growth parameters and soil enzymatic activities, as well as seasonal variations in physiology and structure of ECM root tips. Growth responses and soil enzymatic activities were measured 6 months after inoculation. The physiological characteristics of root tips were also compared at various seasons throughout the year. B. edulis colonization of C. henryi roots was successful at a 60% colonization rate. Height, base diameter, and biomass (especially the underground part) of inoculated seedlings (JG) were higher than those of uninoculated seedlings (CK). JG had higher root total length, root surface area, root volume, root average diameter, and number of root tips than CK. Additionally, JG exhibited higher total nitrogen and phosphorus content. Abnormal mantle and Harting net were observed in winter. No matter the season, ECM tips had higher antioxidant enzyme activities, root activities, soluble protein content, and lower malondialdehyde compared to non-ECM tips (nE) and those without ECM tips (woE), and there were no differences between nE and woE. It is important to understand the growth of the host plant in response to ECM and that the seasonal variation of ECM root tips is important when growing high-quality C. henryi seedlings, due to the crucial role of B. edulis in improving seedling initial survival rate.

Ectomycorrhizas and tipping points in forest ecosystems

The resilience of forests is compromised by human-induced environmental influences pushing them towards tipping points and resulting in major shifts in ecosystem state that might be difficult to reverse, are difficult to predict and manage, and can have vast ecological, economic and social consequences. The literature on tipping points has grown rapidly, but almost exclusively based on aquatic and aboveground systems. So far little effort has been made to make links to soil systems, where change is not as drastically apparent, timescales may differ and recovery may be slower. Predicting belowground ecosystem state transitions and recovery, and their impacts on aboveground systems, remains a major scientific, practical and policy challenge. Recently observed major changes in aboveground tree condition across European forests are probably causally linked to ectomycorrhizal (EM) fungal changes belowground. Based on recent breakthroughs in data collection and analysis, we apply tipping point theory to forests, including their belowground component, focusing on EM fungi; link environmental thresholds for EM fungi with nutrient imbalances in forest trees; explore the role of phenotypic plasticity in EM fungal adaptation to, and recovery from, environmental change; and propose major positive feedback mechanisms to understand, address and predict forest ecosystem tipping points.

Limited overall impacts of ectomycorrhizal inoculation on recruitment of boreal trees into Arctic tundra following wildfire belie species-specific responses

We tested whether post-fire seedling establishment of common boreal tree and expanding shrub species at treeline and in Arctic tundra is facilitated by co-migration of boreal forest mycorrhizal fungi. Wildfires are anticipated to facilitate biome shifts at the forest-tundra ecotone by improving seedbed conditions for recruiting boreal species; at the same time fire alters the composition and availability of mycorrhizal fungi critical to seedling performance. To determine the role of root-associated fungi (RAF) in post-fire seedling recruitment and future biome shifts, we outplanted four dominant boreal tree and shrub species inoculated with one of three treatments at treeline and in tundra: burned boreal forest, unburned boreal forest, or a control treatment of sterilized inoculum. We compared survivorship, growth, and physiological performance of the seedlings in relation to mycorrhizal inoculum treatment and among host species, characterized the RAF communities based on ITS-rDNA sequencing of individual root tips sampled from surviving seedlings, and tested for correlations between RAF composition and the inoculation treatments, host species, and duration of the experiment. We explored correlations between RAF composition and seedling metrics. Both live and sterile autoclaved inoculation treatments had similar effects on seedling survivorship and growth for all species. RAF composition did not vary by treatment, suggesting that most colonization was due to local fungi. However, seedling traits and growth were correlated with RAF species composition, colonization, and the relative abundance of specific RAF taxa. Picea sp. performance in particular showed strong co-variation with RAF metrics. Our results suggest that mycorrhizal co-migration is not a primary limiting factor to boreal seedling recruitment because the experimental provision of inoculum did not affect seedling recruitment; yet, RAF did influence seedling performance, particularly resident RAF at treeline and in tundra, suggesting that mycorrhizal fungi are important to vegetation processes at the treeline-tundra ecotone.

Ectomycorrhizal Fungi: Participation in Nutrient Turnover and Community Assembly Pattern in Forest Ecosystems

Ectomycorrhizal fungi (EcMF) are involved in soil nutrient cycling in forest ecosystems. These fungi can promote the uptake of nutrients (e.g., nitrogen (N) and phosphorus (P)) and water by host plants, as well as facilitate host plant growth and resistance to stresses and diseases, thereby maintaining the aboveground primary productivity of forest ecosystems. Moreover, EcMF can acquire the carbon (C) sources needed for their growth from the host plants. The nutrient regulation mechanisms of EcMF mainly include the decay of soil organic matter via enzymatic degradation, nonenzymatic mechanism (Fenton chemistry), and priming effects, which in turn promote C and N cycling. At the same time, EcMF can secrete organic acids and phosphatases to improve the availability of soil P, or increase mycelium inputs to facilitate plant acquisition of P. The spatiotemporal distribution of EcMF is influenced by a combination of historical factors and contemporary environmental factors. The community of EcMF is associated with various factors, such as climate change, soil conditions, and host distribution. Under global climate change, investigating the relationships between the nutrient cycling functions of EcMF communities and their distribution patterns under various spatiotemporal scales is conducive to more accurate assessments of the ecological effects of EcMF on the sustainable development of forest.