The vegetative propagation of ectomycorrhizal truffle fungi is limited by their slow mycelial growth. Many factors including media, isolate genotypes and environmental conditions can alter fungal mycelial growth rates. This study aimed to improve the in vitro growth rate of Tuber brumale by determining the optimal carbohydrate and nitrogen sources, temperature and pH. After 8 weeks, the highest level of growth and densest hyphal branching were recorded in the medium containing glucose as the main carbohydrate. For nitrogen, glutamine (200 mg N l-1) provided the greatest hyphal growth and density compared to the other amino acid treatments. Regarding temperature, 16?C proved to be optimal for T. brumale growth and branching. Media of pH 6 and pH 7 were most favourable for the growth of T. brumale. The results from this research provide baseline data on the vegetative nutrition of T. brumale and have implications for the in vitro culture of winter truffle hyphae.
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- Date Published:
- Journal Name:
- Frontiers in Microbiology
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Ectomycorrhizal symbiosis is essential for the nutrition of most temperate forest trees and helps regulate the movement of carbon (C) and nitrogen (N) through forested ecosystems. The factors governing the exchange of plant C for fungal N, however, remain obscure.
Because competition and soil resources may influence ectomycorrhizal resource movement, we performed a 10‐month split‐root microcosm study using
Pinus muricataseedlings with Thelephora terrestris, Suillus pungens, or no ectomycorrhizal fungus, under two N concentrations in artificial soil. Fungi competed directly with roots and indirectly with each other. We used stable isotope enrichment to track plant photosynthate and fungal N.
T. terrestris, plants received N commensurate with the C given to their fungal partners. Thelephora terrestriswas a superior mutualist under high‐N conditions. For S. pungens, plant C and fungal N exchange were not coupled. However, in low‐N conditions, plants preferentially allocated C to S. pungensrather than T. terrestris.
Our results suggest that ectomycorrhizal resource transfer depends on competitive and nutritional context. Plants can exchange C for fungal N, but coupling of these resources can depend on the fungal species and soil N. Understanding the diversity of fungal strategies, and how they change with environmental context, reveals mechanisms driving this important symbiosis.
Self‐reinforcing differences in fire frequency help closed‐canopy forests, which resist fire, and open woodlands, which naturally burn often, to co‐occur stably at landscape scales. Forest tree seedlings, which could otherwise encroach and overgrow woodlands, are killed by regular fire, yet fire has other effects that may also influence these feedbacks. In particular, many forest trees require symbiotic ectomycorrhizal fungi in order to establish. By restructuring soil fungal communities, fire might affect the availability of symbionts or the potential for symbiont sharing between encroaching trees and woodland vegetation.
To investigate this possibility, we performed a soil bioassay experiment using inoculum from burned and unburned oak woodlands and Douglas‐fir forests. We examined how fire, ecosystem type, and neighboring heterospecific seedlings affect fungal root community assembly of Douglas‐firs and oaks. We asked whether heterospecific seedlings facilitated fungal colonization of seedling roots in non‐native soil, and if so, whether fire influenced this interaction.
External fungal colonization of oak roots was more influenced by fire and ecosystem type than by the presence of a Douglas‐fir, and oaks increased the likelihood that Douglas‐fir roots would be colonized by fungi in oak woodland soil. Yet, fire increased colonization of Douglas‐fir in oak soil, diminishing the otherwise crucial role played by oak facilitation. Fire also strengthened the positive effect of Douglas‐firs on oak root‐associated fungal diversity in Douglas‐fir forest soil.
Prior work shows that fire supports woodland ecosystems by stemming recruitment of encroaching seedlings. Here, we find evidence that it may contrastingly reduce fungal limitation of invasive seedling growth and establishment, otherwise relieved only by facilitation. Future work can investigate how these opposing effects might contribute to the net impact of changes in fire regime on landcover stability.
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Plain Language Summaryfor this article on the Journal blog.
Successive droughts have resulted in extensive tree mortality in the southwestern United States. Recovery of these areas is dependent on the survival and recruitment of young trees. For trees that rely on ectomycorrhizal fungi (
EMF) for survival and growth, changes in soil fungal communities following tree mortality could negatively affect seedling establishment.
We used tree‐focused and stand‐scale measurements to examine the impact of pinyon pine mortality on the performance of surviving juvenile trees and the potential for mutualism limitation of seedling establishment via altered
Mature pinyon mortality did not affect the survival of juvenile pinyons, but increased their growth. At both tree and stand scales, high pinyon mortality had no effect on the abundance of
EMFinocula, but led to altered EMFcommunity composition including increased abundance of Geoporaand reduced abundance of Tuber. Seedling biomass was strongly positively associated with Tuberabundance, suggesting that reductions in this genus with pinyon mortality could have negative consequences for establishing seedlings.
These findings suggest that whereas mature pinyon mortality led to competitive release for established juvenile pinyons, changes in
EMFcommunity composition with mortality could limit successful seedling establishment and growth in high‐mortality sites.
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