An increase in tree mortality is currently evident in forests around the world. Such mortality could be counterbalanced by the native regeneration of seedlings. Seedling establishment under natural conditions is often limited by inter-plant competition and drought conditions. Many forest ecosystems rely on ectomycorrhizal relationships which could be affected by competition and drought, altering forest resilience. We carried out an experiment testing the combined effects of drought, herbaceous competition, and ectomycorrhizal fungi (EMF) on the growth and shape of Aleppo pine seedlings and the EMF community composition. Pines that germinated in the presence of the EMF spores were taller, had greater biomass, and more side branches. However, under conditions of either competition or drought, the effect of EMF on seedling biomass and height was greatly reduced, while the effect on shoot branching was maintained. Under a combination of drought and competition, EMF had no influence on plant growth and shape. The EMF community was strongly dominated by Geopora species, and its structure was not affected by the treatments. Plants experiencing competition were nitrogen poor but presented the highest levels of EMF sequence abundance. Stressful conditions seem to alter the relationship between EMF and seedling growth. Specifically, under drought, both colonization and seedling response to EMF was small. However, under competition, colonization was maintained while no growth enhancement was evident. This discrepancy highlights the complexity of the benefits provided to seedlings by EMF under ecologically relevant conditions.
Seedling establishment under natural conditions is often limited by
numerous interacting factors. We tested the combined effects of drought,
herbaceous competition, and ectomycorrhizal fungi (EMF) on the growth
and shape of Aleppo pine seedlings and their associated EMF community.
EMF inoculum significantly increased seedlings’ height, biomass, and the
number of side branches. However, under either competition or drought,
the effect of EMF on seedling biomass and height was greatly reduced,
while the effect on shoot branching was maintained. All plants were
strongly dominated by Geopora, a fungal genus known to inoculate
seedlings in dry habitats. Under a combination of drought and
competition, EMF had no influence on plant growth and shape. This
discrepancy highlights the complexity of the benefits provided to
seedlings by EMF under ecologically relevant conditions.
1. The mutualistic interaction between trees and ectomycorrhizal fungi (EMF) can have a major effect on forest dynamics and specifically in seedling establishment. Both intrinsic (i.e., identity of the sapling) and extrinsic (i.e., the identity of mature trees in the vicinity of the sapling) factors can affect the EMF community composition of young saplings. 2. Here, we compared the EMF community composition associated with the roots of young saplings and mature trees of two co-habiting Pinaceae: Pinus halepensis and Cedrus deodara growing together in a planted forest plot, using fungal ITS metabarcoding. 3. We found that the differences between the two sapling groups were mostly attributed to changes in the relative abundance of specific fungal species. Moreover, we found that physical proximity to a specific host species had a significant effect on the community composition of young saplings. However, while no significant differences in sapling size were apparent, the sapling shoot structure was affected by the identity of the nearest mature tree and its unique EMF community composition. 4. Synthesis: These results suggest that the dynamics of the EMF community are greatly determined by extrinsic factors such as the small-scale distribution of mature trees in the forest, with possible cascading effects on the development of young trees.
Seedling establishment under natural conditions is limited by numerous interacting factors. Here, we tested the combinatorial effects of drought, herbaceous competition, and ectomycorrhizal fungi (EMF) on the performance of Aleppo pine seedlings grown under shade house conditions. All pine seedlings were strongly dominated by Geopora, a fungal genus known to inoculate seedlings in dry habitats. EMF inoculum significantly increased seedling height, biomass, and the number of side branches. However, under either competition or drought, the positive effect of EMF on seedling biomass and height was greatly reduced, while the effect on shoot branching was maintained. Further, under a combination of drought and competition, EMF had no influence on either plant growth and shape. The discrepancy in pine performance across treatments highlights the complexity of benefits provided to seedlings by EMF under ecologically relevant settings.
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