ABSTRACT: Sub-alpine environments consist of altitudinal gradients associated with dramatic changes in plant growth and community composition,
but the role of soil feedbacks and microbe interactions is largely unknown. Here, we examine the influence of the overall
soil microbial community, with a focus on ectomycorrhizal and dark septate endophytic root colonizing fungi, from low, mid,
and high elevations on the growth of Pinus contorta and Picea glauca × engelmannii. The influence of the soil microbial community was tested on seedlings from the same three elevations in order to determine
‘home’ versus ‘away’ effects on conspecifics of differing elevations. The low elevation soil was the most fertile and harbored
a soil microbial community with an overall negative effect on seedling growth. In contrast, the high elevation soil was the
least fertile and had a microbial community that enhanced seedling growth. However, only the soil microbial community in the
highest elevation soil resulted in a stronger influence on the native P. contorta seedlings than seedlings originating from lower elevations. Despite the overall influence of the soil microbial community,
ectomycorrhizal colonization was significantly correlated with P. glauca × engelmannii growth rates, but colonization by dark septate endophytes showed no relationship with seedling growth. The results provide
evidence that plant—soil microbial community relationships are dependent on soil environment. Moreover, our results provide
further support for the importance of soil microbes in facilitating seedling growth toward the edge of their elevational range.
KeywordsSoil feedback–Seedling growth–Ectomycorrhiza–Dark septate endophytes–Soil microbial communities–Subalpine soils
Plant and Soil 04/2012; 340(1):491-504. · 2.73 Impact Factor
ABSTRACT: Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with most vascular plants including some gymnosperm species.
Although species in the gymnosperm family Pinaceae normally develop ectomycorrhizal associations, AMF hyphae and vesicles,
typical of members of the Suborder Glomineae, have been reported in the roots of some Pinaceae species. However, it is not
known whether AMF belonging to various species and suborders are able to colonize roots of Pinaceae species and to what extent
this influences the performance of Pinaceae seedlings. We tested in each of the Glomaceae, Acaulosporaceae and Gigasporineae
AMF families two species for their ability to colonize and affect the growth of Pinus strobus (eastern white pine) in the presence or absence of an AMF host plant (Trifolium pretense—red clover). Glomus intraradices was the only AMF that colonized pine roots, predominantly in the presence of clover, forming intracellular hyphae and vesicles
but not arbuscules. Colonization, however, did not relate to increased pine biomass and the overall presence of AMF, regardless
of colonization abilities, resulted in a biomass reduction. This effect on pine seedling biomass was explained by the AMF
family to which the AMF belonged, indicating that the effects of AMF on the non-host pine may be related to phylogeny. Acaulosporaceae
species reduced pine biomass the most whereas, Gigasporineae species had the smallest effect on biomass. These preliminary
results suggest that AMF may affect the soil microflora differently among AMF families in previously unsuspected ways with
potential consequences for non-AMF host growth.
Symbiosis 04/2012; 53(1):41-46. · 1.21 Impact Factor
ABSTRACT: Soil microbes play key roles in ecosystems, yet the impact of their diversity on plant communities is still poorly understood. Here we demonstrate that the diversity of belowground plant-associated soil fungi promotes plant productivity and plant coexistence. Using additive partitioning of biodiversity effects developed in plant biodiversity studies, we demonstrate that this positive relationship can be driven by complementarity effects among soil fungi in one soil type and by a selection effect resulting from the fungal species that stimulated plant productivity the most in another soil type. Selection and complementarity effects among fungal species contributed to improving plant productivity up to 82% and 85%, respectively, above the average of the respective fungal species monocultures depending on the soil in which they were grown. These results also indicate that belowground diversity may act as insurance for maintaining plant productivity under differing environmental conditions.
Ecology Letters 07/2011; 14(10):1001-9. · 17.56 Impact Factor
ABSTRACT: There is a great interest in ecology in understanding the role of soil microbial diversity for plant productivity and coexistence. Recent research has shown increases in species richness of mutualistic soil fungi, the arbuscular mycorrhizal fungi (AMF), to be related to increases in aboveground productivity of plant communities. However, the impact of AMF richness on plant-plant interactions has not been determined. Moreover, it is unknown whether species-rich AMF communities can act as insurance to maintain productivity in a fluctuating environment (e.g., upon changing soil conditions). We tested the impact of four different AMF taxa and of AMF diversity (no AMF, single AMF taxa, and all four together) on competitive interactions between the legume Trifolium pratense and the grass Lolium multiflorum grown under two different soil conditions of low and high sand content. We hypothesized that more diverse mutualistic interactions (e.g., when four AMF taxa are present) can ease competitive effects between plants, increase plant growth, and maintain plant productivity across different soil environments. We used quantitative PCR to verify that AMF taxa inoculated at the beginning of the experiment were still present at the end. The presence of AMF reduced the competitive inequality between the two plant species by reducing the growth suppression of the legume by the grass. High AMF richness enhanced the combined biomass production of the two plant species and the yield of the legume, particularly in the more productive soil with low sand content. In the less productive (high sand content) soil, the single most effective AMF had an equally beneficial effect on plant productivity as the mixture of four AMF. Since contributions of single AMF to plant productivity varied between both soils, higher AMF richness would be required to maintain plant productivity in heterogeneous environments. Overall this work shows that AMF diversity promotes plant productivity and that AMF diversity can act as insurance to sustain plant productivity under changing environmental conditions.
Ecology 06/2011; 92(6):1303-13. · 4.85 Impact Factor
ABSTRACT: Roots encounter a plethora of microorganisms in the soil environment that are either deleterious, neutral, or beneficial to plant growth. Root endophytic fungi are ubiquitous. These include dark septate endophytes whose role in plant growth and the maintenance of plant communities is largely unknown. The objectives of this review were to assess the structural features of the interactions between dark septate endophytic fungi and the roots of both angiopsperms and conifers, and to suggest avenues for further research. Several light microscopy studies of endophyte-root interactions have revealed a variety of structural features, depending on host species and plant growth conditions. In some cases, when fungal hyphae enter roots they cause cell breakdown, whereas in other situations there is little noticeable effect. In some tree species, associations with these endophytes may mimic ectomycorrhizas or ectendomycorrhizas. The few ultrastructural studies indicate that intracellular hyphae lack a host-derived perifungal membrane and interfacial matrix material, features typical of biotrophic fungus - plant cell interactions. This raises questions concerning nutrient exchange between these fungi and plant cells. Further research in this area is needed. New approaches that include molecular cytology and live-cell imaging are needed to determine early changes in plant cells when challenged with these fungi.Dans l'environnement édaphique, les racines rencontrent une pléthore de microorganismes néfastes, neutres ou bénéfiques à la croissance des plantes. Les endophytes racinaires sont ubiquistes. Ceux-ci incluent les endophytes foncés septés, dont on connaît mal le rôle dans la croissance des plantes et le maintien des communautés végétales. Dans cette revue, les auteurs ont pour objectifs d'évaluer les caractéristiques structurales des interactions entre les champignons endophytes foncés septés et les racines des angiospermes aussi bien que des gymnospermes, et de suggérer des avenues pour les recherches futures. L'étude en microscopie photonique des interactions endophyte-racine se retrouve dans plusieurs études qui montrent qu'une variété de caractéristiques structurales dépendent des espèces hôtes et des conditions de croissance. Dans certains cas, lorsque les hyphes pénètrent les racines, elles causent une rupture des cellules, alors que dans d'autres situations, il y a peu d'effet notable. Chez certaines espèces d'arbres, l'association avec ces endophytes peut ressembler à des ectomycorhizes ou à des ectendomycorhizes. Les rares études ultrastructurales indiquent que les hyphes intracellulaires ne possèdent pas d'enveloppe périfongique dérivée de l'hôte et de matériel matriciel interfacial, deux caractéristiques propres aux interactions cellulaires biotrophiques champignon-plante. Ceci soulève la question quant aux échanges entre ces champignons et les cellules végétales. D'autres recherches sur ces aspects sont nécessaires. On doit développer de nouvelles approches incluant la cytologie moléculaire et l'imagerie de cellules vivantes pour déterminer les toutes premières modifications dans les cellules des plantes lorsqu'elles subissent l'attaque par ces champignons.
Botany 04/2008; 86(5):445-456. · 1.25 Impact Factor
ABSTRACT: Although roots of species in the Pinaceae are usually colonized by ectomycorrhizal (EM) fungi, there are increasing reports of the presence of arbuscular mycorrhizal (AM) and dark septate endophytic (DSE) fungi in these species. The objective of this study was to determine the colonization patterns in seedlings of three Pinus (pine) species (Pinus banksiana, Pinus strobus, Pinus contorta) and Picea glauca x Picea engelmannii (hybrid spruce) grown in soil collected from a disturbed forest site. Seedlings of all three pine species and hybrid spruce became colonized by EM, AM, and DSE fungi. The dominant EM morphotype belonged to the E-strain category; limited colonization by a Tuber sp. was found on roots of Pinus strobus and an unknown morphotype (cf. Suillus-Rhizopogon group) with thick, cottony white mycelium was present on short roots of all species. The three fungal categories tended to occupy different niches in a single root system. No correlation was found between the percent root colonized by EM and percent colonization by either AM or DSE, although there was a positive correlation between percent root length colonized by AM and DSE. Hyphae and vesicles were the only AM intracellular structures found in roots of all species; arbuscules were not observed in any roots.
Mycorrhiza 03/2008; 18(2):103-10. · 2.63 Impact Factor