Guoxi Shi

Direct and indirect influences of 8 yr of nitrogen and phosphorus fertilization on Glomeromycota in an alpine meadow ecosystem

We measured the influences of soil fertility and plant community composition on Glomeromycota, and tested the prediction of the functional equilibrium hypothesis that increased availability of soil resources will reduce the abundance of arbuscular mycorrhizal (AM) fungi. Communities of plants and AM fungi were measured in mixed roots and in Elymus nutans roots across an experimental fertilization gradient in an alpine meadow on the Tibetan Plateau. As predicted, fertilization reduced the abundance of Glomeromycota as well as the species richness of plants and AM fungi. The response of the glomeromycotan community was strongly linked to the plant community shift towards dominance by Elymus nutans. A reduction in the extraradical hyphae of AM fungi was associated with both the changes in soil factors and shifts in the plant community composition that were caused by fertilization. Our findings highlight the importance of soil fertility in regulating both plant and glomeromycotan communities, and emphasize that high fertilizer inputs can reduce the biodiversity of plants and AM fungi, and influence the sustainability of ecosystems.

Diverse communities of arbuscular mycorrhizal fungi inhabit sites with very high altitude in Tibet Plateau

Diversity of arbuscular mycorrhizal fungi (AMF) is well studied in many ecosystems, but little is known about AMF in cold-dominated regions with very high altitude. Here, we examined AMF communities associated with two plant species in the Tibet Plateau. Roots and rhizosphere soils of Dracocephalum heterophyllum (pioneer species) and Astragalus polycladus (late-successional species) were sampled at five sites with altitude from 4500 to 4800 m a.s.l. A total of 21 AMF phylotypes were identified from roots and spores following cloning and sequencing of 18S rRNA gene, including eight new phylotypes and one new family-like clade. More AMF phylotypes colonized root samples of D. heterophyllum (5.4±0.49) than of A. polycladus (1.93±0.25). Vegetation coverage was the most important factor influencing AMF community composition in roots. Globally infrequent phylotype Glo-B2 in Glomus group B was the most dominant in roots, followed by globally frequent phylotype Glo-A2 related to Glomus fasciculatum/intraradices group. Our findings suggest that a diverse AMF flora is present in the Tibet Plateau, comprising both potentially habitat-selective and generalist fungi.

Resource availability differentially drives community assemblages of plants and their root-associated arbuscular mycorrhizal fungi

Background and aimsUnderstanding the role of resource availability in structuring biotic communities is of importance in community ecology. This study investigates how light and soil nutrient availability drive assemblages of both plants and their root-associated arbuscular mycorrhizal fungi (AMF).MethodsWe conducted a 4-year light [full light or shade] and soil fertility [unfertilized or fertilized with (NH4)2HPO4] interactive manipulations in an alpine meadow ecosystem. Species and phylogenetic compositions of plant and AMF communities were simultaneously measured, and the primary ecological processes structuring both communities were inferred from the community phylogenetic analysis.ResultsReducing light and/or increasing soil fertility significantly reduced species richness and changed community compositions of both plant and AMF. Plant community phylogenetic structure shifted from random in untreated control to overdispersion in other treatments, whereas AMF communities were phylogenetically clustered and random in unfertilized and fertilized plots, respectively. These results suggest that plant communities in treated plots were mainly determined by competitive exclusion, and that AMF communities in unfertilized and fertilized plots were determined by environmental filtering and random process, respectively.ConclusionsWe observed strong effects of light and soil nutrient availability on both plant and AMF communities, and our findings highlight that the primary ecological processes that drive plant and AMF assemblages should be highly dependent on the level of resource availability.

Wheat cultivars form distinctive communities of root-associated arbuscular mycorrhiza in a conventional agroecosystem

Background and aimsThe effect of plant species on their root-associated arbuscular mycorrhizal (AM) fungi is well studied, but how this effect operates at the cultivar level remains poorly understood. This study investigates how wheat cultivars shape their AM fungal communities.MethodsTwenty-one new wheat cultivars were traditionally cultivated in a dryland of northwestern China, and their agronomic traits, soil characteristics and the abundance and community composition of AM fungi were measured.ResultsBoth spore community in soils and AM fungal phylotypes inside roots were significantly influenced by cultivar even though hyphal abundance, spore density and AM fungal diversity were similar across cultivars. Three out of 16 AM fungal phylotypes interacted with most cultivars, whilst some phylotypes preferred to colonize cultivars with similar agronomic traits. Six wheat cultivars, all which had hosted 6 AM fungal phylotypes, seemed to be generalists. Nestedness analysis and stochastic model fitting revealed that the AM fungal communities colonizing roots were codetermined by deterministic and stochastic processes.ConclusionsA complex pattern of cultivar-AM fungal interactions was observed in this study, and our results highlight that the host effect on the community assembly of AM fungi could be operating on the level of plant cultivar.

Relative Importance of Deterministic and Stochastic Processes in Driving Arbuscular Mycorrhizal Fungal Assemblage during the Spreading of a Toxic Plant

Both deterministic and stochastic processes are expected to drive the assemblages of arbuscular mycorrhizal (AM) fungi, but little is known about the relative importance of these processes during the spreading of toxic plants. Here, the species composition and phylogenetic structure of AM fungal communities colonizing the roots of a toxic plant, Ligularia virgaurea, and its neighborhood plants, were analyzed in patches with different individual densities of L. virgaurea (represents the spreading degree). Community compositions of AM fungi in both root systems were changed significantly by the L. virgaurea spreading, and also these communities fitted the neutral model very well. AM fungal communities in patches with absence and presence of L. virgaurea were phylogenetically random and clustered, respectively, suggesting that the principal ecological process determining AM fungal assemblage shifted from stochastic process to environmental filtering when this toxic plant was present. Our results indicate that deterministic and stochastic processes together determine the assemblage of AM fungi, but the dominant process would be changed by the spreading of toxic plants, and suggest that the spreading of toxic plants in alpine meadow ecosystems might be involving the mycorrhizal symbionts.