Symbiosis: Herbivory Alters Mycorrhizal Nutrient Exchange

A new study shows that a plant gives less carbon to its root-associated mycorrhizal fungus when targeted by herbivores, but the fungus doesn’t retaliate

Data from: Global distribution patterns of mycoheterotrophy

Aim: Mycoheterotrophy is a mode of life where plants cheat the mycorrhizal symbiosis, receiving carbon via their fungal partners. Despite being widespread, mycoheterotrophic plants are locally rare, hampering the understanding of their global environmental drivers. Here, we explore global environmental preferences of mycoheterotrophy, and investigate environmental drivers of differential habitat preferences of mycoheterotrophic plants associated with arbuscular (AM) and ectomycorrhizal (EM) fungi. Location: Global. Time period: Current. Major taxa studied: Mycoheterotrophic flowering plants. Methods: We compiled the largest global dataset of epiparasitic mycoheterotrophic plant species occurrences and examined which environmental factors, including soil type, climate, vegetation type and distribution patterns of mycorrhizal autotrophic plants, relate to occurrence patterns of mycoheterotrophic plant species associated with AM and EM fungi. Results: Mycoheterotrophic plant species avoid cold and highly seasonal climates and show a strong preference for forests. AM-associated mycoheterotrophs are predominantly found in broadleaved tropical evergreen forests whereas EM-associated mycoheterotrophs occur in temperate regions, mostly in broadleaved deciduous and evergreen needleleaved forests. The abundance of AM and EM autotrophic plants was a weaker predictor for mycoheterotrophs occurrences than forest type. Temperature and precipitation variables - but not edaphic factors - were the best predictors explaining the distribution patterns of mycoheterotrophs after accounting for the effects of forest type. For individual lineages, major differences in environmental preferences (often related to edaphic factors) occurred which were significantly associated with plant evolutionary relationships, indicating that these cheater plants have limited adaptive capabilities. Main conclusions: The strong global geographic segregation of AM and EM mycoheterotrophs does not reflect the abundance of their potential autotrophic hosts, but seems to be driven by differential climate and habitat preferences. Our results highlight the non-trivial nature of mycorrhizal interactions, and indicate that identity of the partners is not enough to understand the underlying mechanisms promoting plant-fungal interactions in mycoheterotrophic plants

Fungal diversity driven by bark features affects phorophyte preference in epiphytic orchids from southern China.

Epiphytic orchids exhibit varying degrees of phorophyte tree specificity. We performed a pilot study to investigate why epiphytic orchids prefer or avoid certain trees. We selected two orchid species, Panisea uniflora and Bulbophyllum odoratissimum co-occurring in a forest habitat in southern China, where they showed a specific association with Quercus yiwuensis and Pistacia weinmannifolia trees, respectively. We analysed a number of environmental factors potentially influencing the relationship between orchids and trees. Difference in bark features, such as water holding capacity and pH were recorded between Q. yiwuensis and P. weinmannifolia, which could influence both orchid seed germination and fungal diversity on the two phorophytes. Morphological and molecular culture-based methods, combined with metabarcoding analyses, were used to assess fungal communities associated with studied orchids and trees. A total of 162 fungal species in 74 genera were isolated from bark samples. Only two genera, Acremonium and Verticillium, were shared by the two phorophyte species. Metabarcoding analysis confirmed the presence of significantly different fungal communities on the investigated tree and orchid species, with considerable similarity between each orchid species and its host tree, suggesting that the orchid-host tree association is influenced by the fungal communities of the host tree bark

Deciphering the interactions between plant species and their main fungal root pathogens in mixed grassland communities

Plant diversity can reduce the risk of plant disease, but positive, and neutral effects have also been reported. These contrasting relationships suggest that plant community composition, rather than diversity per se, affects disease risk. Here, we investigated how the diversity and composition of plant communities drive root-associated pathogen accumulation belowground. In a temperate grassland biodiversity experiment, containing 16 plant species (forbs and grasses), we determined the abundance of root-associated fungal pathogens in individual plant species growing in monocultures and in four-species mixtures through Illumina MiSeq amplicon sequencing. In the plant monocultures, we identified three major fungal pathogens that differed in host range: Paraphoma chrysanthemicola, associated with roots of forb species of the Asteraceae family, Slopeiomyces cylindrosporus, associated with grass species, and Rhizoctonia solani, associated with multiple forb and grass species. In mixtures, there was no significant reduction in relative abundance of these pathogens in their host species as compared to monocultures. However, in mixtures, there was a significant increase in relative abundance of each pathogen in several non-host and host plant species. Across mixtures, plant community composition affected pathogen relative abundance in individual plant species. This effect was driven by the presence of a particular neighbouring plant species (depending on the pathogen), rather than functional group composition (i.e. grass/forb ratio) or averaged pathogen pressure (based on monocultures) of all neighbours. Specifically, the presence of neighbour host species Achillea millefolium significantly increased P. chrysanthemicola, but decreased R. solani relative abundance in several host and non-host plant species in mixtures. Synthesis. Our results indicate that interactions between different plant species—both host and non-hosts—and fungal pathogens underlie the effects of plant diversity on root pathogen abundance. Non-host species may act as pathogen reservoirs in diverse plant communities, as they harboured certain pathogens in mixtures, but not in monocultures. Additionally, particular host species can strongly affect pathogen abundance in other (host and non-host) plant species in plant mixtures, suggesting clear effects of species identity in the diversity–disease relationship. Below-ground disease risk thus depends on plant community composition rather than diversity per se, via specific interactions between plant species and their root-associated pathogens

Microbiota in Dung and Milk Differ Between Organic and Conventional Dairy Farms

Organic farming is increasingly promoted as a means to reduce the environmental impact of artificial fertilizers, pesticides, herbicides, and antibiotics in conventional dairy systems. These factors potentially affect the microbial communities of the production stages (soil, silage, dung, and milk) of the entire farm cycle. However, understanding whether the microbiota representative of different production stages reflects different agricultural practices – such as conventional versus organic farming – is unknown. Furthermore, the translocation of the microbial community across production stages is scarcely studied. We sequenced the microbial communities of soil, silage, dung, and milk samples from organic and conventional dairy farms in the Netherlands. We found that community structure of soil fungi and bacteria significantly differed among soil types, but not between organic versus conventional farming systems. The microbial communities of silage also did not differ among conventional and organic systems. Nevertheless, the dung microbiota of cows and the fungal communities in the milk were significantly structured by agricultural practice. We conclude that, while the production stages of dairy farms seem to be disconnected in terms of microbial transfer, certain practices specific for each agricultural system, such as the content of diet and the use of antibiotics, are potential drivers of shifts in the cow’s microbiota, including the milk produced. This may reflect differences in farm animal health and quality of dairy products depending on farming practices

Microbiota in Dung and Milk Differ Between Organic and Conventional Dairy Farms

Organic farming is increasingly promoted as a means to reduce the environmental impact of artificial fertilizers, pesticides, herbicides, and antibiotics in conventional dairy systems. These factors potentially affect the microbial communities of the production stages (soil, silage, dung, and milk) of the entire farm cycle. However, understanding whether the microbiota representative of different production stages reflects different agricultural practices – such as conventional versus organic farming – is unknown. Furthermore, the translocation of the microbial community across production stages is scarcely studied. We sequenced the microbial communities of soil, silage, dung, and milk samples from organic and conventional dairy farms in the Netherlands. We found that community structure of soil fungi and bacteria significantly differed among soil types, but not between organic versus conventional farming systems. The microbial communities of silage also did not differ among conventional and organic systems. Nevertheless, the dung microbiota of cows and the fungal communities in the milk were significantly structured by agricultural practice. We conclude that, while the production stages of dairy farms seem to be disconnected in terms of microbial transfer, certain practices specific for each agricultural system, such as the content of diet and the use of antibiotics, are potential drivers of shifts in the cow’s microbiota, including the milk produced. This may reflect differences in farm animal health and quality of dairy products depending on farming practices