Carbon for nutrient exchange between Lycopodiella inundata and Mucoromycotina fine root endophytes is unresponsive to high atmospheric CO2

Plant-microbe interactions through a lens: tales from the mycorrhizosphere

BACKGROUND

The soil microbiome plays a pivotal role in maintaining ecological balance, supporting food production, preserving water quality and safeguarding human health. Understanding the intricate dynamics within the soil microbiome necessitates unravelling complex bacterial-fungal interactions (BFIs). BFIs occur in diverse habitats, such as the phyllosphere, rhizosphere and bulk soil, where they exert substantial influence on plant-microbe associations, nutrient cycling and overall ecosystem functions. In various symbiotic associations, fungi form mycorrhizal connections with plant roots, enhancing nutrient uptake through the root and mycorrhizal pathways. Concurrently, specific soil bacteria, including mycorrhiza helper bacteria, play a pivotal role in nutrient acquisition and promoting plant growth. Chemical communication and biofilm formation further shape plant-microbial interactions, affecting plant growth, disease resistance and nutrient acquisition processes.

SCOPE

Promoting synergistic interactions between mycorrhizal fungi and soil microbes holds immense potential for advancing ecological knowledge and conservation. However, despite the significant progress, gaps remain in our understanding of the evolutionary significance, perception, functional traits and ecological relevance of BFIs. Here we review recent findings obtained with respect to complex microbial communities - particularly in the mycorrhizosphere - and include the latest advances in the field, outlining their profound impacts on our understanding of ecosystem dynamics and plant physiology and function.

CONCLUSIONS

Deepening our understanding of plant BFIs can help assess their capabilities with regard to ecological and agricultural safe-guarding, in particular buffering soil stresses, and ensuring sustainable land management practices. Preserving and enhancing soil biodiversity emerge as critical imperatives in sustaining life on Earth amidst pressures of anthropogenic climate change. A holistic approach integrates scientific knowledge on bacteria and fungi, which includes their potential to foster resilient soil ecosystems for present and future generations.

Phytophagy impacts the quality and quantity of plant carbon resources acquired by mutualistic arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi associate with the roots of many plant species, enhancing their hosts access to soil nutrients whilst obtaining their carbon supply directly as photosynthates. AM fungi often face competition for plant carbon from other organisms. The mechanisms by which plants prioritise carbon allocation to mutualistic AM fungi over parasitic symbionts remain poorly understood. Here, we show that host potato plants (Solanum tuberosum cv. Désirée) selectively allocate carbon resources to tissues interacting with AM fungi rather than those interacting with phytophagous parasites (the nematode Globodera pallida). We found that plants reduce the supply of hexoses but maintain the flow of plant-derived fatty acids to AM fungi when concurrently interacting with parasites. Transcriptomic analysis suggest that plants prioritise carbon transfer to AM fungi by maintaining expression of fatty acid biosynthesis and transportation pathways, whilst decreasing the expression of mycorrhizal-induced hexose transporters. We also report similar findings from a different plant host species (Medicago truncatula) and phytophagous pest (the aphid Myzus persicae). These findings suggest a general mechanism of plant-driven resource allocation in scenarios involving multiple symbionts.

Niche differentiation of Mucoromycotinian and Glomeromycotinian arbuscular mycorrhizal fungi along a 2-million-year soil chronosequence

Current literature suggests ecological niche differentiation between co-occurring Mucoromycotinian arbuscular mycorrhizal fungi (M-AMF) and Glomeromycotinian AMF (G-AMF), but experimental evidence is limited. We investigated the influence of soil age, water availability (wet and dry), and plant species (native Microlaena stipoides and exotic Trifolium subterraneum) on anatomical root colonisation and DNA profiles of M-AMF and G-AMF under glasshouse conditions. We grew seedlings of each species in soils collected from the four stages of a soil chronosequence, where pH decreases from the youngest to oldest stages, and phosphorus (P) is low in the youngest and oldest, but high in the intermediate stages. We scored the percentage of root length colonised and used DNA metabarcoding to profile fungal richness and community composition associated with treatment combinations. Soil age, water availability, and plant species were important influencers of root colonisation, although no M-AMF were visible following staining of M. stipoides roots. Soil age and host plant influenced fungal richness and community composition. However, response to soil age, potential host species, and water availability differed between M-AMF and G-AMF. Root colonisation of T. subterraneum by M-AMF and G-AMF was inversely correlated with soil P level. Community composition of M-AMF and G-AMF was structured by soil age and, to a lesser extent, plant species. Richness of M-AMF and G-AMF was negatively, and positively, correlated with available P, respectively. These findings are experimental evidence of ecological niche differentiation of M-AMF and G-AMF and invite further exploration into interactive effects of abiotic and biotic factors on their communities along successional trajectories.

Microbial Metabolites Beneficial to Plant Hosts Across Ecosystems

Plants are intimately connected with their associated microorganisms. Chemical interactions via natural products between plants and their microbial symbionts form an important aspect in host health and development, both in aquatic and terrestrial ecosystems. These interactions range from negative to beneficial for microbial symbionts as well as their hosts. Symbiotic microbes synchronize their metabolism with their hosts, thus suggesting a possible coevolution among them. Metabolites, synthesized from plants and microbes due to their association and coaction, supplement the already present metabolites, thus promoting plant growth, maintaining physiological status, and countering various biotic and abiotic stress factors. However, environmental changes, such as pollution and temperature variations, as well as anthropogenic-induced monoculture settings, have a significant influence on plant-associated microbial community and its interaction with the host. In this review, we put the prominent microbial metabolites participating in plant-microbe interactions in the natural terrestrial and aquatic ecosystems in a single perspective and have discussed commonalities and differences in these interactions for adaptation to surrounding environment and how environmental changes can alter the same. We also present the status and further possibilities of employing chemical interactions for environment remediation. Our review thus underlines the importance of ecosystem-driven functional adaptations of plant-microbe interactions in natural and anthropogenically influenced ecosystems and their possible applications.

The potential role of Mucoromycotina 'fine root endophytes' in plant nitrogen nutrition

Mycorrhizal associations between fungi and plant roots have globally significant impacts on nutrient cycling. Mucoromycotina 'fine root endophytes' (MFRE) are a distinct and recently characterised group of mycorrhiza-forming fungi that associate with the roots of a range of host plant species. Given their previous misidentification and assignment as arbuscular mycorrhizal fungi (AMF) of the Glomeromycotina, it is now important to untangle the specific form and function of MFRE symbioses. In particular, relatively little is known about the nature of MFRE colonisation and its role in N uptake and transfer to host plants. Even less is known about the mechanisms by which MFRE access and assimilate N, and how this N is processed and subsequently exchanged with host plants for photosynthates. Here, we summarise and contrast the structures formed by MFRE and arbuscular mycorrhizal fungi in host plants as well as compare the N source preference of each mycorrhizal fungal group with what is currently known for MFRE N uptake. We compare the mechanisms of N assimilation and transfer to host plants utilised by the main groups of mycorrhizal fungi and hypothesise potential mechanisms for MFRE N assimilation and transfer, outlining directions for future research.