Balancing mutualism: choice and sanctions in root–microbe symbioses

Madhavan et al., 2026

Plant roots form symbioses with beneficial microorganisms to enhance nutrient acquisition. Most terrestrial plants form arbuscular mycorrhizal symbiosis (AMS) with obligate biotrophic Glomeromycotina fungi, which supply hosts with mineral nutrients in exchange for carbon through specialized symbiotic hyphal structures (arbuscules) that develop within root cortex cells. Legumes form root nodule symbiosis (RNS) with nitrogen-fixing rhizobia, which are housed as differentiated bacteroids within specialized symbiotic organs (nodules) and provide plants with ammonia in return for carbon. RNS exhibits high partner specificity, occurring only between compatible hosts and microbes. Conversely, AMS is less specific, although symbiosis outcomes are context-dependent and influenced by host and fungal genotype, environmental conditions, and microbial competition. In both cases, plants favor high-performing microsymbionts by recognizing them during symbiosis initiation or by punishing low-performing symbionts through postcolonization sanctions. Microbes, in turn, employ strategies to manipulate plants for their own benefit. Here, we review the molecular mechanisms underlying partner preference in beneficial plant–microbe interactions and discuss how host partner selection strategies maintain mutualistic stability in AMS and RNS, alongside microbial strategies to evade host control. Understanding the dynamic interplay of functionally diverse plant–microbe symbioses provides a basis for improving mutualisms in both natural and agricultural systems.

https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.71107

Plant nutritional and structural diversity shape multitrophic arthropod communities and grassland productivity 

Lu et al., 2026

1. Arthropod communities, comprising diverse trophic groups such as herbivores, predators and parasitoids, are intricately linked to plant traits that provide food and habitat. While it is well-established that changes in plant functional diversity (e.g. trait identity and diversity) can significantly alter arthropod diversity across trophic levels, the cascading effects on ecosystem functions remain less understood. Particularly, the role of multitrophic arthropod diversity in mediating the relationship between plant functional diversity and grassland productivity presents a critical knowledge gap in ecosystem ecology.
2. We employed a long-term plant removal experiment in the Inner Mongolian grassland to systematically investigate how variations in the community-weighted mean and diversity of multiple plant traits influence the diversity (measured by taxon richness and abundance) of herbivores and their natural enemies. Furthermore, we explored how trophic interactions between herbivores and their natural enemies influence plant community productivity.
3. Our findings indicate that high diversity in plant nutritional traits (e.g. nitrogen, phosphorus and sodium contents) negatively impacts plant productivity through both direct and indirect pathways. The adverse effect was mediated by an increase in the richness of sucking and chewing herbivores, which exploited high resource complementarity yet collectively suppressed plant productivity. In contrast, higher community-weighted means of plant structural traits (e.g. vegetative height and leaf lateral spread) were associated with greater plant productivity. This positive effect appears to arise from enhanced top-down control, whereby predators—particularly spiders—reduced both the richness and abundance of herbivores.
4. Synthesis. Our study reveals that herbivores and their natural enemies respond distinctly to the variation in the composition and diversity of plant nutritional and structural traits. We show that cross-trophic interactions—specifically, diversity within herbivore and predator guilds—constitute a primary pathway through which plant functional diversity influences grassland productivity. By disentangling the links between plant trait spectra, arthropod community structure and ecosystem functioning, our findings provide key insights for biodiversity conservation and the design of ecosystem management strategies in grasslands.

https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.70316

The island biology of the host microbiome 

Sarkar et al., 2026

Highlights

The extraordinary biodiversity of the host-associated gut microbiome cannot be explained exclusively by host traits.

Researchers have interpreted hosts as biological islands suitable for microbial colonisation and have applied ecological theories of island biogeography and metacommunity ecology to further understand microbiome composition and variation.

To benefit from the host-as-island metaphor, the metacommunity processes characterising macroscopic and microbial diversity should be explicitly compared. On geological islands, these processes include interspecies interactions, local selection, interisland dispersal, and ecological stochasticity. In host islands, these processes are paralleled by interactions between microbes, host selection, microbial transmission, and microbial stochasticity, respectively.

A critical difference between host islands and geological islands is that host islands are mobile and undergo adaptive evolution, whereas geological islands do not.

Abstract

Microbiomes perform critical functions for their hosts, and understanding microbiome variation is important for both basic and applied science. However, host traits alone cannot explain the entirety of microbiome variation, because, alongside host traits, microbiomes are shaped by multiple ecological processes. Researchers have thus turned to theories of island biology, conceptualising animal hosts as islands and animal microbiomes as metacommunities that assemble within and disperse between host islands. To develop realistic models, this host-as-island metaphor must be examined by explicitly comparing geological and host islands. Here, we critically examine the host-as-island metaphor by evaluating how microbiome variation is shaped by the four metacommunity processes that explain biodiversity on geological islands: local interspecies interactions, local selection, dispersal, and stochasticity. Key differences between host islands and geological islands include the complexity of microbiome transmission networks arising from host mobility and sociality and the capacity of hosts to evolve to control their microbiomes. We conclude with discussions of how eco-evolutionary dynamics differ between geological islands and host islands, and the reciprocal relevance of island biology and microbiome science.

https://www.cell.com/trends/microbiology/abstract/S0966-842X(26)00040-5?

Soil microbial diversity associates with lower prevalence of human bacterial pathogens across global soils

Author links open overlay panel

Xiong et al., 2026

Soil-inhabiting pathogens threaten human health, but their biogeography and associations with soil biodiversity remain poorly understood. Here, we present global patterns of dominant human bacterial pathogens by integrating 1,602 soil metagenomes from 59 countries across continents. We show that dominant human pathogens are more prevalent (i.e., relative abundance) in wet (tropical and temperate) ecosystems and are particularly abundant in cropland soils. We find a global negative association between soil microbiome diversity and pathogen prevalence. We further reveal a significant and positive correlation between the abundance of dominant human pathogens and both disease virulence and global patterns of mortality associated with infectious diseases. Many dominant pathogens are likely to increase their proportion under global change scenarios. Our work provides a global atlas of dominant soil-inhabiting human pathogens and reveals their biogeography and ecology. These findings can guide the development of effective surveillance and risk management strategies to reduce outbreaks and pandemics.

https://www.sciencedirect.com/science/article/abs/pii/S1931312826001198