Poplar-fungal partnerships and their climate-driven changes
Fungal communities have strong interactions with terrestrial plants and play an important role in biogeochemical cycling and soil carbon storage. Using Populus as a model system, a recent study predicts that climate change will lead to fungal dysbiosis, where the abundance and diversity of mutualistic, root-associated fungal communities will decrease, and the prevalence of leaf pathogens is predicted to increase. These findings could have major repercussions for the future resistance and resilience of forest systems to climate change.
by Morgan Raimondo | 15 March 2024
Fig 1|Article author Morgan Raimondo, graduate student at UW Seattle, also studies the microbial partners of Populus around the Cascade Mountain Range.
Fungal partnerships with plants are integral for forest function. Continental-scale studies have revealed that the distribution and diversity of both above and belowground fungal community composition is largely dependent on fungal dispersal, soil characteristics, and climate1,2. Belowground, climatic controls on rates of decomposition help to determine the global distribution of critical root-associated symbioses3. Aboveground, wetter climates exhibit greater pathogen abundance and diversity compared to those in drier conditions, consistent with previous studies4,5. However, few studies have simultaneously investigated the factors that structure above and belowground fungal communities or how these communities might differ in their sensitivity to climate change. Writing for Nature Microbiology, Van Nuland et al. leverage Populus trees as a model system to investigate patterns of fungal community composition above and belowground.
Belowground, poplar is considered a dual-mycorrhizal hosts, forming relationships with both arbuscular and ectomycorrhizal fungi (AMF and EMF, respectively). Van Nuland et al. find that the switch from more EMF to AMF-dominated root communities corresponds to prevailing climatic conditions, where colonization and diversity of EMF on Populus roots decline with increasing mean annual temperature, whereas AMF colonization increases with greater mean annual temperature. Thus, the authors elucidate that different mycorrhizal associations may be expected to prevail across different climatic conditions. The dominance of forest systems by AMF versus EMF has important repercussions for nutrient cycling, carbon storage, and even forest diversity6,7.
Aboveground, foliar pathogens help to mediate interactions between plant hosts, with important outcomes for plant competition and coexistence8. Pathogens differentially affect competing plant communities and can reduce the dominance of major competitors, maintaining or increasing biodiversity within ecosystems. This dynamic is crucial for understanding plant community structure and the effects environmental changes have on forest resilience. Van Nuland et al., shed light onto these interactions, and they find that increased precipitation corresponds to higher leaf pathogen loads and higher pathogen diversity. Similar results have been demonstrated for Populus across a regional scale, where wetter conditions corresponded to higher pathogen loads1. These findings from Van Nuland et al. use a continental-scale approach reinforce how precipitation is an important factor determining the structure of foliar pathogen communities, even across a broad range of different host plants, temperature, and environmental conditions.
Figure 2|Map showing the distribution of different Poplar species. Poplar can inhabit a diversity of ecosystems across the United States, likely with the help of their microbial partners. Image credit: Van Nuland et al. 2023
Further, the authors model how climate change may impact these different fungal functional groups both above and belowground. They find that fungal communities interacting within a single tree above and belowground might have differential responses to a changing climate. By highlighting the potential for asynchronous response of fungal communities to climate change above and belowground, Van Nuland et al. open up a critical area of future research investigating the potential for dysbiosis in trees at important climatic clines.
The dynamic interplay between fungal communities and plants is crucial for ecosystem health and resilience, as fungi play key roles in nutrient cycling, soil health, and plant growth6 and the critical functions of fungal communities in supporting ecosystem health, productivity, and resilience. Van Nuland et al. demonstrate the need for incorporating both above and belowground fungal dynamics into climate models to better predict the impacts of climate change on forest biodiversity and function. Understanding these relationships will aid in better predicting the broader ecological consequences of climate change, emphasizing the need for strategies that consider fungal biodiversity and integration of fungal dynamics into climate models and ecosystem management strategies.
The profound influence of climatic factors in shaping fungal ecosystems is an essential aspect of ecological research that requires further attention. Critical insights from Van Nuland et al. emphasize the intricate relationship between climate variables, pathogen dynamics, and forest ecosystem health. With climate change influencing precipitation and temperature, there is a need for integrating microbial dynamics into forest health measurements given these environmental factors largely influence the diversity and abundance of plant-associated fungal communities. This research’s broad geographic and species scope sets a strong foundation, yet its findings prompt questions about the long-term dynamics of these interactions under varying climate scenarios. Future research which delves deeper into the mechanistic pathways through which climate influences fungal communities and their interactions with host plants is crucial. Moreover, integrating these insights into predictive models could enhance our ability to forecast ecosystem responses to environmental changes, offering valuable guidance for biodiversity conservation strategies.
References
1. Barge, E. G., Leopold, D. R., Peay, K. G., Newcombe, G. & Busby,
P. E. Differentiating spatial from environmental effects on foliar
fungal communities of Populus trichocarpa. J. Biogeogr. 46, 2001–2011 (2019). https://doi.org/10.1111/jbi.1364
2. Peay, K. G., Kennedy, P. G. & Talbot, J. M. Dimensions of
in the Earth mycobiome. Nat. Rev. Microbiol. 14, 434–447 (2016).
3. Steidinger, B. S., Crowther, T. W., Liang, J., Van Nuland, M. E., Werner, G. D. A., Reich, P. B., Nabuurs, G. J., de-Miguel, S., Zhou, M., Picard, N., Herault, B., Zhao, X., Zhang, C., Routh, D., & Peay, K. G. (2019). Climatic controls of decomposition drive the global biogeography of forest-tree symbioses. Nature, 569(7756), 404–408. https://doi.org/10.1038/s41586-019-1128-0
4. Fernandez, C. W., Nguyen, N. H., Stefanski, A., Han, Y., Hobbie, S. E., Montgomery, R. A., Reich, P. B., & Kennedy, P. G. (2017). Ectomycorrhizal fungal response to warming is linked to poor host performance at the boreal-temperate ecotone. Global Change Biology, 23(4), 1598–1609. https://doi.org/10.1111/gcb.13510
5. Van Nuland, M. E., Daws, S. C., Bailey, J. K., Schweitzer, J. A., Busby, P. E., & Peay, K. G. (2023). Above- and belowground fungal biodiversity of Populus trees on a continental scale. Nature Microbiology, 8(12), Article 12. https://doi.org/10.1038/s41564-023-01514-8
6. Averill, C., Fortunel, C., Maynard, D. S., van den Hoogen, J., Dietze, M. C., Bhatnagar, J. M., & Crowther, T. W. (2022). Alternative stable states of the forest mycobiome are maintained through positive feedbacks. Nature Ecology & Evolution, 6(4), 375–382. https://doi.org/10.1038/s41559-022-01663-9
7. Lu, M., & Hedin, L. O. (2019). Global plant–symbiont organization and emergence of biogeochemical cycles resolved by evolution-based trait modelling. Nature Ecology & Evolution, 3(2), 239–250. https://doi.org/10.1038/s41559-018-0759-0
8. Mordecai, E. A. (2011). Pathogen impacts on plant communities: Unifying theory, concepts, and empirical work. Ecological Monographs, 81(3), 429–441. https://doi.org/10.1890/10-2241.1