Pepijn W. Kooij
Kew Science Blog: Celebrating the importance of mycological research [link]
Pepijn Kooij, Tuula Niskanen & Laura Martinez-suz
Although Kew is mostly known for its work on plants, a large part of the research is focused on the diversity and importance of fungi. Pepijn Kooij explains how mycologists at Kew are working to understand a wide variety of topics in fungal biology and the importance of fungi for plant diversity.
There have been many estimates of the total number of fungi species, reaching up to 6 million (Taylor et al., 2014). However, the widely accepted range is “at least 1.5, but probably as many as 3 million” (Hawksworth, 2012), far outnumbering flowering plants (Kew’s estimates go as far as 400,000 species of flowering plants).
As only around 100,000 species of fungi have so far been described worldwide, one of the goals for the mycologists at Kew is to document the missing diversity, but also to investigate their importance for ecosystems as a whole. Key to this task is the Fungarium, containing over 1.25 million specimens of dried fungi, the largest collection of fungal specimens in the world today.
How to investigate fungal diversity
As part of the fungal diversity research at Kew, Tuula Niskanen, one of Kew’s mycologists, studies the diversity and evolution of mushrooms, with a special interest in webcaps (Cortinarius). Webcaps are the most species-rich genus of the Agaricales, the gilled mushrooms, with a worldwide distribution. They are important ectomycorrhizal fungi and play a significant role in the nutrient economy of forest trees. However, they are still very poorly known and many species are not yet described and named. Even in Britain many new species remain to be discovered.
Knowledge of the evolutionary history of fungi provides the means for a better understanding of the current diversity and distribution of species. It also sets a baseline for further studies of diverse evolutionary questions, which cannot advance without the fungal specimens. The vast collections of fungi in Kew and other institutes world-wide provide a significant resource for these studies, which in turn help new expeditions to be targeted to previously unexplored areas.
Plant-fungal symbiosis and environmental change
Globally, plant-fungal partnerships underpin terrestrial ecosystems. "Fungus-roots", or mycorrhizas (myco= fungus, rhiza=root), are ancient, obligate and ubiquitous mutualisms between the vast majority of plants and members of several fungal phyla to exchange carbon derived from photosynthesis for fungal-acquired soil nutrients (Field et al., 2015). We can say that most plants don’t have roots, they have mycorrhizas! For example, tree roots in boreal, temperate and some tropical forests form ectomycorrhizas (ecto=outside), which envelop root tips like gloves, and play crucial ecological roles by determining the nutrient acquisition and drought tolerance of trees. Due to their distinctive ecological niche, mycorrhizal fungi are at particular risk to changes in either their soil environment or host carbon allocation.
Global change is one of the biggest threats to organismal and functional diversity, yet little is known about its potential impacts on plant-fungal interactions. Fungi with different soil exploration types (such as those specialised for long-, medium or short-distance water and nutrient transport) respond strongly to pollution causing eutrophication and acidification in European forests (Suz et al., 2014). Kew researchers Laura Martinez-Suz, Martin I. Bidartondo, Sietse van der Linde and William Rimington (Imperial College London) study the evolution, diversity, ecology and distribution of mycorrhizal fungi and their environmental drivers in different ecosystems. Research on this functional guild of fungi is important because, even though they are still largely neglected when it comes to conservation, they are likely to determine the resilience of ecosystems to environmental change (Suz et al., 2015).
Humans have been domesticating crops for approximately 10,000 years. Ants, however, have been growing fungal crops for 50 million years and are considered to be the oldest farmers in the world. Much like humans did, for instance with bananas, the most recently derived group of these ants, the leaf-cutting ants, created a polyploid (with more than two sets of chromosomes) fungal lineage, while maintaining this crop without sexual reproduction or mushroom growth (Kooij et al., 2015). This polyploidisation may enhance traits the ants benefit from, such as increased nutrition or resistance to disease.
My research focuses on the mechanisms that lie behind the maintenance of the asexuality of these fungi. Even though there doesn’t seem to be any genetic mixing, the fungi cultivated by ants have a high diversity with a still unknown number of species. By investigating fungarium specimens from free-living fungi closely related to the ant crops in the genera Leucoagaricus and Leucocoprinus, it will be possible to find the closest wild relatives from which the ants derived their cultivars. This will in turn help to understand the evolution of this enigmatic mutualism of ants and fungi, and potentially lend insight into our own agricultural symbioses.
Field, K.J., Pressel, S., Duckett, J.G., Rimington, W.R., & Bidartondo, M.I. (2015). Symbiotic options for the conquest of land. Trends in Ecology and Evolution 30: 477-486.
Kooij, P.W., Aanen, D.K., Schiøtt, M., & Boomsma, J.J. (2015). Evolutionarily advanced ant farmers rear polyploid crops. Journal of Evolutionary Biology, DOI: 10.1111/jeb.12718.
Suz, L.M., Barsoum, N., Benham, S., Dietrich, H.P., Fetzer, K.D., Fischer, R., García, P., Gehrman, J., Kristöfel, F., Manninger, M., Neagu, S., Nicolas, M., Oldenburger, J., Raspe, S., Sánchez, G., Schröck, H.W., Schubert, A., Verheyen, K., Verstraeten, A., & Bidartondo, M.I. (2014). Environmental drivers of ectomycorrhizal communities in Europe's temperate oak forests. Molecular Ecology 23(22): 5628-5644.
Suz, L.M., Barsoum, N., Benham, S., Cheffings, C., Cox, F., Hackett, L., Jones, A.G., Mueller, G.M., Orme, D., Seidling, W., Van der Linde, S., & Bidartondo M.I. (2015). Monitoring ectomycorrhizal fungi at large scales for science, forest management, fungal conservation and environmental policy. Annals of Forest Science. DOI 10.1007/s13595-014-0447-4.
Taylor, D.L., Hollingsworth, T.N., McFarland, J.W., Lennon, N.J., Nusbaum, C., & Ruess, R.W. (2014). A first comprehensive census of fungi in soil reveals both hyperdiversity and fine-scale niche partitioning. Ecological Monographs 84(1): 3-20.
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