Mycorrhizal fungi promote greater tree species diversity

Date:
February 24, 2022
Source:
University of Montreal
Summary:
Researchers have found that mycorrhizas promote greater tree
species diversity in North American forests.



FULL STORY ========================================================================== Fungi, specifically those that are "mycorrhizal," are natural allies of
the forest because they improve tree nutrient acquisition. But which of
the mycorrhizal feeding strategies yields the greatest tree diversity in a forest: strategy A (ectomycorrhiza) or strategy B (arbuscular mycorrhiza)?

========================================================================== Biologists from Universite' de Montre'al and the Plant Biology Research Institute asked the question and found the answer is neither one nor
the other, but rather a combination of the two -- proving that there is strength in numbers -- or rather, in diversity.

The powerful nourishing capacity of mycorrhiza "A mycorrhiza, from
the Greek myco-, 'fungus,' and rhiza, 'root,' is a type of symbiotic relationship between a plant and a fungus that has existed since the colonization of land by plants, several million years ago," explained
Alexis Carteron, lead author of the study.

"This positive association for both partners is unquestionably the most widespread and important form of 'mutualistic symbiosis' in terrestrial ecosystems." Carteron has a Ph.D. in biology from Universite' de
Montre'al and is currently working as a post-doctoral researcher in
the Department of Environmental Science and Policy at the University of
Milan, Italy.



==========================================================================
In botany, mycorrhizal fungi have long been known to provide plants with significant nutritional benefits by extending their root systems up to 10
times the initial root surface and enabling them to better absorb water
and minerals from the soil. For instance, mycorrhizal fungi are able to dissolve phosphorus in the soil, making it available to plants. In return,
the plant provides the fungi with sugar produced through photosynthesis.

"For some time now, there has been growing interest in the important
role of mycorrhizal fungi in plant biodiversity," said the supervisor of
the study, Etienne Laliberte', Canada Research Chair in Plant Functional Biodiversity at Universite' de Montre'al.

Two strategies for fungi The two main types of mycorrhizas,
ectomycorrhizas and arbuscular mycorrhizas, seem to influence the
diversity of tree species in forests in different ways.

Ectomycorrhiza affects about 2 per cent of plant species, mostly conifers
in Northern Hemisphere forests. Arbuscular mycorrhiza, the oldest and
most widespread form of symbiotic association between fungi and plants,
affects 80 per cent of terrestrial plants. The two differ in the way
the fungus attaches to the plant's roots.



========================================================================== Scientists have observed that forests with soils colonized by arbuscular mycorrhiza are more diverse. Species-rich tropical rainforests, for
instance, are composed mainly of arbuscular mycorrhizal trees, while species-poor boreal forests are dominated by ectomycorrhizal trees.

For this reason, researchers believed that arbuscular mycorrhiza promotes coexistence and diversity of plant species, while ectomycorrhiza promotes
the dominance of one or only a few species.

Experimental studies of saplings and large-scale observations in different terrestrial biomes (geographical areas that share a similar climate, fauna
and flora) also appeared to support this hypothesis. It is challenged,
however, by the new study.

More than 80,000 forest plots analyzed Forest trees interact with each
other and with mycorrhizal fungi at a very localized level (within a
few meters) over periods of several decades. Carteron and Laliberte'
therefore had to test the hypothesis on forest plots (i.e. an area of
a few hundred square metres) in a multitude of forests to determine
whether the results could be generalized.

"We analyzed about 82,000 forest plots across the United States and
concluded that plots that were very strongly dominated by either
ectomycorrhiza or arbuscular mycorrhiza had lower tree diversity,"
explained Carteron.

"Surprisingly, it was the forests with a mix of both mycorrhizal
strategies that had a greater number of tree species. So our results
indicate that dominance of any one mycorrhiza, regardless of its type,
appears to decrease forest tree diversity." Can mycorrhizas help
fight climate change? While mycorrhizal dominance can be determined
at several scales, such as the root system, forest plot and biome,
this study underscores the importance of considering the impact of
mycorrhiza on ecological processes at the forest plot level. At this
scale, the study shows, the coexistence of mycorrhizal strategies can
promote plant diversity.

"Sometimes forests with a mixture of mycorrhizal strategies are
overlooked by biologists because they're considered less abundant,"
the researchers noted.

"However, our study has shown that this is not always the case and these
mixed types could, in fact, make up a large part of the world's forests."
Such forests may represent a crucial avenue for forest research and
management targeting greater ecosystem services: "Combating and adapting
to climate change is a good example of the services an ecosystem can
provide, because a thriving forest with high tree diversity constitutes
a reservoir favourable to climate balance," Carteron pointed out.

The study was funded by the Natural Sciences and Engineering Research
Council of Canada, the Fonds de recherche du Que'bec -- Nature et
technologies, and the Bourse d'excellence Hydro-Que'bec -- Universite'
de Montre'al.

========================================================================== Story Source: Materials provided by University_of_Montreal. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alexis Carteron, Mark Vellend, Etienne
Lalibert�. Mycorrhizal
dominance reduces local tree species diversity across
US forests. Nature Ecology & Evolution, 2022; DOI:
10.1038/s41559-021-01634-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220224112647.htm

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