View inside one of the three heated cages in the experiment. Photo: Maria Faticov.
Climate warming plays a larger role than plant genes in influencing the number and identity of fungal species on oak leaves, especially in autumn. Recently published research sheds light on how warming and tree genes affect the dynamics of fungal communities across the season.
'One of our major findings was that elevated temperature decreased the number of fungal species and changed their community composition, especially in the late season,' said lead author Maria Faticov, a researcher at the Department of Ecology, Environment and Plant Sciences (DEEP) at Stockholm University.
Plants host thousands of microscopic organisms and leaves are no exception. Leaves harbour a large diversity of microorganisms including fungi, bacteria and, less frequently, archaea. Fungi are among the most diverse groups of microorganisms living on leaves. Some of these microscopic fungi cause disease, others can promote plant growth and defend leaves against biotic and abiotic stresses, and still others play an important role in leaf senescence and decomposition.
Oak leaves and their fungi. Illustration by Maria Faticov.
Climate is one of the main factors influencing fungal development, either directly or indirectly, by triggering plant defences.
'From earlier studies, we know that the number of fungal species and their abundance change as leaves age and the season progresses from spring to autumn. What we do not know is what role climate warming and plant genetic variation play in shaping fungal communities across the growing season,' said Ayco Tack, associate professor at DEEP.
To answer this question, researchers took on a challenging project – they built six identical cages in a field to the north of Stockholm, each cage the size of a small living room. Scientists put 132 young oak trees into the cages that represented five different genotypes. Half of the cages were heated from May to October using ceramic heaters. The remaining cages were left as the control and did not have heaters in them. The temperature in the heated cages was increased by around 2°C to mimic the global temperature increase predicted by scientists to occur by the end of the century. Researchers collected leaves in the early, middle and late growing season and used DNA sequencing to find out which fungi had colonised the leaves. This allowed them to compare the changes in fungal community structure between the control and warming treatment and also among oak genotypes.
The process of setting up the experiment: more than a dozen oak trees representing five different genotypes were brought to a field north of Stockholm. Photo: Maria Faticov.
'We observed that fungal community composition drastically changed from spring to autumn, with yeasts increasing in relative abundance and fungal pathogens decreasing. Interestingly, while experimental warming had a major impact on the fungal community, oak genotype explained only a minor part of the variation in the number of fungal species and their composition,' said Maria Faticov.
These findings suggest that warming is one of the most important environmental factors shaping fungal community development during the growing season and emphasizes how profound the effects of ongoing climate change may be to plant health and ecosystem functioning.
Open field warming experiment. Scientists build six cages with half of them being actively heated with ceramic heaters. In each cage, researchers placed 22-25 oak trees representing five different genotypes. Photo: Maria Faticov.
The researchers did not link the observed change in fungal community structure under warming with plant health and ecosystem functioning. More detailed long-term experiments are needed to predict how changes in the fungal community under climate warming will influence the plants they live on and their surrounding environment.
'In future studies, it will be interesting to investigate how these changes in the number of fungal species and their abundances under warmer climate impact such important processes as plant health, leaf senescence and litter decomposition,' said Maria Faticov.
Read the article: Faticov, M., et al. (2021) Climate warming dominates over plant genotype in shaping the seasonal trajectory of foliar fungal communities on oak. New Phytologist. doi: 10.1111/nph.17434
Read the press release in Swedish.
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