Climate and Pollution Affect the Microbiota of Leaves in European Forests

In an article published in the journal Communications Earth & Environment, an international research group led by scholars from the University of Bologna has identified the factors that shape the microbiota housed in beech and Scots pine canopies and how these bacterial communities vary across Europe, from the forests of Finland to those overlooking the Mediterranean.

“The diversity of the microorganisms that live on leaves is determined by temperature, the host species, and its associated foliar traits”, says Rossella Guerrieri, professor at the Department of Agricultural and Food Sciences of the University of Bologna, who coordinated the study. “Therefore, it will be important to understand how these bacterial communities might change in response to changing climate and increasing pollution”.

The forests included in this study are part of the ICP Forests network, a programme established in 1985 under the Convention on Long-range Transboundary Air Pollution of the United Nations. The aim of the programme is to evaluate and monitor the effects of air pollution on forests in Europe. Among the monitored forests are two Italian sites: the beech wood of Collelongo, in the Abruzzo Region, and the beech wood of Cansiglio, in the Veneto Region.

The researchers have described, for the first time on a continental scale, the composition and diversity of the bacteria that are housed in canopies of trees (the phyllosphere) such as beech and Scots pine trees, two of the most common species in European forests.

Thanks to the work of professional tree climbers, the researchers collected leaves from beeches and needles from Scots pines at three different heights along the profile of the canopy.


Standard DNA extraction protocols were followed to characterise the microbial communities in the phyllosphere, observe whether these bacteria have functions relevant to the nitrogen and carbon cycles, and understand how these communities are influenced by environmental and climatic factors.

The primary factor determining the structure and diversity of bacterial communities on leaves is the host species. For example, microorganisms capable of fixing nitrogen are present in the canopies of Scots pines. This phenomenon could be explained by the lower nitrogen availability in coniferous habitats compared to that of hardwood trees.

Overall, the phyllosphere microbiota plays a fundamental role not only in promoting plant growth and resilience to environmental stresses but also in regulating the cycles of carbon, nitrogen, phosphorus, and sulphur. These functions may be limited or altered by temperature changes and pollution.

“We observed that as we move from Northern to Southern Europe, not only does temperature change, but atmospheric nitrogen deposition also varies. This is somehow determined by the concentration of reactive nitrogen compounds in the atmosphere which serves as an indicator of air pollution levels”, confirms Guerrieri. “After being introduced into the atmosphere, these compounds deposit on aquatic and terrestrial ecosystems, including forests”.
 
The results obtained highlight the need for large-scale studies to clarify how the phyllosphere microbiota mediates the responses of forest ecosystems to global changes. In this respect, the University of Bologna research group has been carrying out an experiment in the beech wood of Cansiglio, Veneto, for over ten years to simulate increasing pollution and monitor its effects. This investigative work was made possible thanks to the support of the “Vittorio Veneto” Carabinieri Command for Biodiversity and the Cansiglio unit.
 
The study was published in the journal Communications Earth & Environment with the title “Host species and temperature drive beech and Scots pine phyllosphere microbiota across European forests”. The members from the University of Bologna who participated in the study are Rossella (Maria Rosa) Guerrieri, Daniela Sangiorgio (a young researcher who led the study), Federico Magnani, and Dario Ravaioli of the research group on Forest Ecology and Silviculture from the Department of Agricultural and Food Sciences.