Plants, soil and microfauna – how does light quality affect forest ecosystems?

The Canopy Spectral Ecology and Ecophysiology group at the University of Helsinki doing field work (photo: Marta Pieristé).

During spring time when the canopy leaves emerge in deciduous trees in temperate forests, there is a drastic change in light quality reaching the forest understorey. In collaboration with the Canopy Spectral Ecology and Ecophysiology group (CanSEE) at the University of Helsinki, researchers from the University of Rouen (Université de Rouen) visited Lammi Biological station this summer to investigate how this drastic change in light quality reaching the forest floor affects the ecosystem as a whole.

Plants in the understorey utilise light signals as cues to help time when their leaves emerge, when they flower, how to tall to grow, how large to make their leaves, as well as affecting their photosynthesis, leaf pigments and root growth.

Over the last three years the CanSEE group led by Dr Matthew Robson has been characterising the changes in the composition of light that reaches the forest understorey, and examining how different plant species respond to the change in these light signals. However these changes seen above ground are only half the story.

How does this affect below ground processes? The properties of soil in close vicinity to plant roots are modified by a large range of processes that occur during plant growth, which in turn affect the rhizosphere microbiota. Plant roots not only contain compounds such as sugars and amino acids for soil microbiota, but also compounds for defence such as antimicrobials and nematicides. Furthermore, the uptake of ions in the soil by roots can drastically affect the pH of the soil.

Researchers Dr Estelle Forey and Marta Pieristé from the University of Rouen are now beginning to investigate these questions, and in collaboration with CanSEE group, seek to understand how light quality in the forest understorey affects the ecosystem as a whole.

After long term plots either blocking out different light signals were set up in 2016, the two research groups have begun to sample the changes that occur in plants, soil and microfauna when these plots are deprived of different light signals.

A filter blocking out blue light over plants in the forest understorey. These long term plots were set up in 2016, where the plants have been monitored over the course of two years (photo: Marta Pieristé)..
A filter blocking out blue light over plants in the forest understorey. These long term plots were set up in 2016, where the plants have been monitored over the course of two years (photo: Marta Pieristé)..
Right: Dr Estelle Forey and PhD student Craig Brelsford from CanSEE group taking soil core samples from the plots. These will then be analysed by for the content of the soil, and the composition of mircofauna inside (photo: Marta Pieristé).
Dr Estelle Forey and PhD student Craig Brelsford from CanSEE group taking soil core samples from the plots. These will then be analysed by for the content of the soil, and the composition of mircofauna inside (photo: Marta Pieristé).

The results from this work may be important in understanding how climate change will affect the forest understorey ecosystem. The date of canopy leaf out in spring is advancing at 2.5 days per decade since 1971 in temperate forests due to rising global temperatures. In turn, this means that the changes in light signals due to canopy shade in the forest understorey will occur earlier, and may have cascading effects on understorey species of plants, soil and microfauna.

Text: Craig Brelsford, PhD Student (Canopy Spectral Ecology and cophysiology (CanSEE) Group).

Photos: Marta Pieristé.

Environmental change on trophic interactions in the Baltic Sea

Eider duck has recently been classified as endangered within the EU (photo: Heikki Eriksson).
The eider duck has recently been classified as endangered within the EU (photo: Heikki Eriksson).

A new research initiative at Tvärminne Zoological Station (TZS) brings together long-term research projects and conducts field and laboratory experiments, all in order to understand the function of the Baltic food web and how it is affected by environmental change. The research focuses on a community module consisting of blue mussels, eider ducks and white tailed sea eagles. This module forms a central part of the Baltic ecosystem and contains a keystone species, a mesopredator and a top predator and it links the marine and the terrestrial environments. We investigate the direct and trophically mediated impacts of environmental change within this group of closely interacting species representing three different trophic levels. Special emphasis is put on the trophic interactions surrounding the eider duck and how these affect its population development. The eider populations are in precipitous decline and the species was recently classified as endangered within the EU. We hope to understand what processes are driving the eider populations and to mitigate potential threats.

Blue mussels covering the rocky bottom (photo: Kim Jaatinen).
Blue mussels covering the rocky bottom. The blue mussel is the main food item for eider ducks (photo: Kim Jaatinen).

In 2017 Kim Jaatinen (TZS) and Markus Öst (Åbo Akademi) conducted their traditional fieldwork studying the Tvärminne eider population. This season was especially interesting and worrisome: the research group recorded an all time low in the population’s offspring production. Normally the 12 km wide research area produces between 1000 and 2000 ducklings, but this year only a mere 41 ducklings were seen in the standard duckling survey conducted at the end of June. Predation by sea eagles plays a major role in this low production but also other causes are under investigation.

Bird number NS1A6243m ready to go (photo: Heikki Eriksson).
One more eider female measured, sampled and ready to go (photo: Heikki Eriksson).
Young eider ducks (photo: Heikki Eriksson).
These less than a day old eider ducklings are ready to go to sea (photo: Heikki Eriksson).

The blue mussel study conducted by Mats Westerbom, Kim Jaatinen and Alf Norkko focuses this year on analysing the effects of climate change on the population dynamics of this species so central to the Baltic ecosystem. In addition to applying new analysis techniques to the long-term data, the group has continued work on monitoring recruitment of young mussels to the population. This year a new monitoring scheme was started, which aims at following spatial and temporal variations in the condition (i.e., meat content) of the mussels.

The findings of this year’s projects will all shed light on the impact we are having on the Baltic Sea and how its ecosystem will be affected. This knowledge may help us mitigate the bad influence we are having on our environment. Stay tuned for upcoming results!

A crushing wave. A typical element in the lives of the eider ducks and the blue mussels (photo: Kim Jaatinen).
A crushing wave. A typical element in the lives of the eider ducks and the blue mussels (photo: Kim Jaatinen).

Text: Dr. Kim Jaatinen, Tvärminne Zoological Station
Photos: Heikki Eriksson & Kim Jaatinen