Colour changes in carnivorous Drosera – a possible bioindicator?
Data suggest that with increasing nitrogen deposition, the leaves of the carnivorous plant Drosera rotundifolia change colour from red to green. Could leaf colour of Drosera be used as a bioindicator for N deposition?
More nitrogen makes vegetation canopies close. The increased shading might generate the observed change in colour of the Drosera leaves. It is currently presumed that the red colour is to attract prey, the idea being that at low N the leaves would be redder because prey is more valuable. Jonathan Millett, Loughborough University, measured prey capture using red or green artificial traps. Capture rates were constantly higher for both green traps and leaves. So the red colour does not attract more prey – in fact the green colour does!
The red colour might instead be a photoprotective response – a sunscreen, useful in the shade. The shaded conditions mean that Drosera does not need the sunscreen and so they lose the anthocyanin. The change in colour is thus an indicator of changing plant-plant interactions in response to N pollution (more intense interactions at higher N deposition).
Another explanation may be that at higher nitrogen levels more chlorophyll is produced by the plants. In the leaves, chlorophyll may mask anthocyanin and the leaves can therefore appear green even though they contain high levels of anthocyanin.
To gain more insight into these questions we are currently measuring leaf colour along with environmental variables across sites in Sweden, the UK, and Ireland. We are also collecting plant material for anthocyanin and chlorophyll content measurements.
About our earlier studies:
Planet Earth Online: Pollution makes carnivorous plants go vegetarian
National Geographic: Meat-Eating Plants Getting “Full” On Pollution
BBC Nature: Pollutant turns fly-traps veggie
Climate change responses in the Subarctic
Here, we study the response of subarctic vegetation to increasing levels of temperature and carbon dioxide. This is done in a large climate-change project at Abisko, northern Sweden, and includes recording vegetation changes, and monitoring the growth and demography of the dominating ericaceous dwarf shrubs, i.e., Vaccinium myrtillus, V. vitis-idaea, and Empetrum hermaphroditum. The coordinator of the project is J. M. Melillo, Woods Hole, USA, and its Swedish part is supported by the Swedish Environmental Protection Board.
Population dynamics – demographic analyses of long-lived species
At Abisko, in northern Sweden, three species of carnivorous Pinguicula are common. Starting in 1984, I have followed the fate of mapped individuals together with Bengt Carlsson. We are now developing demographic analyses by constructing stochastic models to examine the effect of environmental variability on the populations.
We will try to answer questions like: What does the long-term population growth look like if the environmental conditions that the plants have experienced during a 23-year period were repeated, in the same order? How would this differ from the scenario that the environmental conditions varied stochastically, but within the limits set by what happened during the 23 years?