A dark place

Since a couple of years, I have gotten quite interested in the effects of artificial light at night, especially on plant-mediated interactions. This interest was mostly sparked by many kitchen table conversations with my friend and former house mate Davide, who has studied effects of light at night on bird behaviour for many years. It appears to be quite problematic for some of them. I think many people probably do not realize it, given that light pollution is active mostly when we are not, but it is pretty damn hard to find a dark place in most populated areas in the world. Some light is almost always seeping in. And it is an ever-growing problem. I find this both interesting and worrisome, so I wanted to study its effects more in-depth. Given that I work on plant-mediated interactions, and plants are quited tuned into light for their physiological processes, the link was easily made. I had digested several ideas for two years, before I applied to my position in Freising, but when I shared them in my job interview, they were met with great interest. (I got the job!)

When I arrived in Germany, I was immediately offered space in seven separate greenhouse chambers available a couple of months after my arrival. I have since used these spaces to conduct several experiments to investigate how various aspects of artificial light at night affect a particular plant model system. The results were very interesting, and quite unexpected, which is always good to keep oneself curious (more on this experiment will follow as soon as I have all the data analyzed, and a manuscript in a more final shape). It was a great way to start this new research line of mine, which had been on my mind for so long.

What I had not thought about much is how to follow up on my first results, once I would have the first. Interesting results always spark many ideas for follow-up experiments. At least they do for me. First of all, I did not consider that space for experiments would be an issue, given that there is a serious plant growth facility near our campus. A second problem, that relates to space as well, is that I never thought deeply about how to separate light treatment and dark controls if you don’t have separate spaces. This is obviously because I had seven climate chambers available, and they separated the treatments perfectly. Now, a problem is that the climate chambers I have used before are in heavy demand. That is, I have used my time, and now I have to wait my turn to do more work in them. Upon submission of a proposal for the next call for experiments, I have recently been granted several months of space… but it will be only from late 2022. As you can imagine, this sort of time frame is not very useful if you want to make some progress in the foreseeable future.

So my thoughts went into different directions, being alternative separation of treatments, and collection of lit and unlit field data.

For a while now I have been breaking my head over options to create lit and unlit spaces in the same greenhouse. Of course this would be doable, by fencing the treated areas off entirely, and placing a light inside. However, at the same time, it would be important not to block the entrance of daylight into the space. Therefore, a closed box would not work. This would separate treatments, but have no daylight. An open-top box with sides fenced-off, perhaps? I’m a bit worried that the glasshouse, being made of glass, will scatter the light all over the place. My most recent idea is to have open top chambers in the greenhouse, with lights that are semi-covered from above (to prevent scatter into the greenhouse). In my mind, this will severely reduce spillover of light from the treatment into the control. But will this work in practice? And maybe more importantly, will it convince a reviewer at all? Maybe I will give this system a go over the next few months, just to see how it would look.

The second brain fart – the one about collecting field data – was also a thought that was easier said than done. Of course collecting plant material from the field is easy. Measuring various plant parameters related to growth and fitness should not be too hard. However, what I had characterized as an easy-peasy job, turns out to be a bit more difficult than anticipated. Of course street lights are everywhere. Some of the weeds that I work on are also everywhere. So far, that all sounds like a perfect scenario for success. However, it is well-known that plants strongly respond to local conditions such as soil (a)biotic conditions, and other environmental characteristics such as temperature. A lit plant is easy to find. But ideally, my unlit control plants should be somewhat local, at least under similar soil and vegetation conditions. This turns out more challenging than I thought. Street lights often being placed in road verges, whenever you move away from them, you almost always meet different soil conditions (e.g., agricultural fields or tarmac) or the next street light… These bloody street lights are everywhere! If that isn’t difficult enough, there turns out to be a lot of traffic at night in many areas, that shine their confounding lights on potential plants. In a student project, we have now tried to collect data from plants at different distances from light sources (considering that light intensity decreases with distance from the source). Given the proximity of most street lights to other street lights, the distances to the light poles are 10-15 metres at most. I wonder if these small differences in light conditions will cause an observable effect in plants. We’ll see – if you don’t measure it, you will never know.

Regardless of the challenges, I still think this often overlooked driver of global change, being light pollution, is still highly relevant and interesting to study. I can’t help but wonder if these challenges are among the reasons why this is not so heavily studied? If anyone has brilliant ideas (pun intended) on how to create a dark place next to a lit place, let me know. I’d be happy to collaborate in any future experiment.

Published by Robin Heinen

Father of two | Husband | Entomologist and Ecologist | Postdoctoral Researcher @ TUM | Traveler | Coffee Addict

3 thoughts on “A dark place

    1. I had not seen it specifically, although I have used several of the papers as references for an invited views piece that is currently under review (submitted early Feb). I think there is one relevant piece in this collection that I should still read and cite in a revised version.


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