Forest moss and its microbes and atmospheric pollution

The Images of Science format allows you to decode an image of particular interest from a scientific point of view, describe it and understand its challenges.

And yes, foams also contain microbiota, but they fail to be internal, like those in our gut, as they are on the surface of the foam. This is colonized in particular by bacteria and fungi, Protists And invertebrates.

This strand of terrestrial algae, for example, is a species Thuidium tamariscinum, Collected in Fontainebleau Forest in April 2017. Around its central stem, we see leaves covered with small, round spurs, “mamilles.” On the stem, minute dendrites appear: these are secondary photosynthetic structures, “paraphylls,” whose role and origin have been controversial for several decades. What shines on here in its relative absence are the germs in the foam, which are called the “atmosphere”. These different biological components depend on environmental conditions and meteorology, and in particular on ambient pollution.

Terrestrial algae to assess pollution locally

The foams are excellent Vital signs Air quality. In fact, unlike “higher” plants, it has no roots and therefore must obtain the elements they need by absorbing them into the atmosphere. It is therefore particularly susceptible to atmospheric pollution of heavy metals and nitrogen, and by using appropriate conversion factors, the analyzed concentrations in the foams can be compared with the levels of trace elements in the contaminated areas.

The capacity for “bioaccumulation”, that is, the accumulation of organic or inorganic material polluted from the surrounding environment, is used in many national and European monitoring programs and in the framework of the Geneva Convention on Long-range cross-border air pollution.

The main goal of the French system Bram, For “biological monitoring of atmospheric metallic precipitation by foams”, is to monitor the evolution of 26 polluting chemical elements. In 445 French sites, every 5 years since 1996, the trace element content of five Bryopsid algae species, including T. tamariscinum, Is analyzed by Mass spectrometry. This global approach to biological monitoring is complementary to those that use physical and chemical sensors. It makes it possible to draw a national map that identifies areas that, although often far from sources of pollution, are vulnerable to pollutants that pose a risk to the health of the population.

This monitoring demonstrates that the concentration of measured pollutants in foams and in the atmosphere varies with the seasons, sometimes dramatically and unpredictably as well. Several causes have been suggested, for example age and formation of algae or exact weather and climatic conditions.

Our piece of moss, air and weather pollution

April 2017 was dry spring, and it confirms the existence of these fallen partshypothesis According to these structures it will develop to increase photosynthesis capacity in the dry period. The development of weeds also forms thick felting on the surface of the stalk, which also makes it possible – secondarily – to retain the maximum amount of water for algae survival. Paraphylls will be one of the protective mechanisms to survive in arid conditions.

Although this hypothesis is currently controversial, we were actually able to observe very strong differences in the deciduous forms between a rainy and mild winter and a dry and mild spring on the same type of algae from the same study site.

We add a hypothesis The study remains to be verified. We believe that the “atmosphere” – algal microbes – could be responsible for seasonal variations by absorbing and bioaccumulating some airborne pollutants. For example, several studies show that a very current group of Cyanobacteria Able to convert atmospheric nitrogen into organic nitrogen and form a true symbiosis with algae. Others are able to bioaccumulate certain heavy metals, such as lead and copper.

So the similes we see in this picture have a double benefit. On the one hand, it can affect the biological process, by greatly reducing the habitat available for the development of the atmosphere: we see very few microorganisms on the stem and leaves. On the other hand, it can influence the physical mechanism, by disrupting the flow of moist mineral deposits along the rod and thus reducing the extracellular absorption capacity of the foam.

Over the next few years, one of the challenges will be to distinguish between differences inherent in the physiological processes of the foam and its microbes and those associated with so-called “abiotic” factors, that is, the amount of pollutants and the weather. Thus, the reliability of the results can be enhanced and the true value of foams can be assessed as biological indicators of air quality at the national and European levels.

Géraldine Toutirais, a study engineer at MNHN, co-authored the article. Image taken from Valentin Patton’s main work 2 from 2017.

The French BRAMM (Biosurveillance des Fallées Atmosphere Métalliques par les mousses) has been under the auspices of the National Museum of Natural History and Scientific Guidance of Sebastian LeBlond since 2005..