On your next visit to the park, enjoy all the different species you can see, but there is also another world of wildlife floating all around you. This is the biodiversity that we can’t see with the naked eye – the secret life of the air we breathe.
The air is full of microscopic life forms: dense clouds of bacteria, tiny fungi and algae which surround us. There are single-celled organisms called protozoans and vast quantities of viruses, moss spores and plant pollen. There may even be a few microscopic moss-dwelling animals called tardigrades.
Studies have shown that up to a million microbial cells can be found in a single cubic metre of air, and people can inhale a whopping 100 million bacteria each day.
A recent study in Scientific Reports suggested that many of the life forms floating in the air actually originate in the soil beneath our feet. Soil is arguably the most biodiverse habitat on Earth.
Microbes are incredibly light, so they become airborne easily and are carried far and wide on the wind. The study shows that distinct layers of bacteria form in the air, with different species and quantities of microbes occurring at different heights. At the average head-height of a standing adult, there were fewer but also different kinds of bacteria compared with those in the air lower down at the head height of a child or sitting adult.
Exposure to lots of different types of microbial life, particularly in childhood, allows our immune systems to build up a strong army of cells that protect us from pathogens. The greater number of microbial species detected closer to the ground could be vital in ensuring children develop robust immunity later in life.
It also matters which environments we spend time in. The air in wooded areas of an urban park has been shown to contain more bacterial species but fewer potential human pathogens than nearby sports fields. Trees appear to filter the microbial communities in a given airspace, reducing the risk of exposure to microbes that cause disease. Because trees also seem to increase microbial diversity in the air, allowing more of them to grow in urban areas could provide an important health benefit by enhancing our immune systems.
Microbes and the other members of the microscopic world around us are fundamental to the proper functioning of ecosystems, plant health and even climate regulation. We would be wise to learn more about and encourage this unseen life and the important roles that it plays.