This column originally appeared in the November 11, 2007 issue of the Poughkeepsie Journal.
November is a great time of year to think about microbial ecology. Trees drop their fall finery and dead leaves cover the ground. In manicured landscapes, we rake and haul away dead leaves. But what happens to the leaves that blanket natural areas? And given that leaves fall each year, why aren't forests filling up with them? The short answer: microbes.
When most of us think about microbes, the first thing that comes to mind is disease, such as the bacteria that cause bubonic plague, or methicillin-resistant Staph aureus. In reality, however, the vast majority of microbes are either harmless or quite helpful. Examples include the yeast that makes bread rise and the diverse group of soil bacteria that decompose dead leaves.
Soil is alive; it teems with microbial life. A single spoonful can contain billions of beneficial bacteria and fungi. Each year, these diligent microbes perform housekeeping duties on the leaf litter that covers the forest floor. When they consume dead leaves, microbes reduce them to their most basic components: carbon, water, and chemical elements.
The majority of leaf biomass is broken down into carbon dioxide (CO2), which is released back into the atmosphere. During photosynthesis, plants remove CO2 from the atmosphere to power plant growth. When leaves are cast off for the season, microbial activity unlocks the carbon that was stored in plant biomass. Microbial decomposition represents the final step in the carbon cycle.
Through the act of breaking down leaves, microbes enrich the soil for another round of plant growth. Nutrients such as nitrogen and phosphorus are released from the decomposing leaves and added to the soil, where plants can take them up the next spring. In the end, this creates soil that is rich in organic humus and nutrients. Due to its structure, humus helps soil store and retain water.
Institute of Ecosystem Studies scientists have long studied the ecological importance of microbes. Several projects at IES are actively investigating the role that human activities, such as land use and air pollution, have on soil microbial communities IES educators are also working to teach students about microbes, nature's smallest form of life.
Last summer, IES educators developed lessons geared at getting elementary and middle school-aged students to appreciate these tiny powerhouses. While hiking through the Institute's forests, students explored fallen leaves and dead logs for signs of microbial activity. Suddenly, the significance of shelf fungi, sticking out of dead trees like steps, came to life. They are eating dead wood!
While traipsing around Cary Pond, students came to understand that the pungent odor being emitted from pond muck was a sign of microbes—bacteria in this case—decomposing organic matter. These microbes work in no oxygen conditions and the odor is, in essence, bacteria breath.
By the end of the five day camp, students recognized the importance of nature's recyclers. When asked what the world would look like without microbes, some students would lament the absence of bread and mushrooms. But most of them focused on the myriad of all things that would never decay: tree stumps, leaf litter, last year's vegetable garden, compost, dead animals, and so on. Most importantly, when asked to construct an ecosystem mural, the students made sure that microbes were not forgotten.
The living world consists of plants, animals, and microbes. Next time you are out in the forest, or even in your backyard, consider the roles being played by microbes. While they might be easy to over look, they play a critical ecological role. In the act of sustaining themselves, they unlock nutrients, and thereby rejuvenate soil fertility for forest growth.
Dr. Peter Groffman is a microbial ecologist at the Institute of Ecosystem Studies in Millbrook, NY; Kim Notin teaches the Institute's ecology field programs |
