Like many other nutrients, nitrogen is crucial for life on earth; nitrogen is needed for the production of nucleic acids and amino acids, which make up proteins, which in turn builds the very physical beings of organisms. Producers depend on soil bacteria to fix nitrogen gas into the form of ammonium or nitrate in order to use it. But what if one species of a producer consumed all the available nitrogen in the soil like a vacuum cleaner cleaning up dust? That species would grow as if it had its own personal fertilizer. Needless to say, that particular species would flourish, and other plant populations, on the other hand, would dwindle.
Mahtaab Bagherzadeh, an undergraduate at Virginia Tech, participated in a study of how rhododendrons (more commonly known as azaleas) disrupt the nitrogen cycle with their greediness for nitrogen. In recent years, there has been a trend in areas losing various plant species when they are densely populated with rhododendrons. Declining plant species include chestnut and hemlock. Figure 1 is an example of dying hemlock leaves. Figure 2 is an example of a healthy bough of hemlock.
How does this nitrogen feud work? Well, microbes need nitrogen to sustain themselves as well. The relationship between microbes and plants is not one of commensalism; it’s not as if microbes exist for the sake of the life above ground. So they take whatever nitrogen they need and leave what’s left over for the plants. Rhododendrons release complex proteins that are difficult for microbes to break down. These proteins lock the nitrogen in organic compounds to create a hoard of nitrogen accessible to only rhododendrons. And without nitrogen, non-rhododendrons can’t survive.
Bagherzadeh and his advisor, Jeb Barrett, continue to study nitrogen and soil communities to address this issue with rhododendrons, but the take-away I am getting from this report is actually a reinforcement of the idea that these cycles and food-chains are more interactive with each other than a textbook would emphasize. Yes, nitrogen cycles through the atmosphere and the earth and so do carbon compounds. And yes, consumers eat producers before being decomposed into the ground by bacteria. But those cycles weave through one another, and if a species like the rhododendron disrupts a cycle, multiple issues pertaining to trophic interactions and nutrient cycles will ensue, not just ones respective to that one cycle.