How do ecosystems change as they age? It’s a question we address in our most recent article – read it here! We identify how ecosystems might continue accumulating nitrogen even after they stop growing.
Oak forests in Pennsylvania. Young forest stand (about 10 years old) on the left, and older forest stand (over 100 years old) on the right. The older forest has accumulated abundant soil organic matter, and has great potential for capturing nitrogen and holding it in a stable form.
Succession, or the progressive change in ecological systems as they age, has long been an important concept in ecology that helps organize the discipline. For example, ecologists who focus on the cycling of energy and essential nutrients might investigate how these cycles change as an ecosystem ages. Ecologists know that young, growing ecosystems can increase their stockpile of nutrients (such as nitrogen) by storing it in accumulating plant matter. We also know that soils are a huge reservoir for storing nitrogen, and that even old ecosystems can continue to accumulate nitrogen in soil even after the plants have stopped growing. Our research, conducted with Jason Kaye at Penn State and Michael Castellano at Iowa State, suggests a couple mechanisms by which nitrogen can continue to accumulate in the soil of old forests. First, we show that new inputs of nitrogen are captured by soil organic matter much faster than are released, meaning the soil must accumulate nitrogen over time. Second, we found that the potential for this accumulation was greater in older forests because those forests had more soil organic matter. This research helps us understand the link between ecosystem succession and the nutrient economy of ecosystems, and highlights a significant ecosystem service—the capture of nitrogen, which can severely impair air and water quality—of mature ecosystems.
Ecosystems Lab at USF 