Researchers have found that an unbalance of nutrients in an ecosystem can reduce biodiversity. Human activity often results in the addition of nutrients to the environment, such as nitrogen and phosphorous. These extra nutrients cause plants to shift competition from a battle for soil nutrients to competition for sunlight. The details are in a paper just published in the journal Nature.
Plants must compete for a limited set of resources, there are limited nutrients naturally found in soil. This prevents any one plant species from taking over and encourages the formation of niches. Fertilization by humans, whether intentional or from run-off, adds an excess of nutrients to the environment. This may remove the limiting factors allowing so many plant species to coexist and was the focus of this study.
A group of researchers studied the effect of human-induced nutrient imbalances on ecosystems in 45 grassland sites across multiple continents. The team found that as extra nutrients were added to an ecosystem, the variety of plant species decreased. There was a direct relationship; as more nutrients made their way into an ecosystem, there was a greater loss of local biodiversity. Mathematical models could even be used to predict how much biodiversity would decrease with the addition of more nutrients. The greatest loss of diversity happened when multiple nutrients were added to an environment in combination, such as nitrogen and phosphorous together.
Human activity leads to an imbalance of natural nutrient cycles. Different types of pollution, including agricultural run-off, can add an excess of nutrients such as nitrogen, phosphorous, and potassium. The research team found that these additional nutrients decreased biodiversity in affected ecosystems. When soil nutrients are no longer limited, plants begin to compete for space and light. This favors some species over others, leading to an overall decrease in the number of plant species that can coexist. The team believes that this human-influenced change is damaging ecosystems throughout the world.
Stanley Harpole et al. Addition of multiple limiting resources reduces grassland diversity. Nature (2016).