Cedar Creek LTER

How Will Nitrogen Pollution Affect Carbon Storage?

Carbon is a natural feature of the environment and necessary part of life on our planet. In excess, carbon becomes a pollutant, and is a common component of the “greenhouse” gasses such as carbon monoxide (CO), carbon dioxide (CO2) and methane(CH4). Soil, water and vegetation have some capacity to store and process carbon—just how much is an important feature for determining the effects of global climate change.

Nitrogen is another natural feature of the environment that, in excess, becomes a pollutant. Through agricultural and industrial activities, humans are increasing the amount of nitrogen pollution worldwide. However, it is unclear how elevated nitrogen pollution will affect the processing, or cycling of carbon, particularly decomposition processes. In a grassland study in which plant biodiversity, CO2, and nitrogen deposition were manipulated (a.k.a. the BIOCON experiment), we have been examining how the interactions between plant species composition and nitrogen pollution influence soil organic matter dynamics. Using the isotopic tracers provided by the elevated CO2 and nitrogen treatments in BIOCON, we have demonstrated that elevated nitrogen inputs decrease decomposition of soil organic carbon, but only in the presence of plants that produce lignin-rich litter. For example, in Kentucky bluegrass, which has high lignin roots, elevated nitrogen inputs decrease soil organic matter decomposition; however, in quackgrass, which has low root lignin, elevated nitrogen inputs have no effects on soil organic matter decay. Thus, increased nitrogen pollution could lead to carbon accumulation and storage in soils, but only in communities with species that have high concentrations of lignin in their tissues. To our knowledge, this is the first time that such an interaction between nitrogen deposition and plant species traits has been shown to influence soil carbon sequestration.

(This work has been submitted to Nature by Feike Dijkstra, Sarah Hobbie, and Jean Knops, and Peter Reich.)