Evidence, causes, and consequences of declining nitrogen availability in terrestrial ecosystems

The productivity of ecosystems and their capacity to support life depends on access to reactive nitrogen (N). Over the past century, humans have more than doubled the global supply of reactive N through industrial and agricultural activities. However, long-term records demonstrate that N availability is declining in many regions of the world. Reactive N inputs are not evenly distributed, and global changes-including elevated atmospheric carbon dioxide (CO2) levels and rising temperatures-are affecting ecosystem N supply relative to demand. Declining N availability is constraining primary productivity, contributing to lower leaf N concentrations, and reducing the quality of herbivore diets in many ecosystems. We outline the current state of knowledge about declining N availability and propose actions aimed at characterizing and responding to this emerging challenge.

Automated summary

The productivity and life-supporting capacity of ecosystems depend on access to reactive nitrogen. However, long-term records show that nitrogen availability is declining in many regions of the world. Global changes, such as elevated atmospheric carbon dioxide levels and rising temperatures, are affecting the balance between ecosystem nitrogen supply and demand. This decline in nitrogen availability is limiting primary productivity and reducing the quality of herbivore diets in many ecosystems. We outline the current state of knowledge about declining nitrogen availability and propose actions to address this emerging challenge.