Symbiotic nitrogen fixation and the delivery of multiple ecosystem services: a global change perspective

A key challenge facing humanity in the coming decades will be ensuring food supply to a growing human population without compromising the sustainability of many agro-ecosystems worldwide. Although agricultural soils remain firmly at the foundation of human life-support systems, human domination of terrestrial ecosystems over the last century has greatly affected their long-term sustainability as well as reducing soil biological diversity. This has mainly occurred through widespread land-use changes and through the chronic deposition of biologically available nutrients, such as nitrogen (N) and phosphorous (P). Here I argue that a better understanding of the ecological role of symbiotic N-fixers could help in developing more sustainable multifunctional agro-ecosystems. N-fixers are beneficial for the delivery of multiple ecosystem services such as greater primary productivity (i.e. increased crop yields), increased soil carbon (C) and N sequestration, and higher soil biological diversity. Understanding the ecological mechanisms responsible for the provision of these ecosystem services may also be critical for reducing the global-warming potential of many agricultural practices worldwide.