Preface: Towards a full greenhouse gas balance of the biosphere

Ecosystem greenhouse gas (GHG) emissions (CO₂, CH₄, and N₂O) represent a major driver of global environmental change (IPCC, 2014). While there exists an emerging understanding on the net exchange of CO₂ across terrestrial and aquatic ecosystems due in part to the existence of large measurement and modeling networks (Baldocchi et al., 2001; Friend et al., 2007; Raymond et al., 2013; Tranvik et al., 2009), similar information on the biosphere–atmosphere exchange of non-CO2 greenhouse gases (i.e., CH₄ and N₂O) is sparsely available in comparison. To date, a strong focus has been given to so-called high-emission ecosystems, such as wetlands, rivers and lakes, rice cultivations and ruminants for CH4 (Nisbet et al., 2014) and agricultural ecosystems for N₂O emissions (Butterbach-Bahl et al., 2013; Sutton et al., 2007). Even though CO₂, CH₄, and N₂O emissions have been increasing during the last century, a combined quantification of the exchange of these three major greenhouse gases from a wide range of terrestrial and aquatic ecosystems is still missing. Therefore, approaches to develop full greenhouse gas monitoring networks, as currently undertaken in larger environmental research infrastructures such as ICOS (Integrated Carbon Observation System) and NEON (National Ecological Observation Network), are highly valuable.