Temporal and spatial variations of soil CO2, CH4 and N2O fluxes at three differently managed grasslands

[摘要] A profound understanding of temporal and spatial variabilities of soil carbondioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxesbetween terrestrial ecosystems and the atmosphere is needed to reliablyquantify these fluxes and to develop future mitigation strategies. Formanaged grassland ecosystems, temporal and spatial variabilities of thesethree soil greenhouse gas (GHG) fluxes occur due to changes in environmentaldrivers as well as fertilizer applications, harvests and grazing. To assesshow such changes affect soil GHG fluxes at Swiss grassland sites, we studiedthree sites along an altitudinal gradient that corresponds to a managementgradient: from 400 m a.s.l. (intensively managed) to 1000 m a.s.l.(moderately intensive managed) to 2000 m a.s.l. (extensively managed). Thealpine grassland was included to study both effects of extensive managementon CH₄ and N₂O fluxes and the different climate regime occurring atthis altitude. Temporal and spatial variabilities of soil GHG fluxes andenvironmental drivers on various timescales were determined along transectsof 16 static soil chambers at each site. All three grasslands were N₂Osources, with mean annual soil fluxes ranging from 0.15 to1.28 nmol m⁻² s⁻¹. Contrastingly, all sites were weak CH₄sinks, with soil uptake rates ranging from −0.56 to−0.15 nmol m⁻² s⁻¹. Mean annual soil and plant respirationlosses of CO₂, measured with opaque chambers, ranged from 5.2 to6.5 μmol m⁻² s⁻¹. While the environmental drivers andtheir respective explanatory power for soil N₂O emissions differedconsiderably among the three grasslands (adjusted r² ranging from 0.19 to0.42), CH₄ and CO₂ soil fluxes were much better constrained(adjusted r² ranging from 0.46 to 0.80) by soil water content and airtemperature, respectively. Throughout the year, spatial heterogeneity wasparticularly high for soil N₂O and CH₄ fluxes. We found permanenthot spots for soil N₂O emissions as well as locations of permanentlylower soil CH₄ uptake rates at the extensively managed alpine site.Including hot spots was essential to obtain a representative mean soil fluxfor the respective ecosystem. At the intensively managed grassland,management effects clearly dominated over effects of environmental drivers onsoil N₂O fluxes. For CO₂ and CH₄, the importance of managementeffects did depend on the status of the vegetation (LAI).

[学科分类] 地球化学与岩石