摘要：Alpine and subalpine meadows are often hotspots of water availability and biodiversity in montane landscapes, but we know little about whether these attributes also make meadows hotspots of greenhouse gas (GHG) emission. Furthermore, many of these meadows will likely become drier during the growing season in the future because of less precipitation, earlier timing of snowmelt, and increased evapotranspiration associated with climatic warming. To evaluate the potential effects of soil drying on GHG emission, we studied a soil moisture gradient in a Sierra Nevada subalpine meadow in California. Our objectives were: (1) to assess the strength of hydrological control for soil carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) fluxes both earlier and later in the growing season; and (2) to quantify the contribution of CH 4 and N 2 O to net GHG emission. The replicated gradient spanned 50 m, from the wet middle to dry edge of the meadow, and soil volumetric water content was measured 0 to 12 cm deep. Fluxes of CO 2 , CH 4 , and N 2 O were measured using static chambers at 10 m intervals across the gradient. We found that the wet side of the gradient was not a CH 4 or N 2 O source on either sampling date. Net CH 4 emission from soil was rare and CH 4 uptake was prevalent, particularly on the dry side of the gradient. Soil N 2 O fluxes shifted from net uptake at the middle of the meadow to net emission at the edge, but only earlier in the growing season. Of the three GHGs, CO 2 fluxes showed the most temporal variation but surprisingly varied little across the hydrological gradient. Other environmental factors—including plant species richness and soil carbon concentration—appeared more important than soil moisture in explaining CO 2 fluxes. Therefore, the strength of near-surface hydrological control increased in the following order: CO 2 < N 2 O < CH 4 . Our results suggest that non-CO 2 greenhouse gases will need proper accounting during the snow-free season in order to more accurately predict the effects of future soil drying on GHG emissions in heterogeneous montane landscapes.
