The only known terrestrial sink of the greenhouse gas methane (CH4) occurs in well-drained soils as a result of the activity of methanotrophic bacteria. Though methanotrophs are present in arid and semi-arid soils, there are relatively few estimates of soil CH4 uptake in arid ecosystems. Consequently, there is an opportunity to elucidate the controls of CH4 uptake in deserts. Here, we report the first known estimates of soil CH4 uptake from the central Great Basin in the United States. We sought to characterize patterns of CH4 uptake among Great Basin ecosystems and identify the mechanisms that control soil CH4 uptake in arid environments. In situ soil CH4 uptake was measured every three weeks during the growing season using static chambers at five sites located across an elevation gradient in central Nevada that represented common vegetation zones: pinyon-juniper woodland, meadow, sagebrush, salt desert, and playa ecosystems. Simultaneously, we measured temperature, soil water content and potential, soil texture, and soil nitrogen availability, all of which are hypothesized to be important controls on soil CH4 uptake.
Results/Conclusions
All five Great Basin ecosystems represented by the elevation gradient exhibited net soil CH4 uptake. However, the rate of soil CH4 uptake varied significantly by site (repeated measures ANOVA site effect P = 0.001), with playa soils generally having lower rates of uptake and salt desert and sagebrush ecosystems generally exhibiting higher rates of soil CH4 uptake. Soil CH4 uptake did not vary significantly by sampling date alone, but uptake rates among sites varied as a function of sampling dates (repeated measures ANOVA site by sampling date interaction P = 0.004). Despite large variability in edaphic characteristics among sites, individual soil physical and chemical properties poorly explained variability in soil CH4 uptake. Using regression tree analysis, we show that soil nitrate, temperature, silt content, and water content were important thresholds that partitioned soil CH4 uptake in a non-linear model. Rates of soil CH4 uptake in the Great Basin are substantial and vary by elevation. However, we are unable to attribute this variation in soil CH4 uptake across the landscape to a single edaphic characteristic. Therefore, our results are not consistent with previous studies that suggest that soil CH4 uptake is strongly correlated with edaphic conditions, such as texture and water content, alone. The proximate controls of soil CH4 uptake in the Great Basin remain to be discovered.