Abstract
Abstract. Tropical lowland forest soils are significant sources and sinks of trace gases. In order to model soil trace gas flux for future climate scenarios, it is necessary to be able to predict changes in soil trace gas fluxes along natural gradients of soil fertility and climatic characteristics. We quantified trace gas fluxes in lowland forest soils at five locations in Panama, which encompassed orthogonal precipitation and soil fertility gradients. Soil trace gas fluxes were measured monthly for 1 (NO) or 2 (CO2, CH4, N2O) years (2010–2012) using vented dynamic (for NO only) or static chambers with permanent bases. Across the five sites, annual fluxes ranged from 8.0 to 10.2 Mg CO2-C, −2.0 to −0.3 kg CH4-C, 0.4 to 1.3 kg N2O-N and −0.82 to −0.03 kg NO-N ha−1 yr−1. Soil CO2 emissions did not differ across sites, but they did exhibit clear seasonal differences and a parabolic pattern with soil moisture across sites. All sites were CH4 sinks; within-site fluxes were largely controlled by soil moisture, whereas fluxes across sites were positively correlated with an integrated index of soil fertility. Soil N2O fluxes were low throughout the measurement years, but the highest emissions occurred at a mid-precipitation site with high soil N availability. Net negative NO fluxes at the soil surface occurred at all sites, with the most negative fluxes at the low-precipitation site closest to Panama City; this was likely due to high ambient NO concentrations from anthropogenic sources. Our study highlights the importance of both short-term (climatic) and long-term (soil and site characteristics) factors in predicting soil trace gas fluxes.
Highlights
Soils can be both sources and sinks of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and nitric oxide (NO)
All sites were CH4 sinks; within-site fluxes were largely controlled by soil moisture, whereas fluxes across sites were positively correlated with an integrated index of soil fertility
Soil NO fluxes in tropical forests are often low (Keller and Reiners, 1994; Koehler et al, 2009b) and the canopy can act as a sink for a large proportion of soil-emitted NO (Rummel et al, 2002), even low emissions may be important in regulating atmospheric oxidant production (Keller et al, 1991; Chameides et al, 1992)
Summary
Soils can be both sources and sinks of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and nitric oxide (NO). Annual soil trace gas fluxes in Central and South American (CSA) tropical lowland forests can vary significantly; in one study, N2O emissions varied by 1 order of magnitude (1.23 to 11.39 kg N ha−1 yr−1; Silver et al, 2005). Such disparity in measurements, caused by the temporal and spatial variability found in tropical forests (Townsend et al, 2008), makes it challenging to model soil trace gas fluxes from these areas and to predict how they might be affected by climate change.
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