Effects of soil temperature and moisture on methane uptake and nitrous oxide emissions across three different ecosystem types

Abstract

Abstract. In this paper, we investigate similarities of effects of soil environmental drivers on year-round daily soil fluxes of nitrous oxide and methane for three distinct semi-natural or natural ecosystems: temperate spruce forest, Germany; tropical rain forest, Queensland, Australia; and ungrazed semi-arid steppe, Inner Mongolia, China. Annual cumulative fluxes of nitrous oxide and methane varied markedly among ecosystems, with nitrous oxide fluxes being highest for the tropical forest site (tropical forest: 0.96 kg N ha−1 yr−1; temperate forest: 0.67 kg N ha−1 yr−1; steppe: 0.22 kg N ha−1 yr−1), while rates of soil methane uptake were approximately equal for the temperate forest (−3.45 kg C ha−1 yr−1) and the steppe (−3.39 kg C ha−1 yr−1), but lower for the tropical forest site (−2.38 kg C ha−1 yr−1). In order to allow for cross-site comparison of effects of changes in soil moisture and soil temperature on fluxes of methane and nitrous oxide, we used a normalization approach. Data analysis with normalized data revealed that, across sites, optimum rates of methane uptake are found at environmental conditions representing approximately average site environmental conditions. This might have rather important implications for understanding effects of climate change on soil methane uptake potential, since any shift in environmental conditions is likely to result in a reduction of soil methane uptake ability. For nitrous oxide, our analysis revealed expected patterns: highest nitrous oxide emissions under moist and warm conditions and large nitrous oxide fluxes if soils are exposed to freeze–thawing effects at sufficiently high soil moisture contents. However, the explanatory power of relationships of soil moisture or soil temperature to nitrous oxide fluxes remained rather poor (R2 ≤ 0.36). When combined effects of changes in soil moisture and soil temperature were considered, the explanatory power of our empirical relationships with regard to temporal variations in nitrous oxide fluxes were at maximum about 50%. This indicates that other controlling factors such as N and C availability or microbial community dynamics might exert a significant control on the temporal dynamic of nitrous oxide fluxes. Though underlying microbial processes such as nitrification and denitrification are sensitive to changes in the environmental regulating factors, important regulating factors like moisture and temperature seem to have both synergistic and antagonistic effects on the status of other regulating factors. Thus we cannot expect a simple relationship between them and the pattern in the rate of emissions, associated with denitrification or nitrification in the soils. In conclusion, we hypothesize that our approach of data generalization may prove beneficial for the development of environmental response models, which can be used across sites, and which are needed to help achieve a better understanding of climate change feedbacks on biospheric sinks or sources of nitrous oxide and methane.

Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil

“…The influence of these factors on rates of CH 4 oxidation has been widely studied both at the ecosystem level and under laboratory conditions. Positive correlations have been consistently reported between temperature and rates of CH 4 oxidation in soil (Castro et al, 1995;Butterbach-Bahl and Papen, 2002;Rosenkranz et al, 2006;Luo et al, 2013). Atypically low and high soil moisture levels both have a negative impact on rates of atmospheric CH 4 consumption.…”

“…2.3.5). The CH 4 uptake rates Dasselar et al (1998) and Luo et al (2013), which indicate that excess soil moisture strongly attenuates CH 4 uptake rates across a range of ecosystem types. Finally, the global significance of each ecosystem type as a CH 4 sink depends strongly on spatial extent as well as CH 4 oxidation rates.…”

“…Parameterization of k 0 in MeMo has been refined using time-series data recently published by Luo et al (2013), which consist of daily soil CH 4 uptake rates and temperature and soil moisture data from three contrasting environments: temperate forest (Höglwald, Germany), tropical rainforest (Bellenden Ker, Australia) and steppe (Inner Mongolia, China). The data sets were used to explore potential variations in apparent k 0 values in different environments, including comparison with k 0 values from the R99 and C07 models; however, the uncertainty of this value could not be characterized due to a dearth of available observational data.…”

“…Table 3. k 0 values from the R99 and C07 models, and new k 0 values employed in MeMo that were determined based upon temperate forest, tropical forest and steppe data from Luo et al (2013). ployed in MeMo for their respective biomes and the k 0 value from the C07 model (k 0 = 5.0 × 10 −5 s −1 ) was used for all other regions for which no biome-specific k 0 values exist (Table 3).…”

“…reduction in free pore space). MeMo also accounts for inhibition of microbial CH 4 oxidation rates at elevated soil moisture content, predicting lower CH 4 uptake flux as a result of more realistic r SM values determined from the Gaussian response observed in field data from three different global biomes (Luo et al, 2013).…”