To shake or not to shake: Silicone tube approach for incubation studies on CH4 oxidation in submerged soils

Lichao Fan; Muhammad Shahbaz; Tida Ge; Jinshui Wu; Yakov Kuzyakov; Maxim Dorodnikov

doi:10.1016/j.scitotenv.2018.12.090

To shake or not to shake: Silicone tube approach for incubation studies on CH₄ oxidation in submerged soils

Sci Total Environ. 2019 Mar 20:657:893-901. doi: 10.1016/j.scitotenv.2018.12.090. Epub 2018 Dec 7.

Authors

Lichao Fan¹, Muhammad Shahbaz², Tida Ge³, Jinshui Wu³, Yakov Kuzyakov⁴, Maxim Dorodnikov⁵

Affiliations

¹ Department of Soil Science of Temperate Ecosystems, University of Göttingen, 37077 Göttingen, Germany. Electronic address: lfan@gwdg.de.
² Department of Soil and Environment, Swedish University of Agricultural Sciences, Box 7014, 75007 Uppsala, Sweden.
³ Key Laboratory of Agro-ecological Processes in Subtropical Region & Changsha Research Station for Agricultural and Environmental Monitoring, Institute of Subtropical Agriculture, Chinese Academy of Sciences, 410125, Hunan, China.
⁴ Department of Soil Science of Temperate Ecosystems, University of Göttingen, 37077 Göttingen, Germany; Department of Agricultural Soil Science, University of Göttingen, 37077 Göttingen, Germany; Institute of Environmental Sciences, Kazan Federal University, 420049 Kazan, Russia.
⁵ Department of Soil Science of Temperate Ecosystems, University of Göttingen, 37077 Göttingen, Germany.

PMID: 30677954
DOI: 10.1016/j.scitotenv.2018.12.090

Abstract

Incubation experiments are the most common approach to measure methane (CH₄) oxidation potential in soils from various ecosystems and land-use practices. However, the commonly used headspace CH₄ injection into microcosms and the shaking of the soil slurry during incubation fully removes CH₄ (soil-born) and O₂ (air-born) gradients common in situ, and may also induce various errors and disturbances. As an alternative, we propose CH₄ input into microcosm soils via a silicone tube located within the slurry. We hypothesized that (i) poor CH₄ diffusion in slurry will be compensated by direct CH₄ delivery into the slurry via a silicone tube and, consequently, (ii) shaking of microcosms can be substituted with the soil silicone tube CH₄ injection. During a 29-day submerged paddy soil incubation, the highest net CH₄ oxidation rate was 1.6 μg C g^-1 dry soil h^-1, measured between the 3rd and 7th day after injecting ¹³CH₄ into the slurry via a silicone tube without shaking. This rate was 1.5-2.5 times faster than the respective CH₄ oxidation after headspace injection without shaking (1st hypothesis supported). As expected, shaking accelerated CH₄ oxidation regardless of injection methods by 3.2-3.7 times (most intensively on days 3-7) compared to headspace injection without shaking. Nonetheless, the rates were similar between silicone tube injection without shaking and headspace injection with shaking. This supports the hypothesized potential of silicone tubes to substitute the common shaking method (2nd hypothesis). Furthermore, shaking increased the incorporation of ¹³C from CH₄ into soil organic matter and microbial biomass by 1.8-2.7 times compared with CH₄ injection into tubes and the static control without tubes. This reflects an overestimation of CH₄ oxidation due to shaking. We conclude that direct soil CH₄ injection via silicone tubes is advantageous in incubation experiments because gas concentration gradients are maintained and thereby more realistically reflect natural soil conditions.

Keywords: (13)C-CH(4); Methane oxidation; Paddy soil; Shaking; Silicone tube; Slurry.