Submerged paddy soil is considered as a natural source of the greenhouse gas methane (CH₄) because it provide the optimal condition (anaerobic condition) and hotspots for methanogens which lead to CH₄.

Controlled microcosms incubation experiments (CH₄ injection into the microcosms' headspace and subsequent shaking of soil as slurry) is commonly used to estimate CH₄ oxidation in soil, but there is uncertainties associated with this methods because transition of CH₄ from air to water is a limiting factor for the CH₄.

To overcome the problem, scientists from the Institute of Subtropical Agriculture (ISA) of Chinese Academy of Sciences in cooperation with University of Gottingen, invented a novel approach for lab incubation studies by using silicone tube located in soil and compared with the conventional headspace CH₄ injection.

Therefore they developed a microcosm with a silicone tube ( inner diameter: 4 mm, wall thickness: 1 mm, surface area: 18.8 cm², volume: 1.2 ml) fixed around a plastic cap and tied with stainless steel wires form both ends, one of end connected with a needle as a sampling port.

Then they conducted an incubation experiment with/without soil silicone tube and with/without shaking in addition to test the location of CH₄ injection-into the headspace (with/without tube) or into the soil (with tube) and the CH₄ oxidation rate with time.

Scientists found that net CH₄ oxidation rate reached the maximum values (1.6 μg C g^-1 dry soil h^-1) between the 3rd and 7th with novel approach method, which was 1.5–2.5 times faster than the respective CH₄ oxidation after headspace injection without shaking.

However, shaking accelerated CH₄ oxidation regardless of injection methods by 3.2–3.7 times (most intensively on days 3–7)

Furthermore, they found an overestimation of CH₄ oxidation due to shaking because it increased the incorporation of ¹³C from CH₄ into soil organic matter and microbial biomass by 1.8–2.7 times compared with novel approach the static control without tubes.

They concluded that conventional headspace CH₄ injection can be substituted by novel approach for lab incubation studies.

The study entitled "To shake or not to shake: Silicone tube approach for incubation studies on CH₄ oxidation in submerged soils" was published in Science of the Total Environment. Details can be found at https https://www.sciencedirect.com/science/article/pii/S0048969718349301.

The study was supported by the National Natural Science Foundation of China, Youth Innovation Team Project of ISA, CAS.

Contact: GE Tida

E-mail: gtd@isa.ac.cn

Institute of Subtropical Agriculture, Chinese Academy of Sciences