There are more and more climate disasters which happen every year due to the greenhouse effect, so the governments and researchers all over the world are doing many efforts on the main origin gases, such as CO₂ and CH₄ and so on. The warming potential of CH₄ is about 20-30 times of CO₂, which has been concerned by many researchers, especially by the agricultural scientists. Ruminants approximately produce 95 million tons of CH₄ annually, which accounts for a quarter of all anthropogenic CH₄ emissions. It's very important to reduce CH₄ emissions origin from ruminants.

Many methods have been reported to study the mechanism of the CH₄ emissions produced by ruminants. Feeds in the rumen can be hydrolyzed by protozoa and bacteria to monomers, then fermented to end products such as volatile fatty acid(VFA), carbon dioxide(CO₂) and hydrogen(H₂), the CO₂ and H₂ which can be used to synthetize CH₄ by ruminal methanogens. Because CO₂ utilized for CH₄ production may be derived from bicarbonate in media and/or from the fermented substrates, PhD Qiao Junyi in Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA)used NaH¹³CO^₃ and H₂ as materials to investigate the ¹³CH₄ production efficiency(PE) produced by the reduction of NaH¹³CO^₃, and they used lucerne hays as substrates to evaluate the effects of NaH¹³CO^₃and H₂ additions on ruminal fermentat_ion, CH₄ production and methanogen populations used in the vitro gas production techniques.

Qiao found the ¹³CH₄ production was quadratically increasing with the NaH¹³CO_³ added, while the ¹³CH₄ PE was quadratically decreasing with the increased addition of NaH¹³CO_³; The H₂ addition could increase the ¹³CH₄ production linearly and the ¹³CH₄ PE quadratically. There was interaction of  NaH¹³CO^₃*H₂ on ¹³CH₄ production and ¹³CH₄ PE.

The total CH₄ production and apparent dry matter degradability(ADMD) of Lucerne hays were quadratically increasing with the greatest values when 36 ml of H₂ was added, but there was no NaHCO₃ addition effect on ADMD. The interactions of NaH¹³CO^{₃ *}H² were observed by most tests on NH3-N and total VFA. The pH values, total VFA and molar proportions of acetate and propionate were quadratically changing with the H2 addition.

As the CH₄ was produced by the methanogens in the rumen, the team also investigated the methanogenic population, who found there were significant interaction of NaH¹³CO^₃*H₂ on populations of M. barkeri, M. stadtmanae, M.ruminantium and M. smithii. And there were no differences on the copy numbers of 16S rRNA genes for the populations of M. stadtamanae, M. ruminantium and M. smithii in response to the incubation time except M. barkeri. It was increasing by incubation time with the highest values being at 24 h. 

This study indicates that both CO₂ and H₂ concentrations can influence the methanogenesis in the rumen, and a small part of the CO₂ utilized for methanogenesis is from bicarbonate(such as NaHCO₃) in media. The headspace hydrogen and media bicarbonate had significant effects on CH₄ production and rumen fermentation. 

This research was supported by the National Natural Science Foundation of China (Grant No. 31320103917), "Strategic Priority Research Program - Climate Change: Carbon Budget and Relevant Issues"(Grant No. XDA05020700) and "International Atomic Energy Agency"(Grant No.16315) 

The research has been published in the October of Animal Feed Science and Technology, details could be found at http://www.sciencedirect.com/science/article/pii/S0377840115001492 

TAN Zhiliang

zltan@isa.ac.cn 

Institute of Subtropical Agriculture, Chinese Academy of Sciences