Abstract

Compared to a phosphate free medium containing citrate buffer, effects of phosphate concentrations (10, 20, 50 ,and 100 mmol/L) in the modified Menke and Steingass’s medium on methanogenesis of a maize-rich substrate (Leymus chinensis hay:maize meal = 1:4) were determined in comparison with using an in vitro cumulative gas production technique. After the 48 h batch cultures, phosphate additions decreased total gas production (GP₄₈, ml/g dry matter (DM)) (P < 0.05) as well as the gas production rate to reach maximum digestion (RmaxG, mL/h) (P < 0.01). Total volatile fatty acids (VFA) concentrations (mmol/L) were decreased by 28%, while the phosphate concentration increased up to 50 to 100 mmol/L (P < 0.05). Volatile fatty acid production shifted from an initially acetate dominated production towards a propionate production as demonstrated by the ratio of non-glucogenic to glucogenic acids (NGR) (P < 0.01). Although, the molar proportions of CO₂, CH₄, and H₂ in the fermentation gases were not altered, the net fractional CH₄ production (ml/g DM) in the phosphate levels of 10, 20, 50, and 100 mmol/L were reduced by 6.2, 11.8, 18.57, and 26.2%. The results obtained in the present study showed that a phosphate-mediated reduction in methane emissions occurred without the expense of a reduction in the digestion of the substrate, and the mechanism that phosphate inhibited acetoclastic methanogenesis on rice roots may exist in the rumen.

Key words: Rumen, methanogenesis, phosphate buffer, citrate buffer, in vitro batch culture.