Weaning methods affect ruminal methanogenic archaea composition and diversity in Holstein calves

The objective of the present study was to examine the effect of different weaning methods on the ruminal methanogenic archaea composition and diversity in Holstein calves.Thirty-six newborn Holstein bull calves were assigned to 1 of 3 treatments:(1)conventional weaning(d 56)and fed a high proportion of solid feed(CWS);(2)conventional weaning(d 56)and fed a high proportion of liquid feed(CWL);(3)early weaning(d 42)and fed with a high proportion of solid feed(EWS).High-throughput sequencing of the methyl coenzyme M reductase(mcr A)gene,which encodes theα-subunit of methyl coenzyme M reductase-the enzyme that catalyzes the final step in methanogenesis was used to determine the composition and diversity of rumen methanogens.No significant difference(P>0.05)was observed for operational taxonomic units(OTUs)or richness indices,but diversity indices increased(P<0.05)for calves fed high dietary solids.Predominant families across the three treatments were Methanobacteriaceae,Thermoplasmataceae and Methanomassiliicoccaceae.Calves in the EWS treatment had a higher(P<0.05)relative abundance of Methanobrevibacter sp.strain AbM4 and Methanosphaera stadtmanae,while calves in the CWL treatment had a higher(P<0.05)abundance of Methanosphaera sp.strain SM9.A positive(P<0.05)relationship was identified between butyrate and Methanobrevibacter sp.strain AbM4.In conclusion,the composition and diversity of methanogens in the rumen of Holstein calves varied under the different weaning methods.This study identified a positive relationship between butyrate and Methanobrevibacter sp.strain AbM4,potentially reflecting correlations between ruminal fermentation variables and methanogenesis function.These in-depth analyses provide further understanding of weaning methods for intensified production systems.

Responses of the methanogenic pathway and fraction of CH4 oxidization in a flooded paddy soil to rice planting

Rice planting(RP)is significant to methane(CH4_(4))emissions from paddy fields,but its effect on the relative contribution of the acetoclastic methanogenesis to total CH4_(4) production(F_(ac))and the fraction of CH4_(4) oxidized(Fox)is poorly understood.To quantify the responses of the F_(ac) and Fox to RP,we investigated CH4_(4) fluxes,CH4_(4) production and oxidation potentials,dissolved CH4_(4) concentrations,and their stable carbon isotopes in a flooded paddy soil.The mcrA and pmoA gene copies were also determined by quantitative polymerase chain reaction(qPCR).Compared with the unplanted soil(control,CK),the seasonal CH4_(4) emissions from the planted soil were significantly enhanced,13.6 times,resulting in large decreases in the CH4_(4) concentrations in the soil solution.This indicated that much more CH4_(4) was released into the atmosphere by the RP than was stored in the soils.Acetoclastic methanogenesis became more important from the tillering stage(TS)to the ripening stage(RS)for the CK,with F_(ac) values increased from 17%-20% to 46%-55%.With RP,the F_(ac) values were enhanced by 10%-20%,and it significantly increased the copy numbers of the mcrA gene at the four rice stages(TS,booting stage(BS),grain-filling stage(GS),and RS).Furthermore,the effect of the RP on the abundance of the mcrA gene was highly concurrent with the effect on the F_(ac) values.At the TS,the Fox values at the soil-water interface were around 50%-75% for the CK,being 15%-20% lower than those of the RP in the rhizosphere.It increased to 65%-100% at the GS,but was reduced by 20%-30% after the RP.These differences might be because the copy numbers of the pmoA gene were significantly raised at the TS while lowered at the GS by the RP.This was further demonstrated by the strong correlations between the effect of the RP on the abundance of the pmoA gene and the effect on the Fox values.These findings suggest that RP markedly impacts on the abundances of the mcrA and pmoA genes,affecting the pathway of CH4_(4) production and the fraction of CH4_(4) oxidization,respectively.