Methanogenic archaea community in relation to methane production in oil palm planted on tropical peatland

Understanding the microbial processes that regulate methane emissions in the tropical peatlands can facilitate their future management. However, the microbiota of Malaysian tropical peatlands specifically the methanogens (methane producers) and methanotrophs (methane consumers) remains poorly characterised. This study aimed to determine the key players in methane production and to assess their spatial distribution in different oil palm management zones (i.e., avenue, cover crop, frond pile, and weeded circle) across depths namely 0-15 cm, 15-30 cm, and 30-45 cm in an 11-year-old oil palm plantation that was established on the peatland of Sarawak. Based on high-throughput Illumina sequencing targeting the 16S hypervariable V4-V5 regions of archaeal rRNA amplicon, the diversity indices (Shannon and Simpson) and richness (Chao1 and ACE) were highest in the upper peat layers across management zones, and the microbial diversity and composition are influenced by depths. Taxonomic profiling revealed that the domain Archaea was dominated by Halobacteriota, Thermoproteota, and Thermoplasmatota that increased with depth across management zones. Meanwhile, the order Methanomassiliicoccales was predominant, with Methanomethylophilus sp002495325 as the most abundant species in the upper peat layers in the frond pile zone due to a high decomposition rate of organic matter. The key players of methanogenic archaea belonging to Methanomassiliicoccales, Methanosarcinales, Methanomicrobiales, and Methanobacteriales were detected in oil palm peat soils, providing indirect genetic evidence for the biogeochemical processes associated with methane production in the oil palm plantation. Having established the feasibility of utilising high-throughput sequencing to characterise the archaeome of Malaysian oil palm plantation, future works in correlating the relative abundance of methanogens and methanotrophs with methane production will be instrumental in providing valuable insights for prediction and mitigation of methane emissions in oil palm cultivation on peat.