Diversidade de bactérias e arqueias em camas de criação de vacas leiteiras do tipo compost barn: ciclagem de nutrientes e emissão de gases de efeito estufa

Abstract

Microorganisms are the most diverse living beings on the planet and many are still unknown or unclassified. It is no different in the bedding of compost barn (CB) dairy farming systems. In this study, we evaluated the diversity of prokaryotes (bacteria and archaea) in the bedding of various CB dairy farms. Firstly, we assessed the structure and dynamics of the nitrifying bacteria community in the litter of two farms in the south of Minas Gerais/MG with different installation and operating times: one in the early succession stage and the other mature. The densities of ammonia- and nitrite-oxidizing bacteria, quantified by the fluorescent in situ hybridization (FISH) technique, were different in the beds of the two farms over time. These bacteria linked to the nitrogen cycle participate in a complex interaction between microorganisms and abiotic components of the systems. The second study was carried out in a CB system at the Experimental Farm EMBRAPA Dairy Cattle in Coronel Pacheco/MG. The density of bacteria from the orders Methanosarcinales and Methanobacteriales was assessed, also using the FISH technique, in the bedding of this system over time. The role of the tractor on the density of these methanogenic archaea and their distribution at different depths of the bed was also assessed. We also related these densities to the methane concentrations measured before and after aeration by the tractor. In the first few months after the bed was installed and after the tractor had passed through, there was greater variation in the densities of these archaea. The densities of the archaea were ten times higher after the system had been in operation for 18 months. The lowest densities and proportions of Methanosarcinales were found in the first collection, during bed installation. After aeration and homogenization of the particle size by the tractor, a greater number of Methanobacteriales were observed at both sampling depths. Finally, in the third study, bacterial diversity was assessed by sequencing the 16S rRNA gene in bedding samples from five farms in Minas Gerais/MG and one in Goiás/GO, with different types of bedding material, system size, number of cows per area, bedding age, amount of nutrients and greenhouse gases produced during collection. The bedding from each farm presented a distinct bacterial community, with many amplicon sequence variants (ASVs) without a taxonomic signature at family level. Some bacteria were found in low methane flows and others in high methane emissions. Therefore, it is essential to study the CB system, its advantages and potential impacts, in order to increase understanding of this system and identify strategies capable of influencing decision-making towards sustainable alternatives.