The Effect of Karst Carbonate Rock Dissolution on Nitrogen Metabolism Microorganisms and Their Functions in Paddy Soils

Carbonate rock dissolution (CRD) in karst areas generates abundant ions, which contribute significantly to nitrogen (N) transformation in paddy ecosystems. However, little is known about the microbial mechanisms by which CRD ions (Ca2+, Mg2+, HCO3−/CO32−, and OH-) regulate N balance. In this experiment, rice pot studies were conducted using karst soil (S1), karst soil with removed carbonate minerals (S2), non-karst soil (S3), and non-karst soil with additional carbonate minerals (S4). The effects of CRD on N-metabolizing microorganisms and functional genes in N metabolism were investigated using metagenomic sequencing technology. Six N metabolism pathways, including N fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA), assimilatory nitrate reduction to ammonia (ANRA), and complete nitrification (comammox) were revealed. Compared with S3, the relative abundance of the denitrification module (M00529) in S1 clearly increased by 1.52%. Additionally, compared to S3, the relative abundance of the complete nitrification (comammox) module (M00804) in S4 decreased by 0.66%. Proteobacteria and Anaeromyxobacter were significant contributors to variations in N metabolism. Key factors that influenced variations in N metabolism included Ca2+, Mg2+, and pH. This study explored the effects of CRD on N-metabolizing microorganisms and functions, which was of great significance to the N cycle in karst paddy ecosystems.