Lignocellulosic fraction-induced niche differentiation within dissimilatory iron reducing bacterial groups in a paddy soil

Responses of soil DIRB to lignocellulosic fractions during a 6-week microcosm incubation were investigated.Anaeromyxobacter,Bacillus,and Clostridium maintained their domi-nance throughout the incubation.Distinct DIRB groups proliferated under specific lignocellulosic fraction amendments.Limits of insufficient ferric iron on the proliferation varied by DIRB group.Dissimilatory iron reducing bacteria(DIRB)are phylogenetically and physi-ologically diverse in paddy soils,where iron reduction closely couples with the oxidation of rice straw-derived carbon in the straw returning scenarios.However,few studies have addressed the niche differentiation within DIRB groups during the degradation of lignocellulosic fractions of rice straw.This study conducted a 6-week microcosm incubation experiment to reveal the distinct responses of DIRB groups under specific lignocellulosic fraction amendments with and without ferrihydrite(Fh)addition in a flooded paddy Ultisol.Results showed that the total absolute abundance of the 19 detected DIRB groups did not vary significantly during the incubation.Anaeromyxobacter,Bacillus,and Clostridium were the dominant DIRB groups for all lignocellulosic treatments whereas Thermincola was dominant but only under xylan amendment with Fh addition.DIRB-nodes in the co-occurrence networks of bacterial community mainly belonged to Anaeromyxobacter and Bacillus.Clostridium and Thermincola,Alkaliphilus and Anaeromyxobacter,and Alicyclobacillus,Desulfobulbus,and Desulfosporosinus were specifically proliferated under xylan,cellulose,and lignin amendments,respectively.Whether the proliferation was limited by insufficient ferric iron varied by bacterial group.These findings suggested the lignocellulosic fraction-induced niche differentiation within DIRB groups,which advanced our understanding of the ecology of DIRB in paddy soils under straw returning.