Objectives To explore the changes of structure and function of bacterial communities in maize rhizosphere and roots with continuous cropping years, as well as their responses to soil physiochemical properties.
Methods The investigation was carried out in Zhangye City, Gansu province. Soil and plant samples were collected in seed production fields under 1, 5 and 15 continuous cropping years at the big trumpet stage of maize, respectively. The soil physicochemical properties were analyzed using conventional methods, and the bacterial diversity, community composition, and function in maize rhizosphere and roots were determined using high-throughput sequencing technology.
Results Compared to 1 year, the soil bulk density, total P, total N, available P, available N, and pH significantly increased in the 5 and 15 year fields, while the total porosity, available K, and organic matter significantly decreased (P<0.05). The composition of maize rhizospheric and endophytic bacterial community changed, and the diversity and network complexity of bacterial community decreased with the increasing of continuous cropping years. The relative abundance of Acidobacteria, Proteobacteria, Bacteroidetes, Planctomycetes and Gemmatinonadota decreased in rhizosphere soil, while the relative abundance of Chloroflexi and Actinobacteriota increased. The relative abundance of beneficial Nitrospira, Sphingomonas, Lysobacter, Haliangium and Bryobacter decreased in rhizosphere soil. The relative abundance of inner phylum of Proteobacteria increased, while the relative abundance of Firmicutes, Bacteroidetes and actinomycetes decreased. The relative abundance of inner beneficial genera of Pseudomonas, Sphingomonas, Flavobacterium, Rhizobium and Pantoea decreased. In addition, the relative abundance of rhizospheric bacteria involved in antibiotics biosynthesis, amino acid biosynthesis, fatty acid synthesis, C5-branched dibasic acid metabolism, lipoic acid metabolism, pantothenate and CoA biosynthesis, peptidoglycan biosynthesis, D-alanine metabolism, lipopolysaccharide biosynthesis, cell cycle – caulobacter, and sulfur relay systems decreased with increasing years of continuous cropping. The relative abundances of endophytic bacteria invloved in the biosynthesis of amino acid, pantothenic acid, vancomycins, pantothenate and CoA, peptidoglycan, streptomycin, lipoate, as well as the metabolism of alanine and glutamate were decreased, while the relative abundance of biacteria in volved in the biosynthesis of anisamycins, synthesis and degradation of ketone bodies, bacterial chemotaxis, and the metabolism of C5-branched dibasic acid were overall increased.
Conclusions Soil nitrogen and phosphorus content, bulk density, and pH significantly increased with the extending of cropping years, while total porosity, organic matter and available potassium content significantly decreased. The composition and function of bacterial communities in maize rhizosphere and roots were affected, and rhizospheric and endophytic bacterial diversity, complexity and function decreased. And rhizospheric bacterial communities were more variable than endophytic bacteria.