Response of rhizosphere bacterial community structure to nitrogen application rate during ginseng fruit (Solanum muricatum Aiton) growth stages

Objectives We studied the effects of nitrogen (N) application rates on bacterial community structure and diversity in rhizosphere soil of ginseng fruit, so as to provide theoretical basis for rational fertilization and maintain a health rhizospheric environment for the cultivation of ginseng fruit.

Methods Field experiments were conducted in 2020 and 2021 in Wuwei City, Gansu Province. Four N rates of 0, 50, 100 and 150 kg/hm² (denoted as N0, N50, N100 and N150) were designed. All the designed nitrogen fertilizers were evenly divided into five parts, and applied with drip irrigation in frequency of every 30 days. Rhizosphere soil samples were collected one day before topdressing for determination of bacterial diversity and community composition, using high-throughput sequencing method.

Results Compared with N0, N50 increased Shannon, Chao1 and ACE (abundance coverage-based estimator) index by 1.19%, 4.46% and 4.86%, respectively, N100 did not change them significantly, while N150 decreased them by 3.31%, 2.79% and 6.20%. At the phylum level, the dominant bacterial communities in rhizosphere soil were Proteobacteria (30.80%), Firmicutes (4.77%), Acidobacteriota (5.88%), Cyanobacteria (1.16%), Crenarchaeota (1.24%), Bacteroidota (7.21%), Actinobacteriota (4.02%), Gemmatimonadota (4.81%), Myxococcota (3.60%). Compared with N0, N50 increased the relative abundance of Firmicutes, Acidobacteriota, Crenarchaeota, Myxococcota and Gemmatimonadota from flowering to maturity, while N100 and N150 decreased the relative abundance of Acidobacteriota by 2.99% and 15.66%. Pseudomonas, Sphingomonas, Bacillus, Devosia, RB41, MND1 and Haliangium were core genus of ginseng fruit. Compared with N0, N50 enriched Pseudomonas by 8.07% and Devosia by 32.41%, N100 was beneficial to the growth and reproduction of MND1, while N150 inhibited RB41, Sphingomonas, Bacillus, MND1 and Haliangium.

Conclusions Medium and low N application rate is conducive to the diversity of bacteria community and the enrichment of core genus in rhizosphere, such as Pseudomonas, Devosia, MND1, Haliangium, Sphingomonas, which could maintain a healthy microenvironment of rhizosphere for root growth. N level of 50−100 kg/hm² is recommended for ginseng fruit cultivation.