Plant Growth Promoting Rhizobacteria Alleviate Aluminum Toxicity and Ginger Bacterial Wilt in Acidic Continuous Cropping Soil

Abstract

Long-term monoculture cropping is usually accompanied by soil acidification and microbial community shifts. Soil aluminum ions are dissolved under acidic condition (pH < 5.0), and the resulting aluminum bioavailability can cause toxic effects in plants. In this study, we investigated the bacterial community compositions and aluminum toxicity in fields monocultured with ginger for 35 years, 15 years, and 1 year. Within these fields are ginger plants without and with ginger bacterial wilt disease. The results confirmed that the degree of aluminum toxicity in the diseased soil was more severe than that in the healthy soil. Continuous cropping can significantly increase the bacterial diversity and change the bacterial community composition of ginger rhizosphere soil. The relative abundance of plant growth-promoting rhizobacteria (PGPRs) was increased in the soils used for the continuous cropping of ginger. Additionally, aluminum toxicity had a significant positive correlation with Bacillus, Pseudomonas, Arthrobacter, and Serratia in healthy soils. Based on these results, aluminum stress may stimulate the increase of PGPRs (Bacillus, Pseudomonas, Arthrobacter, and Serratia), thereby alleviating ginger aluminum toxicity and bacterial wilt in extremely acidic soil (pH < 4.5).

Evolutions and Managements of Soil Microbial Community Structure Drove by Continuous Cropping

“…Soil microbial community structure affects plant health and can also be used as an indicator of soil health ( Zhou and Wu, 2012 ; Dong et al, 2016 ). High-throughput sequencing analysis showed that long-term continuous cropping could reduce soil bacterial biomass and increase fungal biomass ( Dong et al, 2016 ; Liu et al, 2016 , 2020a ), while longer-term continuous cropping could increase the bacterial diversity to suppress soil-borne diseases by forming bacteriostatic soil ( Shen et al, 2018 ; Zhang et al, 2020 ). Studies have shown that the higher the ratio of bacterial to fungal in soil, the better condition of the soil ecosystem, the more stable the structure of bacteria, and the stronger the resistance of soil to disease ( Liu et al, 2015a , b ).…”

“…Some bacteria, which belong to plant growth promoting rhizobacteria (PGPR), can secrete antibiotics to inhibit pathogenic microorganisms. Still, continuous cropping reduces bacteria-secreted antibiotics ( Zhang et al, 2020 ) and the inhibition of pathogenic bacteria ( Tan et al, 2017 ) and then causes an increase in plant diseases incidence. Meanwhile, the secondary metabolites secreted by harmful microorganisms recruit microorganisms that are beneficial to themselves, further damaging the soil microecology, evolving in a direction conducive to the survival of those, and aggravating the obstacles of continuous cropping ( Chen et al, 2018a ; Pascale et al, 2019 ; Bakker et al, 2020 ).…”

“…In recent years, the mitigation of continuous cropping obstacles has become a hot issue to be solved urgently in production ( Liu et al, 2020a , c ; Zeng et al, 2020 ; Ding et al, 2021 ). One of these methods that can mitigate continuous cropping obstacles is improving or recombining microbial community structure underground ( Larkin, 2008 ; Han et al, 2010 ; Liu et al, 2015a , 2021a ; Chen et al, 2018c ; Zhang et al, 2020 ). Special cultivation control measures can solve some problems of soil community structure caused by continuous cropping, but most of them have no feasible reduction techniques.…”

Alleviating Soil Acidification Could Increase Disease Suppression of Bacterial Wilt by Recruiting Potentially Beneficial Rhizobacteria

“…When plants are in a stressful environment, root exudates can attract beneficial microbes from the environment, which is called a “cry for help” strategy ( 65 ). Aluminum stress can stimulate the increase of Bacillus and Pseudomonas to alleviate ginger aluminum toxicity and bacterial wilt in extremely acidic soil (pH less than 4.5) ( 7 ). In this study, in a high-aluminum soil environment with pH 4.45, the growth of tobacco was not significantly affected (Fig.…”

“…At pH 4.5 or below (extremely acid), the Al 3+ predominates in the soil solution and has the greatest impact on plant growth ( 5 ). In addition, many researchers revealed that soil acidification is closely related to the occurrence of soilborne disease ( 6 – 9 ).…”