Soil bacterial community response to continuous cropping of cotton

Biochar-based organic fertilizer application promotes the alleviation of tobacco (Nicotiana tabacum L.) continuous cropping obstacles by improving soil chemical properties and microbial community structure

BACKGROUND

Intensive monoculture poses a serious threat to agricultural sustainable development due to the phenomenon of continuous cropping obstacles. Although organic amendment has been considered an efficient and environmentally friendly solution to mitigate this tough issue, the associated mechanisms remain poorly understood. Here, a two-year field experiment was conducted with the application of four fertilizers, wood, rice straw, compound biochar-based organic fertilizers (WBF, RBF, CBF) and chemical fertilizer (CF) under tobacco rotation with broad bean and oilseed rape, respectively. This work aims to determine how BFs application alleviates tobacco CCO and to further reveal the underlying action mechanisms primarily focusing on the change of soil micro-ecology environments.

RESULTS

The results depicted that BFs addition decreased tobacco morbidity (by 15.7-85.0%), heavy metals (Cd, V, Cu, Zn) contents in tobacco, and improved tobacco leaf production yield (by 4.5-20.5%), economic value (by 14.6-34.4%) and chemical quality compared with CF. Rhizosphere soil chemical properties and the structure and diversity of microbial communities were enhanced under BFs treatments, reflecting in the growth of bacterial OTUs number, microbial alpha-diversity, the abundances of some beneficial genera (Arthrobacter, Pseudomonas, Gemmatimonas, Trichoderma, Mortierella, Penicillium, Chaetomium, etc.), and the reduction of the numbers of detrimental microbes (Alternaria, Phytophthora nicotianae and Fusarium oxysporum). Moreover, CBF amendment improved the stability and complexity of microbial co-occurrence networks. Soil total carbon, microbial structure, and diversity were the most important explanatory factors for the increase of tobacco leaf yield and economic value.

CONCLUSIONS

Collectively, BFs application under rotation regime showed the great potential as a practical and environmentally friendly strategy to alleviate tobacco CCO by providing an optimized soil environment.

Emerging nitrogen-fixing cyanobacteria for sustainable cotton cultivation

Amid growing environmental concerns and the imperative for sustainable agricultural practices, this study examines the potential of nitrogen-fixing cyanobacteria as biofertilizers, particularly in cotton cultivation. The reliance on synthetic nitrogen fertilizers (SNFs), prevalent in modern agriculture, poses significant environmental challenges, including greenhouse gas emissions and water system contamination. This research aims to shift this paradigm by exploring the capacity of cyanobacteria as a natural and sustainable alternative. Utilizing advanced metabarcoding methods to analyze the 16S rRNA gene, we conducted a comprehensive assessment of soil bacterial communities within cotton fields. This study focused on evaluating the diversity, structure, taxonomic composition, and potential functional characteristics of these communities. Emphasis was placed on the isolation of native N2-fixing cyanobacteria strains rom cotton soils, and their subsequent effects on cotton growth. Results from our study demonstrate significant plant growth-promoting (PGP) activities, measured as N2 fixation, production of Phytohormones, Fe solubilization and biofertilization potential of five isolated cyanobacterial strains, underscoring their efficacy in cotton. These findings suggest a viable pathway for replacing chemical-synthetic nitrogen fertilizers with natural, organic alternatives. The reintegration of these beneficial species into agricultural ecosystems can enhance crop growth while fostering a balanced microbial environment, thus contributing to the broader goals of global sustainable agriculture.

Microecological Shifts in the Rhizosphere of Perennial Large Trees and Seedlings in Continuous Cropping of Poplar

The cultivation of poplar trees is hindered by persistent cropping challenges, resulting in reduced wood productivity and increased susceptibility to soil-borne diseases. These issues primarily arise from alterations in microbial structure and the infiltration of pathogenic fungi. To investigate the impact on soil fertility, we conducted an analysis using soil samples from both perennial poplar trees and three successive generations of continuously cropped poplar trees. The quantity and community composition of bacteria and fungi in the rhizosphere were assessed using the Illumina MiSeq platform. The objective of this study is to elucidate the impact of continuous cropping challenges on soil fertility and rhizosphere microorganisms in poplar trees, thereby establishing a theoretical foundation for investigating the mechanisms underlying these challenges. The study found that the total bacteria in the BT group is 0.42 times higher than the CK group, and the total fungi is 0.33 times lower than the CK group. The BT and CK groups presented relatively similar bacterial richness and diversity, while the indices showed a significant (p < 0.05) higher fungal richness and diversity in the CK group. The fractions of Bacillus were 2.22% and 2.41% in the BT and CK groups, respectively. There was a 35.29% fraction of Inocybe in the BT group, whereas this was barely observed in the CK group. The fractions of Geopora were 26.25% and 5.99%, respectively in the BT and CK groups. Modifying the microbial community structure in soil subjected to continuous cropping is deemed as the most effective approach to mitigate the challenges associated with this agricultural practice.