Effects of water-biochar coupling on asparagus rhizosphere soil microbial community structure

Soil microbes at the rhizosphere are one of the key factors in maintaining soil health. However, it is unclear on the effect of different water-biochar coupling on the microbial environment of soil at the rhizosphere. Particularly, asparagus is one type of perennial herbaceous plant. There is a seriously continuous cropping disorder in asparagus, with the growth of years, leading to weak growth, low yield, and quality. The crop failure can be attributed to the soil's physicochemical properties and the unbalance of the rhizosphere soil microbial community. This study aims to explore the effects of water-biochar coupling on the structure of soil microbial communities in the asparagus rhizosphere. The mechanisms were also given to regulate the rhizosphere ecosystem. The field positioning experiment of asparagus planting was carried out on four irrigation levels (W₀: severe deficit irrigation, I = 320 mm; W₁: middle deficit irrigation, I = 375 mm; W₂: mild deficit irrigation, I = 430 mm; W₃: adequate irrigation, I = 480 mm, I represents the amount of irrigation) and four biochar application levels (0 t/hm² (B₀), 10 t/hm² (B₁₀), 20 t/hm² (B₂₀), and 30 t/hm² (B₃₀)). Illumina next-generation sequencing (NGS) technology was used to investigate the changes in the structure and abundance of the soil microbial community in the asparagus rhizosphere using water-biochar coupling treatments. The results showed that moderate deficit irrigation was promoted to form the bacterial abundance and diversity of asparagus rhizosphere soil. The relative abundance of soil fungi increased by 4.48% to 22.05% in the asparagus rhizosphere, with the increasing soil moisture; Biochar application increased the abundance and diversity of rhizosphere soil microorganisms. Furthermore, the number of rhizosphere bacterial communities increased, whereas, the number of fungal communities decreased under the B₂₀ (20 t/hm²) treatment, compared with the B₀ and B₁₀ treatments. There was a significant inhibitory in the application of 30 t/hm² biochar. In addition, there was no significant effect on the structure of bacterial and fungal communities under different water-biochar coupling. The biochar application reduced the growth and reproduction of the root rot causal fungus Fusarium, indicating a better soil microenvironment asparagus rhizosphere. Optimal deficit irrigation was maintained on the microbial diversity and community stability. The higher numbers of soil bacterial communities were observed in the medium and mild deficit irrigation than those in the rest. There was the greatest community richness and diversity of rhizosphere soil bacteria at the medium deficit irrigation level. Therefore, the W₁B₂₀ treatment was more favorable to regulating the asparagus rhizosphere ecosystem, where the growth of the bacterial community was promoted to suppress the abundance of harmful fungal communities. This finding can also provide the theoretical basis to regulate the soil microcosm of the asparagus rhizosphere in continuous cropping, particularly for sustainable agriculture in the seasonal arid areas of Southwest China.