Purpose To clarify the synergistic variation patterns of soil nutrients and microorganisms in pomelo orchards with different planting years in Xishuangbanna, providing a theoretical basis for high-quality, stable yield and sustainable pomelo cultivation.
Methods Rhizosphere soil from pomelo trees planted for 3, 6, 10, 15 and 30 years was taken as the research object. Soil nutrient indicators were determined, and high-throughput sequencing was applied to analyze microbial diversity, community structure, and their correlations with soil nutrients.
Results Soil nutrients showed stage-specific evolutionary characteristics. They tended to be stable during 10-15 years and continued to evolve after 15 years. Compared with 10-year-old orchard soils, total phosphorus (1.95 g/kg) and available phosphorus (70.30 mg/kg) in 30-year-old orchard soils surged by 267.92% and 323.49%, respectively; but soil organic matter (13.25 g/kg), total nitrogen (0.65 g/kg) and hydrolyzable nitrogen (60.00 mg/kg) plummeted by 86.19%, 95.38% and 107.78%, respectively. Available boron was below 0.5 mg/kg in most years, remaining long-term deficient. Planting years had a significant impact on the rhizosphere microbial community structure. Bacterial diversity indices showed no significant changes with planting years. The fungal Shannon index dropped significantly from 6.78 (10-year-old) to 3.76 (30-year-old). The relative abundance of the bacterial genus Bacillus increased continuously. In 30-year-old orchard soils, the relative abundance of the fungal genus Trichoderma and Penicillium were significantly higher than that in 10-year-old or 15-year-old orchards soils. Meanwhile, the relative abundance of the pathogenic fungal genus Fusarium decreased significantly.
Conclusion Orchards with over 15 years of planting need to focus on supplementing organic matter. Long-term boron deficiency may be a key factor causing unstable fruit quality. Soil pH, phosphorus, potassium, available sulfur, available copper and available boron are core factors regulating microbial community composition. The optimization of microbial communities, including enrichment of beneficial bacteria and reduction of harmful bacteria, is the key mechanism for stable and high-quality pomelo production under long-term monoculture.
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