Effects of nitrogen fertilizer reduction on soil bacterial community structure in Korla fragrant pear orchards at ripening stage

【Objective】 The study aimed to explore the effects of nitrogen fertilizer reduction on the composition and diversity of the bacterial community in the soil（0-20 cm soil layer）of Korla fragrant pear orchards at ripening stage，providing theoretical basis for reducing nitrogen fertilizer application，improving the soil microbial community in pear orchards，and ensuring the high-quality development of Korla fragrant pear industry. 【Method】 Treatments were set up for Korla fragrant pear plants，including no fertilization（N₀P₀K₀），no nitrogen fertilizer（N₀PK），conventional fertilization （NPK）treatments，as well as 3 nitrogen reduction gradients：nitrogen application reduced by 10%（N₁PK），20% （N₂PK）and 30%（N₃PK）compared to conventional fertilization. High-throughput sequencing technology was employed to study the response of soil bacterial community composition and diversity to nitrogen fertilizer reduction in fragrant pear orchards，and to analyze the correlation between soil physicochemical properties and the structure of soil bacterial community. 【Result】 Compared to the N₀P₀K₀ treatment，the content of soil alkali hydrolyzable nitrogen in the N₁PK，N₂PK and N₃PK treatments was significantly increased（P<0.05，the same below）. The soil bacterial community was dominated by the phyla Actinobacteria，Proteobacteria and Firmicutes，and the relative abundance of Actinobacteria under the N₁PK treatment increased by 13.99% compared to the NPK treatment. The dominant bacterial genera were Bacillus，Kocuria， Halomonas and Arthrobacter，with the relative abundance of Arthrobacter under the N₂PK treatment greatly reduced by 87.50% compared to the NPK treatment with complete nitrogen fertilizer application. The Simpson index under the N₁PK treatment was significantly higher than that under the NPK treatment. The Chao1 index and Observed_species index were the lowest under the N₂PK treatment，which reduced by 43.23% and 39.01% compared to N₀PK treatment respectively. The results of principal coordinate analysis（PCoA）showed that the first principal coordinate（PCoA1）and the second principal coordinate（PCoA2）together explained 33.6% of the total variation in soil bacterial community in orchards under different treatments during the ripening stage of Korla fragrant pear. Additionally，the available potassium content was extremely significantly and negatively correlated with the Chao1 index and Observed_species index（P<0.01， the same below），while it exhibited an extremely significant positive correlation with the Goods_coverage index. 【Conclusion】 Available potassium is the primary factor influencing the diversity of soil bacterial community in Korla fragrant pear orchards. Reducing nitrogen application by 10% on the basis of complete nitrogen fertilizer application greatly promotes the relative abundance of Actinobacteria and the diversity of bacterial communities in the orchard soil. The appropriate nitrogen fertilizer application rate is 270 kg/ha in actual production.