The Effects of Different C/N Ratios on Rhizosphere Soil Environment of Lonicera caerulea L.

Aiming to solve the problems of excessive chemical fertilizer application and reduced soil fertility in Lonicera caerulea cultivation, this study investigated soil carbon and nitrogen nutrients, enzyme activities, and rhizosphere microbial characteristics using potted seedlings. Seven treatments, including control, single straw application, single nitrogen fertilization, and four C/N ratios (10, 15, 20, 25), were established. The results showed that a soil C/N ratio of 15–25 achieved the optimal soil fertilization effect. The 20:1 C/N ratio produced the highest soil total nitrogen and active organic carbon contents, as well as the maximum nutrient-converting enzyme activity. C/N ratio significantly regulated rhizosphere microbial communities: increasing nitrogen improved bacterial diversity but slightly reduced fungal diversity, and C/N imbalance altered dominant fungal phyla. Soil nitrogen and active organic carbon were positively correlated with bacterial diversity and negatively correlated with fungal diversity. Based on a comprehensive analysis of various indicators, a C/N ratio range of 15:1 to 25:1 improves soil fertility, while a ratio of 20:1 yields the most balanced overall results, enhancing soil carbon and nitrogen reserves, optimizing the microbial community, and reducing nutrient loss. This study provides a reference for fertilizer reduction and efficiency improvement in Lonicera caerulea cultivation.