Effects of root extracts from different vegetables on rhizosphere soil properties and microbial communities of...

Continuous cropping of celery in the mountainous areas of southern Ningxia results in soil degradation and yield reduction. To investigate the potential of crop rotation to mitigate such challenges, we conducted a field experiment to systematically evaluate the effects of root extracts from various vegetables, including celery (AG, control), baby cabbage (BC), pepper (CA), welsh onion (AF), and broccoli (BO), on the physicochemical properties, enzyme activities, and microbial community structure of rhizosphere soil. The results showed that all treatments enhanced soil nutrient content and enzyme activities in the celery rhizosphere. Under the AF treatment, the contents of soil nitrate, alkali-hydrolyzable nitrogen, available phosphorus, and organic matter, as well as urease activity, all reached their maximum values, which were significantly increased by 10.1%, 84.3%, 167.7%, 93.2%, and 42.8%, respectively. In addition, sucrase and catalase activities peaked under the BC treatment, with significant increases of 136.8% and 76.0%. Both CA and AF treatments significantly reduced the disease incidence of celery by 64.3% and improved yield by 22.7% and 31.5%, respectively. None of the five extract treatments had a significant impact on the α-diversity of soil bacterial and fungal communities, but distinct changes in community composition were observed at the genus level. Compared with the AG treatment, other treatments significantly increased the relative abundance of the beneficial bacterium Sphingomonas. Furthermore, the AF treatment decreased the relative abundance of pathogenic fungi, such as Plectosphaerella and Fusarium. Spearman correlation analysis and redundancy analysis indicated that ammonium, alkali-hydrolyzable nitrogen, and sucrase activity were the main factors affecting soil bacterial community, while ammonium, alkali-hydrolyzable nitrogen, urease and sucrase activity were the key factors regulating soil fungal community. Comprehensive evaluation via grey relational analysis demonstrated that the promoting effects of all treatments on the rhizosphere soil biological properties and celery yield were in the order of AF>CA>BC>AG>BO. In conclusion, vegetable root extracts tested here effectively enhanced soil fertility and optimized soil microbial community structure, with root extract of onion showing the most remarkable effect. It was recommended that celery-onion rotation could be adopted to mitigate celery continuous cropping obstacles.