Two types of covering crops are beneficial to improve the nitrogen metabolism of Citrus roots.

Citrus is the world's largest fruit category, yet it is frequently damaged by weeds during cultivation and management. As a green cultivation measure, covering crops in orchards effectively controls weeds and enhances soil quality. At present, the research on covering crops is mostly focused on soil, but there is still a lack of research on how crops affect citrus trees. This study aims to provide theoretical support for the widespread adoption of the green management practices. The previous research of us found that rattail fescue and vicia villosa had notably enhanced the organic matter and alkali-hydrolyzable nitrogen levels in orchard soils. Consequently, this study treated citrus orchards with sowing rattail fescue and vicia villosa between rows, with manual tillage serving as the control, to investigate the impact of two-year grass cultivation on N metabolism in citrus roots. Results indicated that both types of grass significantly enhanced amino acid metabolism in citrus roots at depths of 0-20 cm, significantly increasing activities of nitrate reductase, nitrite reductase, glutamine synthetase, NADH-glutamate synthetase, and NADPH-glutamate dehydrogenase, as well as expression levels of NR and NiR. Rattail fescue demonstrated superior effects. There was no discernible pattern in amino acid levels at depths of 20-40 cm, with both grass types significantly increasing NR, NADH-GOGAT enzyme activity, and also increasing gene expression levels for NiR, GDH1, and GDH2. Both types of grass significantly promoted N metabolism in citrus roots at depths of 0-20 cm, with rattail fescue outperforming vicia villosa.