Allelopathic potential of Turnera subulata leaf extract on choy sum (Brassica chinensis var. parachinensis) via untargeted metabolomics

Allelopathic plants release phytotoxic compounds that contribute to their invasiveness by suppressing nearby species. However, it remains unclear which exact mode of action (MOA) underlies the allelopathy. This study explores the allelopathic mechanisms of Turnera subulata on the recipient indicator plant choy sum using a metabolomics approach. Briefly, T. subulata leaf aqueous extracts (LAEs) at different concentrations (0.0, 0.1, 1.0, 10.0, 50.0, and 100.0 mg/mL) were sprayed at 100 mL/m2 on choy sum seedlings at the two to three leaf stage. After 21 days, the Soil Plant Analysis Development (SPAD) values and photosynthetic pigments of the exposed choy sum were measured, and their metabolites were subjected to a gas chromatography-mass spectrometer (GC-MS) analysis. The results revealed a 25% decrease in the SPAD, a reduction of 65% (chl a) and 71% (chl b), and a 45% reduction in the stomatal length at 100 mg/mL. A total of 15 significant metabolites (P < 0.05) with variables important for the projection score exceeding 1 (VIP > 1) were selected as the important biomarkers. These metabolites were identified as amino acids, carbohydrates, and fatty acids. The findings reveal the allelopathic potential of T. subulata and provide insights into the response of choy sum in response to the allelopathic activity of T. subulata LAEs.