Allelopathic effects of tree peony extracts on bok choy, spinach and tatsoi

Although tree peony (Paeonia ostii) is widely cultivated in China, it has not been fully utilized as an arable resource. To investigate the suitability of tree peony in intercropping systems, we examined the allelopathic effects of aqueous extracts from the leaves and roots of P. ostii 'Fengdan' on the seed germination, growth, and physiological responses of tatsoi, spinach, and bok choy. Among these vegetables, tatsoi exhibited the best seed germination and seedling growth. Lower concentrations of aqueous extracts of 'Fengdan' roots (5-10 g L^-1 for tatsoi and 5 g L^-1 for spinach and bok choy) promoted seed germination, biomass, chlorophyll content, root activity, photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, and antioxidant enzyme activity. However, high concentrations of the leaf extract (40 g L^-1 for tatsoi and 20-40 g L^-1 for spinach and bok choy) significantly increased levels of malondialdehyde and reduced seed germination, dry weight, chlorophyll content, root activity, and antioxidant enzyme activity. These deleterious effects increased with higher extract concentrations. The allelopathic effect of the leaf extract was greater than that of the root extract. The order of the allelopathic effect of tree peonies on the three vegetables was bok choy, spinach, and tatsoi. Therefore, tatsoi is the most suitable vegetable for interplanting with tree peonies.