Evaluation of the biological activity of extracts from Acer negundo L. and Robinia pseudoacacia L. composted leaves on seedlings of test cultures

Abstract

Ash-leaved maple and black locust are invasive woody species that require the measures for their spread control. In the case of mechanical elimination of these plants, the possibility of using their phytomass as a fertilizer after composting is considered. For such kind of application, it is necessary to evaluate the allelopathic effects of the phytomass on other plants. Aerobic passive composting of A. negundo and R. pseudoacacia leaves was carried out outdoor during 10 month (from September to July). In the article, the activity of compost water extracts was tested in vitro on germinating seeds of Lepidium sativum, Raphanus sativus, and Daucus carota; the percentage of germinated seeds, the length of the root and hypocotyl were measured, at concentrations of the extract 5, 10, 50, and 100 g/l of dry powdered composted leaves, with control on distilled water. The second control was the water extracts from dried green leaves of A. negundo and R. pseudoacacia, i.e. from non-composted phytomass. The composting process described above led to a significant decrease of allelopathic inhibition effect of A. negundo composted leaves compared to non-composted ones. In particular, 3,7 % of carrot seeds germinated on extract (50 g/l) from non-composted leaves and 112 % to control on extract from composted ones. The extracts from compost of R. pseudoacacia demonstrated near unchanged or increased allelopathic inhibition properties compared to non-composted leaves. Moreover, extracts from R. pseudoacacia compost showed the increase of inhibition
properties on seedlings, when their concentration increased from 5 to 100 g/l. Such regularity was little pronounced for extracts from A. negundo compost. In several cases, the extracts from compost had stimulating effect: from A. negundo and R. pseudoacacia, 5 g/l, provoked 1.7–1.9 times elongation of root in radish seedlings; from A. negundo, 5–50 g/l, stimulated 1.3–1.9 times elongation of hypocotyl in radish; from R. pseudoacacia, 5 and 10 g/l, led to 1.4 times elongation of hypocotyl in radish; from R. pseudoacacia, 10 g/l, stimulated 1.3 times elongation of hypocotyl in watercress. Three test cultures involved in this research demonstrated different sensitivity to the same compost extracts. E.g., A. negundo extract inhibited the elongation of roots in watercress seedlings, whereas it had neutral or stimulating effect on radish. The same extract stimulated the development of hypocotyl in radish only, and inhibited in watercress only. Extract from R. pseudoacacia compost, 50 g/l, decreased the germination rate to 0% for watercress, but to 58.6 % in radish.