Allelopathy of uncomposted and composted invasive aster (Ageratina adenophora) on ryegrass

In many areas invaded by Ageratina adenophora, the piles of A. adenophora residue need to be safely treated and economically utilized. To explore a new potential use for these residues, on-site aerobic composting, seed germination test and greenhouse experiment were conducted to compare the phytotoxic allelochemicals in uncomposted and composted A. adenophora plants (UA and CA, respectively) and their influence on ryegrass seed germination and seedling growth. The phytotoxicants 4,7-dimethyl-1-(propan-2-ylidene)-1,4,4a,8a-tetrahydronaphthalene-2,6(1H,7H)-dione (DTD) and 6-hydroxy-5-isopropyl-3,8-dimethyl-4a,5,6,7,8,8a-hexahydronaphthalen-2(1 H)-one (HHO) in UA decreased by 10.09 and 11.01 times in CA on average, respectively. Aqueous extracts of CA increased the seed germination rate, root dehydrogenase activity, leaf chlorophyll content and nitrate reductase activity; those of UA behaved oppositely. Compared with chemical fertilizers (CF), CF + CA promoted plant growth, increased plant nutrient uptake, and resulted in higher soil available nutrients, enzyme activity and microbial biodiversity, whereas CA alone had similar or better influences on plants and soils than CF. The predominant bacterial and fungal composition was the same in the soils supplied with CA and CF + CA. Therefore, on-site aerobic composting eliminated the phytotoxicity of CA and provided a new, simple and economical approach for the potential use of A. adenophora biomass as a plant- and soil-friendly organic fertilizer.