Difference of phytotoxicity between undecomposed and microbially decomposed plant residues.

Abstract

Extracts of fresh and decomposed plant materials of tall goldenrod [Solidago altissima], mugwort [Artemisia vulgaris], Japanese plume-grass [Erianthus sp.], soyabeans, maize and black wattle [Acacia mearnsii] were monitored for phytotoxicity with a bioassay system using lettuce seeds. Extracts of fresh material of all plant species did not suppress germination considerably, with germination remaining between 80 and 100%. Material of S. altissima, A. vulgaris, Erianthus sp., soyabeans and maize which had been decomposing for 1 month caused germination to fall to <50%. However, this inhibitory effect was not observed with plant material which had been decomposing for 3 or 6 months. Root elongation was inhibited to ≤50% with extracts of fresh material of all species, but A. vulgaris and A. mearnsii which had decomposed for 1 month actually promoted the elongation of lettuce radicles, although this effect diminished with longer periods of decomposition.