Abstract
Phytotoxic effects of the bark and sawdust extracts from several woody forest species were examined. We mainly used two kinds of bark : hinoki cypress (Chamaecyparis obtusa Sieb. et Zucc. ex Endl.) and cryptomeria (Cryptomeria japonica D. Don). In Japan, the afforestation area of these species is on the increase in recent years. The results obtained are as follows :
1. Rice seedlings were cultured in water extracts of sawdust from Chamaecyparis obtusa, Cryptomeria japonica, Japanese red pine (Pinus densiflora Sieb. et Zucc.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), western spruce (Tsuga heterophylla (Raf.) Sarg.), apitong (Dipterocarpus spp.) and red lauan (Shorea negrosensis Foxw.), or in water extracts of bark from Chamaecyparis obtusa, Cryptomeria japonica, Douglas fir, western spruce and apitong. Extracts of Chamaecyparis obtusa sawdust and bark, Douglas fir saw-dust and bark, western spruce sawdust and bark, Pinus densiflora sawdust and apitong bark inhibited the growth of rice seedlings. Particularly, inhibitory effects of Chamaecyparis obtusa sawdust and bark, Douglas fir sawdust and bark, and Pinus densif-lora sawdust were very severe. However, extracts of Cryptomeria japonica sawdust and bark, apitong sawdust and red lauan sawdust did not impede rice growth. Pretreatment of bark extracts of Chamaecyparis obtusa, Douglas fir, western spruce and apitong with insoluble polyvinylpyrrolidone (PVP) reduced inhibition which indicates that the inhibi-tory substances are phenolic compounds.
2. Water extracts of Chamaecyparis obtusa bark were fractionated with ethyl ether (EE), ethyl acetate (EA) and n-butanol (NB), and each fraction was examined by chroma-tography and spectral analysis. Every fraction inhibited the growth of rice and trifoliate orange seedlings. Several phenolic acids, such as benzoic acid and gallic acid, in EE frac-tion and condensed tannins in EA and NB fractions were separated and identified by chromatography. Condensed tannins, in particular, severely inhibited the growth of tri-foliate orange seedlings.
3. Volatile substances from Chamaecyparis obtusa bark inhibited root elongation of tri-foliate orange seedlings. Cryptomeria japonica bark, however, did not inhibit root growth. Volatile terpenes, such as a-pinene, 19-pinene and D-limonene, and ethylene evolved from the barks of Chamaecyparis obtusa and Cryptomeria japonica were detected by gas chroma-tography. In particular, the concentration of α-pinene was high, but in Cryptomeria japonica bark it was about one-third that of Chamaecyparis obtusa bark. Inhibitory effects of α -pinene and β-pinene on trifoliate orange seedlings were observed. The volume of ethylene evolved by soil to which the Chamaecyparis obtusa bark was incorporated was about twice as much as that evolved by soil to which Cryptomeria japonica bark was added.
