Allelopathic Potentials Of Water Extracts Of The Main Organs Of Eucalyptus Grandis On Pastures

To study the effect of the inclusion of eucalyptus(Eucalyptus grandis)on pastures,effects of the different concentration(1:10,1:20,1:50,1:100w/v)of the water extracts of the main organs of E.Grandis on the seed germination and seedlings growth of some species of pastures were researched.The organic compounds of litterfall of Eucalyptus grandis have been ultrasonically extracted with hexane,and identified with Gas Chromatograph-Mass Spectrometer.The results in hydroponic culture and pot culture indicated that:1 The allelopathy of the water extracts of the roots,the fresh leaves,the litterfall and the mixture of Eucalyptus grandis varied with receptor variations,the allelopathic substances categories and the concentration of water extracts.The water extracts of the main organs of Eucalyptus grandis inhibited the seed germination of whiteclover, inhibited the seedlings root growth of Italian ryegrass(lolium multiflorum Lam.),the allelopathic inhibition rate increased with intense concentration of the water extracts. The water extracts of the main organs of Eucalyptus grandis promoted seedlings growth of alfalfa(Eupatorium coelestinum L.) and whiteclover(Trifolium repens L.) at low concentration.2 The results in long-term hydroponic culture indicated that:The water extracts of the mixture of Eucalyptus grandis reduced seedlings root growth and promoted seedlings growth of Italian ryegrass and whiteclover.Pastures'tolerance time decreased with intense concentration of the water extracts.3 To examine the effect of water extracts of Eucalyptus grandis on two species of pastures under water stress conditions as well as normal conditions.The results obtained indicated that water stress were more important than water extracts of Eucalyptus grandis.In water stress conditions,the water extracts of the mixture of Eucalyptus grandis reduced seedlings growth at high concentration,promoted seedlings growth at low concentration of talian ryegrass and whiteclover.4 The change tendency of net photosynthetic rate(pn),transpiration rate(tr), stomatal conductance(gs),intercellular CO₂ conertation(ci)of pastures is the same,which is lower than control at high concentration and is higher than control at low concentration.The ci and pn'change tendency varied with receptor variations, water stress and the concentration of water extracts.5 The extracts of litterfall of E.Grandis contains 35 components of 8 different categories including alkanes,alkenes,arenes,alcohols,aldehyde,ketone, hydroxybenzene,esters.The research indicates that the main allelochemicals of litterfall of E.grandis are alkanes,arenes and esters which may have important affects on the seed germination and seedlings growth.The results has reference meaning on the research of allelopathy influence on other plants in the underlayer of E.Grandis..