Study Of Larch Allelopathy On Manchurian Walnut

Manchurian walnut is one kind of rare tree species in northeast China. It is assured that mixed plantation of larch and Manchurian walnut is successful. Larch can distinctly accelerate Manchurian walnut growth in their mixed plantation. The former study suggested that reasonable and effective utilization of soil water and nutrient condition was the main reason why Manchurian walnut growed excelled in mixed plantation than in pure Manchurian walnut plantation. These studies did not refer to the allelopathy between two tree species.The effects of larch allelochemicals on Manchurian walnut seeds germination and seedlings growth, isolation and identification of larch allelochemicals were made by bioassay, seedling-potted experiment and compounds analysis methods. Meanwhile the interaction between larch and Manchurian walnut was initially probed by field experiment. The results suggested:(1) In four concentrations of larch aqueous extract (0.1, 0.05, 0.025, 0.0125 g/mL), low concentration (0.0125 g/mL) root, bark and branch larch aqueous extract could obviously accelerate germination and seedlings growth of Chinese cabbage and radish. Every kind of leaf aqueous extract concentrations could accelerate germination and seedlings growth of Chinese cabbage and radish, however, the promotion was gradually descended with aqueous extracts concentration descended.(2) Root, bark and branch larch aqueous extracts with 0.0125, 0.025 g/mL concentrations could accelerate significantly germination rate and germination index of Manchurian walnut seeds. Seedling height and collar diameter of Manchurian walnut seedlings were significantly accelerated by 0.0125 g/mL root and bark larch aqueous extracts. Leaf larch aqueous extracts with high concentration could accelerate significantly seeds germination and seedlings growth of Manchurian walnut, however, the promotion was gradually descended with leaf aqueous extracts concentration descended.(3) The aqueous extract with low and moderate concentrations (0.0125, 0.025 g/mL) could accelerate the growth of Manchurian walnut seedlings in collar diameter and biomass, increase its root/shoot ratio. The aqueous extract from branches and barks with low and moderate concentrations (0.0125, 0.025 g/mL) could accelerate height growth of Manchurian walnut seedlings. But aqueous extract from leaves and roots could slightly decrease height growth of Manchurian walnut seedlings.(4) Every kind of larch root exudation concentration levels could accelerate Manchurian walnut seedlings growth, however, whole plant biomass, root biomass, total chlorophyll content, chlorophyll a and b content declined with the descent of concentration levels. Thewhole plant biomass, root biomass, total chlorophyll content, chlorophyll a content separately increased with abstraction concentrations of 1, 0.1 g/L compared with control without abstraction. On the contrary, they separately decreased with abstraction concentrations of 0.01, 0.001 g/L compared with control without abstraction. High concentrations (1.0, 0.1 g/L) of larch abstraction could significantly increase soluble sugar content.(5) Manchurian walnut seedlings tended to easier survive and survival rate got highly to 89.57% in pure larch plantation in 2004 and remained 84.00% in 2005. The survival rate in pure larch plantation was significantly higher than in other two plantations. Manchurian walnut seedlings were almost died after two years. Seedlings height and biomass were all got to significantly difference compared with two other plantation. On the whole, soil nutrient in pure Manchurian walnut plantation were better than in interplanted plantation of larch and Manchurian walnut and pure larch plantation, however, soil microbial counts and enzyme activities (except polyphenol oxidase and hydrogen peroxidase) in the interplanted plantation were much higher than in pure Manchurian walnut plantation.(6) The isolation and identification results of larch allelochemicals suggested that there were many kinds of compounds including catechins, lignans compounds, polyphenols, coumarin compounds and so on. Although counts and relative content were different, kinds were the same between larch root extraction and its extract liquid.