Allelopathic Effects Of Poplar On Agroforestry System In Huaibei Plain

Huaibei plain is the main area of grain、cotton、oil production, but it also face with the shortage of land resource and frequent natural disasters. It become an important issue of competition for land resources between forestry and agriculture. The application of agroforestry systems is an effective approach to reduce the destruction of natural disasters. Study on interspecific relationships of agroforesty system could help us understand the stability of stucture and function of the ecosystem, and provide theoretical basis for exploration of reasonable and effective utilization way, selection and configuration of species. Plant allelopathy is one naturally chemical regulation phenomenon, and widely exists in the agroforest ecosystem, which proved as significant selectivity and specificity. In order to give a full play to the advantage of agroforestry, we should select appropriate plant species that is suitable to grow under the tree canopy.Poplar is one of the important timber tree species, and proved with allelopathy in agroforestry systems. This study focused on Poplar 2025, the main afforestation tree species of Huaibei plain. We studied the allelopathic effect of Poplar allelochemical on seed germination and seedlings growth of Radix isatidis, Platycodon grandiflorum, Rhizoma anemarrhenae, wheat (Triticum aestivumLinn.), cabbage (Chinese Cabbage) by the bioassay method in order to clarify allelopathy mechanism of the receptor plant, and to provide theoretical basis for giving full play to the ecological benefits and economic benefits of agoforestry management. The results are as follows.The allelopathic effect of extracts from Poplar 2025 leaves on seed germination and seedlings growth of Radix isatidis, Platycodon grandiflorum, Rhizoma anemarrhenae, wheat and cabbage included promotion effect, inhibitor effect,promotion at low concentration and inhibition at high concentration or the dual concentration effect. The allelopathic effect showed selectivity and specificity with the difference in extract concentration of Poplar 2025 leaves and receptor plant species. There existed a promotion effect at low concentration and an inhibition effect at high concentration for the germination percentage of Platycodon grandiflorum and Rhizoma anemarrhenae. The germination percentage of Radix isatidis reached the highest at the mass concentration of 5 mg·mL-1 of popar-leaf extract. When the mass concentration reached 30 mg·mL-1, the germination of wheat and Cabbage seeds were inhibited. All treatments of leaf-extract showed significant effect on the seed vigor except for Rhizoma anemarrhenae. Seed vigor of wheat was highly significant. The simplified vigor index of wheat seed increased with the decrease of concentration of leaf-extract, while increased with the raising of concentration for cabbage.The allelopathic effect of leaf-extract of Poplar 2025 was different due to the different receptor, even different parts of the same receptor. It showed an inhibiting effect on seed germination of Platycodon grandiflorum, Radix isatidis and wheat, a promotion effect on seed germination of cabbage; low-concentration promotion and high-concentration inhibition of seed germination of Rhizoma anemarrhenae. An inhibiting effect on seedling height occurred in Platycodon grandiflorum and Rhizoma anemarrhenae, with significant difference between the different treatments. The seedling growth of Radix isatidis was promoted when the mass concentration was 5 mg·mL-1. In addition, the root growth of Radix isatidis, Platycodon grandiflorum, Rhizoma anemarrhenae, and wheat were inhibited. And seed vigors of Rhizoma anemarrhenae, Radix isatidis and wheat were also inhibited. Seed vigor of cabbage was promoted. The results demonstrate that the tolerance of cabbage to allelopathic effect is the best and is more suitable to agroforestry system.Low mass concentration (5 mg·mL-1) of leaf-extract of poplar showed a promotion effect on biomass of Iris tectorum and Belam canda, SPDA content, net photosynthetic rate, stomatal conductance. However, the high mass concentration (100mg·mL-1) of leaf-extract of poplar showed an inhibitor effect on the various index of Iris tectorum and Belam canda. The inhibiting effect on Iris tectorum was smaller than on Belam canda.Mass concentrations of 0.025,0.05,0.1,0.2,0.4 g·mL-1 of leaf-extracts of poplar showed significant destructive effect on the memberane permeability of Iris tectorum and Belam canda. The memberane permeability was great with the increase of mass concentration.Allelochemicals from poplar lead to increase concentrations of soluble sugar and MDA and to decrease chlorophyll content of Iris tectorum and Belam canda, destroying the normal metabolism of plant growth, diminishing the resistance, and then showed inhibitor effect on receptor plants.