| The studies of soil and water conservation plantation structure, function and its ecosystem stability are vegetation construction important theoretical problem in loess hilly region.It also has significance for the production practice. Study on interspecific relation is an important part of the study.This paper aims to analyze the relationship between species through research allelopathic and provide a theoretical basis for build the ecosystem. Allelopathic effect refers to plants release chemicals into the environment, thus affecting the growth and distribution of other plants as well as microorganisms to determine the type of vegetation,forest ecosystem structure. This paper aims to analyze interspecific relationship from the allelopathic effect aspect of the afforestation tree species, providing theoretical support for plantation ecosystem construction. Pinus tabuliformis and Robinia pseudoacacia, the main afforestation tree species in loess hilly area are investigated. The receptor plants are P. tabuliformis, R. pseudoacacia, Platycladus orientalis, Lespedeza bicolor, Spiraea salicifolia, Agropyron cristatum, and Medicago sativa. By using bioassay and GC-MS detection to test P. tabuliformis and R. pseudoacacia roots allelopathy intensity and allelochemicals component, the conclusions could be drawn as follows:(1) The root of P. tabuliformis has the allelopathic effect of "low density to promote, high density to suppress" on P. tabuliformis, L. bicolor, S. salicifolia. There is the biggest boost when density is 1 mg/mL, and the allelopathic effect indexes are 0.137,0.086,0.123 respectively. At 5 mg/mL allelopathy effect turns to suppress, and the allelopathic effect indexes respectively are -0.145,-0.144 and -0.113. At the 10 mg/mL allelopathy inhibition effect maximizes, and indexes respectively are -0.356,-0.418,-0.310. The root of P. tabuliformis inhibits the growth of R. pseudoacacia, A. cristatum, and M. sativa, and such effect increased with the increase of the concentration. In the 10 mg/mL, allelopathy inhibition effect maximizes, and indexes respectively are -0.345,-0.519,-0.309. The inhibition effect is obvious. The root of P. tabuliformis constantly promotes the growth of P. orientalis at each concentration In the 1 mg/mL allelopathy promotion effect maximizes, and index is 0.346. Considering the allelopathic effect of the root of P. tabuliformis on the receptors, P.orientalis should be given priority to constructing compound arbor-shrub-herb vegetation in P. tabuliformis forest and R. pseudoacacia, A. cristatum, and M. sativa should be chose carefully. When choosing P. tabuliformis,L. bicolor and S. salicifolia, the thinning and intercropping density of P. tabuliformis forest should be noticed.(2) The root of R. pseudoacacia has the allelopathic effect of "low density to promote, high density to suppress" on P. tabuliformis, R. pseudoacacia, P.orientalis, S. salicifolia, A. cristatum, and M. sativa. For R. Pseudoacacia. In the portion of 3,1,1 mg/mL, it maximizes the promotion to P. tabuliformis, R. pseudoacacia, S. salicifolia, with the indexes respectively being 0.317,0.220,0.213. At 7 mg/mL allelopathic effects convert from promotion to suppression ---heir allelopathic effect indexes respectively are -0.126,-0.081,-0.133. In the portion of 10 mg/mL the allelopathic effects of inhibition maximizes ---ndexes respectively are -0.394,-0.189,-0.293. In the proportion of 1 mg/mL, promotion effect on P.orientalis, A. cristatum, and M. sativa reach to the top., and indexes respectively are 0.125,0.134,0.070. At 5,3,5 mg/mL allelopathic effects converts from promotion to suppression and their allelopathic effect indexes respectively are -0.160,-0.030,-0.110. In the 10 mg/mL allelopathic effects of inhibition maximizes, and their indexes respectively are -0.585,-0.567,-0.240. The root of R. pseudoacacia promotes the growth of L. bicolor at each concentration, among which, in the portion of 3 mg/mL allelopathy promotion effect reaches to its top ---its index is 0.464. When constructing compound arbor-shrub-herb vegetation in R. pseudoacacia forest, L. bicolor should be first taken into consideration from the perspective of allelopathic effect of the root of R. pseudoacacia on receptors. When choosing P. tabuliformis, R. pseudoacacia, P.orientalis, S. salicifolia, A. cristatum, and M. sativa, the thinning and intercropping density of P. tabuliformis forest should be controlled.(3) By GC/MS detection, it has been identified that there are 53,37 kinds of allelochemicals respectively in the P. tabuliformis root and R. pseudoacacia root. Thereinto, the allelochemicals in P. tabuliformis belong to 11 types of compounds, and the content of acid (19.43%),acetylene (18.94%) and esters (13.61%) are higher. The allelochemicals in R. pseudoacacia roots belong to 10 types of compounds, and the proportion of alcohol (36.92%), esters (20.10%) and acid (14.72%) are higher. |
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