| Juniperus rigida is a useful plant species in many ways, such as soil and water conservation, environment improvement and so on. But because of the human doing, habitat destruction, slow-growing, it has been listed to the endangered plant species in Shaanxi province. With the helps of various statistical analyses we studied the composition, species diversity and liaison between species in the communities, as well as the niche, distribution pattern, modular structure of the populations. The main results are as follows:There are 24 species of 16 genera in 22 families of higher plants in the Juniperus rigida communities. Among those higher plants in the communities there are 2 species of 2 genera in 2 families of gymnospermae accounting of 8.33% of the total, 14 species of 20 genera in the 22 families of angiospermae accounting for 91.67% of the total. Among the angiosperm there are 11 species of 16 genera in 18 families of dicotyledon, 3 species of 4 genera in 4families of monocotyledon.The vertical structure of community is relatively simple which can be divided into tree layer, shrub layer and herb layer as well as little number of interstratum plants. The species diversity index of different layers shows: herb layer>shrub layer>tree layer. A serious destruction has taken place toⅡpopulation, so effective action should be taken to protect it.However,Ⅲpopulation is intact.Little seedlings from germination observed in the populations of Juniperus rigida. The main reproduction of the species is asexual reproduction.There was significantly difference among populations and among individuals within populations. There were significant differences exist in 11 character indices among populations, and there were also 7 character indices within population are significant. The variation among populations, that is the mean phenotypic differentiation coefficien(tVst), was 66.63% and more than that within population(33.37%), among populations variation mainly contributes to phenotypic variation. The needle width became larger, upon increase of the altitude. The needle length and number of primary branches got smaller as the crown density became higher. Under branch height became larger, upon increase of the degree of slope. According to the UPGMA cluster analysis, the 6 populations could be divided into 4 groups. There existed inhibitive substances against the growth in the aqueous extract from litter, pericarp, seed, root and rhizosphere soil, and volatile oil of Juniperus rigida. Effects of aqueous extract of Juniperus rigida on seed germination and seedling growth of Brassica napus, Triticum aestivum and Pinus tabuliformis are different with treatment concentrations, part of physiological indexes were highly significantly inhibited when concentration of aqueous extracts was increased to 0.10gDw·mL-1; the root activity and chlorophyll contentin the seedlings of Triticum aestivum and Pinus tabuliformis were reduced, respectively, compared with the control. At 0.025gDw·mL-1, the extract significantly increased the activities of, peroxidase(POD), catalase(CAT) and superoxide dismutase(SOD); whereas at 0.10gDw·mL-1 the extract reduced the activities of those enzymes while significantly increased the content of malondialdehyde(MDA) in the seedling of Triticum aestivum and Pinus tabuliformis. The identification test had proven that some phenolic allelochemicals existed in the aqueous extract of leaf litter, pericarp and root.In summary, although the phenotypic diversity level of Juniperus rigida is at high level, many factors, such as human disturbance, high death rate of seeding and sapling etc have made it very difficult to regenerate naturally. Measures to be taken to conserve the species effectively are very necessary. |
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