Slope-related Variations Of Main Functional Traits In Robinia Pseudoacacia In The Northern Mountains Of Lanzhou

Plant functional traits are the results of interaction between plants and environment in the long evolution process, they can reflect ability of plants to adapt the external environment. As the connection between plants and the environment, plant functional traits have strong effect on plant’s morphogenesis, survival to adapt, reflecting adaption to environment and life or evolution trade-off among different functions. Robinia pseudoacacia are temperate deciduous trees that belong to Leguminous robinia genus. They have fast growth speed, developed root system, strong environment adaptive and they are main plantation type of vegetation restoration in the loess plateau. Researching main functional traits of Robinia pseudoacacia is good to understand phenotypic plasticity and environmental adaption mechanism of Robinia pseudoacacia. In view of this, in the Green base of Northwest Normal University, Lanzhou, Robinia pseudoacacia and Populus bolleana were selected for study, ArcGIS was used to construct the digital elevation model (DEM), standardized major axis estimation method(SMA) was used, this paper studied the relationship of height-crown width, height-diameter, cross-sectional area of twigs-total leaf area, leafing intensity-average area of a single leaf, leaf mass-leaf area, leaf mass-leaf volume of Robinia pseudoacacia at different slope aspects on the northern mountains of Lanzhou. The result showed that:(1) With a change of the aspect from South to west, east and north, the cover, height and the soil moisture of the plant community increased.(2) With a change of the aspect from South to west, east and north, the height, crown width, diameter declined, there were significant differences on south and north slope aspect (p < 0.05), there were no significant differences on west and east slope aspect (p>0.05), the growth rate of crown width was greater than that of height on south slope, but it is quite on the contrary on north slope, in the meantime, the growth rate of height and width were similar on west and east slope. On all slope aspects, the growth rates of diameter were greater than those of height.(3) With a change of the aspect from south to west, east and north, the cross-sectional area of twigs, total leaf area, average area of a single leaf increased, leafing intensity declined. Significant, positive relationships between twig cross-sectional area and total leaf area were found in R. pseudoacacia in all aspect (p<0.05), and the common slope of the regressions was significantly greater than 1. Significant, negative relationships between leafing intensity and average area of a single leaf were found in R. pseudoacacia in all aspects (p<0.05), and the common slope of the regressions was significantly close to -1. In addition, when the aspect changed from south to west, east and north, the y-intercepts in the scaling relationships of twig cross-sectional area vs. total leaf area and leafing intensity vs. average area of a single leaf both increased.(4) With a change of the aspect from South to west, east and north, the leaf mass, leaf area and leaf volume increased, there were no significant differences in all aspect of leaf mass(p>0.05), there were significant differences in south and north slope aspect (p<0.05), there were no significant differences in west and east slope aspect(p>0.05). The growth rate of leaf mass was greater than that of leaf area in south slope, but it is quite on the contrary on north slope, The growth rate of leaf volume was greater than that of leaf mass in south slope, but it is quite on the contrary on north slope. In the meantime, the growth rate of leaf area-leaf mass and leaf mass-leaf volume were similar on west and east slope.The chage of allometric growth relationship among main plant functional traits reflected the investment weighing mechanism on main components in heterogeneous habitats, and the survival strategies that to adapt to environmental change.