Abstract: By using traditional morphological data and modern truss network data, this paper analyzed the morphological characteristics of three Plagiognathops microlepis populations (Longwo Lake population, Liangzi Lake population, and Huaihe Rive population), and approached the relative relationships among the populations. One-way analysis of variance (ANOVA) indicated that there were no significant differences (P>0.05) in 8 countable characters among the populations. Cluster analysis demonstrated that Liangzi Lake population was grouped with Longwo Lake population first, and then clustered with Huaihe Rive population. In discriminant analysis, 7 parameters were selected from 28 measured parameters to establish discriminant functions of the populations. Discriminant accuracy was 93.55%-100%, and synthetic discriminant accuracy was 96.81%. The three populations could be separated each other by discriminant functions, with highly significant differences (P<0.01). Three principal components with accumulative variance percentage 82.99% were summarized in principal component analysis. The principal components 1, 2, and 3 reflected the morphological variations of trunk, head, and caudal peduncle, with the variance percentage being 52.83%, 22.22% and 7.94%, respectively. The 2D-plot of principal components 1 and 2 showed that the three populations could be clearly separated each other, though there was a small overlap between Longwo Lake population and Liangzi Lake population. The coefficient of morphological dissimilarity was less than 1.28, suggesting that the morphological differences among the three populations were still within the level of subspecies.

Key words: Long term fertilization, NO₃^--N distribution pattern, Loess Plateau dry highland