Study On Diversity And Ecological Stoichiometry Characteristics Of Plants Grown In Farmland Ditches Of Ganfu Plain

Ditches are important "corridor" of farmland landscape ecosystem and plants grown in ditches play an important role in mataining the biodiversity and ecological security of farmland ecosystem. In this study, we explored the floristic composition, diversity and mechanism of community construction, as well as stoichiometry of leaf C, P and N of plants grown in farmland ditches of GanFu plain through investigation of typical functional triats and measurement of total N, P, C content of farmland ditch associated plants from substantial community plots in these plains.The main obtained results are as follows:(1) Analysis of the floristic characteristic and geographic distribution of farmland ditch associated plants in GanFu plain region indicated that there were 127 species of plants in the farmland ditches we studied, belonging to 56 families and 115 genera, including 13 invasive species. Specifically, plants belonging to big family accounted for 4% of the total, with composition of rich species. On the contrary, small family contained less genuses than the big family did, taking 96% of the total plants. The geographical distibutions of genera were complicated and the R/T value was 1.61, implying a nature close to that of the tropic. Floristic charatersitic was examined with cluster analysis and the results indicated that ecological system of farmland ditches in GanFu plain region was similar to wetland as well as river ecosystem, partly proved to be a special type of wetland ecology system.(2) Ditches were classified based on their width and the flow patterns of water. Community of Leptochloa chinensis(L.) Nees was the most common in these ditches. Diversity index of α and β were calculated from different grades of ditches of three plots in GanFu plain. Analysis showed that ditches of the first grade contained the greatest number of individuals, with the fourth grade the smallest. The third grade ditches exhibited the greatest species richness and evenness while the fourth grade ditches were composed primarily of the predominant species.The fitting curve of β index change was a V-shaped curve. The comparison curves of the aboundance and biomass indicated that there were predominant species in all of the four different grades ditches, since the curve applied to a geometric series model. Length of the horizontal axis and the slope of the curve indicated that the third grade ditches obtained the greatest diversity and evenness.(3) Five functional triats of common plants in farmland ditches were tested and a zero distribution model was established based on the results. Inspections of differences of similarity and discreteness generated by the random process between the model and the real community revealed the mechanism of plant community construction of farmland ditches plants. Species with suitable plant height and leaf thickness survived habitat selection, and were further sculvated by ecological condition differentiation. Species of the strongest growth competiveness became dominant eventually. Plant height, basal diameter, specific leaf aera and the proportion of leaf dry matter content tended to be steadily distributed within the plant community.(4) Total carbon, nitrogen, phosphorus of 68 predominant kinds of GanFu plain farmland ditches plants were measured. The average content of carbon was 454.17 mg/g, more than that of the wetland ecological system. Content ranges of total nitrogen and phosphorus were also greater than those of typical wetland ecological systems. Significant differences were observed in total organic carbon among different life form plants through one-way analysis of variance. Phaenerophyte contained the highest level of total organic carbon, while the lowest level of total phosphorus. The trend of average ratio of C/N in plants with different life form was: hemicryptophyte < chamaephytes < cryptophytes < phanerophyte < therophyte, consistent with the trend of the average ratio of C/P and that of N/P. Pearson correlation analysis for total organic carbon, nitrogen, phosphorus and their stoichiometric proportion indicated complicated relationships among these elements.