采用水洗镜检法对江苏省31 个农田样点(包括旱田和水田)0 ~15 cm 土层土壤杂草种子库的种类组成和物种多样性进行了调查研究;采用典范对应法分析了杂草种子库种类与环境因子(包括淹水天数、土壤有机质含量、土壤pH、年降水量、年均温、样点经度和样点纬度)的相关性并绘制了样点和种类与环境因子的二维排序散点图。调查结果表明:在31 个样点的土壤杂草种子库中共检测到杂草种子15 科54 种,旱田和水田各有41 和45 种,二者共有种类占多数但优势种有差异,通泉草[Mazus japonicus (Thunb.) Kuntze]、异型莎草(Cyperus difformis L.)、水苋菜(Ammannia baccifera L.)、千金子[Leptochloa chinensis (L.) Nees]、棒头草(Polypogon fugax Nees ex Steud.)和牛繁缕[Malachium aquaticum (L.) Fries]等种类为二者的共有优势种;杂草种类最多的为禾本科(Gramineae)和莎草科(Cyperaceae),分别占种类总数的22. 6%和20. 8%。旱田不同样点杂草种子库的优势种类变化较大,而水田杂草种子库优势种较稳定;二者优势种频度差异较大,旱田中频度高于0. 30 的杂草有19 种,水田中频度高于0. 50 的杂草有20 种;旱田和水田中平均重要值大于0. 03 的杂草各有11 和9 种,这些频度高的种类重要值也较大。旱田和水田土壤种子库种子密度分别为21 015 和37 847 m^-2 ,平均为31 008 m^-2 ;旱田3 层土壤中种子密度差异不显著,而水田上、中层土壤的种子密度显著高于下层。旱田以夏熟和秋熟杂草为主,而水田则以水田和夏熟杂草为主。按形态类型划分,水田及旱田中杂草种类数和密度从大到小均依次排序为阔叶草类、禾草类、莎草类,且水田中这3 类杂草的种类数和种子密度均高于旱田。与旱田相比,水田杂草种子库的物种丰富度指数(S)、Shannon-Wiener指数(H’)和Simpson 指数(D)较高,但Pielou 均匀度指数(E)较低;旱田杂草种子库的S、H’和D 指数随土层深度增加而降低、E 指数逐渐升高,水田各土层的物种多样性指数则无明显变化趋势。第1 种类排序轴与淹水天数负相关性最高(R =-0. 814 3),第2 种类排序轴与年降水量和经度也有较高的负相关性;相关性分析和CCA 分析结果均表明淹水天数是影响杂草种子库群落构成的最大因素。通过二维排序可将31 个样点分为旱田和水田2 大类,旱田可划分为长期旱连作和水旱轮作2 个亚类;水田可划分为淮河以北地区和淮河以南长江流域地区2 个亚类。研究结果说明:杂草种子库潜群落优势种与地上部农田杂草显群落优势种具有一致性,通过土壤杂草种子库的研究可以预测地上杂草的发生和危害情况。

The species composition and diversity of weed seed bank of 0-15 cm soil layer in 31 sample sites of main crop fields (including upland and paddy fields) in Jiangsu Province were investigated by water washing-microscopic examination method. And correlation between species in weed seed bank and environmental factors (including waterlogging days, organic matter content and pH in soil, annual precipitation, annual mean temperature, latitude and longitude of sites) was analyzed by canonical correspondence analysis (CCA), and scatter diagrams of CCA two-dimensional ordination about sites-and species-environment factors were also drawn. The investigation results show that weed seeds of 54 species (41 and 45 species respectively in upland and paddy fields) belonging to 15 families are detected in weed seed bank of 31 sample sites, in which, common weed species are in the majority but dominant species are various in upland and paddy fields. The common dominant species are Mazus japonicus (Thunb.) Kuntze, Cyperus difformis L., Ammannia baccifera L., Leptochloa chinensis ( L.) Nees, Polypogon fugax Nees ex Steud. and Malachium aquaticum (L.) Fries, etc., and number of weed species in Gramineae and Cyperaceae are the most, accounts for 22. 6% and 20. 8% of total number of weed species, respectively. The dominant species in weed seed bank in different sites of upland field changes greatly but that of paddy field is relatively stable, while difference of dominant species frequency between upland and paddy fields is greater. There are 19 weeds in upland field with frequency higher than 0. 30, while 20 weeds in paddy field with frequency higher than 0. 50. And there are 11 and 9 weeds respectively in upland and paddy fields with average important value higher than 0. 03, important value of these weeds with high frequency is also high. Seed density of weed seed bank in upland and paddy fields is 21 015 and 37 847 m-2, respectively, with an average density of 31 008 m-2. Weed seed density in three soil layers in upland field has no significant difference, but that in upper and middle soil layers in paddy field is significantly higher than that in lower layer. Summer and autumn weeds are main types in upland field, while paddy and summer weeds are main types in paddy field. According to morphological type, the species number and density of weed from high to low in order is broadleaf grasses, grasses, sedges, and their species number and density in paddy field are higher than those in upland field. Compared with upland field, species richness (S), Shannon-Wiener index (H’) and Simpson index (D) of weed seed bank in paddy field are higher, while Pielou index (E) is lower. And with increasing of soil depth, S, H’and D of weed seed bank in upland field decrease gradually but E increases, but change trend of species diversity indexes of different soil layers in paddy field are not obvious. Negative correlation between the first axis of species and waterlogging days is the highest (R = -0. 814 3), and negative correlations between the second axis of species and annual precipitation, longitude are also higher. The results of correlation and CCA analyses all indicate that waterlogging days is the most important factor for impacting the structure of weed seed bank community. According to results of CCA two-dimensional ordination, the 31 sample sites can be divided into two groups of upland and paddy fields, and the upland field group is further divided into two sub-groups of long-term drought continuous cropping and paddy-upland rotation, while paddy field is further divided into two sub-groups of the north area of Huai River and the south area of Huai River-Yantze River basin. It is suggested that dominant species in potential community of weed seed bank is similar to ones in emerged community of above-ground weeds, therefore, status of occurrence and harm of above-ground weeds may be predicted through investigation of weed seed bank in soil.