不同作物轮作制度对土壤杂草种子库特征的影响

为明确不同作物轮作制度对杂草种子库特征的影响，比较研究了玉米-小麦(MW)、大豆-小麦(SW)轮作和原水稻-小麦(RW)轮作方式下杂草种子库的特征。结果表明，作物轮作显著影响杂草种子库的密度和种类组成，进行玉米-小麦或大豆-小麦轮作2年后，杂草种子库密度分别比稻麦轮作降低27．16％、44．44％。在原水稻-小麦轮作方式下，种子库中主要杂草为陌上菜、异型莎草、菵草、水苋菜、千金子等。玉米-小麦轮作使种子库中马唐、碎米莎草、飘拂草的相对优势度显著上升，鸭舌草、水苋菜、菵草的相对优势度显著下降。而在大豆-小麦轮作方式下，种子库中通泉草、马唐、鳢肠、飘拂草的相对优势度显著上升。玉米-小麦轮作种子库的物种多样性指数高于大豆-小麦轮作和水稻-小麦轮作。玉米-小麦与大豆-小麦轮作种子库的物种组成相似性较高。作物轮作影响杂草种子库密度和种类组成的机制，可能在于通过轮换种植不同的作物，提供了多样化的选择压，限制了某些对单一种植系统有着良好适应性的杂草种类的生长。

Effects of different crop rotation system on the characteristics of soil weed seedbank

Field studies were conducted to evaluate the effects of three different crop rotation systems,rice-wheat (RW),maize-wheat (MW) and soybean-wheat (SW) rotation,on the characteristics of soil weed seedbank.The results showed that crop rotation significantly affects the density and species composition of weed seedbank.By rotation of wheat with maize (MW) and soybean (SW) for 2 years,seedbank density decreased 27.16% and 44.44% respectively compared with RW.Major weed species in the soil seedbank under rice-wheat cropping were Lindernia procumbens,Cyperus difformis,Beckmannia syzigachne,Ammannia baccifera and L.chinensis .In MW,relative abundance (RA) of Digitaria sanguinalis,C.iria and Fimbristylis dichotoma increased significantly,but the RA of Monochoria vaginalis,A.baccifera,B.syzigachne decreased remarkably.While in SW,RA of Mazus japonicus,D.sanguinalis,Eclipta prostrata,F.dichotoma had shown marked increase.The species diversity of MW was higher than that of SW and RW.Based on the species similarity index of weed seedbank,the index between MW and SW was the highest.The reason why crop rotation affects the density and species composition of the weed seedbank is that the use of crop sequences diversify the selection pressure and prevent the proliferation of some weed species that has adapted well to a single cropping system.