普通野生稻-长喙毛茛泽泻-柳叶箬混作种群的竞争效应

以正交实验探讨了普通野生稻、长喙毛茛泽泻和地箬３因子各５个种植密度水平对各种群的影响，结果表明，混作３种地有不利影响，影响越大，中种群对于来自种间的竞争是敏感的，对来自种内竞争的影响也不可忽视。３个因子中，普通野生因子作用最大，柳叶箬因子次之，从测定的项目看，在不同的种植水平上，每一种群的无性繁殖率和单株生物量明显受到自身和其它因子的影响。初始密度越大，无性繁殖率越小。普通野生 稻和柳叶箬种群的单

Viewpoints on the study of economic thresholds of cotton bollworm

In the present paper,competitive effects on Oryza rufipogon,Ranalisma rostrata and Isachne globosa populations were studied by orthogonal designed experiment of three species factors and five planting density levels.The results showed great disadvantages for each of the three mixed crops,the bigger the initial density was,the greater the negative effects were.Each population was sensitive to inter specific competition,while intra specific competition should also not be ignored. O.rufipogon was the most important factor among the three species,and follwed by I.globosa . According to the items examined,clonal reproductive ratio and biomas per branch of each population were affected obviously by itself,and also by other factors.The bigger the total initial density was,the smaller the clonal reproductive ratio was.Biomass per branch of O.rufipogon and I.globosa population increased as initial density increased,but that of R.rostrata population showed a contradictionary result.The latter was more sensitive than the other two in biomass allocations to leaf and to sexual reproduction,and its ramet death ratio also increased as total initial density did. Overall, I.globosa has the most powerful competitive ability and than O.rufipogon ,while R.rostrata the least.The latter was always in disadvantage position in competition,and was excluded after one growth season in the experiment of mixed crops.