SOIL FACTORS REPRESSING ESTABLISHMENT of DINITROGEN FIXING SYSTEM in Phaseolus vulgaris L..

通过田间栽培和人工蛭石栽培的比较，研究了抑制菜豆幼苗根系结瘤的土壤因素。田间土壤与蛭石理化性质的显著差异如下：a。土壤中可交换性钙，特别是镁的含量远低于蛭石中，而它们在水相中的浓度则相反。土壤中硝态氮含量高于蛭石；蛭石中的粒径分布比土壤中的粒径分布偏大。土壤栽培植株播后10 d的根瘤分生组织形成率远低于蛭石栽培植株，且次生根比第三生根差异更明显。田间土壤化学性质的差异对三次根而非次生根上根瘤分生组织的形成和结实率有影响。在一定的土壤条件下，三级根上曾经出现的部分分生组织消失了。在田间土壤中添加Mg和Ca对根瘤分生组织的形成有轻微的促进作用。而土壤和蛭石之间交换性或可溶性Mg和Ca含量的差异并不是土壤和蛭石之间分生系统形成差异的主要因素。虽然降低土壤硝酸盐水平显著恢复了次生根分生组织形成的抑制，但估计还有其他抑制因素。田间土壤中结核分生组织的形成与颗粒大小之间不存在线性关系。然而，通过比较蛭石、珍珠岩和土壤培养的植物的根瘤分生组织形成，表明土壤相对较低的透气性是抑制根瘤分生组织形成的一个因素。

Soil factors repressing nodule establishment on the roots of Phaseolus vulgaris seedlings were investigated by comparing the plants cultured on field soils and artificial vermiculite. Significant differences in physical and chemical properties between field soils and vermiculite were as follows :a. Exchangeable Ca and particularly Mg were much less in the soils than in vermiculite, and their concentration in water phases was the contrary,b. Nitrate nitrogen was more abundant in the soils than vermiculite, andc. Particule-size distribution in vermiculite was more biased to larger than in the soils.The rate of nodule meristem formation till 10 days after sowing was much less in plants cultured with soil than in vermiculite plants, and the difference was more prominent on secondary roots comparing to that on tertiary one. Differences of chemical properties among field soils affected to formation and setting of nodule meristem on tertiary roots rather than on secondary roots. And, a portion of meristems once appeared on tertiary roots was disappeared by a certain soil condition.Mg and Ca supplement into a field soil gave slight increase of nodule meristem formation. Whereas the dissimilarity in exchangeable or soluble Mg and Ca content between soils and vermiculite was not a primary factor bearing the difference in the meristem formation between soils and vermiculite.Though lowering soil nitrate level significantly recovered repression on the meristem formation in secondary roots, additional repressive factors were estimated to be.There was no linear relationship between nodule meristem formation and particle-size of a tested field soil. However, it was suggested by comparison of nodule meristem formation among plants cultured with vermiculite, perlite and the soil that relatively low air permeability of the soil was a factor repressing nodule meristem formation.