局部供磷对玉米根系生长、磷吸收速率的影响

玉米幼苗种子根局部供磷可明显改变根系的形态。供磷区侧根生长增加,无磷区侧极生长减少。供磷区1次、2次侧根长度与2次侧根数量明显增加;而1次侧根数量则不增加。供磷区缩小时,根系生长加快,单位根区磷吸收速率增加,但单位根重磷吸收速率的增加不很明显。磷局部供应植株主要通过供磷区根系的生长来增加磷的吸收,以满足植株对磷的需求。局部供磷植株中转运到供磷根区的光合产物明显多于无磷根区。

Effects of Localized Supply of Phosphate on Root Growth and Phosphate Uptake Rate in Maize

Using a solution culture system,in which a nutrient solution containing100 umol phosphate/L was supplied toa 15 mm, 25 mm or 40 mm segmentof the primary root while the remain-der of the root system received a phos-phate--free nutrient solution, effects oflocalized supply of phosphate on rootgrowth and phosphate uptake rate werestudied in maize (Zea mays L.). The results showed that thegrowth of laterals was depressed onthose parts of the root system receivingno phosphate from the external solutionbut was increased in the zone withphosphate supply. This resulted in con-siderable modification of root form.Compared with the same zone of thecontrol, in which the nutrient solutioncontaining phosphate was supplied tothe entire root system, the length ofboth first and second order laterals inthe localized phosphate supply zone wasincreased, but the number of first or-der laterals was not. When the lengthof the zone with phosphate supply wasreduced, the growth of the laterals wasfurther increased. Though the phos-phate uptake rate through the root zonewith phosphate supply was promoted,the phosphate uptake rate per unit rootdry weight, however, was not signifi-cantly stimulated. This localized stim-ulation of lateral growth and the conse-quent increase in phosphate uptakelargely compensated for the deficiencyin phosphate supply in the other partsof the root. After an early period ofslightly retarded shoot growth, thegrowth of shoot was restored to a levelsimilar to that of the control. ~(14)C-labelling experiment showedthat the phosphate supply zone receivedmore photosynthates than the phos-phate--free zones. Possible regulatorymechanisms which co--ordinate rootgrowth, phosphate uptake and shootgrowth, are discussed.