Mechanism of the inhibition of absorption and translocation of phosphorus by aluminum in crop plants

1.对于耐铝性较弱的大麦，（1）无论培养基中的磷水平如何，铝都显著地延缓了根的伸长;（2）当培养基中的磷水平较高时，单位根长的磷吸收速率不因铝的加入而降低2 ppm，而当培养基中的磷水平较低时，单位根长的磷吸收速率因铝的加入而降低2 ppm.磷铝共沉淀在根上减少了磷向地上部的转运，而与作物的耐铝性无关。但下降幅度较小.结果表明，在耐铝性弱的作物中，在磷水平低于0.05ppm P的条件下，铝强烈地促进了磷的缺乏，铝毒和磷缺乏同时成为生长限制因子.在耐铝性强的水稻植株中，铝和磷在根表的共沉淀成为铝对磷的吸收和转运减少的唯一因素。因此，铝对磷素吸收和转运的抑制作用很小.当培养基中铝浓度为10 ppm时，耐铝性弱的小麦品种地上部磷含量低于耐铝性强的小麦品种，铝对根伸长的抑制是导致地上部磷含量降低的主要因素，而铝对根伸长的抑制导致了单株磷吸收率的降低，铝降低了单位根长对磷的吸收量，并使磷和铝在根上共沉淀。

1. In the case of barley which is weak in the aluminum tolerance, (1) the root elongation is retarded by aluminum remarkably regardless of phosphorus status of growth media, (2) the phosphorus absorption rate per unit root length is not decreased by 2 ppm Al when the phosphorus level in the growth medium is high, but (3) the rate is decreased by 2 ppm Al when the phosphorus level is low.2. Co-precipitation of phosphorus and aluminum on the roots decreses the translocation of phosphorus to the shoot irrespective of aluminum tolerance of crop plants. But, degree of the decrease is small.3. As a result, in the case of crop plants weak in the aluminum tolerance, phosphorus deficiency is promoted strongly by aluminum under conditions of which phosphorus level is lower than 0.05 ppm P, and both aluminum toxicity and phosphorus deficiency become growth limiting factors at the same time.4. In the case of rice plant which is strong in the aluminum tolerance, co-precipitation of phosphorus and aluminum on the root surface becomes only factor to decrease absorption and translocation of phosphorus by aluminum. Thus, inhibiting effect of aluminum on the absorption and the translocation of phosphorus is very small.5. Phosphorus contents in the shoot of wheat varieties weak in the aluminum tolerance are lower than those strong in the aluminum tolerance when aluminum level in the growth medium is 10 ppm Al. As factors to decrease phosphorus contents in the shoot, retardation of root elongation by aluminum ehich induce the decrease of phosphorus absorption rate per plant is the most important, followed by the decrease of phosphorus absorption per unit root length by aluminum and the co-precipitation of phosphorus and aluminum on the roots.