Annals of Botany

It helps to have P when resisting Al

Plants are subject to many environmental stresses, several of which interact with each other. Thus, as discussed by Sun et al. (Nanjing and Beijing, pp. 795–804), Al toxicity in acid soils is often compounded by P deficiency, leading to poor growth and, in crops, greatly reduced yields. With this in mind, the authors have investigated the interactions of Al and P in two legumes, Lespedeza bicolor and L. cuneata, the former of which has potential as a forage crop. Here we focus on just a part of their extensive investigation. In a hydroponic growth system, L. bicolor was twice as resistant to Al as L. cuneata, indicated by the effects on root elongation. Interaction between P deficiency and Al toxicity was studied by exposure on alternate days to P and Al. Measurement of root Al contents suggested that L. bicolor was more capable of excluding Al than L. cuneata: over a range of external Al concentrations, roots of L. cuneata contained nearly twice as much Al as roots of L. bicolor. The ability of L. bicolor to exclude Al was enhanced by pre-treatment with P, whereas the pre-treatment had no effect on accumulation of Al in roots of L. cuneata. However, the ability of L. bicolor to exclude Al was not directly related to the extrusion of chelating acids. Although L. bicolor roots extruded malate and citrate while those of L. cuneata did not, extrusion in L. bicolor was decreased after supplying P. There were also related effects on root morphology: Al inhibited root growth and especially lateral root formation much more in L. cuneata than in L. bicolor; these effects in L. cuneata were not reversed by supplying P. In respect of reciprocal interactions, in the Al-resistant L. bicolor, Al had little effect on the transport of P from root to shoot, but strongly inhibited P transport in L. cuneata.