Al avoidance and Al tolerance of <i>Mucuna pruriens</i> var. <i>utilis</i>:Effects of a heterogeneous root environment and the nitrogen form in the root environment

In Mucuna pruriens var. utilis, grown with nitrate-N in a hydroponic split-root system, an Al avoidance reaction of root growth was observed, which was ascribed to local P stress in the Al containing compartment. The Al avoidance reaction was similar to the avoidance of Mucuna roots of acid subsoil in the field where roots grew preferentially in the topsoil. In the present paper the effect of different N forms (NO3- and NH4+) on the reactions of Mucuna to Al were studied, since in acid soils N is present as a mixture of NO3- and NH4+. No interaction between the N form and Al toxicity was found. A hydroponic split-root experiment with NH4NO3 nutrition, which is comparable to the situation in the field, showed that under these conditions Al avoidance did not occur. It is concluded that a relation between the Al avoidance reaction of Mucuna and P stress is still likely.