Changes in root morphology of white lupin (Lupinus albus L.) and its adaptation to soils with heterogeneous alkaline/acid profiles

The ability of Lupinus albus L. to adapt to a heterogeneous soil profile co ntaining acid subsoil below limed topsoil of the same type, and to utilize nutrients by significantly altering its root system structure, was investig ated using specially constructed soil profile tubes. Plants grown in homoge neous acid profiles had the fastest growth while those grown in homogeneous limed-soil profiles showed the slowest growth and exhibited some chlorosis after 19 days. Limed topsoil combined with an acid subsoil profile initial ly retarded plant growth similar to that in a homogeneous limed soil. Howev er, after 68 days significantly greater growth had occurred in the limed/ac id soil treatment relative to the homogeneous limed soil, indicating plants had benefited from the acid subsoil stratum. Plants in the homogeneous lim ed soil profile had lower concentrations of P, Fe and Mn in shoots compared with those in heterogeneous soils. In contrast, the concentration of Ca in creased by 74%, due mainly to an increase in the water-soluble Ca fraction. When grown in a heterogeneous limed/acid soil profile, concentrations of P , Ca, K, Mg, Fe, Mn and Zn in shoots were comparable to those grown in a so il with a homogeneous acid profile. Although total root production was lowe r in the homogeneous limed-soil profile compared to the acid-soil containin g profiles, cluster root mass was maintained at a level comparable with tha t in acid soil. The roots in heterogeneous soil profiles exhibited extensiv e plasticity, demonstrating a root-type specific, morphological response to the soil conditions. Within the acid subsoil of a heterogeneous profile, t here was a large increase in cluster root mass compared with non-cluster ro ots. The proliferation of cluster roots in acid soil below limed topsoil ma y enhance the plant's ability to exploit this soil and facilitate the culti vation of L. albus on limed soil.