Drying of surface soil decreased Lupinus angustifolius root length and manganese uptake in a split-root experiment

Abstract

In a glasshouse, a split-root experiment was used to determine the ability oflupins (Lupinus angustifolius L.) to take up manganese(Mn) from dry soil either when young or at mid-flowering of the primarybranches. Three soil-watering regimes (maintained at field capacity,maintained below wilting point, and alternating from field capacity to wellbelow wilting point) were imposed after taproots had grown through topsoil andinto a nutrient solution below. Four sequential harvests (11, 22, 37, and 49days after sowing) were taken to determine the effect of soil drying on lupingrowth, Mn uptake, and soil-extractable Mn.Soil drying early in the lupin plant's life stopped the growth of lateralroots in the soil and slowed the growth of roots grown in subsoil solution andthe growth of lupin tops. Soil drying decreased uptake of Mn in the tops to13% of that under continuous wet soil conditions. Of the 13%,most (11%) was taken up while the soil was drying. Soil re-wettingenabled the plants to resume uptake of Mn and soil re-drying (just beforeanthesis) decreased the Mn concentration in the lupin stems to 4·8µg/g, whereas stems of lupins grown in the wet and dry soilscontained 10·3 and 3·3 µg/g, respectively. Easilyreducible and plant-available soil Mn were not affected by soil wetting anddrying treatments.This study confirms that the uptake of Mn by lupin may be severely restrictedby drying of surface soil at both the beginning and the end of the lupinplant's life. The decrease in root length rather than the chemical form of Mn restricted Mn uptake.