Phosphate and calcium uptake in beech (Fagus sylvatica) in the presence of aluminium and natural fulvic acids

Abstract

In the present study we examine the effects of Al on the uptake of Ca2+ and H2PO‐4 in beech (Fagus sylvatica L.) grown in inorganic nutrient solutions and nutrient solutions supplied with natural fulvic acids (FA). All the solutions used were chemically well characterized. The uptake of Al by roots of intact plants exposed to solutions containing 0, 0.15 or 0.3 mM AlCl3 for 24 h, was significantly less if FA (300 mg l−1) were also present in the solutions. The Ca2+(45Ca2+) uptake was less affected by Al in solutions supplied with FA than in solutions without FA. There was a strong negative correlation between the Al and Ca2+ uptake (r2=0.98). When the Al and Ca2+ (45Ca2+) uptake were plotted as a function of the Al3+ activity (or concentration of inorganic mononuclear Al), almost the same response curves were obtained for the ‐FA and +FA treatments. We conclude that FA‐complexed Al was not available for root uptake and therefore could not affect the Ca2+ uptake. The competitive effect of Al on the Ca2+ uptake was also shown in a 5‐week cultivation experiment, where the Ca concentration in shoots decreased at an AlCl3 concentration of 0.3 mM. The effect of Al on H2PO−4 uptake was more complex. The P content in roots and shoots was not significantly affected, compared with the control, by cultivation for 5 weeks in a solution supplied with 0.3 mM AlCl3, despite a reduction of the H2PO−4 concentration in the nutrient solution to about one‐tenth. At this concentration Al obviously had a positive effect on H2PO−4 uptake. The presence of FA decreased 32P‐phosphate uptake by more than 60% during 24 h, and the addition of 0.15 or 0.3 mM AlCl3 to these solutions did not alter the uptake of 32P‐phosphate.