EFFECT OF ALUMINUM ON YIELD AND PLANT-CHEMICAL CONCENTRATIONS OF SOMETEMPERATE LEGUMES

The aluminium (Al) tolerance of 34 temperate legume species (143 genot ypes, including 57 from Trifolium repens) was determined in 60 experim ents over a 3 year period in a low ionic strength (2.7 x 10(-3) M) sol ution culture. For each genotype, the relationship between solution Al 3+ activity (mu M) and relative yield was determined and the Al3+ acti vity associated with a 50% reduction in yield (Al-RY50) calculated. In addition, plant chemical concentrations were determined in at least o ne genotype from most species. For white clover, Al-RY50 over all geno types had an approximately normal distribution with mean of 1.31 mu M for the tops and 1.51 mu M for the roots, and a standard deviation of about 0.4. This suggested that Al tolerance had a polygenic inheritanc e. For the other species tested, Al-RY50 ranged from 0.15 to 4.53 mu M in the tops and from 0.21 to 4.89 mu M in the roots. In the tops and roots, 37% and 26% respectively of the genotypes had an Al-RY50 less t han 1 mu M, including all species tested in the genera Melilotus and M edicago. Only 8% or 23% of the genotypes, based on the tops and roots respectively, had an Al-RY50 greater than 2, including all genotypes i n the species Lotus pedunculatus. Except for Lotus, there were no cons istent differences between genera in plant chemical concentrations. In Lotus, concentrations of Ca, Zn, Mn and Cu in the tops and of all ele ments except B in the roots were lower than that of the other species. The Al-RY50 Of the species was not related to plant chemical concentr ations in the absence of Al Depending on the plant element, increasing solution Al concentrations had no significant effect on plant chemica l concentrations for 56-94% of the species. When a significant effect did occur, increasing Al in solution generally decreased S and K conce ntrations and increased Mn, Zn, Cu Fe, B and Al concentrations in the tops and roots and decreased Ca concentrations in the tops. Plant P co ncentrations decreased in the tops but increased in the roots. Increas ing Al in solution increase plant Al at the average rate of 44 mu g g( -1) mu M(-1) (range 20-87) in the tops and 333 mu g mu M(-1) (range 16 2-616) in the roots.