Seedlings from two genotypes of Arabidopsis thaliana (L.) Heynh. that had similar uptake kinetics for inorganic phosphate (P1), but differed in the levels to which they could deplete P, from solution (different Cmin values), were placed together for 21 h in the absence of exogenous P1 to determine the effect of differences in Cmin on short-term competition for P1, as reflected by the movement of the phosphate isotope, 32P. P1-starved seedlings were grown at two photon flux densities (30 and 90 μmol−2 S−l). Genotype LC (with the lower Cmin) was better able to deplete a 2.5 μM P1 solution than genotype HC. We predicted that when placed together in a P1-free solution, the Cmindifferences between the genotypes would result in a continual transfer of P1 from genotype HC to LC. This did not occur, since genotypes LC and HC did not differ in the proportion of 32P obtained from labelled HC seedlings. However, LC obtained 1.3 times more 32P from HC than HC obtained from LC, for seedlings grown at both the lower (P < 0.05) and the higher (P < 0.001) photon flux densities.
Differences in Cmin between the genotypes were more pronounced for seedlings grown at the higher photon flux density. Here, genotype LC obtained significantly more 32P from genotype HC than it did from seedlings of its own genotype (P < 0.001). Genotype HC obtained less 32P from seedlings LC than it did from those of its own genotype, for seedlings grown at both photon flux densities (P < 0.001).