Secondary compounds that serve more than one function may enhance the competitiveness of species. 8-hydroxyquinoline (8HQ) and catechin, allelochemicals produced respectively by the invasive plant species Centaurea diffusa and C. maculosa, are also known to chelate metals.  We hypothesized that, along with having a toxic effect on neighboring plants, 8HQ and catechin directly increase nutrient uptake and thus growth of these Centaurea species.  Facilitation of nutrient uptake and growth of Centaurea spp. was studied in a hydroponic system with different forms of Fe as follows: FeEDDHA as control, freshly precipitated Fe(OH)₃, Fe(OH)₃ + activated carbon, Fe-allelochemical complex and Fe- deficient.

Results/Conclusions

Leaf nutrient concentration, chlorophyll content and fluorescence, and plant biomass were similar in FeEDDHA, Fe(OH)₃, and Fe-allelochemical treatments, but markedly lower in Fe(OH)₃ + activated carbon and Fe-deficient treatments. This indicates that plants were able to uptake Fe even from water-insoluble Fe(OH)₃.  However, addition of activated carbon, that sequesters the allelochemical, resulted in reduced uptake of Fe from water-insoluble form, demonstrating the direct role of allelochemical in nutrient acquisition. The allelochemicals were also able to mobilize metal-nutrients in soils; other related as well as non-related species of plants were able to take up the allelochemical-chelated nutrient forms; and studies using mutants of Zea mays demonstrated the uptake of the chelated metal-nutrients as passive. Together, these results confirm that 8HQ and catechin function to enhance metal-nutrient acquisition, and suggest that these compounds may serve a dual role, directly increasing the growth of invasive species of Centaurea by increasing nutrient availability, as well as indirectly increasing their growth by suppressing neighbors.