THE ECOLOGICAL SIGNIFICANCE OF IRON MOBILIZATION IN WILD GRASSES

The objective of this study was to investigate the potential role of phytosiderophore (PS) release for the ecological distribution of wlld Poaceae species. Enhanced phytosiderophore release under Fe-deficiency stress conditions could contribute to a better adaptation to, and greater competitive ability on calcareous soils. In a screening experiment, 30 calcicolous and calcifugous grass species were grown in solution culture. Root washings from Fe-deficient and Fe-supplied plants of each species were collected daily at mid-morning and their Fe-solubilizing- capacity was determined by the method of Takagi (9). Six of the species were cultivated at four levels of FeEDTA in nutrient solutions to obtain information about the relationships among Fe demand, Fe supply, and relative growth rate. In general Fe(III)-chelator release was found to increase much more in calcicolous than in calcifugous species under Fe-deficiency stress, suggesting that calcifuges would be excluded from calcareous soils because of an insufficient Fe-mobilizing ability. However, in a few calcicolous species with very low growth rates, chelator release rates were relatively low under Fe-deficiency stress. Thus, since growth rates and Fe demand differ widely among wild plant species, they have to be taken into account when considering the Fe efficiency of species.