Nitrate and Iron Concentration Effects On Nitrate and Iron Uptake and Assimilation in Vaccinium Species

Cultivated blueberry (Vaccinium species) production is constrained by strict soil requirements for optimal growth, including low pH, high iron, and nitrogen primarily in the ammonium form. Since these types of soils are limited, extensive soil amendments are necessary for good production. V. arboreum is a wild species adapted to a broader range of soils that do not require amendments. Our previous work indicates that the wider soil adaptation in V. arboreum is correlated with increased efficiency of nitrate uptake/assimilation compared with cultivated Vaccinium species. However, the effects of external iron concentration or interactions between nitrate and iron concentrations on uptake and assimilation of nitrate and iron and subsequent growth responses in these species are unknown. To test this, nitrate and iron uptake, and activities of nitrate reductase (NR, the rate limiting enzyme for NO₃ assimilation) and ferric chelate reductase (FCR, the rate limiting enzyme for iron assimilation) were compared in V. arboreum and V. corymbosum interspecific hybrid (southern highbush blueberry). Plants were grown hydroponically in either 1.0 or 5.0 mM NO₃ with either 0.01 or 0.09 mM Fe. There was no effect of NO₃ or Fe concentration on specific NO₃ uptake or NR activity, although cumulative NO₃ uptake was greater at the higher external NO₃ concentration. Nitrate uptake and NR activity were greater in V. arboreum compared with V. corymbosum, and this was reflected in an increase in plant DW of V. arboreum at the higher external NO₃ concentration compared with the other treatments. Root and leaf FCR activity and iron uptake were significantly higher in V. arboreum than in V. corymbosum. Total iron concentration in roots was higher in V. arboreum compared with V. corymbosum, but concentrations in stems and leaves were similar between the two species. On the other hand, concentrations of “active” or loosely bound iron were higher in V. arboreum organs, especially at the lower external iron concentration. V. arboreum appears to be more efficient in assimilating both nitrate and iron compared with V. corymbosum, possibly due to increased NR and FCR activities, and this may partially explain the wider soil adaptation of V. arboreum.