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Blueberries battle for nutritious nitrogen
Vaccinium corymbosum (high blueberry or swamp blueberry) is one of several Vaccinium species cultivated in the USA for their fruit. Unlike most agricultural and horticultural crops, cultivated Vaccinium species are very selective in respect of soil type. Poonnachit and Darnell (University of Florida, Gainsville, USA; pp. 399-405) describe the ideal soil for Vaccinium as acidic (pH 4.0-5.5), with a high level of organic matter, readily available iron and ammonium-nitrogen. At higher pH values, uptake of both iron and nitrogen is limited and growth is poor. However, it would be very helpful for growers if the plants could be produced that are more versatile. To help achieve this end it would thus be useful for breeders if a related species more tolerant of a range of soil types could be found. Accordingly, the authors have looked at a species, V. arboreum, which shows adaptation to a wider range of soils than most other members of the genus. They demonstrate its ability to grow in soils just on the acid side of neutral, with low iron content and with nitrogen mainly in the form of nitrate. Although both species actually prefer ammonium as a nitrogen source, V. arboreum is able to utilize nitrate much more efficiently than V. corymbosum. Paradoxically, both show increased root nitrate reductase activity in response to nitrate but, in V. corymbosum, the activity declines again after 3 weeks. With respect to iron, V. arboreum, despite its ability to grow on soils with low iron content, does not appear to possess any specific adaptation to iron deficiency, whereas in V. corymbosum ferric chelate reductase activity increases under iron deficiency. This results in increased iron uptake on return to iron-sufficient conditions. There was no discernible direct connection between iron and nitrogen metabolism, despite the presence of iron in the nitrate reductase enzyme. The authors conclude that the adaptation of V. arboreum to a wider range of soil types is related to its greater ability to utilize nitrate.
Professor J. A. BryantUniversity of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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