Effect of ammonium or nitrate nutrition on net photosynthesis, growth, andactivity of the enzymes nitrate reductase and glutamine synthetase in blueberry, raspberry and strawberry

Blueberry, raspberry and strawberry may have evolved strategies for surviva l due to the different soil conditions available in their natural environme nt. Since this might be reflected in their response to rhizosphere pH and N form supplied, investigations were carried out in order to compare effects of nitrate and ammonium nutrition (the latter at two different pH regimes) on growth, CO2 gas exchange, and on the activity of key enzymes of the nit rogen metabolism of these plant species. Highbush blueberry (Vaccinium cory mbosum L. cv. 13-16-A), raspberry (Rubus idaeus L. cv. Zeva II) and strawbe rry (Fragaria x ananassa Duch. cv. Senga Sengana) were grown in 10 L black polyethylene pots in quartz sand with and without 1% CaCO3 (w: v), respecti vely. Nutrient solutions supplied contained nitrate (6 mM) or ammonium (6 m M) as the sole nitrogen source. Compared with strawberries fed with nitrate nitrogen, supply of ammonium nitrogen caused a decrease in net photosynthe sis and dry matter production when plants were grown in quartz sand without added CaCO3. In contrast, net photosynthesis and dry matter production inc reased in blueberries fed with ammonium nitrogen, while dry matter producti on of raspberries was not affected by the N form supplied. In quartz sand w ith CaCO3, ammonium nutrition caused less deleterious effects on strawberri es, and net photosynthesis in raspberries increased as compared to plants g rown in quartz sand without CaCO3 addition. Activity of nitrate reductase ( NR) was low in blueberries and could only be detected in the roots of plant s supplied with nitrate nitrogen. In contrast, NR activity was high in leav es, but low in roots of raspberry and strawberry plants. Ammonium nutrition caused a decrease in NR level in leaves. Activity of glutamine synthetase (GS) was high in leaves but lower in roots of blueberry, raspberry and stra wberry plants. The GS level was not significantly affected by the nitrogen source supplied. The effects of nitrate or ammonium nitrogen on net photosy nthesis, growth, and activity of enzymes in blueberry, raspberry and strawb erry cultivars appear to reflect their different adaptability to soil pH an d N form due to the conditions of their natural environment.