Some effects of nitrate versus ammonium nutrition on the nutrient fluxes in Pinus sylvestris seedlings. Effects of mycorrhizal infection

Abstract

As a result of the high deposition of ammonium compounds in The Netherlands the forest trees are under a severe nitrogen stress. Effects of increasing amounts of ammonium on the major nutrient fluxes by Scots pine seedlings have been studied. In addition, the effect of mycorrhization of the roots has been taken into account. With nitrate-N nutrition only, the seedlings accumulate calcium, magnesium, potassium, and protons. When a low ammonium concentration is present, the seedlings lose their cations. When the medium is depleted of ammonium, a reuptake of the cations occurs. In the presence of a high ammonium concentration (based on field studies) a continuous loss of cations from the roots takes place. The reverse has been found for phosphate uptake. Ammonium stimulates phosphate accumulation. It is shown that ammonium inhibits the unidirectional influx rate of 86Rb, while concurrently stimulating the unidirectional efflux rate. Mycorrhization of the roots has a beneficial effect on the nutrient fluxes. With nitrate-N nutrition mycorrhizal seedlings accumulate more nitrate, calcium, magnesium, and protons than nonmycorrhizal seedlings. With high ammonium-N nutrition mycorrhizal seedlings lose fewer cations than nonmycorrhizal seedlings. In conclusion, the ecological significance of ammonium deposition on forest stands is discussed.