Nitrogen Fixation and Nitrogen Assimilation in a Temperate Saline Ecosystem

Abstract

AbstractAs nitrogen is known to be a limiting factor for plant growth, we were interested in the relationship between soil microbial activity and the nitrogen assimilation of 5 different halophytes from 4 saline sites near the lake “Neusiedlersee”, Austria. The following were studied between May and October 1985: nitrogen fixation (15N2 and acetylene reduction): N‐mineralization; several soil characteristics and in vivo nitrate reductase activity of roots and shoots of these plants. NO−3, org. N‐ and carboxylate contents of both roots and shoots, as well as the effect of NO−3‐fertilization on the amounts of these substances, were determined on plants growing in the field during a 3‐day period in September 1985.Fertilization led to a decrease in acetylene reduction activity at most sites, and an increase in the nitrate reductase activity of the shoots of all plants. Overall, carboxylate and organic nitrogen contents of these halophytes did not change in response to fertilization. Only in the roots of Aster tripolium and Atriplex hastata was there a marked increase in the nitrate reductase activity in response to fertilization. Species growing at the same site, such as Plantago maritima and Lepidium crassifolium showed contrasting levels of assimilatory activity. Apparent low rates of ammonification and nitrification were detected in soils from the 4 sites. The results are discussed in relation to the nitrogen and carbon economies of the microorganisms and plants.