caa a22 4500 397521219 CHVBK 20180308164633.0 cr unu---uuuuu 161202e199509 xx s 000 0 eng 10.1093/jxb/46.9.1113 doi (NATIONALLICENCE)oxford-10.1093/jxb/46.9.1113 Nitrogen utilization by plant species from acid heathland soils [Elektronische Daten] II. Growth and shoot/root partitioning of NO3− assimilation at constant low pH and varying NO3−/NH4+ ratio1 [S.R. Troelstra, R. Wagenaar, W. Smant] The growth of four heathland species, two grasses (D. flexuosa, M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix), was tested in solution culture at pH 4.0 with 2 mol m−3 N, varying the N03−/NH4+ ratio up to 40% nitrate. In addition, measurements of NRA, plant chemical composition, and biomass allocation were carried out on a complete N03−/NH4+ replacement series up to 100% nitrate. With the exception of M. caerulea, the partial replacement of NH4+ by NO3− tended to enhance the plant's growth rate when compared to NH4+ only. In contrast to the other species, D. flexuosa showed a very flexible response in biomass allocation: a gradual increase in the root weight ratio (RWR) with NO3− increasing from 0 to 100%. In the presence of NH4+, grasses reduced nitrate in the shoot only; roots did not become involved in the reduction of nitrate until zero ambient NH4+. The dwarf shrubs, being species that assimilate N exclusively in their roots, displayed an enhanced root NRA in the presence of nitrate; in contrast to the steady increase with increasing NO3− in Calluna roots, enzyme activity in Erica roots followed a rather irregular pattern. Free nitrate accumulated in the tissues of grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO3− [(proportion of nitrate in N uptake)/(proportion of nitrate in N supply)] was lowest in M. caerulea and highest in D. flexuosa. Whereas M. caerulea and the dwarf shrubs always absorbed ammonium highly preferentially (relative uptake ratio for NO3− <0.20), D. flexuosa showed a strong preference for NO3− at low external nitrate (the relative uptake ratio for N03− reaching a value of 2.0 at 10% NO3−). The ecological significance of this prominent high preference for NO3− at low NO3−/NH4+ ratio by D. flexuosa and its consequences for soil acidification are briefly discussed. © Oxford University Press RESEARCH PAPERS nationallicence Ammonium nationallicence heathland lants nationallicence N03−/NH4+ ratio nationallicence nitrate nationallicence nitrate reductase activity nationallicence soil acidification nationallicence specific absorption rate nationallicence Troelstra S.R. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, PO Box 40, NL-6666 ZG Heteren, The Netherlands aut Wagenaar R. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, PO Box 40, NL-6666 ZG Heteren, The Netherlands aut Smant W. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, PO Box 40, NL-6666 ZG Heteren, The Netherlands aut Journal of Experimental Botany Oxford University Press 46/9(1995-09), 1113-1121 0022-0957 46:9<1113 1995 46 exbotj https://doi.org/10.1093/jxb/46.9.1113 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1093/jxb/46.9.1113 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Troelstra S.R. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, PO Box 40, NL-6666 ZG Heteren, The Netherlands aut NATIONALLICENCE 700 1- Wagenaar R. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, PO Box 40, NL-6666 ZG Heteren, The Netherlands aut NATIONALLICENCE 700 1- Smant W. Netherlands Institute of Ecology, Centre for Terrestrial Ecology, PO Box 40, NL-6666 ZG Heteren, The Netherlands aut NATIONALLICENCE 773 0- Journal of Experimental Botany Oxford University Press 46/9(1995-09), 1113-1121 0022-0957 46:9<1113 1995 46 exbotj Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford