ISSN:
1573-5036
Keywords:
ammonium
;
carboxylates
;
H+/OH- efflux
;
ionic balance
;
nitrate
;
nitrate reductase activity
;
nitrogen starvation
;
Rumex acetosa
;
Rumex crispus
;
Rumex maritimus
;
Rumex palustris
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract Growth, chemical composition, and nitrate reductase activity (NRA) of hydroponically cultured Rumex crispus, R. palustris, R. acetosa, and R. maritimus were studied in relation to form (NH4 +, NO3 -, or both) and level of N supply (4 mM N, and zero-N following a period of 4mM N). A distinct preference for either NH4 + or NO3 - could not be established. All species were characterized by a very efficient uptake and utilization of N, irrespective of N source, as evident from high concentrations of organic N in the tissues and concurrent excessive accumulations of free NO3 - and free NH4 +. Especially the accumulation of free NH4 + was unusually large. Generally, relative growth rate (RGR) was highest with a combination of NH4 + and NO3 -. Compared to mixed N supply, RGR of NO3 -- and NH4 +-grown plants declined on average 3% and 9%, respectively. Lowest RGR with NH4 + supply probably resulted from direct or indirect toxicity effects associated with high NH4 + and/or low Ca2+ contents of tissues. NRA in NO3 - and NH4NO3 plants was very similar with maxima in the leaves of ca 40 μmol NO2 - g-1 DW h-1. ‘Basal’ NRA levels in shoot tissues of NH4 + plants appeared relatively high with maxima in the leaves of ca 20 μmol NO2 - g-1 DW h-1. Carboxylate to organic N ratios, (C-A)/Norg, on a whole plant basis varied from 0.2 in NH4 + plants to 0.9 in NO3 - plants. After withdrawal of N, all accumulated NO3 - and NH4 + was assimilated into organic N and the organic N redistributed on a large scale. NRA rapidly declined to similar low levels, irrespective of previous N source. Shoot/root ratios of -N plants were 50–80% lower than those from +N plants. In comparison with +N, RGR of -N plants did not decline to a large extent, decreasing by only 15% in -NH4 + plants due to very high initial organic-N contents. N-deprived plants all exhibited an excess cation over anion uptake (net proton efflux), and whole-plant (C-A)/Norg ratios increased to values around unity. Possible difficulties in interpreting the (C-A)/Norg ratio and NRA of plants in their natural habitats are briefly discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00010350
Permalink
