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Effects of pH on ammonium uptake by Typha latifolia L.
Author(s) -
DYHRJENSEN K.,
BRIX H.
Publication year - 1996
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1996.tb00022.x
Subject(s) - kinetics , chemistry , ammonium , nuclear chemistry , saturation (graph theory) , typha , reaction rate constant , zoology , biology , ecology , wetland , physics , mathematics , organic chemistry , combinatorics , quantum mechanics
The effects of solution pH on NH 4 + uptake kinetics and net H + extrusion by Typha latifolia L. were studied during short‐term (days) and long‐term (weeks) exposure to pH in the range of pH 3.5–8.0. The NH 4 + uptake kinetics were estimated from depletion curves using a modified Michaelis‐Menten model. T. latifolia was able to grow in solution culture with NH 4 + as the sole N source and to withstand a low medium pH for short periods (days). With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing. The solution pH affected NH 4 + uptake kinetics. The affinity for NH 4 + , as quantified by the half saturation constant ( K 1/2 ) and C min (the NH 4 + concentration at which uptake ceases), decreased with pH. K 1/2 was increased from 7.1 to 19.2 mmol m −3 and C min from 2.0 to 5.7 mmol m −3 by lowering the pH in steps from 8.0 to 3.5. V max was, however, largely unaffected by pH (∼22 μmol h −1 g −1 root dry weight). Under prolonged exposure to constant pH, growth rates were highest at PH 5.0 and 6.5. At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped. NH 4 + uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH 4 + uptake almost completely stopped. The ratio between net H + extrusion and NH 4 + uptake decreased significantly at low pH. The adverse effects of low pH on NH 4 + uptake kinetics are probably a consequence of a reduced H + ‐ATPase activity and/or an increased re‐entry of H + at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.