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Dynamics of nitrogen remobilization in defoliated Phleum pratense and Festuca pratensis under short and long photoperiods
Author(s) -
Bakken Anne Kjersti,
Macduff James H.,
Collison Mike
Publication year - 1998
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1998.1030316.x
Subject(s) - shoot , phleum , festuca pratensis , poa pratensis , biology , temperate climate , photoperiodism , festuca rubra , botany , photosynthesis , zoology , horticulture , agronomy , poaceae , lolium perenne
The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy ( Phleum pratense L. cv. Bodin) and meadow fescue ( Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 m M NH 4 NO 3 and pre‐treated by extending the 11 h photosynthetically significant light period either by 1 h (short‐day or SD plants) or 7 h (long‐day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, 15 N‐labelled NH 4 + or NH 4 + + NO 3 − was supplied over a 20‐day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO 3 − reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO 3 − uptake restarting 1 or 2 days earlier than NH 4 + uptake, even when NH 4 + was the only form of N supply. LD timothy plants supplied solely with NH 4 + were slowest to resume uptake of mineral N. Supplying NO 3 − in addition to NH 4 + after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short‐term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink‐driven rates of N remobilization and their interactions with mineral N uptake following defoliation.