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Oxygen‐induced recovery from short‐term nitrate inhibition of N 2 fixation in white clover plants from spaced and dense stands
Author(s) -
Faurie Olivier,
Soussana JeanFrançois
Publication year - 1993
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 - 10.1111/j.1399-3054.1993.tb05200.x
Subject(s) - trifolium repens , nitrogenase , nitrate , nitrogen fixation , respiration , oxygen , rhizosphere , chemistry , nitrogen , botany , horticulture , zoology , biology , organic chemistry , genetics , bacteria
Nitrogenase (N 2 ase; EC 1.18.6.1) activity (H 2 evolution) and root respiration (CO 2 evolution) were measured under either N 2 :O 2 or Ar:O 2 gas mixtures in intact nodulated roots from white clover ( Trifolium repens L.) plants grown either as spaced or as dense stands. The short‐term nitrate (5 m M ) inhibition of N 2 ‐fixation was promoted by competition for light between clover shoots, which reduced CO 2 net assimilation rate. Oxygen‐diffusion permeability of the nodule declined during nitrate treatment but after nitrate removal from the liquid medium its recovery parallelled that of nitrogenase activity. Rhizosphere pO 2 was increased from 20 to 80 kPa under N 2 :O 2 . A simple mono‐exponential model, fitted to the nodule permeability response to pO 2 , indicated NO − 3 induced changes in minimum and maximum nodule O 2 ‐diffusion permeability. Peak H 2 production rates at 80 kPa O 2 and in Ar:O 2 were close to the pre‐decline rates at 20 kPa O 2 . At the end of the nitrate treatment, this O 2 ‐induced recovery in nitrogenase activity reached 71 and 82%; for clover plants from spaced and dense stands, respectively. The respective roles of oxygen diffusion and phloem supply for the short‐term inhibition of nitrogenase activity in nitrate‐treated clovers are discussed.