The effect of potassium deficiency on growth and N2-fixation in Trifolium repens

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The effects of potassium (K) deficiency on growth, N2-fixation and
photosynthesis in white clover (Trifolium repens L.) were investigated
using natural occurring gas fluxes on the nodules in real time of plants
under three contrasting relative addition rates of K causing mild K
deficiency, or following abrupt withdrawal of the K supply causing
strong K deficiency of less than 0.65% in dry matter. A steady-state
below-optimum K supply rate led to an increase in CO2-fixation per unit
leaf surface area as well as per plant leaf surface. However,
nitrogenase activity per unit root weight and per unit nodule weight was
maintained, as was the efficiency with which electrons were allocated
to the reduction of N2 in the nodules. Abrupt K removals stimulated
nodule growth strongly without delay, but as K concentrations decreased
in the plant tissue a significant decline in nitrogenase activity per
unit root weight as well as per unit nodule mass occurred. Further, the
rate of photosynthesis per unit leaf area was unaffected, while the CO2
acquisition for the plant as a whole increased due to an expansion of
total leaf area whereas the leaf area per unit leaf weight was
unaffected. The ratio between CO2-fixation and N2-fixation increased,
although not statistically significant, under short-term K deprivation
as well as under long-term low K supply indicating a downregulation of
nodule activity following morphological and growth adjustments. This
downregulation took place despite a partly substitution of the K by Na.
It is concluded that N2-fixation does not limit the growth of
K-deprived clover plants. K deprivation induces changes in the relative
growth of roots, nodules, and shoots rather than changes in N and/or
carbon uptake rates per unit mass or area of these organs.

Original languageEnglish
JournalPhysiologia Plantarum
Issue number3
Pages (from-to)440-449
Publication statusPublished - 2003
Externally publishedYes

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