Light regulation of root and leaf NO3 uptake and reduction in the floating macrophyte Lemna minor


Author for correspondence: Nina Cedergreen Tel: +45 35 283397 Fax: +45 35 282175 Email:


  • • The regulation of NO3 uptake kinetics and reduction in relation to long- and short-term changes in irradiance was explored in roots and photosynthetic tissues of Lemna minor.
  • • The NO3 uptake kinetics, nitrate reductase activity, plant morphology, chlorophyll and tissue NO3, organic-N, starch and sugars were measured on roots and fronds of L. minor grown at four combinations of irradiance- and NO3 availability.
  • • Long-term acclimatizations paralleled those of terrestrial plants. Short-term changes in irradiance, however, changed frond NO3 uptake proportionally with frond chlorophyll and N content, indicating a relationship between responsiveness and the metabolic potential of the plants. Root uptake changed to balance the change in frond uptake keeping whole plant uptake varying by < 40%. Nitrate reductase activity was primarily located in the roots and was correlated with frond uptake, indicating a transport of NO3 from shoot to root before reduction.
  • • This study shows that irradiance can affect the contribution of root and leaf uptake by aquatic plants and that roots play a major role in NO3 reduction despite large foliar uptake.