LEAF PHOTOSYNTHESIS OF EVENING PRIMROSE CROP (Oenothera spp.).
Arturo Chong, "Universidad Autonoma Chapingo, Dpto", Carrt. Mexico-texcoco Km. 38.5 Chap, "Chapingo, Edo. De Me", 56230, MEXICO and J.L.I. Morison, University of Essex, Wivenhoe Park CO4 3SQ, Colchester, United Kingdom.
The leaf gross assimilation rate (Ag) and the leaf nitrogen content (NL) of the evening primrose crop (Oenothera spp.) were measured during all the different development phases on plants treated with four different nitrogen applications (0, 60, 120 and 180 kg N/ha). For the successive development phases Ag was different. The highest values were observed at the first development phases (rosette and stem elongation; 24.5 and 26.1 µmol CO2 m-2 s-1, respectively). Ag dropped at the next phases (16.3, 10.6, and 6.1 µmol CO2 m-2 s-1 for flower differentiation, flowering and fruit maturation, respectively). A similar patter was observed for NL (0.09, 0.13, 0.12 and 0.08 mg N cm-2 for rosette, stem elongation, flowering and fruit maturation phases, respectively). The Ag and NL were affected positively by the nitrogen applications at the rosette, stem elongation, flower differentiation phases and the beginning of the flowering phase. The 0 kg N ha-1 application had values of 11.1 µmol CO2 m-2 s-1 and 0.10 mg N cm-2 while for the 180 kg N ha-1 application they were 33.2 µmol CO2 m-2 s-1 and 0.16 mg N cm-2, respectively, at the stem elongation phase. At the last part of the flowering phase and during the fruit maturation phase the nitrogen applications did not affect both Ag and NL. The high Ag at the beginning of the plant cycle was due to the high concentration of photosynthetic proteins, when the leaf area was small and grew at a slowly rate. As the cycle advanced Ag and NL dropped because proteins were diluted by the fast growing leaves or by their translocation to new tissues. The nitrogen applications did not affect Ag and NL at the end of the plant cycle due to the translocation of nitrogen to the growing fruits and seeds.