GROWTH AND NUTRIENT EFFICIENCY IN OENOTHERA-BIENNIS PLANTS GROWN UNDER DIFFERENT WATERING CONDITIONS

Oenothera biennis is a plant which, although considered generally well adapted to different enviroments, has not been studied for its respon se to different water regimes. The influence of two water availabiliti es on the growth, the water status and the accumulation of nutrients i n the above ground parts of the plants during the growth was studied. Water deficit was imposed from the beginning of the flowering until th e end of the growth cycle, reducing the watering to 25 and 15% of fiel d capacity. The highest water deficit significantly reduced elongation and biomass production of the plants, as well as Psi(w), Psi(x) and P si(p), whereas epsilon did not change. Relative water content did not appear influenced by water deficit. Macronutrients showed a general re ducing trend when water availability was reduced. On the contrary, mic ronutrient contents generally showed a fluctuant trend, in fact only M n was strongly reduced by the highest water deficit. The efficiency in dex of N, P and K, unexpectedly higher for the plants with low availab ility of water, may be a possible reason of the good adaptation of thi s plant to critical conditions.