Effects of phosphate deficiency on photosynthesis and accumulation of starch and soluble sugars in 1-year-old seedlings of maritime pine (Pinus pinaster Ait)

Abstract

Maritime pine seedlings were grown in 4 L pots filled with coarse sand in a greenhouse. Seedlings were supplied with a nutrient solution with three different concentrations of phosphorus (0, 0.125 and 0.5 mM). After 1 year of growth, gas exchange measurements were performed on mature needles. From these measurements, the main parameters of CO2 assimilation (the carboxylation efficiency, the apparent quantum efficiency and the maximal rate of electron transport) were estimated using the biochemical model of photosynthesis as described by Farquhar et al (1980). Leaf nonstructural carbohydrates were also analyzed. Phosphorus deficiency decreased the phosphorus foliar concentration, but did not affect foliar nitrogen concentration. The maximal rate of photosynthesis, the carboxylation efficiency and the apparent quantum efficiency decreased in phosphorus deficient seedlings. However, the maximal rate of electron transport and stomatal conductance were not affected by phosphorus supply. Low phosphorus nutrition caused a dramatic increase in foliar starch level at the end of the photoperiod. These results indicate that inadequate phosphorus nutrition principally affected the dark reactions of photosynthesis, the apparent quantum efficiency and starch accumulation.