Osmotic adjustment in Pinus pinaster cuttings in response to a soil drying cycle

Two-year-old cuttings of five genotypes of maritime pine (Pinus pinaster Ait.) were subjected to a four-month treatment of slowly decreasing water availability in pots. Final predawn needle water potential varied from -0.82 to -1.48 MPa, and was negatively correlated with plant size. Osmotic adjustment was estimated as the slope of the regression line fitted between relative water content (RWC) and osmotic potential () assessed during the drying cycle, and as the value of the relative water content for a given level of (i.e. = -1.7 MPa). Under the experimental conditions, the genotypes showed a high capacity for osmotic adjustment in needles, and one genotype distinguished itself with a smaller capacity. The results are discussed in terms of protocol and interpretation when ranking genotypes for osmotic adjustment.