CADMIUM AND COPPER CHANGE ROOT-GROWTH AND MORPHOLOGY OF PINUS-PINEA AND PINUS-PINASTER SEEDLINGS

Heavy metal loads in forest soils have been increasing over time due to atmospheric inputs. Accumulation in the upper soil layers could affect establishment of seedlings and forest regeneration. Mediterranean species show a high initial root development, allowing seedlings to reach the moisture of deeper soil layers. In the present work seedlings of stone pine (Pinus pinea L.) and maritime pine (Pinus pinaster Ait.), were grown in culture solution supplied with 0.0, 0.1, 1 or 5 mu M CdSO4 or with 1 mu M CdSO4 and 1 mu M CuSO4 combined. In both species tap-root elongation was drastically reduced in the 5 mu M Cd2+ and in the (Cd2+ + Cu2+) treatments. A supply of 0.1 or 1 mu M Cd2+, however, enhanced root elongation in Pious pinea without significantly influencing root elongation in Finns pinaster. In both species the root density (weight per unit length) and the width of the cortex increased in response to Cd2+ exposure. In Pinus pinaster the mitotic index decreased at the higher Cd2+ concentrations and when Cd2+ and Cu2+ were combined. The data suggest that cell elongation is more sensitive to Cd2+ than cell division. The number and length of the lateral roots were also affected by Cd2+ treatment to a higher degree in Pinus pinaster than in Pinus pinea, reflecting the different Cd-tolerance of the two species.