Germination and seedling growth of carrots under salinity and moisture stress

Poor crop stand is a common problem in saline areas. Germination and seedling emergence may be depressed as a result of impeded aeration, saline or dry conditions. In this study, we examined the effects of salinity and moisture stress and their interactions on seed germination and seedling growth of carrots. Variable soil matric and osmotic potentials were either obtained by equilibrating soil salinized to different degrees on a 0.5 MPa ceramic plate soil moisture extractor or by adding different amounts of salt solutions to the same mass of air-dried soil, based on a previously determined soil moisture release curve, and allowing to equilibrate for 1 week. Germination decreased significantly in the investigated silty soil (Aquic Ustifluvent) at soil moisture potentials higher than -0.01 MPa, whereas osmotic potentials as low as -0.5 MPa did not influence germination. Matric potentials of -0.3 and -0.4 MPa, respectively, resulted in a strong decrease (35-95%) of germination and delayed germination by 2 to 5 days in the silty soil to which different amounts (18 and 36%, respectively) and sizes (0.8-1.2 mm and 1.5-2.2 mm, respectively) of sand particles had been added. No effect of sand and grain diameter was detected. Germination was not affected by comparable osmotic potentials. Seedling growth showed a much higher sensitivity than germination to decreasing matric potentials, but was not affected by osmotic potentials ranging from -0.05 to -0.5 MPa. Optimum shoot growth occurred at matric potentials between -0.025 and -0.1 MPa. Shoot and root growth decreased markedly at matric potentials higher than -0.01 MPa. Fresh weight of shoots decreased gradually at matric potentials lower than -0.2 MPa. Root growth was significantly increased at matric potentials of -0.1 to -0.3 MPa, whereas comparable osmotic potentials did not have equivalent effects. It is concluded that germination and seedling growth are differently affected by comparable matric and osmotic stresses and that water stress exerts a more negative effect than salt stress.