盐胁迫对弗吉尼亚栎生长及矿质离子吸收、运输和分配的影响

以低浓度(50 mmol.L-1)和高浓度(150 mmol.L-1)NaC l处理弗吉尼亚栎(Quercus virginiana)2年生扦插苗,研究了弗吉尼亚栎生长和根系形态学参数变化以及Na+、K+、Ca2+、Mg2+、NO3-等矿质离子在不同器官的吸收、运输和分配。结果表明,盐胁迫不同程度促进了地上部和根系生长,地上部和根系干重、根长、表面积和体积在低浓度盐胁迫下明显增加(P0.05),而在高浓度盐胁迫下变化不大。随着根系对Na+和C l-吸收的增加,K+、Ca2+、Mg2+在根部和茎部的积累明显降低,矿质离子由根部向茎部运输的能力在低浓度盐胁迫增加而高浓度下受到抑制。叶片在低浓度和高浓度盐胁迫下对K+、NO3-具有很强的选择吸收能力,这对于维持叶片离子平衡和正常的光合作用及代谢过程具有重要意义。Na+和C l-在根部的浓度远远大于地上部,说明弗吉尼亚栎根系对盐离子具有较高的耐受性,而减少盐离子在地上部的积累,对于维持地上部的正常生长具有重要意义,这也是弗吉尼亚栎对盐胁迫的适应机制之一。

Effects of NaCl stress on growth and mineral ion uptake, transportation and distribution of Quercus virginiana

Quercus virginiana, an evergreen oak tree, also called live oak, is one of the main tree species along southeastern coast of the United States. This species is distributed naturally from Texas, east to Florida and north to Virginia. It is an important landscape and shade tree species native to the southeastern U.S. Due to their tolerance to high concentration of salt fog , they are used extensively along the U.S. Gulf Coast and East Coast, and as far north as the outer banks of North Carolina. Live oak was introduced to China in 2000 for the first time. Although a certain field experiments were conducted to study the saline adaptability of live oak in China and the salt stress tolerance of live oak in the regional trial has been confirmed around the Yangtze River Delta, little is known about the effects of salt stress on growth of seedlings of live oak and its possible mechanisms of salt tolerance under controlled laboratory conditions. To assess the effects of salt stress on 2-year-old seedlings of live oak, experiment was carried out by sand culture in the greenhouse by adding NaCl into Hoagland solution with lower concentration (50 mmol•L-1) and higher concentration (150 mmol•L-1). During the test, the parameters such as plant growth, root morphology and the uptake, translocation and distribution of mineral nutrients including Na+, K+, Ca2+, Mg2+, NO3- in different organs of Q. virginiana were measured. The results showed that the growth of shoots and roots were enhanced to some extent under both lower and higher concentration of NaCl. Compared with the redult of control, the dry weight of shoots and roots, root length, root surface area and root volume increased significantly with 50 mmol•L-1 NaCl treatment (P<0.05) while changed slightly with 150 mmol•L-1 NaCl treatment. With the increasing uptake of Na+ and Cl- by roots, the accumulation of K+, Ca2+ and Mg2+ in roots and shoots decreased significantly (P<0.05). The ability of K+, Ca2+ and Mg2+ transporting from root to shoot was enhanced under lower concentration of NaCl whereas inhibited under higher concentration of NaCl. The K+ and NO3- selective absorption to leaves of Q. virginiana were strengthened under lower and higher concentration of NaCl, which was significant for keeping iron homeostasis and photosynthesis in leaves. The results also showed that the concentrations of Na+ and Cl- in roots were much higher than that in shoots under the situation of salt stress, which may suggest the tolerance mechanism of Q. virginiana to salt strees can be ascribed to the high ability in accumulation of Na+ and Cl- in roots while transport few amount of Na+ and Cl- to shoots thereby maintaining the normal growth of shoots.