盐胁迫对2种栎树苗期生长和根系生长发育的影响

以低浓度(50 mmol/L)和高浓度(150 mmol/L)NaCl处理弗吉尼亚栎(Quercus virginiana)和麻栎(Quercus acutissima)1年生幼苗,研究了2种栎树在盐胁迫下的生长、对盐分的敏感性和耐受性及其根系形态学参数变化以及根系对盐离子的吸收与积累。结果表明,高浓度盐胁迫明显抑制了2种栎树地上部生物量的积累(P0.05),而低浓度盐胁迫对弗吉尼亚栎地上部干重的影响不明显,但显著抑制了麻栎地上部干重(P0.05);2种栎树的根冠比在盐胁迫下呈增加趋势,特别是在高浓度盐胁迫下,2种栎树的根冠比明显增加(P0.05),盐胁迫下增加生物量在根部的分配是植物应对盐胁迫的方式之一。2种栎树根部生物量积累在盐胁迫下变化不明显,但2种栎树根系形态学参数在盐胁迫下的响应不同,弗吉尼亚栎根系总长度、总表面积和总体积在盐胁迫下均有不同程度增加,特别是在低浓度盐胁迫下,根系形态学参数明显增加(P0.05),但麻栎根系形态学参数有下降趋势,但与对照相比变化不明显;通过对不同径级根系总长的分析发现,弗吉尼亚栎根系总长度的增加主要是由于直径小于2 mm的细根总长的增加,细根长度的增加对于植物吸收水分和营养物质具有重要意义;通过对Na+和Cl-在根系的含量分析表明,盐胁迫下2种栎树根系盐离子的积累均有明显增加,但弗吉尼亚栎根系盐离子的含量在低浓度和高浓度盐胁迫下的差异不明显,而麻栎在高浓度盐胁迫下根系盐离子的含量明显高于弗吉尼亚栎。综合2种栎树盐胁迫下的生物量分配策略和根系形态学响应以及盐离子的积累规律,证明2种栎树尽管在生物量分配策略方面具有相同的特点,但根系的响应策略截然不同,弗吉尼亚栎在盐胁迫下能够扩大根系吸收范围,维持较高的K+/Na+比值,而麻栎在盐胁迫下根系由于吸收过多的盐离子,导致根系的生长发育受到抑制,影响了根系在逆境中的分布范围,从而在一定程度上避免了进一步的盐害。

Effects of salt stress on growth and root development of two oak seedlings

It is well known that saline soil, which takes up about 25% of the whole land area, is one of the most widely distributed soils on Earth. In China, the saline area is over 34 million hm², including one million hm² coastal saline soil. Soil salinity refrains the development and growth of most plant species, except for few species like halophytes. To understand the mechanism of salt tolerance, many studies have been carried out on the herbaceous halophytes, the tolerant woody plants and the sensitive and tolerant crop plants, but much less is known concerning the salt susceptibility and tolerance of oak trees. Quercus virginiana and Quercus acutissima are two different origin oak trees. Q. virginiana, is considered as a moderately sensitive tree species to soil salinity according to US Salinity Laboratory classification. It is one of the dominant tree species along southeastern coast of the United States and has the extreme tolerance to high concentration of salt fog. Q. virginiana acorn was introduced to China in 2000 for the first time, and its tolerance to salts has been confirmed through the regional trial along the coastline of southeastern China. Q. acutissima is widely distributed in China and few researches are reported about its response on salt stress.The response of plants to excess salt is complex and involves some changes in morphology, physiology and metabolism. Among these changes, the variations changes in the biomass allocation and root morphological characteristics of plants are two important adaptive mechanisms under salt stress. In this research, the changes of root morphology and biomass accumulation of 1-year-old seedlings of Q. virginiana and Q. acutissima were investigated under higher concentration (150 mmol/L) and lower concentration (50 mmol/L) of sodium chloride solution treatments. The results showed that the growth of shoots of two oak trees were significantly inhibited under higher concentration of salt stress, while no obvious changes were observed for the growth of shoots of Q. virginiana under lower concentrations of NaCl. The ratio of root to shoot for two oak trees increased under both concentration of NaCl, which was considered as a biomass allocation strategy for a certain class of plants under salt stress.For the two oak trees, salinity did not induce the significant change on the root biomass accumulation. While the root morphological responses under salt stress were different between two oak trees. For Q. virginiana, the total root length, root surface area and root volume were increased in various degrees under both lower and higher concentration of NaCl, and significant increasement was observed under lower concentration of NaCl, especially for the stimulation of fine roots with the diameter less than 2mm. The fine roots are more effective than the thicker roots in nutrient and water absorption. For Q. acutissima, although its root development and expandation were inhibited under salt stress, no significant difference was observed when compared to that of control. It was also observed that the different patterns of accumulation of Na⁺ and Cl^- in roots for two oak trees. Therefore, according to the biomass allocation strategy and root morphological responses and ions accumulation patterns of two oak trees under salt stress, it may be deduced that the both oak trees have the similar biomass allocation strategy when exposed to salinity, but have totally different responses on the root development and salt ions accumulation. Q. virginiana could expand the root scope for more effective nutrient absorption to relieve the toxicity of redundant salt ions, while Q. acutissima restricted the expanding of roots in salinity environment due to the redundant uptake of salt ions, and thus lessens the further damage to roots.