不同耐盐植物根际土壤盐分的动态变化

以甘肃秦王川引大灌区盐渍化土壤为研究背景,用盆栽根袋法对4种耐盐植物根际和非根际土壤pH和盐分离子的动态变化进行了分析比较。结果表明:4种待测植物随着培养时间的延长土壤pH和EC值呈降低趋势。新疆大叶(Medicago Sativa L.cv.Xinjiangdaye)、向日葵(Helianthus annuus)和霸王(Zygophyllum xanthoxylum)生长90 d后根际土壤pH明显低于非根际,而裸麦(Hordeum vulgare var. vulgare)根际较非根际pH差异不大。霸王和新疆大叶根际土壤EC值较非根际高,而裸麦和向日葵的根际与非根际差异不大。4种供试植物根际K⁺均出现亏缺,Ca²⁺、Na⁺、Mg²⁺、SO^2-₄和Cl^-在新疆大叶、霸王和向日葵3种植物根际均出现富集,对于裸麦:Ca²⁺、Mg²⁺和SO^2-₄ 3种离子在植物根际富集,而Cl^-和Na⁺在根际亏缺。随着待测植物培养时间的增加Na⁺/K⁺、Na⁺/Ca²⁺和Na⁺/Mg²⁺ 这3个比值呈降低趋势,说明Na⁺相对于K⁺、Ca²⁺和Mg²⁺的含量降低,生物措施对Na⁺的移除效果较显著。

Dynamic change of salt contents in rhizosphere soil of salt-tolerant plants

Secondary salinization of soil is a major limiting factor for agricultural sustainability development in irrigated agriculture in arid and semi-arid regions. At present, the problem of soil salinity is further deteriorating in inland arid regions as the dry lands have become irrigated fields, which caused the substantial rise of groundwater table. The majority of comparative studies suggested that phytoremediation (plant-assisted approach) is more effective in the amelioration process in recent years. Rhizosphere is an important interface in substance exchange and energy transformation between plants and soil. Affected by physiological activities of plant roots, there is a marked difference in physichemistry properties between the rhizosphere soil and bulk soil. Based on a calcareous salt-affected soil in the irrigated region of Qingwangchuan, Gansu, a rhizobag experiment was conducted on four salt-tolerant plants to investigate dynamic changes of pH, EC (Electrical Conductivity) and salt ions in the rhizosphere and bulk soil, and to compare the differences between them at the different plant growth stages. The results showed that pH, EC and concentrations of six major salt ions in four tested plants decreased with the extension of incubation days. There was significantly (P<0.05) lower pH in rhizosphere soil than in corresponding bulk soil after 90-day growth periods for all tested plants, such as alfalfa (Medicago Sativa L.cv.Xinjiangdaye), sunflower (Helianthus annuus) and common beancaper (Zygophyllum xanthoxylum) except for barley (Hordeum vulgare var. vulgare). Soil EC was higher in rhizosphere soil than in bulk soil for common beancaper and alfalfa, but not for sunflower and barley. K⁺ concentrations reduced significantly in the rhizosphere of four tested plants, but other major salt ions in the rhizosphere soil of alfalfa, common beancaper and sunflower exhibited enrichment. However, Ca²⁺, Mg²⁺ and SO^2-₄ concentrations increased in the rhizosphere of barley, whereas the other ions behaved in an opposite way. The Na⁺/K⁺, Na⁺/Ca²⁺ and Na⁺/Mg²⁺ ratio showed a decrease trend with the extension of incubation days. The results indicated that the deficit of Na⁺ in the soil was more profound than those of K⁺, Ca²⁺ and Mg²⁺. In the present study, the main reasons which were responsible for the relative change of ions between rhizosphere and bulk soil might be the combination effects, namely effects of different ions were absorbed selectively by plant root and the amounts of soil mineral-salt compound can be mobilized by different rhizosphere processes. Besides, the rate of different salt moving to the rhizosphere also played a key role in this case. In addition, we should consider the distance between sampling site and plant rhizosphere at different plant growth stages as pH and salt contents in the saline soil were measured.