淋洗与植物作用耦合对盐渍化土壤的改良效应

以甘肃秦王川引大灌区盐渍化土壤为背景,以当地5种耐盐植物为材料,采用根袋法盆栽试验动态研究了淋洗结合植物种植对盐渍化土壤改良的效应。结果表明:与种前相比,单纯的淋洗作用对土壤pH值影响不大,而淋洗结合植物种植明显降低了土壤pH值,且根际土壤pH值小于非根际土壤的,5种耐盐植物中霸王根际土壤pH值降低幅度最大,达0.6个单位。K+、Ca2+、Na+、Mg2+、Cl-和SO2-4在5种植物根际土壤中均有不同程度的富集,富集程度因物种的不同而不同,随培养时间的延长而呈波动状态。5种供试植物和对照组土壤中的6种主要的可溶性盐分离子随淋洗次数和培养时间的延长呈下降趋势。在培养120d后,单纯淋洗的土壤中K+、Ca2+、Na+、Mg2+、Cl-和SO2-4的含量相比种前平均分别降低了33.3%、26.1%、35.6%、32.5%、35.5%和36.3%,植物吸收带走的上述各离子的含量平均分别占种前的46.2%、8.1%、30.2%、7.2%和21.6%,其中霸王吸收带走的盐分离子最多,而淋洗结合种植植物的土壤中上述各离子的含量与种前相比平均分别降低了67.25%、63.73%、83.8%、67.5%、81.55%和78.46%,由此可见,淋洗结合植物种植的脱盐效果优于单纯淋洗,且土壤中主要的盐分离子Na+、Cl-和SO2-4的含量降低幅度最大,通过计算得出,在Cl-、SO2-4和Na+减少的总量中还有37.73%的Na+、38.22%的Cl-和35.14%的SO2-4的减少量是由植物根系的物理化学作用机制引起的。

Amelioration of salt-affected soils via combination of leaching and plant cultivation

Salinization of soil is a major limiting factor for sustainable development of irrigated agriculture in arid and semi-arid regions. At present, the majority of comparative studies suggest that a plant-assisted approach is more effective in ameliorating soil salinization. Cultivation of salt-tolerant plants improves physical properties of salt-affected soil due to penetration and extrusion of extensive and thick root systems of plants, which promote leaching of salts from top to deeper soil layers. Furthermore, due to physiological activities of plant roots, there is a marked difference in physical and chemical properties of soils between the rhizosphere soil and bulk soil. Based on a background of calcareous salt-affected soil in the irrigated region of Qingwangchuan, Gansu, a pot experiment with rhizobag was carried out for five salt-tolerant plant species to investigate the coupling effect of leaching and plant cultivation on salt-affected soil and to compare the changes of the dynamics of salt ions in the rhizosphere and bulk soils at different plant growth stages. Results indicated that soil pH was not influenced by leaching alone compared to initial soil pH before plants were grown, but leaching and plant cultivation combined significantly decreased soil pH, resulting in lower pH in rhizosphere soil than in bulk soil. Reduction in soil pH in the rhizosphere of Zygophyllum xanthoxylum was the highest among the five salt-tolerant plant species, by up to 0.6 units, whereas in the rhizosphere of Medicago sativa cv. Xinjiangdaye, pH was reduced to a smallest extent, by only 0.25 units. The enrichment with K⁺, Ca²⁺, Na⁺, Mg²⁺, Cl^-, SO₄^2-, and HCO^-₃ varied greatly in the rhizosphere soil of the five salt-tolerant plants. The enrichment levels were dependent on plant species and fluctuated as incubation days increased. Combining leaching with plant cultivation was more efficient in salt reduction than using leaching alone. Thus concentrations of six major salt ions in both control soil (soil without plants) and soils cultivated with five plant species significantly decreased with the extension of incubation days and leaching times. After 120 days of cultivation, total concentrations of six major salt ions in the control soil were reduced by 51.5%, whereas those in the treated soils were reduced by 77.7% compared to those in the soils before plants were grown. Among them, K⁺, Ca²⁺, Na⁺, Mg²⁺, Cl^-, and SO₄^2- concentrations in soils exposed to leaching alone were reduced on average by 33.3%, 26.1%, 35.6%, 32.5%, 35.5%, and 36.3% compared to those in soils before plants were grown. The concentrations of these cations and anions that were absorbed by plants accounted for 46.2%, 8.1%, 30.2%, 7.2%, and 21.6% respectively. Among the cultivated plants, Zygophyllum xanthoxylum removed more salt ions than other plants, whereas the cation and anion concentrations in soils with leaching and plant cultivation combined were reduced on average by 67.25%, 63.73%, 83.8%, 67.5%, 81.55%, and 78.46% compared to those in soils before plants were grown. Therefore, leaching and plant cultivation combined were more efficient than leaching alone in significantly reducing the main salt ions in salinized soil such as Na⁺, Cl^- and SO₄². The analyses showed that of total reduction of Cl^-, SO₄^2- and Na⁺ about 37.73% of Na⁺, 38.22% of Cl^-, and 35.14% of SO₄^2- were derived from the physical and chemical mechanisms caused by plant roots.