Abstract:

Nutrient regulation can enhance the efficiency of phytoremediation. Populus yunnanensis is a promising candidate tree for remediation of soil cadmium (Cd) pollution due to its relatively high Cd tolerance with relatively low Cd accumulation capability. Thus, P. yunnanensis was selected as the research object, and a nutrient control pot experiment, using “3414” design plan with three-factor (nitrogen (N), phosphorus (P), and potassium (K)) and four-level (0, 100, 200, and 400 mg∙kg⁻¹), total of 15 treatments, combined with fertilizer effect model was conducted to calculate the optimal fertilizer application, maximum Cd accumulation, and the optimal fertilization scheme for increasing Cd accumulation of P. yunnanensis. It was found that: The application of N, P, and K fertilizers could enhance the biomass of P. yunnanensis under Cd stress with the enhancement ratios ranged from 70.49% to 132.31%, The biomass exhibited a trend of increase followed by decrease with increasing concentrations of N, P, and K, reaching their respective maximum at 200 mg∙kg⁻¹. and the most significant enhancement was observed for N application. The effects of fertilizer application on Cd accumulation in P. yunnanensis followed the sequence as N>P>K. The lowest Cd accumulation was observed in the treatments without N (N0P0K0, N0P2K2), whereas the highest Cd accumulation was observed in the treatments with high levels of N and P (N2P4K2, N4P2K2). The results of unitary model fitting indicated that the maximum accumulation of Cd (2.168 mg∙pot⁻¹) occurred when N was applied at 374.704 mg∙kg⁻¹, equation: y= −0.0000090x²+0.0067x+0.92. In the binary model fitting, Cd accumulation was greater when N and P were applied at 344.125 and 278.633 mg∙kg⁻¹, respectively, equation: y=0.091+0.0090x₁+0.0028x₂ −0.000021x₁x₂−0.0000047x₁²+0.0000074x₂². However, in the ternary model fitting, Cd accumulation was greater when N, P, and K were applied at 468.911, 46.774, and 305.529 mg∙kg⁻¹ respectively, equation: y=0.81+0.0025x₁−0.0015x₂+0.0029x₃+0.000012x₁x₂− 0.0000065x₂x₃−0.000017x₁x₃+0.000011x₂²+0.0000015x₃². Based on the measured data and model fitting results, the recommended optimal fertilization program for the matrix nutrient background was N 374.704 mg∙kg⁻¹, P₂O₅ 200.000 mg∙kg⁻¹, and K₂O 200.000 mg∙kg⁻¹. The redundancy analysis revealed positive correlations between Cd accumulation in P. yunnanensis and biomass and available N and P, whereas negative correlations were found between Cd accumulation and pH and available K, which suggested that nutrient regulation could influence the accumulation of Cd by altering the biomass of P. yunnanensis and soil properties. The findings could provide a scientific basis for the application of P. yunnanensis in the phytoremediation of Cd-contaminated soil.

Key words: P. yunnanensis, phytoremediation, cadmium contaminated soil, nitrogen, phosphorus, and potassium, cadmium accumulation, model analysis

摘要：

营养调控是强化植物修复效率的重要手段。滇杨（Populus yunnanensis）作为修复土壤镉（Cd）污染的重要候选树种，Cd耐受能力较强，但Cd积累量不高。以滇杨为研究对象，采用“3414”试验设计，开展氮（N）、磷（P）、钾（K）三因素四水平（0、100、200、400 mg∙kg⁻¹）共15个处理的营养调控盆栽试验。通过肥料效应模型推算最佳施肥量、最大Cd积累量以及提升滇杨Cd积累量的最佳施肥方案。结果表明，施加N、P、K均能提升Cd胁迫下滇杨的生物量，提升比例为70.5%－132%，生物量随N、P和K浓度增加而呈现先增加后降低趋势，均在200 mg∙kg⁻¹时达到最大值，施N对生物量的促进最显著。滇杨Cd积累量受N影响最大，其次为P，再次是K。无N处理（N0P0K0、N0P2K2）的Cd积累量最低，高N、高P处理（N2P4K2、N4P2K2）的Cd积累量最高。一元模型拟合结果显示，N以374.704 mg∙kg⁻¹施加时可获得最大Cd积累量（2.168 mg∙pot⁻¹），拟合方程为y= −0.0000090x²+0.0067x+0.92;二元模型拟合时，N、P分别按344.125、278.633 mg∙kg⁻¹施加时Cd积累量较大，达到2.057 mg∙pot⁻¹，拟合方程为y=0.091+0.0090x₁+0.0028x₂−0.000021x₁x₂−0.0000047x₁²+ 0.0000074x₂²;三元模型拟合时，N、P、K分别按468.911、46.774、305.529 mg∙kg⁻¹施加时Cd积累量较大，拟合方程为y=0.81+0.0025x₁−0.0015x₂+0.0029x₃+0.000012x₁x₂−0.0000065x₂x₃−0.000017x₁x₃+0.000011x₂²+0.0000015x₃²。结合实际最大处理（N4P2K2）与模型拟合结果，推荐基质营养背景下最佳施肥方案为：N 374.704 mg∙kg⁻¹+P₂O₅ 200.000 mg∙kg⁻¹+K₂O 200.000 mg∙kg⁻¹。由冗余分析可知，滇杨Cd积累量与生物量、土壤速效N、速效P呈正相关，与pH、速效K呈负相关，说明营养调控可通过改变滇杨生物量以及土壤性质影响Cd积累。研究结果可为滇杨修复Cd污染土壤的应用实践提供科学依据。

关键词: 滇杨, 植物修复, 镉污染土壤, 氮磷钾, 镉积累, 模型分析