不同阴离子钠盐对土壤Cd形态与微生物群落的影响

为了探明污染土壤在盐碱胁迫条件下镉（Cd）有效性与微生物群落的响应，采集污灌区Cd污染农田土壤，模拟北方土壤典型盐碱胁迫情景，设置不同阴离子钠盐配置处理，利用微生境培养实验，采用高通量测序技术，结合对土壤性质、土壤Cd形态等的测定.结果表明：施用钠盐可显著提高钠吸附比（SAR）、碱化度（ESP），降低有机碳（SOC）含量、阳离子交换量（CEC）；促进土壤中小粒径团聚体（<0.002mm）的形成，增加了Cd在小颗粒团聚体的质量负载；与对照相比，两种土壤中T1处理（主要阴离子为SO₄^2-、Cl^-）均显著（P<0.05）增加交换态Cd含量（27.06%和11.00%）.钠盐的添加降低了土壤中细菌的丰度和多样性，其中T1处理的微生物群落均匀度最低；盐碱胁迫处理改变了土壤细菌的关键类群，如增加了耐盐碱腈基降解菌科、葡萄球菌科、假单胞菌科和耐重金属芽孢杆菌科的菌群丰度，不同处理菌群结构差异与土壤阴离子组成有关，如相比而言，T1处理可增加变形菌门、芽单胞菌门、拟杆菌门的丰度.冗余分析结果表明土壤pH值、交换态Cd含量、SAR和ESP是影响细菌群落组成变化的关键环境因子，拟杆菌门、芽单胞菌门和变形菌门的丰度与pH值呈正相关，而酸杆菌门、绿弯菌门的丰度与交换态Cd含量、SAR呈现显著正相关.可见，盐碱胁迫增加了土壤Cd的有效性，显著改变了土壤微生物群落结构.

Effect of sodium salt with varied anions on Cd fractions and microbial community in soil

In order to explore the impact of saline-alkaline stress on soil microbial community structures and Cd availability, different Cd-contaminated soils from wastewater-irrigated agricultural land were collected, the actual saline-alkali environment was simulated by adding the neutral and alkaline salts in different proportions. Soil microcosm incubations were conducted, Illumina high-throughput sequencing of 16S rRNA genes was used to estimate microbial community structures, and basic soil physiochemical properties and Cd content were determined. The results showed that salt addition positively affected sodium adsorption ratio (SAR), alkalinity (ESP), but reduced the content of soil organic carbon (SOC), cation exchange capacity (CEC). Increased soil salinity and alkalinity increased the proportion of small soil aggregates (<0.002mm), and promoted Cd translocation from large aggregates into clay/silt size fractions. Treatment T1 (mainly contained ions of SO₄^2- and Cl^-) enhanced exchangeable Cd content in both test soils by 27.06% and 11.00%. Soil saline-alkali stress decreased bacterial abundance and diversity, comparatively, soil microbial community in T1 showed the highest difference. Meanwhile, salt addition changed major soil bacterial taxa, for example, increased saline stress enriched saline-alkali tolerant taxa Nitriliruptoraceae, Staphylococcaceae, Pseudomonadaceae and heavy-metal resistant taxa Bacillaceae, microbial structure difference under different treatments probably depended the components of soil anions. For instance, comparatively, the abundance of Proteobacteria, Gemmatimonadetes and Bacteroidetes was significantly enriched in T1treatment. Redundancy analysis (RDA) of the abundant bacterial phyla and soil properties suggested that soil pH, exchangeable Cd content, SAR and ESP were the most influential environmental factors driving the changes in community composition, the abundances of Bacteroidetes, Gemmatimonadetes, and Proteobacteria were positively correlated with pH, and the abundances of Chloroflexi and Acidobacteria were strongly positively correlated with soil exchangeable Cd content, SAR. Therefore, saline-alkali stress increased soil Cd availability, significantly altered soil bacterial community.