生物质炭对Cd污染土壤根际微团聚体Cd形态转化的影响

为明确生物质炭对土壤Cd形态分布的团聚体机制，采用盆栽试验，以秸秆生物质炭为试验材料，研究了秸秆生物质炭对Cd在不同粒级微团聚体中的富集以及根际、非根际微团聚体Cd形态转化的影响.结果表明:外源Cd进入土壤后，主要分布于土壤不同粒级微团聚体中且随粒级减小而增加，富集顺序由大到小为 < 0.01、0.05~0.01、0.25~0.05、 > 2 mm.添加生物质炭后显著降低了Cd在不同粒级微团聚体中的富集系数（P < 0.05）.与对照相比， > 2、0.25~0.05、0.05~0.01、 < 0.01 mm粒级微团聚体土壤对Cd的富集系数分别降低了0.04~0.16、0.04~0.15、0.07~0.17、0.06~0.21.不同处理下，根际、非根际土壤不同粒级微团聚体中Cd主要以残渣态为主且向小粒级团聚体（< 0.01 mm）富集，其中可交换态、碳酸盐结合态、铁锰氧化物结合态和有机物结合态Cd的含量（以质量分数计）及占比均有不同程度的下降.对于根际、非根际不同粒级微团聚体各形态中有机结合态Cd，与对照相比，在Cd1B10处理下，分别于 < 0.01、0.05~0.01 mm微团聚体中的降幅最高，达49.5%、62.3%；对于残渣态Cd，在Cd1B10处理下，分别于0.25~0.05、0.05~0.01 mm微团聚体中的降幅最高，达19.8%、20.5%，但各处理下残渣态Cd占比趋于上升，最高占比分别达74.0%、78.2%.表明Cd进入土壤后主要转化成了残渣态，土壤中Cd的生物有效性降低，其中，当Cd污染程度（1 mg/kg）较低、生物质炭施用量（10 g/kg）最高时，该效果达显著水平.研究显示，施用高量（10 g/kg）生物质炭能够降低土壤不同粒级微团聚体中各形态Cd的含量，并且Cd污染程度越低、粒级越小，降低效果越显著. 

Effects of Biochar on the Transformation of Cd Forms in Rhizosphere Micro-Aggregates of Cd-Contaminated Soil

For clear biochar on the mechanism of the distribution of Cd forms in soil aggregates, a pot experiment was conducted out for straw biochar as raw material to study the effects of straw biochar on the enrichment of Cd in different size fractions of micro-aggregates and the transformation of Cd forms in micro-aggregates of rhizosphere and non-rhizosphere. The results indicated that when Cd was added to the soil, it was mainly distributed in the soil of different particle size micro-aggregates, and increased with the decrease of particle size. According to the order from big to small, the enrichment sequence was <0.01, 0.05-0.01, 0.25-0.05, >2 mm. After adding biochar, the enrichment coefficient (P<0.05) of Cd was significantly decreased in different particle size micro-aggregates. Compared with the control, the enrichment coefficients of >2, 0.25-0.05, 0.05-0.01 and <0.01 mm decreased by 0.04-0.16, 0.04-0.15, 0.07-0.17, 0.06-0.21 times respectively. The contents of rhizosphere and non-rhizosphere Cd in different particle size micro-aggregates were mainly dominated by residual fractions, and the content of Cd in each form was mainly concentrated in small grain micro-aggregate (<0.01 mm) under different treatments. Rhizosphere and non-rhizosphere Cd content of exchangeable, Fe Mn oxides and carbonate bound and organic bound decreased in different degrees, and residual Cd increased. Compared with the control, rate of decline of the organic bound Cd was highest in the rhizosphere and non-rhizosphere of different micro-aggregates in various forms that were 49.5% and 62.3%, respectively in <0.01 and 0.05-0.01 mm micro-aggregates respectively under Cd1B10 treatment. The rate of reduction of the residual form Cd were the highest that were 19.8% and 20.5%, respectively in 0.25-0.05 and 0.05-0.01 mm micro-aggregates respectively under Cd1B10 treatment. However, the percentage of residue state tended to increase under each treatment, with the highest percentage reaching to 74.0% and 78.2% respectively. The results showed that Cd was mainly transformed into residual state after soil entry, and the bioavailability of Cd decreased in soil. The Cd-contaminated of low concentration (1 mg/kg) and the highest biochar application (10 g/kg), the effect was significant. Studies have shown that the application of high biochar(10 g/kg) can reduce the content of Cd in soil micro-aggregates of different sizes and contents of different forms of Cd, and the lower concentration of Cd, particle size is smaller, the more significant effect.