淹水培养时间对水稻土中Fe（Ⅲ）异化还原能力的影响

为了模拟水稻土淹水过程,探讨不同淹水培养时间水稻土中铁还原微生物群落利用不同碳源的活性变化特征,以接种不同淹水时期的浙江水稻土浸提液作为微生物群落来源,以人工合成的Fe（OH）3为惟一的电子受体,不同碳源作为惟一电子供体,在30℃恒温条件下厌氧培养,定期测定Fe（Ⅱ）含量和pH值变化,采用Logistic模型进行动力学分析。研究结果表明,葡萄糖作为电子供体时,不同淹水时期的微生物群落总体上对Fe（OH）3还原反应有较快的响应;丙酮酸盐作为碳源时,铁还原反应启动的时间整体迟于葡萄糖,Fe（Ⅱ）累积量在反应30d才表现出显著累积并逐渐趋于稳定;淹水20d的微生物群落能最先利用乳酸盐还原Fe（Ⅲ）,反应15 d的Fe（Ⅱ）累积量达到601.60 mg.L^-1;淹水30 d的铁还原微生物群落对乙酸盐的利用能力增强,最大Fe（Ⅱ）累计量升高到538.47 mg.L^-1,Fe（Ⅲ）还原率达到75.81%。不同淹水时期利用各种碳源的体系pH表现为葡萄糖从中性下降至酸性,丙酮酸盐和乳酸盐中性偏酸,乙酸盐的pH略微偏碱,不同淹水时期出现的水稻土微生物群落结构不同是导致Fe（OH）3还原能力不同的主要原因。不同的碳源利用可以指示不同的铁还原微生物群落变化：淹水培养早期的铁还原微生物群落对葡萄糖和丙酮酸盐的利用较为迅速和显著,同一时期出现的微生物群落不能以乙酸盐作为电子供体;淹水培养后期的铁还原微生物群落以乳酸盐和乙酸盐为优势碳源来还原Fe（OH）3。

Effect of Flooding Time on Dissimilatory Iron（Ⅲ）Reduction in Paddy Soil

Dissimilatory Fe（Ⅲ）reduction shows important impacts on the geochemistry of anaerobic environments.The community structure of iron-reducing microorganisms in dried paddy soil changed continually after flooding.The objective of this study was to investigate the characteristics of iron reducing microbial community in different flooding period with various carbon sources.Solutions extracted from Zhe-jiang paddy soil in different flooding period were used as inoculums while ferrihydrite synthesized artificially was used as a sole electronic ac-cepter.These solutions including ferrihydrite were cultured under anaerobic condition at 30 ℃.Yield of Fe（Ⅱ）and pH were mensurated termly and analyzed by Logistic model.The results showed that microorganism communities under iron reduction in different flooding periods had rapid response on glucose while they showed a later response on pyruvate,comparing to glucose.When pyruvate was used as a carbon source,accumulation of Fe（Ⅱ）reached to a very high level after 30 days incubation.When lactate was used as a carbon source,both of flooding 20 days treatment and 30 days treatment had significant higher accumulation of Fe（Ⅱ）in 15 days incubation than the other treatments.The maximum Fe（Ⅱ）accumulation of this treatment was 538.47 mg.L-1 and rate of Fe（Ⅲ）reduction was 75.81%.During the incubation,pH of solution decreased from neutral to acidic for glucose,stayed around neutral with slight acidic for pyruvate and lactate,and was slightly alkaline for acetate.Diversity of community structure in different flooding period induced the different potential of iron reduction.Various carbon sources could index the different iron reducing microbial community.Iron reducing microbial community in short flooding pe-riod could use glucose and pyruvate as predominant electronic donors while those in longer flooding period used lactate or acetate very well.