不同长度秸秆还田对土壤汞甲基化与水稻植株甲基汞富集的影响

Effect of straw returning with different lengths on mercury methylation in paddy soil and methylmercury accumulation in rice plants

为降低秸秆还田引起稻田系统甲基汞(MeHg)升高的风险,采用盆栽试验,研究了添加不同长度水稻秸秆(5 cm、2 cm、粉末)条件下,在水稻整个生长期内土壤汞的甲基化以及水稻植株各组织中MeHg的含量变化特征.结果表明,添加秸秆能显著促进稻田土壤汞的甲基化,并能提升稻米MeHg的富集.不同长度秸秆对土壤MeHg净增长的影响时间不同,较长秸秆能长时间内对土壤汞的甲基化产生促进作用,在水稻生长后期土壤MeHg含量持续偏高,致使晚熟期稻米中MeHg质量浓度偏高;粉碎的秸秆在土壤中能快速降解,尽管在短时间内能引起土壤MeHg含量升高,但在水稻生长后期土壤MeHg含量明显下降,完熟期稻米中MeHg含量也远低于其他两种处理方式.因此,秸秆进行粉碎处理后再还田有利于降低稻米的MeHg富集风险.

To explore a reasonable straw returning pattern to alleviate the methylmercury(MeHg)exposure risk in paddy ecosystems,pot experiments were conducted in this study by adding rice straw with three different lengths(5 cm,2 cm and pulverized rice straw)into paddy soil.The methylation of mercury(Hg)in soil and MeHg distribution in rice plants were investigated during the whole growing period of paddy.The results showed that rice straw returning could promote soil Hg methylation and increase the MeHg levels in rice.The length of straw for returning to field could influence the net MeHg production.The longer straw(5 cm)showed a prolonged promotion for Hg methylation in paddy soil,resulting in higher MeHg concentrations in soil at later growth stage and increased MeHg accumulation in rice.The pulverized rice straw could bring about a MeHg increase in soil in a shorter incubation time,however,MeHg concentrations in soil decreased at later growth stage,which further made a lower rice MeHg compared to other treatments with 5 cm and 2 cm straw.Therefore,it is clear from this study that straw smashing before returning to field could alleviate the methylmercury(MeHg)exposure risk of rice induced by straw returning.