Cd胁迫对湿地沉积物反硝化与氨化相对重要性的影响
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摘要
【目的】探讨全球变暖及人为活动加速背景下,重金属对滨海湿地氮素转化的影响,揭示湿地沉积物中镉(Cd)含量及其形态变化对沉积物反硝化(Den)和硝态氮氨化(DNRA)强度及二者相对重要性(Q_(DNRA/Den))的影响。【方法】采集崇明东滩湿地3种覆被(芦苇、互花米草和光滩)类型下的沉积物,外源添加不同剂量的Cd,借助~(15)N同位素示踪技术观测沉积物Den和DNRA强度的变化,分析不同含量及形态Cd的影响。【结果】添加低剂量Cd(0.05～0.30 mg/kg)条件下,3种覆被类型沉积物的Q_(DNRA/Den)均明显升高(6.9%～53.4%),硝态氮的还原趋向DNRA途径。相比较而言,互花米草植被下沉积物的Q_(DNRA/Den)高出芦苇3.1～5.4倍。这表明,互花米草植被可能加速沉积物中硝态氮通过DNRA途径还原。此外,芦苇植被下沉积物Den、DNRA强度主要受可交换态和可还原态Cd的影响,但互花米草植被下主要为可氧化态Cd。【结论】滨海湿地沉积物中低剂量Cd刺激硝态氮的还原趋向DNRA途径,影响沉积物Den、DNRA强度的Cd形态因覆被类型不同而存在明显差异。
【Objective】Variations in and unreliability of nitrogen transformation under heavy metal stress in coastal wetland ecosystems, caused by global warming and increasing anthropogenic activities, have drawn much attention. In this study, we aimed to examine the relative importance of denitrification(Den) and dissimilatory nitrate reduction to ammonium(DNRA) in sediments with various Cd contents.【Method】Sediment samples were obtained from under Phragmites australis, Spartina alterniflora community and mudflats without vegetation in the Chongming Dongtan wetlands. Den and DNRA rates in the sediments were measured using the ~(15)N isotope tracing technique after incubation with various concentrations of Cd. The effectiveness of Cd was evaluated using the modified BCR 3 step sequential extraction method.【Result】Low doses of Cd(0.05-0.30 mg/kg) increased DNRA/Den values by 6.9%-53.4%, indicating nitrate reductions in sediments being induced mainly with DNRA pathway. In contrast, the ratios under Spartina alterniflora community were 3.1 to 5.4 times higher than those under Phragmites australis community. This suggests that Spartina alterniflora community may be beneficial for nitrate reductions via the DNRA pathway. In addition, Den and DNRA rates under Phragmites australis community were mainly dominated by exchangeable and reducible Cd in the sediments, whereas the content of oxidized Cd substantially affected the relative importance of Den and DNRA under Spartina alterniflora community. 【Conclusion】Low doses of Cd input in coastal wetlands probably stimulate nitrate reduction in sediments by enhancing the DNRA pathway. Cd fractions affecting Den and DNRA rates significantly depend on the vegetation type.
【Objective】Variations in and unreliability of nitrogen transformation under heavy metal stress in coastal wetland ecosystems, caused by global warming and increasing anthropogenic activities, have drawn much attention. In this study, we aimed to examine the relative importance of denitrification(Den) and dissimilatory nitrate reduction to ammonium(DNRA) in sediments with various Cd contents.【Method】Sediment samples were obtained from under Phragmites australis, Spartina alterniflora community and mudflats without vegetation in the Chongming Dongtan wetlands. Den and DNRA rates in the sediments were measured using the ~(15)N isotope tracing technique after incubation with various concentrations of Cd. The effectiveness of Cd was evaluated using the modified BCR 3 step sequential extraction method.【Result】Low doses of Cd(0.05-0.30 mg/kg) increased DNRA/Den values by 6.9%-53.4%, indicating nitrate reductions in sediments being induced mainly with DNRA pathway. In contrast, the ratios under Spartina alterniflora community were 3.1 to 5.4 times higher than those under Phragmites australis community. This suggests that Spartina alterniflora community may be beneficial for nitrate reductions via the DNRA pathway. In addition, Den and DNRA rates under Phragmites australis community were mainly dominated by exchangeable and reducible Cd in the sediments, whereas the content of oxidized Cd substantially affected the relative importance of Den and DNRA under Spartina alterniflora community. 【Conclusion】Low doses of Cd input in coastal wetlands probably stimulate nitrate reduction in sediments by enhancing the DNRA pathway. Cd fractions affecting Den and DNRA rates significantly depend on the vegetation type.
引文
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[8] 杨杉,吴胜军,蔡延江,等.硝态氮异化还原机制及其主导因素研究进展[J].生态学报,2016,36(5):1223-1232.DOI:10.5846/stxb201407181464.YANG S,WU S J,CAI Y J,et al.The synergetic and competitive mechanism and the dominant factors of dissimilatory nitrate reduction processes:a review [J].Acta Ecologica Sinica,2016,36(5):1223-1232.
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[11] 徐莎,陈圆,印杰,等.典型滨海湿地沉积物反硝化与硝态氮氨化相对重要性研究[J].南京林业大学学报(自然科学版),2016,40(2):9-15.DOI:10.3969/j.issn.1000-2006.2016.02.002.XU S,CHEN Y,YIN J,et al.The relative importance of dissimilatory nitrate reduction to ammonium and denitrification in sediments in a typical coastal wetland [J].Journal of Nanjing Forestry University (Natural Sciences Edition),2016,40(2):9-15.
[12] 韩建刚,曹雪.典型滨海湿地干湿交替过程氮素动态的模拟研究[J].环境科学,2013(6):2383-2389.DOI:10.13227/j.hjkx.2013.06.054.HAN J G,CAO X.Effects of drying-rewetting alternation on nitrogen dynamics in a typical coastal wetland:a simulation study [J].Environmental Science,2013(6):2383-2389.
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[16] 马俊,傅成诚.不同剂量外源重金属注入对土壤重金属形态分布的影响[J].科学技术与工程,2016,35(16):129-135.DOI:10.3969/j.issn.1671-1815.2016.35.020.MA J,FU C C.Effect of different doses of exogenous heavy metals on the fractionation of heavy metals in soil [J].Science Technology and Engineering,2016,35(16):129-135.
[17] 傅成诚,周亮,梅凡民.塿土中外源重金属Pb、Zn、Cd 形态分布随时间变化的规律[J].土壤与作物,2012,1(4):199-204.FU C C,ZHOU L,MEI F M.Changes of form for exogenous heavy metals Pb,Zn and Cd in Lou soil [J].Soil and Crop,2012,1(4):199-204.
[18] 周健,李虎,李晓林,等.外源Cd胁迫下施污土壤中重金属的形态特征和土壤酶活性的关系[J].环境化学,2016,35(10):2036-2043.DOI:10.7524/j.issn.0254-6108.2016.10.2016031404.ZHOU J,LI H,LI X L,et al.The relationship between forms of Cd and soil enzymatic activities in sludge-amended soil [J].Environmental Chemistry,2016,35(10) :2036-2043.
[19] 刘霞,刘树庆,王胜爱.河北主要土壤中重金属镉、铅形态与土壤酶活性的关系[J].河北农业大学学报,2002,25(1):33-37.DOI:10.3969/j.issn.1000-1573.2002.01.009.LIU X,LIU S Q,WANG S A.The relationship between heavy metal forms and soil enzymatic activities in the main soils of Hebei Province [J].Journal of Agricultural University of Hebei,2002,25(1):33-37.
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