崇明东滩湿地沉积物反硝化酶活性对干湿交替过程的响应研究

Denitrifying Enzyme Activities under Alternation of Drying and Rewetting for wetland Sediments in Chongming East Intertidal Flat

滨海湿地周期性干湿交替过程对沉积物氮素转化产生深刻影响，以崇明东滩湿地为原型对象，采集现场沉积物及海水样，通过室内模拟方法研究了沉积物反硝化酶一硝酸还原酶（Nar），亚硝酸还原酶（Nir），羟胺还原酶（Hyr）活性对干湿交替过程的响应。结果表明，半月潮驱动下干湿交替过程中，沉积物从干燥（7％）状态变湿（46％～49％）使Nar、Nir活性迅速增加，较高的酶活性（NO3- -N6．4-9．6mg10g-124h-1；NO2- -N5．5～7．8mg10g-1 24 h-1）至少维持24h以上；变干过程中，当含水量降至10％左右时，Nar活性短暂升高后逐渐降至很低水平，Nir活性呈现低但稳定的变化特征。Et潮驱动下的干湿交替过程中，Nar、Nir活性分别稳定的变化在NO3--N14．7±2．1mg10g-124h-1和NO2- -N8．7±1．8mg10g-124h-1；沉积物短暂淹水期间Hyr表现出较高活性。持续淹水过程中，Nar、Nir活性变化在N03--N10-3～13．9mg10g-124h-1和NO2 --N6．6-9．6mg10g-1·24h-1；Hyr活性随淹水时间的持续有所增加但变异性较高。滨海湿地中、低潮滩带沉积物Nar、Nir活性相似并明显高于高潮滩带沉积物的酶活性，变干过程两种酶的活性低于较高含水量时沉积物的酶活性。

Periodic alternation of drying and rewetting for intertidal sediments in coastal wetland is physically characterized by four kinds of special cycle periods, semi-lunar and diurnal tides, desiccated and waterlogged systems, which produces strong influence on nitrogen transformation in sediments. In order to uncover the influence, sediment samples from Chongming east intertidal flat were incubated under the four simulated conditions, and the activities of denitrifying enzyme in sediments, including nitrate reductase （Nar）, nitrite reductase （Nir） and hydroxylamine reductase （Hyr）, were assayed. During the cycle of semi-lunar tide （sediments from high tidal flats）, the process of rewetting the dry sediments （from 7% to 46% - 49%） effectively enhanced Nar and Nir activities. The Nar and Nir activities increased from NO3--N 6.4 - 9.6 mg 10 g-1 24 h-1 and NO2--N 5.5 - 7.8 mg 10 g-1 24 h-1, respectively, maintaining a duration of 〉24 hours. Nar activity variations appeared a short-term increase and then decreased gradually during the drying period when the moistures failed to about 10%, while Nir activities failed into a low and almost constant level. In contrast, Nar and Nir activities in sediment from middle tidal flats varied stably with means of NO3--N 14.7 ± 2.1 mg 10 g-1 24 h-1 and NO2--N 8.7 ± 1.8 mg 10 g-1 24 h-1 during the cycle of diurnal tide, respectively. The Hyr activities appeared a short increase during the period of inundation. Under the waterlogged condition, Nar and Nir activities in sediment from low tidal fiats ranged stably between NO3--N 10.3 and 13.9 mg 10 g-1 24 h-1, and NO2--N 6.6 and 9.6 mg 10 g-1 24 h-1. Hyr activities increased to addition, sediments in low and middle tidal flats had a certain degree with higher variation during the incubation. In similar activities of Nar and Nir which were higher than those of sediments in high tidal fiats. It could be noted that the Nat and Nir activities during than those when the sediment had high water content.