崇明东滩湿地土壤生物固氮沿潮滩水淹梯度的特征

以长江口崇明东滩为研究区，研究了植被和裸滩表层（0~5cm）土壤固氮速率（BNF）、固氮功能基因（nifH）丰度和理化性质.土壤BNF随着水淹频率增加而降低，即由高潮滩向低潮滩表现出显著的差异（P<0.05）.土壤BNF表现为夏季大于冬季，植被覆盖土壤高于裸滩.夏季植被和裸滩土壤BNF分别为0.61~17.90，1.41~12.10μmol N/（kg·h），冬季分别为0.64~3.54，0.47~2.60μmol N/（kg·h）植被和裸滩土壤nifH丰度分别为（1.28~4.61）×10⁷copies/g和2.56×10⁷~12.3×10⁸copies/g.土壤nifH丰度水平与BNF呈极显著正相关关系（P<0.01）.此外，土壤BNF还受到土壤盐度、硝酸盐、Fe³⁺和总磷的影响.研究结果表明，河口潮滩湿地水淹梯度的变化通过改变土壤微生物和理化性质，进而影响土壤BNF和氮的生物地球化学循环.

Soil biological nitrogen fixation along with hydrological gradient in Chongming Dongtan wetland

In this study, potential rate of nitrogen fixation (BNF), functional gene (nifH) abundance and soil properties were investigated in the rhizosphere soil and bulk soil of Chongming Dongtan wetland in the Yangtze estuary. The rates of soil BNF decreased from high tidal habit to low tidal habit and varied significantly in the water intrusion frequencies (P < 0.05). The rates of BNF were higher in summer than in winter, and higher in rhizosphere soil than bulk soil. The BNF rates ranged from 0.61 to 17.90μmol N/(kg·h) and from 1.41 to 12.10μmol N/(kg·h) in rhizosphere soil and bulk soil in summer, while they were in the range of 0.64~3.54μmol N/(kg·h) and 0.47~2.60μmol N/(kg·h) in winter. The abundances of nifH functional gene ranged from 1.28×10⁷ to 4.61×10⁷copies/g and 2.56×10⁷ to 12.3×10⁸copies/g in rhizosphere soil and bulk soil, respectively. The abundance of nifH gene was significantly related to the rates of BNF (P<0.01). In addition, soil salinity, nitrate, Fe³⁺ and total phosphorus had great influence on BNF activity. Therefore, these results highlight that water intrusion can alter soil microbial quantity and soil properties, which furthermore affect nitrogen biogeochemical cycling.