黄河三角洲湿地土壤氮库沿水盐梯度的时空分布特征

Spatial and seasonal changes in soil nitrogen astocks along a water and salinity gradient in the Yellow River Delta,China

为了分析湿地土壤总氮沿水盐梯度的时空分布规律,以黄河三角洲湿地为研究对象,沿自河向海的水盐梯度设置3条样带(每条样带上包括假尾拂子茅湿地(S1)、香蒲湿地(S2)、芦苇湿地(S3)、柽柳和盐地碱蓬湿地(S4)和盐地碱蓬湿地(S5)共5类湿地),于2014—2015年的4个季节在样带上的各类型湿地内采集50cm深的剖面土壤并测定土壤总氮及其他理化性状.研究结果表明:在水平方向上,湿地表层(0~10cm)土壤总氮沿水盐梯度总体呈现先下降后上升的趋势,最高值出现在低盐湿地的S2样地,最低值出现在高盐湿地的S4样地;但各类湿地0~50cm的土壤全氮质量分数基本上不存在显著差异(P>0.05).在垂直方向上,低盐和中盐湿地总氮主要累积在20cm以上土壤,占50cm深土壤氮储量的50%左右,中盐湿地底部土层氮储量也相对较高;低盐和高盐湿地土壤总氮质量分数及储量总体上沿土壤剖面深度呈现下降趋势,中盐湿地土壤总氮则随深度增加呈现先下降后上升的变化趋势.相关分析表明,土壤总氮质量分数及储量与水土质量比、黏粒、粉砂粒和有机碳呈显著正相关关系(P<0.05),与钠离子、镁离子、氯离子、氯离子与硫酸根摩尔比、钠吸附比、pH、容重、沙粒质量分数和碳氮比呈显著负相关关系(P<0.05).

Soil samples were collected to the depth of 50 cm in three sampling belts in the Yellow River Delta,including Calamagrostis pseudophragmites wetlands（S1）, Typha orientalis wetlands（S2）,Phragmites australis wetlands（S3）,Tamarix chinensis and Suaeda salsa wetlands（S4）and Suaeda salsa wetlands（S5）along a water and salt gradient in each sampling belt in four sampling seasons in 2014 and 2015.Total nitrogen contents and other selected soil properties were analyzed to examine the effects of water and salinity changes on soil total nitrogen contents and stocks along the water and salt gradient.Total nitrogen in the top 10 cm soils showed a‘decreasing-then-increasing＇tendency along the water and salinity gradient,with the highest level at S2 and the lowest at S4.For the top 50 cm soils,no significant differences in average total nitrogen were observed in five sampling sites（P〈0.05）.Soil nitrogen contents and stocks generally decreased in both low-and high-salinity wetlands along the soil profile.However,soil nitrogen in medium-salinity wetland increased after an initial decrease.Soil total nitrogen in wetlands with low-and high-salinity mainly accumulated in the top 20 cm soils,accounting for about 50% of the nitrogen stocks in the top 50 cm soils.However,soil nitrogen stocks of〉40-50 cm soils in medium-salinity wetlands ranked only second to the 0-10 cm soils and were higher than other three soil increments.Correlation analysis showed that soil nitrogen contents and stocks were positively correlated with soil moisture,clay,silt and soil organic carbon（P〈0.05）,but a negative correlation was observed between soil nitrogen and Na^＋,Mg^2＋,Cl^-,Cl^-/SO4^2- ratio,SAR,pH,bulk density,sand and C/N ratio（P〈0.05）.