紫色土丘陵区农田源头沟渠一氧化氮排放的季节差异及影响因素

Seasonal Variation in Nitric Oxide Emission from an Agricultural Headwater Ditch in the Hilly Purple Soil Area and the Factors Influencing Emission

农田源头沟渠是农田养分迁移的重要水文通道和非常活跃的氮转化场所.本研究以紫色土丘陵区农田源头沟渠为对象,在2014年12月~2015年11月,采用静态箱-化学发光法对其一氧化氮(NO)排放开展原位观测.结果表明,有自然植被覆盖的农田源头沟渠生态系统(V)中的NO年累积排放量为14.17 g·(hm^2·a)^(-1),而无自然植被覆盖的对照处理(NV,代表沟渠中的沉积物-水界面系统)则为-0.4 g·(hm^2·a)^(-1).总体而言,沟渠生态系统的年综合排放通量是11.27 g·(hm^2·a)^(-1),全年平均排放通量为0.13μg·(m^2·h)^(-1).农田源头沟渠仅在夏季是NO的排放源,且夏季NO累积排放量显著高于(P<0.05)春季、秋季或冬季.沟渠上覆水NO_3^--N浓度和温度是影响NO排放季节变化的主要控制因素.同时,沟渠生态系统中植物存在可显著提高所观测的NO排放通量,但对全年NO累积排放量无显著影响.

Agricultural headwater ditches are important pathways of reactive nitrogen loss from adjacent croplands,and also act as hotspots for reactive nitrogen transformation. In this study,NO emissions from a typical agricultural ditch in the hilly area of central Sichuan Basin were measured by the closed static chamber-chemiluminescence method,from December 2014 to November 2015. The results showed that the cumulative NO emissions from the sediment-water interface without vegetation（ NV） and the ditch ecosystem with natural vegetation（ Ⅴ） were-0. 4 g·（hm^2·a）^-1 and 14. 17 g·（hm^2·a）^-1,respectively. The combined annual NO emission flux for the agricultural headwater ditch ecosystem was 11. 27 g·（hm^2·a）^-1,with a mean NO emission rate of 0. 13 μg·（m^2·h）^-1 A net source of NO from the ditch ecosystem only occurred in summer,which had a significantly higher cumulative NO emission than those in the other seasons. The seasonal variation in NO emissions was mainly regulated by the seasonal changes in NO3^--N concentrations and temperature in the overlying water. Meanwhile,the presence of vegetation in the ditch ecosystem significantly increased NO emission rates,whereas it did not markedly influence the annual NO emission.