太湖地区农田NO排放不连续测量最佳时间

Diurnal Variation of NO Emission from an Ecosystem and the Optimum Observation Time for Intermittent Flux Measurement

以我国南方太湖地区稻麦轮作生态系统的旱地阶段为例，在通过自动连续测量揭示ＮＯ排放的时间变异规律性基础上，讨论了ＮＯ排放不连续测量结果矫正及最佳观测时间选择．根据自动连续测量结果，ＮＯ排放表现出日间极大值型和夜间极大值型２种规律性日变化形式．前者发生在温度比较适宜，但植物生长较弱的情况下，此日变化形式直接与温度有关；后者发生在植物旺盛生长的情况下，且主要取决于植物对铵态氮的吸收，而与温度没有直接关系．在植物生长强弱变换的过渡期，日变化的规律性不明显．不连续测量结果的矫正因子也因植物生长状况而异．当观测时间选择不当，又不进行任何矫正处理时，根据不连续测量结果估计的ＮＯ排放可能偏高１２％ ～４７％ 或偏低１８％ ～６８％ ．无论哪种植物生长情形，１５ｖ００～１６ｖ００都是ＮＯ排放不连续测量的最佳观测时间．这时的观测结果不需要日变化矫正。

Based on a continuous in situ measurement with an automated system during the non flooding period of the rice wheat rotation ecosystem,which is a typical agricultural ecosystem in South China,the diurnal variability of NO emission was analyzed theoretically.Then correction of results from intermittent measurement and the optimum time for intermittent observation were discussed.There are two types of diurnal variation patterns of NO emission from the investigated crop ecosystem.One is day peak pattern and another is night peak pattern.The former continuously occurs under situations with low plant activity and is mainly determined by temperature.The latter,which does not directly depends on temperature,usually occurs under situations with intensive plant activity and is primarily determined by up take of soil ammonium by plant roots.During the transition period,when plant activity gradually decreases,almost no diurnal variation occurs regularly.Correction coefficients are closely correlated to situations of plant activity.If the time for intermittent measurement is not selected perfectly and no correction is performed for the measured data,the NO emission from the investigated ecosystem may be overestimated by 12%～47% or underestimated by 18%～68%.No correction is necessary for measurements carried out at 15∶00～16∶00,which is recommended as the optimum time for intermittent measurement under any situation of plant activity.