紫色土坡耕地农田生态系统蒸散发与水分利用效率及其影响因素

蒸散发与水分利用效率是农田生态系统碳水循环的重要衡量指标。本研究利用涡度相关技术对紫色土坡耕地生态系统进行连续观测,获取2014—2018年碳水通量数据,分析紫色土冬小麦-夏玉米轮作下的雨养坡耕地农田生态系统蒸散发和水分利用效率变化特征及其对主要环境因子的响应规律。结果表明:紫色土坡耕地农田生态系统蒸散发日变化规律呈单峰型趋势,最大值均在14:00前后出现;一年中8月日蒸散发最高,1月最低;夏季日变化幅度最大,春季次之,冬季和秋季变化较为平缓。叶面积指数、温度为影响紫色土坡耕地蒸散发的最主要因子,其次为饱和水汽压差。水分利用效率在9:00—17:00期间基本呈先下降后回升的变化规律,冬季水分利用效率为全年最高;叶面积指数、CO2通量为影响水分利用效率的主要因子,其次为温度,相对湿度、饱和水汽压差等水分条件也显著影响了水分利用效率。年际差异分析结果表明,紫色土坡耕地夏季玉米生长盛期的水分利用效率对降雨响应更为敏感,同时冬季土壤水分为冬季蒸散发和水分利用效率的关键影响因子。未来仍需对紫色土坡耕地农田生态系统生长盛期蒸散发与水分利用效率动态进行深入研究,从而为探明当地主要作物应对春夏季季节性干旱威胁的系统性策略提供科学依据。

Temporal characteristics and influencing factors of evapotranspiration and water use efficiency on sloping farmlands with purple soil

Evapotranspiration (ET) and water use efficiency (WUE) are important indices of the carbon and water cycles in farmland ecosystems. There are few systematic studies on the water cycle process in the soil-plant-atmosphere continuum in purple soil areas, and analyses of long-term changes in ET and WUE and its influencing factors in agroecosystems are lacking. In this study, the eddy covariance system was used to obtain carbon-water flux data from 2014 to 2018. The dynamic characteristics of ET and WUE in agroecosystems under rain-fed winter wheat-summer corn rotations on sloping farmlands with purple soil and the impact of major environmental factors were analyzed to provide a scientific basis for seasonal drought and rational water responses. The results showed that the diurnal dynamics of ET had a single peak, and the maximum value of each month occurred around 14:00. ET was highest in August and lowest in January. Seasonally, the magnitude of ET diurnal variation was the largest in summer, followed by spring, and there was relatively little variation in winter and autumn. Leaf area index and air temperature were the most important environmental factors affecting ET of the purple soil in sloping farmlands, followed by the vapor pressure deficit. ET had a linear relationship with net radiation and vapor pressure deficit (P<0.05). ET also had an exponential growth relationship with air and soil temperature (P<0.05) but tended to decrease with increasing air relative humidity (P<0.05). The diurnal dynamics of WUE from 9:00 to 17:00 was first decreasing and then increasing. Seasonally, WUE in winter was the largest, and in winter and autumn was higher than in spring and summer. The leaf area index and carbon dioxide (CO₂) flux were the dominant factors affecting WUE of the purple soils in sloping farmland, and air temperature, relative humidity, and vapor pressure deficit were the secondary factors influencing WUE. WUE decreased exponentially with net radiation and soil temperature (P<0.05) and decreased linearly with the increasing air temperature (P<0.05). WUE first decreased and then increased with the soil water content. WUE was significantly negatively correlated with the vapor pressure deficit (P<0.05) and significantly positively correlated with the air relative humidity (P<0.05). The differences between two hydrological years showed that WUE in the maize planting period in summer may be more sensitive to precipitation, and the soil moisture in winter had a significant effect on ET and WUE in the sloping farmlands. Due to the lack of data series during this study, further study of the detailed dynamics of ET and WUE in the purple soil sloping farmland ecosystem is needed to explore the systematic adaptation strategies of seasonal drought in the local crops during spring and summer.