节水灌溉稻田土壤呼吸变化及其影响因素分析

为了揭示节水灌溉稻田土壤呼吸变化特征及其影响因素,基于蒸渗仪试验结果,分析了不同灌溉模式对稻田土壤呼吸速率日变化的影响,阐明了土壤呼吸速率对节水灌溉干湿交替过程的响应;同时,分析了节水灌溉稻田土壤呼吸速率的影响因子。结果表明,在处理间土壤水分状况差异较小的生育阶段,节水灌溉和常规灌溉稻田土壤呼吸速率日变化规律基本一致;在处理间水分差异较大的生育阶段,控灌稻田土壤呼吸日变化幅度较大,且速率和变化幅度均要大于常灌稻田土壤。控灌稻田全生育期土壤呼吸速率日变化均值为常灌稻田的1.47倍。控灌稻田土壤一般在复水和脱水的临界点上会出现土壤呼吸速率峰值。控灌稻田土壤呼吸速率受土温和土壤水分影响较大。稻田土壤呼吸速率与5 cm土温有较好的指数相关性,控灌稻田土壤达到了显著水平(P0.05)。土壤体积含水率在35%~55%之间时,土壤体积含水率43%为控灌稻田土壤呼吸的一个临界值,当土壤体积含水率低于临界值时,土壤呼吸速率随着土壤含水率的升高而逐渐增大(P0.05),当土壤体积含水率超过临界值时,土壤呼吸速率随着土壤含水率的增大而降低(P0.05)。研究结果为更加全面地评价节水灌溉的生态环境效应,同时为准确评估稻田生态系统碳源/汇特征提供依据。

Changes of soil respiration of paddy fields with water-saving irrigation and its influencing factors analysis

Abstract: The temporal and spatial variation of soil respiration of farmland has great influence on regional and global carbon cycle. Irrigation is an important factor to soil respiration in farmland. Existing study on the effect of irrigation on farmland soil respiration mainly focused on the dry farmland, but less research focused on paddy fields. Relationships between soil respiration and water depth and short-term drying of paddy fields with flooding irrigation were analyzed in existing studies. In order to reveal the difference of soil respiration in paddy fields with water-saving irrigation and traditional irrigation, the diurnal variation of soil respiration, the impact of alternation of wetting and drying on soil respiration, and the influencing factors of soil respiration for paddy fields were analyzed based on lysimeter experiment. The results showed that diurnal variations of soil respiration of paddy fields with water-saving irrigation and normal irrigation were similar at the period when the status difference of soil moisture was small between the two irrigation modes. Diurnal variations of soil respiration of paddy field with water-saving irrigation showed wider range, and the fluxes and rangeability of soil respiration of paddy field with water-saving irrigation were larger than those for traditional irrigation when the status difference of soil moisture was large. The mean value of soil respiration of diurnal variation during the whole growth period for water-saving irrigation was 1.47 times that for traditional irrigation. But during early tillering stage, jointing-booting stage and milk stage in which water managements were obviously different, the mean values of soil respiration diurnal variations for water-saving irrigation were 3.85, 1.42 and 3.74 times those for traditional irrigation. This results could contribute to frequent alternation of wetting and drying of paddy fields with controlled irrigation. The processes of soil rewatering and soil moisture depletion both had a certain effect on soil respiration of paddy fields. Peaks of soil respiration appeared at the critical point of soil moisture depletion. In the critical point of soil rewatering, the increase of soil respiration rate was not obvious if the rewatering depth was thicker, and the increase was significant if the rewatering depth was thinner. And small peaks of soil respiration appeared when soil water content decreased close to the lower limit of soil water content of paddy field with controlled irrigation during the irrigation interval. Soil temperature and soil moisture had great impact on soil respiration of paddy field with water-saving irrigation. Good exponential dependence was showed between soil respiration flux and soil temperature in the depth of 5 cm in paddy fields, and the correlation reached significant level for paddy field with water-saving irrigation (P<0.05). Management mode without water layer for controlled irrigation led the soil moisture conditions to be similar to dry farmland, so the relationship between soil respiration and soil temperature of paddy fields with controlled irrigation was more consistent with the existing results in dry farmland and forest. Water layer was kept in field surface for a long time under traditional irrigation, which led the soil into strict anaerobic conditions, and the effects of soil temperature on soil respiration was relatively weaken. The soil volumetric moisture content of 43% was the critical point for soil respiration of paddy field with water-saving irrigation when the soil volumetric moisture content ranged from 35% to 55%. Soil respiration flux in paddy field with water-saving irrigation increased with the enhancement of soil moisture content when the soil volumetric water content was lower than the critical value (P<0.05). And soil respiration flux in paddy field with water-saving irrigation decreased with the increase of soil moisture content when the soil volumetric water content was larger than the critical value (P<0.05). This conclusion was consistent with the existing research results. The appropriate soil volumetric moisture content was about 43%, which could create a suitable environment for respirations of rice roots, soil microbes and so on, and increase soil respiration rate. The results of this paper can support for more comprehensively evaluating the ecological environment effect of rice water-saving irrigation. At the same time, it can be helpful to accurately evaluate the carbon source/sink features of paddy field ecosystem.