【作者】 郎红东；

【导师】 杨剑虹； 郑循华；

【作者基本信息】 西南农业大学 ， 土壤学， 2004， 硕士

【摘要】 当前全球变暖已成为科学界关注的热点问题之一。由此引起的气候环境变化将可能对陆地生态系统产生重要的影响。但是，科学家们对于土壤温度、土壤含水量和土壤CO₂浓度之间确切的内在关系还不是很清楚。因此，我们需要正确理解温度和水分对土壤CO₂浓度的影响，这在预测土壤呼吸对于气候变化的响应方面特别重要。关于大气CO₂浓度升高对农田土壤CO₂浓度的影响研究还处于探索阶段，迄今为止，几乎没有实测数据和相关报道。本文在无锡稻麦轮作麦田试验观测的基础上，对土壤CO₂浓度与土壤温度、含水量之间的关系做了详细的分析，同时利用浓度梯度法初步模拟了地表-大气界面CO₂排放通量，所得结果如下： 1)在0～30cm土层中，土壤CO₂浓度与土壤深度具有稳定的显著相关性，且土壤CO₂浓度分布呈现底层土壤高于浅层土壤的分布规律。底层土壤CO₂浓度比地表的约高10～20倍。在0～30cm土层中，上层土壤气体中的CO₂向上垂直扩散要比下层土壤快。本文所研究的土壤最深层为30cm，对于种植作物的农田，作物旺盛生长期的土壤CO₂浓度在27cm～30cm处已趋于稳定，但更深层土壤CO₂浓度如何变化尚不清楚，有待进一步研究。 2)土壤CO₂浓度与土壤温度呈显著正相关，而且深层的要明显大于浅层。在土壤含水量相对稳定的条件下，实验观测期内土壤温度在15～16℃左右时，土壤微生物活性和呼吸作用最为有利。土壤温度影响土壤空CO₂浓度的机制可以从以下两方面进行解释：（1）直接作用：土壤温度强烈影响微生物和根系活性，进而影响微生物和根系呼吸释放到土壤空气中的CO₂；（2）间接作用：温度升高促进植物根系生长，从而增加根系呼吸向土壤中释放CO₂； 3)无锡地区麦田土壤CO₂浓度与土壤含水量呈正相关性。原因可以解释为：（1）无锡春夏季节，降水充足，土壤处于湿润期。这可以促进土壤呼吸，出现土壤CO₂浓度的高峰值；（2）高土壤含水量和低孔隙度降低了土壤CO₂扩散率从而导致土壤CO₂聚积。浓度升高。（3）大的降雨会阻断土壤向大气释放CO₂的路径，影响土壤CO₂的分布。 4)小麦生长季的土壤CO₂浓度与小麦生长密切相关。三种田间处理的土壤CO₂浓度为：FACE＞对照＞空白。在作物旺盛生长期，大气CO₂浓度升高200μmol mol^-1使0～30cm土层的土壤CO₂浓度显著提高，高浓度的大气CO₂促进了小麦的根系生长，根系分泌物增多，刺激了土壤微生物种群的增长，导致FACE区的根系呼吸和土壤微生物呼吸均强于对照区，从而导致土壤气体中的CO₂浓度增高。大气CO₂浓度升高所致的土壤CO₂浓度偏高，可能将导致土壤内部的理化过程发生变化，这一点有待进一步研究。 5)在土壤含水量较低（本文的结果为34％～41％）的条件下，浓度梯度法能有效地模拟地表—大气界面CO₂排放通量，但由于这种方法是基于土壤含水量和充气孔隙度间接地计算土壤空气扩散系数，因此不能精确地计算地表—大气表面CO₂排放通量，通常模拟所得数据略低于实际值。更多还原

【Abstract】 Assessing the dynamics of gaseous production in soil is of interesting because soil is important sources and sinks of greenhouse gases. Changes in soil air carbon dioxide (CO2) concentrations were studied in a rice-wheat rotation ecosystem in east of China. Concentrations were measured in situ over 6 months period to a depth of 30cm.Based on the measurement and analysis of CO2 concentrations in soil profile, soil temperature and moisture, Some results could be outlined as follows.CO2 concentrations generally increased with depth. CO2 concentrations in soil profiles were about 10~20 times than those in atmosphere. By analyzing respectively under elevated CO2, ambient CO2 and the bare land soil CO2 concentration profiles in wheat fields, some preliminary results were obtained. Within 0 ~ 30 cm in soil depth, CO2 in the pores of the upper soil layers vertically diffused upwards much more quickly than that in the lower soil layers. During the period with active wheat growth, elevated atmospheric CO2 by 200 + 40 nmol-mol-l significantly increased the CO2 concentration in soil air within 0 ~ 30 cm in depth by 14%?% (t-test, P < 0.001), which may lead to changes in soil physical and chemical properties. But further study is required to corroborate these changes.CO2 concentrations in soil air were closely relative to soil temperature and moisture, and it was variation with the wheat up-growth.Not surprisingly, soil temperature was the major driver for soil CO2 concentrations, and it was noted to be a strong and positive predictor of soil CO2 concentrations. It can be explained as follows: Soil temperature strongly effect on the root and soil metabolic activity, accelerating soil microorganism respiration and root respiration, so as to increase CO2 concentrations.Like other results reported in some review articles, soil moisture showed to a certain extent effect on the variability in soil CO2 concentrations. And their relationship showed positive correlation. The influence of moisture content on soil CO2 concentrations is complicated through its effect on respiratory activity of roots and microbes and on transport through the soil.Our studies show that the concentration gradient approach can yield a reasonable estimate of respiration rates under 34~41% soil water content. However, this method is not necessarily accurate and typically underestimates CO2 fluxes, and results showed that representative properties for the soils at the shallowest depth must be accurately determined to apply this method since the effective diffusion coefficient of CO2 is very sensitive to moisture content.更多还原