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近20年来,青藏高原高寒湿地经历了明显的气候变化,从而导致多数湿地水位下降和氮沉降的增加。对于湿地生态系统来说,水位下降意味着土壤通气性能的改善,可能会导致土壤呼吸的增加;而氮沉降的增加可能会降低土壤微生物生物量和pH值,从而可能抑制土壤呼吸。为此,在青海海北高寒草地生态系统国家野外科学观测研究站利用中宇宙(Mesocosm)实验方法,探讨了青藏高原高寒泥炭型湿地土壤呼吸对水位降低和氮添加的响应。结果表明:(1)水位降低显著增强了土壤呼吸,而氮添加对土壤呼吸的影响依赖于水位的变化:对照水位下,氮添加显著抑制土壤呼吸;而水位降低时,氮添加对土壤呼吸速率无显著影响。(2)土壤呼吸速率与地上生物量、枯落物累积量之间呈显著正相关关系,而与根系生物量无显著相关关系。(3)水位降低显著提高了土壤呼吸的温度敏感性,而氮添加对其无显著的影响。因此预测:随着氮沉降的升高,高寒泥炭湿地土壤CO2的排放量将会减少;然而随着暖干化背景下水位的降低,青藏高原高寒湿地会排放更多的CO2。
In the recent 20 years, the alpine wetlands of Qinghai-Tibet Plateau experienced obvious climate change, which led to the decrease of water level and increase of nitrogen deposition in most wetlands. For wetland ecosystems, declining water levels mean improved soil aeration performance, which may lead to increased soil respiration. Increased nitrogen deposition may reduce soil microbial biomass and pH, which may inhibit soil respiration. Therefore, the Mesocosm experiment was used to investigate the response of soil respiration to water level reduction and nitrogen addition in the alpine and semi-humid peat wetlands of Qinghai-Tibet Plateau at the National Field Observation Station of Alpine Grassland Ecosystem in Qinghai. The results showed that: (1) The decrease of water level significantly enhanced the soil respiration, while the effect of nitrogen addition on soil respiration was dependent on the change of water level. Nitrogen addition significantly inhibited soil respiration under the control water level. When water level decreased, the effect of nitrogen addition on soil respiration rate No significant effect. (2) There was a significant positive correlation between soil respiration rate and aboveground biomass and litter accumulation but no significant correlation with root biomass. (3) The decrease of water level significantly increased the temperature sensitivity of soil respiration, while nitrogen addition had no significant effect on it. Therefore, it is predicted that with the increase of nitrogen deposition, CO2 emission in soils with cold soil will decrease. However, more CO2 will be released in the alpine wetlands of Qinghai-Tibet Plateau with the decrease of water level in the context of warming and drying.