不同放牧条件下锡林郭勒草原冻融作用对土壤水热及温室气体排放的影响

发布时间：2018-11-21 09:28

【摘要】：我国作为世界第三冻土大国,多年和季节性冻土面积占陆地面积的75%,主要分布在青藏高原和内蒙古高原等气候变化敏感区。冰雪覆盖、土壤冻结及其消融过程,会显著改变土-气界面水热交换和平衡特征。尤其是近年来全球变暖引起冰冻区消退加速,以及人类活动对自然环境的影响日益加深,有关冻土水文效应及其温室气体排放的评价越来越得到重视。本研究依托中国科学院内蒙古草原生态系统定位研究站,选取区域内具有不同围牧年限以及放牧条件下的三种土地利用方式(UG79(1979年以来禁牧)、UG99(1999年以来禁牧)、HG(1979年以来持续放牧))作为研究对象。依据测定结果探讨不同放牧条件下冻融交替对土壤水分、温度以及土壤温室气体排放的影响,为准确评估变化环境下(全球变化和土地利用变化)内蒙古季节性冻土区土壤冻融的水文效应以及N_2O排放提供更准确的科学依据。本试验研究结果表明:1、一定厚度的积雪可以有效隔绝气温的影响,从而降低土壤温度下降幅度。HG处理积雪厚度远小于其它处理,其土壤温度变化最剧烈,土壤冻结和融化速率最快。浅层土壤(0~30 cm)UG79和UG99处理土壤温度明显高于HG处理,而在深层100 cm深度处三种放牧条件下土壤的温度变化趋势基本一致,放牧对深层土壤温度的影响有限。2、土壤冻结期,UG99“聚墒区”分布范围最广,且集中在牧草根系发达区域,对牧草根系层的储水保墒效果最佳。土壤消融期,土壤液态含水量高于冻融前,表层土壤UG99液态含水量增加幅度大于UG79和HG处理,其最大值达到了0.19 m3/m3,“冻后聚墒”效应最为明显,为春季植被的生长发育提供了良好的水分环境。3、锡林郭勒草原CO_2排放通量主要集中在生长季和非生长季的解冻期。尽管解冻期对于全年CO_2排放量的贡献很低,但其CO_2累积释放量占非生长季排放量的50%以上,在年际尺度上对CO_2的排放起促进作用。CO_2排放通量与土壤温度表现出极显著正相关关系,但与土壤含水量无显著相关关系。4、在土壤冻结期(11月~2月),不同处理部分土层表现为弱“汇”,而土壤解冻期N_2O存在脉冲式集中释放,在全年排放总量中有着举足轻重的作用。土壤温度及含水量对N_2O影响相对复杂,研究区N_2O排放与土壤温度水分无显著的相关性。非生长季和冻融期HG处理N_2O累积排放通量高于UG79、UG99处理,其原因可能与研究样地以及放牧年限有关。
[Abstract]:As the third largest permafrost country in the world, China accounts for 75% of the land area for many years and seasonal permafrost, mainly distributed in the sensitive areas of climate change such as the Qinghai-Tibet Plateau and the Inner Mongolia Plateau. Ice and snow cover, soil freezing and melting process will significantly change the characteristics of soil-gas interface hydrothermal exchange and balance. Especially in recent years, global warming has accelerated the retreat of frozen regions, and the impact of human activities on the natural environment has become more and more serious. More and more attention has been paid to the evaluation of hydrological effects of frozen soils and their greenhouse gas emissions. Based on Inner Mongolia grassland ecosystem location Research Station of the Chinese Academy of Sciences, this study selected three land use patterns (UG79 (no grazing since 1979) and UG99 (no grazing since 1999) in the region with different grazing years and grazing conditions. HG (continuous grazing since 1979) was used as the research object. The effects of freeze-thaw alternation on soil moisture, temperature and greenhouse gas emissions under different grazing conditions were studied. It provides a more accurate scientific basis for accurately evaluating the hydrological effects of soil freezing and thawing and N2O emission in seasonal frozen soil regions of Inner Mongolia under changing environment (global change and land use change). The results of this experiment show that: 1. The snow cover with a certain thickness can effectively insulate the effect of temperature, thus reducing the decrease of soil temperature. The thickness of snow in HG treatment is much smaller than that in other treatments, and the change of soil temperature is the most severe. The freezing and melting rate of soil is the fastest. The temperature of shallow soil (0 ~ 30 cm) treated with UG79 and UG99 was significantly higher than that of HG treatment, but the variation trend of soil temperature at the depth of 100 cm was basically the same, and the effect of grazing on the temperature of deep soil was limited. 2. During the period of soil freezing, UG99 was the most widely distributed area and concentrated in the developed area of forage root system, which had the best effect on water storage and moisture conservation of forage root layer. During the period of soil ablation, the water content of liquid soil was higher than that before freezing and thawing, and the increase of liquid water content of UG99 in surface soil was larger than that of UG79 and HG, and the maximum value was 0.19 m3 / m3, and the effect of "accumulating moisture after freezing" was the most obvious. It provides a good water environment for the growth and development of vegetation in spring. 3. The CO_2 emission flux of Xilinguole grassland is mainly concentrated in the thawing period of growing season and non-growing season. Although the thawing period contributed very little to the annual CO_2 emissions, the cumulative release of CO_2 accounted for more than 50% of the non-growth season emissions. CO_2 emission flux was positively correlated with soil temperature, but had no significant correlation with soil moisture content. 4. During the period of soil freezing (November to February), the emission flux of CO_2 was positively correlated with soil temperature. Some soil layers of different treatments showed weak "sink", while the pulse concentrated release of N _ 2O existed in the thawing period of soil, which played an important role in the total emission of the whole year. The effect of soil temperature and water content on N2O is relatively complex. There is no significant correlation between N2O emission and soil temperature and moisture in the study area. The cumulative emission flux of N2O in HG treatment in non-growth season and freeze-thaw period was higher than that in UG79,UG99 treatment, which may be related to the study land and grazing years.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S812

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