塔里木河下游生态输水对胡杨林生态系统碳循环的影响

Effects of ecological water conveyance on carbon cycle of Populus euphratica forest ecosystem in the lower reaches of Tarim River

2000—2020年期间向塔里木河下游的生态输水有效抬升了下游的地下水位,并对下游胡杨林生态系统的碳循环产生了重要影响。综述了生态输水对塔里木河下游胡杨林生态系统植被固碳作用可能产生的影响,分析了植被类型变化可能对胡杨林土壤有机碳含量和土壤有机碳储量产生的影响,总结了生态输水后胡杨林碳释放关键过程-土壤呼吸对生态输水的响应,解析了间歇性生态输水所致的水淹干扰对胡杨凋落叶分解的影响。综述分析表明,生态输水工程的实施对塔里木河下游荒漠河岸林生态系统的碳固定和碳释放过程均产生了作用,从而对荒漠河岸林生态系统碳循环产生了复杂的影响。总体而言,20 a的生态输水增大了塔里木河下游生态系统碳汇面积,提高了下游胡杨林生态系统植被生产力,遏制了下游胡杨林的退化,使部分裸地逐渐变为草地、林地或灌丛地,这种演变可增加土壤有机碳含量和区域土壤有机碳储量。生态输水所致的地下水位和土壤水分的变化会影响胡杨林土壤碳释放过程,其中胡杨林土壤呼吸速率与地下水位有关,而水淹干扰对胡杨凋落叶质量损失速率产生了影响。

Desert riparian forests are an important vegetation type for inland river valleys in the arid region of northwest China.In the lower reaches of Tarim River,natural Populus euphratica forest ecosystems are dependent on streamflow.Streamflow in the lower reaches(at 321 km)completely ceased since 1972.The soil has been seriously desertified,and plants have seriously degenerated in the region.A series of environmental measures have been taken to restore the natural P.euphratica forest in the lower reaches of Tarim River,including an ecological water conveyance project.In this paper,on the basis of the results of many studies in the last 20 years,the effects of ecological water conveyance on the carbon cycle of natural P.euphratica forest ecosystems in the lower reaches of Tarim River were comprehensively reviewed.The possible effects of ecological water conveyance on carbon sequestration of P.euphratica forest ecosystems were reviewed,and the effects of vegetation type changes on soil organic carbon content and regional soil organic carbon storage in the lower reaches of Tarim River were analyzed.In addition,the rates of soil respiration and P.euphratica leaf litter decomposition of the P.euphratica forest were reviewed.The implementation of ecological water conveyance affected the carbon cycle of the P.euphratica forest in the lower reaches of Tarim River.Overall,with the implementation of the ecological water conveyance,the carbon sink area and vegetation productivity of the P.euphratica forest increased from 2001 to2019.The ecological water conveyance restrained vegetation degradation,and some bare land gradually changed into grassland,woodland,or shrubland,which could increase soil organic carbon content and regional soil organic carbon storage in the lower reaches of Tarim River.The groundwater level and soil moisture were affected by the ecological water conveyance in the lower reaches of Tarim River.The soil respiration rate of the P.euphratica forest was related to the groundwater level,and the mass loss rates of P.euphratica leaf litter were affected by moisture during decomposition in the lower reaches of Tarim River.Carbon cycle changes in desert riparian forest ecosystems in arid areas may have a profound influence on regional and even global climate change.Therefore,under the background of limited water resources,conserving and restoring the desert riparian forest in the lower reaches of Tarim River through an ecological water conveyance project is of great significance.