荒漠草原与典型草原NPP、碳积累对不同降雨年份和利用方式的响应

Response of net primary productivity and C accumulation of plant communities in desert steppe and semiarid steppe with different land use types during two hydrologically contrasting growing seasons

不同草原利用方式正在影响着内蒙古的草原生态系统,而且在未来降水空间格局变化的背景下,它们共同决定了生态系统植被类型、净初级生产力(NPP)和生态系统碳积累。选取内蒙古中部两个重要的草地类型:荒漠草原和典型草原,研究不同草原利用方式(围栏禁牧、划区轮牧、割草、自由放牧)植物群落在降雨量不同的两个生长季节地上(ANPP)、地下净初级生产力(BNPP)的变化,同时也评估了植物群落的碳积累,研究结果表明:1)在降雨量亏缺年份,与围封相比,荒漠草原自由放牧区ANPP、BNPP及碳积累分别下降了57.1%、51.7%和56.0%,而典型草原自由放牧区分别下降了18.4%、25.1%和17.9%。2)在降雨量充足年份,与围封相比,荒漠草原划区轮牧区ANPP、BNPP以及碳积累分别增加了18.2%、9.8%和21.9%,而典型草原各处理下围封禁牧区ANPP仍是最高;3)两种草地类型下,降雨量对自由放牧的调控作用高于其它草地利用方式;4)荒漠草原ANPP在丰雨年是欠雨年的2倍,而典型草原仅增加了79.0%,降雨量对荒漠草原生产力的季节调控作用远高于典型草原。在未来全球气候变暖和降水格局变化的情况下,荒漠草原降雨量是影响荒漠植物群落NPP和碳积累的主导因子。

Climate change scenarios predict increases in temperature,changes in precipitation patterns and longer drought periods in most arid and semi-arid regions of the world.Land-use type changes are considered to be the dominant component of global change in terms of impacts on terrestrial ecosystems.Ecosystems in these regions are prone to land degradation,which may be aggravated by climate change.With a changing climate,the effect of different use types and the intensity of changes in the spatial patterns of precipitation will combine to determine ecosystem vegetation types,net primary productivity and C accumulation in the grassland ecosystems of Inner Mongolia,China.A field experiment with different land use types was conducted in two important grassland types in Inner Mongolia：desert steppe（ a site in Sunite Banner）and typical steppe（ a site in Baiyinxile Banner） to study the response of arid and semi-arid grasslands to different land-use types and precipitation.The change of above-ground net primary productivity（ ANPP） and below-ground net primary productivity（ BNPP） for each plant community was studied and C accumulation of the plant communities were also assessedfor four different land use types 1） enclosure,2） rotational grazing,3） clipping and 4） grazing during two hydrologically contrasting growing seasons（ a dry season and a wet season） both in a desert steppe and in a semiarid steppe.The results follow：1） In the deficit precipitation year,compared with the enclosure,ANPP,BNPP and C accumulation decreased by57.1%,51.7% and 56.0% and by 18.4%,25.1% and 17.9% under grazing in the desert steppe and the typical steppe,respectively;meanwhile,in the adequate precipitation year,compared with enclosure,ANPP,BNPP and C accumulation increased by 18.2%,9.8% and 21.9% under rotational grazing in the desert steppe,respectively,whereas ANPP was still the highest in enclosure in the typical steppe;2） Different grassland use types also have a significant effect on ANPP,BNPP and C accumulation.Compared with other use types,the grazing enclosure was a reasonable land use types both in desert and typical steppe to increase ANPP,BNPP and C accumulation;3） The different grassland use types had different responses to the change of interannual precipitation.The effect of precipitation on grazing was higher than on other land use types in both the desert steppe and the typical steppe;4） The ANPP in the wet year was twice that of the dry year in the desert steppe,but ANPP only increased by 79.0% in the wet year when compared with the dry year in the typical steppe.The impact of precipitation was larger on the desert steppe than on the semiarid steppe.ANPP,BNPP and C accumulation in arid and semiarid ecosystems are primarily limited by precipitation.A change of temporal and spatial patterns for precipitation plays an important role in determining ANPP,BNPP and C accumulation.Under future climate change scenarios,precipitation and grassland use types were the principal environmental factors affecting plant community net primary productivity and C accumulation in the arid and semi-arid steppe in northern China.