| The intensification of global climate changes(such as global warming)seriously affects the grassland ecosystem functions,and grassland aboveground productivity is an important component of grassland ecosystem processes and grassland ecosystem functions.Therefore,it is particularly important to explore the spatial and temporal dynamics of aboveground net primary productivity(ANPP)as well as its climate drivers in the natural grassland.In this study,natural grassland was studied in arid and semi-arid regions.Specifically,the ANPP change in natural grassland was explored from 1980 s to 20l0 s as well as the climate factors.With various statistical methods,we systematically explored the long-term variable trend of grassland ANPP in different grassland ecosystem and the climate driving force which causes the long-term ANPP changing trend in different grassland ecosystems.Moreover,we also explored the spatial variation trend of ANPP in natural grassland along the hydrothermal gradient,and explored the scale effect on spatial variation of ANPP in natural grassland.Those are contributed to understand the impact of global climate change on grassland ecosystems,and the impact of climate change on grassland ecosystems is helpful for exploring terrestrial ecosystem carbon cycle.The study has made the main conclusions:(1)The study area is mainly located at the intersection of the Qinghai-Tibet Plateau,the Loess Plateau and the Inner Mongolia Plateau.With diverse climate types,it has evolved diverse grassland types.The ANPP in different grassland types showed a common decreasing trend,but the variation range of grassland ANPP in different grassland ecosystems was different.The ANPP decreased by 13% in alpine grassland while decrease by 3% in temperate grassland.Compared with the temperate grassland ecosystem,the ANPP in alpine grassland decreased more rapidly,mainly for the sensitive of climate change in alpine grassland.(2)In natural grasslands,the grassland ANPP change is determined by temperature,humidity and radiant energy.When long-term precipitation changes are not significant,temperature(including ground soil temperature and atmospheric temperature)will be the main climate drivers that affect the changing ANPP in natural grassland.The increase of temperature decreases the soil moisture and causes the soil desiccation,which in turn leads to limited vegetation growth and the ANPP transfer into the ground,which ultimately reduces the grassland ANPP.Solar radiation is an essential climate driving factor for the ANPP decline in alpine grassland,and the increase in solar radiation will enhance the effect of temperature on grassland productivity.(3)The study area a is divided into four regions,arid region,semi-arid region,semi-humid region and humid region in terms of humid index.From northwest to southeast of the study area,there is a general trend from dry-hot to wet-cold.From arid region to humid region,the grassland ANPP has increased significantly,but there is no significant variation in dry-hot regions or wet-cold regions.The difference of grassland ANPP in dry-hot regions is not significant due to the hysteresis of grassland plant growth to precipitation,while the difference in grassland ANPP in wet-cold regions is not significant due to the intense species competition with abundant resources.(4)At local and regional scales,the grassland ANPP increases with the increase of humid index,while the coefficient of determination of linear regression model at regional scale is more than twice that of local scale,thus scale effects should be taken into consideration when exploring the relationship between grassland ANPP and surrounding environment.Specifically,the grassland ANPP from dry-hot to wet-cold region increases slowly and then rapidly.The rapid decrease of grassland water use efficiency in dry-hot region is caused by the slow increase of grassland ANPP,while the increase of grassland water use efficiency in wet-cold region is caused by the rapid increase of grassland ANPP. |
PDF Full Text Request