降水时间对内蒙古温带草原地上净初级生产力的影响

全球气候变化下降水时间的改变将深刻影响草原生态系统地上净初级生产力(ANPP),而草原生态系统ANPP是区域碳循环的重要过程.利用1998-2007年的SPOT-VEG NDVI数据并结合111个样点的ANPP地面样方调查数据,获得了内蒙古温带草原1998-2007年的ANPP区域数据,依此分析了中国内蒙古温带草原以及区域内的3种植被类型(荒漠草原、典型草原、草甸草原)降水时间对ANPP的影响.研究结果表明,对于整个内蒙古温带草原来说,一个水分年内(从上一年9月份到当年地上生物量达最大值时的8月份)影响ANPP较为重要的降水月份为2-7月份,其中,5-7月份降水尤为重要.具体到每个月降水的影响,研究发现,7月份降水最重要,而仍处于生长季的8月份降水相对于其他生长季降水作用最小;影响不同草地类型最重要的降水时期存在一定差异,对荒漠草原和典型草原地区来说,ANPP达最大值前3个月(5-7月份)的生长季降水最重要,而8月份降水影响较小,而草甸草原地区8月份和非生长季的3、4月份降水最重要,但各个降水时期降水对ANPP的影响都较荒漠草原和典型草原小,大部分地区降水对ANPP的影响不显著.

Effects of precipitation timing on aboveground net primary productivity in inner mongolia temperate steppe

Aboveground net primary productivity (ANPP) of grassland ecosystems is one of critical processes in regional carbon cycle, and is dramatically impacted by concomitant changes in precipitation timing in the context of global climate change. In this study, we firstly acquired ANPP data of the entire Inner Mongolia temperate steppe from 1997 to 2008 with a statistic model, which was derived from linear regression between SPOT-VEG NDVI data in August (from 1997 to 2008) and field ANPP data obtained at 111 specific sites. Secondly, we addressed effects of precipitation timing on ANPP for the entire Inner Mongolia temperate steppe and further for its three main component grassland types (desert steppe, typical steppe, and meadow steppe). Our results demonstrated that, for the entire Inner Mongolia temperate steppe, precipitation periods from February to July was the relatively important periods that affected ANPP during the whole water year (defined here as the 12-month period from September of previous year to August of the current year when the aboveground biomass reaches its peak), while the period from May to July was the most important. In terms of occurrence of monthly rain, rain in July had the greatest effect on ANPP, while rain in August, although still one of the growing months, had the minor effect. With respect to the grassland types, the desert steppe and typical steppe received the greatest impact from the precipitation from May to July, which is in accordance with the observation from the entire temperate steppe, while ANPP of the meadow steppe was relatively little affected by the timing of precipitation, evidenced by not significant (P>0.05) correlations between precipitation of different periods in most area of meadow steppe. Spatial pattern of most meaningful timing (month, different accumulated periods) of rainfall was consistent with the analysis of correlation coefficients, which showed that precipitation from May to July was the most meaningful accumulated period for ANPP of most of the entire Inner Mongolia temperate steppe. In terms of monthly rain, rain in July was most important in almost 40% of the area. Also, spatial pattern was grassland type specific. Most part of the desert steppe and typical steppe was affected by precipitation during May to July, while the meadow steppe was mostly affected by rain in current month when ANPP reached its peaks (August) and non-growing season rain of March.