中国东北地区近50年净生态系统生产力的时空动态

东北地区处于我国最高纬度地区,是全球气候变化最敏感的区域之一,研究东北地区净生态系统生产力对气候变化的响应,对阐明北半球中高纬度陆地生态系统碳源汇格局具有重要意义。基于CEVSA(Carbon Exchange between Vegetation,Soil and Atomasphere)模型,对1961—2010年东北地区净生态系统生产力NEP的时空格局及变化趋势进行分析,并探讨了气候变化与区域碳源汇的关系。结果表明:(1)1961—2010年,东北地区年NEP总量在-0.094PgC/a—0.117PgC/a之间波动,年平均0.026PgC/a,占全国NEP总量的15%—37%。过去50年东北区域NEP没有明显的线性变化趋势,20世纪80年代碳吸收量最高,20世纪90年代后碳吸收量开始下降。(2)东北地区NEP的空间分布呈现出东部高,西部和中部低,北部高,南部低的空间格局。过去50年来,碳源区向大气释放的碳量在减少,碳汇区从大气吸收的碳也在减少。(3)NEP的年际变化与温度呈负相关(r=-0.343,P0.05),与降水呈显著正相关(r=0.859,P0.01),东北地区NEP和年降水量的变化规律基本一致,即同期上升或达到最高值,温度和降水共同作用导致东北地区NEP的年际变化,而年降水量的变化对NEP年际变化起主要作用。在空间上,东北地区NEP与降水呈极显著正相关(P0.01)的面积占研究区域总面积的91.5%,与温度呈显著负相关(P0.05)的面积占31.6%,降水也是决定NEP空间分布的最主要因子。(4)升温伴随降水增加导致1961—1990年NEP呈增加趋势,而其后升温伴随降水减少则是近20年东北区域碳汇能力减弱的重要原因。

Temporospatial variations in net ecosystem productivity in Northeast China since 1961

The northeast of China (c. 44°30' N, 123°40'E) is one of the most sensitive regions to global climate change. Over the last 50 years, meterological records show significant trends for warmer temperatures and reduced precipitation. These changes have significantly influenced the region's carbon balance. Net ecosystem productivity (NEP) represents the net carbon uptake or loss of an ecosystem through biological activity. To help understand, carbon source/sink behavoural patterns in mid- and high-latitude terrestrial ecosystems, it is thus useful to investigate the impact of climate change on NEP in this region. Because NEP cannot be measured directly at regional or global scales, its estimation using models is the only way to proceed. In this study, we analyse the temporospatial patterns and trends of NEP in Northeast China between 1961 and 2010 using the process-based ecosystem model CEVSA(Carbon Exchange between Vegetation, Soil and Atomasphere). We also discuss correlations between regional carbon balance and climate variability, and reveal the effects of warming and precipitation change on NEP. The results show: (1) The NEP for Northeast China fluctuated between -0.094 and 0.117 PgC/a during the 50 years period, with an average value of 0.026 PgC/a. This represents between 15% and 37% of China's national NEP. There were no significant linear trends in NEP during the 50 years period. NEP was highest during the 1980s and the carbon sequestration has decreased since the 1990s. (2) NEP varies within the northeast region. It seems to be generally higher in the east and north, and lower in the west, centre and south. During the 50 years period, carbon release in the carbon-source areas decreased and carbon sequestration in the carbon-sink areas also decreased. (3) Total annual NEP correlated significantly and negatively with mean annual temperature (r=-0.343, P < 0.05) and highly significantly and positively with total precipitation (r=0.859,P < 0.01). Interannual variations in NEP are tightly coupled to changes in mean annual precipitation, with both NEP and precipitation usually either increasing or reaching their highest values at the same time. While both temperature and precipitation affected the interannual variations in NEP, precipitation was the dominant controlling factor. Spatially, annual NEP was positively correlated (P < 0.01) with annual mean precipitation over 91.5% of the region, while annual NEP was negatively correlated (P < 0.05) with annual mean temperature over 31.6% of the region. Therefore, precipitation is considerd to be the dominant factor determining spatial variations in NEP. (4) A period of warming, accompanied by increased precipitation contributed to the trend for increasing NEP between 1961 and 1990. Meanwhile, warming and decreased precipitation were the main causes of a nearly 20 years period of decreasing carbon sequestration.