温性草原利用方式对生态系统碳交换及其组分的影响

为了解管理利用方式变化对原本以放牧利用为主的草地生态系统的碳交换及碳平衡将产生怎样的影响。在中国北方温性草原区域利用连接同化箱的便携式红外分析系统,在相互毗连的地块调查了3种典型草地管理利用方式植被生长旺季的生态系统碳交换及其精细组分。结果表明,相比放牧草地,开垦农用显著降低生态系统的日均碳交换(下降56%,P0.05),而长期围封也趋向降低生态系统的日均碳交换,但变化并不显著(P0.05)。与之近似,NPP在放牧与禁牧草地间差异不显著,开垦农用使NPP显著下降,但降幅小于NEP。GPP在3种管理利用方式间差异相对较小。生态系统总呼吸、自养、异养、地上和地下呼吸在放牧和禁牧草地间均无显著差异,均显著低于开垦后的麦田,根系呼吸在3种管理利用方式间无显著变化。相比草地放牧,草地开垦显著增加自养呼吸在总呼吸中的占比,而土壤呼吸和根系呼吸的占比均显著下降,禁牧对呼吸组成的影响不明显。不同管理利用方式草地的地下生物量能很好的解释土壤呼吸占比(95%)和根系呼吸占比(77%)的变化,而LAI则与自养呼吸占比显著正相关(P0.001)。草地开垦利用增强生态系统的碳释放、减少CO_2固定,相比开垦农用,禁牧对放牧草地碳交换及其组分的影响相对较小。

The impact of different land uses and management strategies on ecosystem carbon exchange and its components in a typical temperate grassland area

Land use change and new management strategies have extensively and rapidly altered farming-in the pastoral ecozone of the northern China temperate steppe. Little is known about ecosystem carbon exchange responses to human-induced land use change, which limits the accurate evaluation of the regional carbon balance and its climatic consequences. The influence of three typical land use patterns on the farming-pastoral ecozone in northern China temperate steppe and ecosystem carbon exchange and its components were investigated by studying the components of ecosystem carbon exchange in three ecosystems. These were grazing, no grazing, and steppe cultivated cropland on adjacent areas in Xilinhot, Inner Mongolia. This study used the chamber attached portable infrared analysis system (Li-6400) to investigate the effects of these three land uses on carbon exchange. The results showed that steppe cultivated cropland significantly decreased the daily ecosystem carbon exchange (56% lower, P<0.05) compared to grazed steppe. Long term grazing exclusion tended to decrease carbon exchange and its components, but the decrease was not significant (P>0.05). There was no significant difference between grazed and grazing excluded steppe, which was similar to the results for net ecosystem productivity (NEP). In contrast, cultivation significantly decreased net primary productivity (NPP). The gross primary productivity (GPP) differences among the three land uses were lower. The total ecosystem respiration (Re), autotrophic respiration, heterotrophic respiration, and the above and below ground respiration results for grazed steppe were not significantly different from the results recorded for grazing excluded steppe, whereas they were all significantly higher in steppe cultivated cropland. Root respiration was not significantly different among the three land uses. Cultivation significantly increased the autotrophic respiration to Re proportion compared to grazed steppe, whereas soil respiration and root respiration significantly decreased. Grazing exclusion had no significant influence. The below ground biomass has important effects on the variation in the soil respiration (95%) and root respiration (77%) proportions to Re. In addition, the leaf area indexes (LAIs) of the different grassland use patterns in the adjacent areas were very significantly positively correlated with the autotrophic respiration to Re proportion (P<0.001). Temperate steppe cultivated to cropland enhances ecosystem carbon release and reduces CO₂ fixation compared to grassland steppe. However, grazing exclusion had a low influence on ecosystem carbon exchange and its composition.