典型森林和草地生态系统呼吸各组分间的相互关系

生态系统呼吸是陆地生态系统碳收支的重要组成部分，分析其组分间的相互关系对理解生态系统呼吸过程和精确评价生态系统碳收支具有重要意义，也是当前碳循环研究工作的一大难点。本研究利用ChinaFLUX的长白山温带针阔混交林（CBS），鼎湖山亚热带常绿阔叶林（DHS）和海北灌丛草甸（HBGC）三个典型生态系统的通量观测数据，采用经验统计方法，分析了其在中国典型生态系统中的适用性及敏感性，揭示了生态系统呼吸各组分的动态变化特征及相互关系。结果表明：采用本研究中的呼吸组分拆分方法所获结果与理论推测及实测数据大致相同，拆分结果对净初级生产力与总初级生产力的比值（NPP/GPP）较为敏感，NPP/GPP变化0.1时，自养呼吸在生态系统呼吸中的比例（Ra/RE）改变0.05。各生态系统中，生态系统呼吸及其组分在年内均表现出明显的单峰型变化特征，在夏季生长旺盛的时节达到最大值。异养呼吸与生态系统呼吸的比值（Rh/RE）也具有明显的季节变化，但在生态系统间表现出明显差异，CBS和HBGC分别表现出先增大后减小和先减小后增大的变化趋势，DHS则相对稳定，在0.5附近波动， Ra/RE的季节动态与Rh/RE相反。在年总量上，HBGC主要通过异养呼吸向大气排放CO2，异养呼吸占生态系统呼吸的60%，而CBS和DHS的自养呼吸和异养呼吸所占比重大致相似，异养呼吸占生态系统呼吸的49%。这说明，该统计学模型可以用来进行生态系统呼吸组分的拆分，进而可以为生态系统碳循环过程的精细研究提供参考数据，但今后应加强NPP/GPP的测定，以提高生态系统呼吸拆分的精度。

The interaction between components of ecosystem respiration in typical forest and grassland ecosystems

Ecosystem respiration (RE), the release of carbon from an ecosystem into the atmosphere, is a key component of the terrestrial ecosystem carbon budget and plays an important role in the global carbon balance. Analyzing the interaction between RE components is essential to understanding RE and accurately evaluating the ecosystem carbon budget. There are many methods for separating RE into autotrophic respiration (Ra) and heterotrophic respiration (Rh), but each approach has disadvantages. Large RE data have obtained through long-term eddy covariance measurement, while the interaction between Ra and Rh is poorly documented, which inhibits the accurate assessing of global carbon budget. In this study, we use an empirical statistical method to separate RE into its two components and examine component relationships and seasonal dynamics at three ChinaFLUX sites: 1) Changbaishan temperate mixed forest (CBS); 2) Dinghushan subtropical evergreen broad-leaf forest (DHS); and 3) Haibei shrub meadow (HBGC). The applicability and sensitivity of this method to typical ecosystems in China were also evaluated. The method used in this study was based on the ratio of Ra to RE (Ra/RE). The range of Ra/RE was obtained by calculating two ratios: the ratio of RE to net ecosystem productivity (NEP) (RE/NEP) and the ratio of net primary productivity (NPP) to gross primary productivity (GPP) (NPP/GPP). Within the range of Ra/RE, 1000 Ra/RE was randomly selected and the value of Ra/RE used in this study was set as the mean of the 1000 random Ra/RE. Ra and Rh were then calculated using Ra/RE and RE. Our study shows that the RE separating method produces consistent results with those obtained through static chamber/gas chromatographic techniques performed at the same sites, as well as with biomass surveys and theoretical speculation. The interaction of RE components was sensitive to the variation of NPP/GPP: a ten-percent increase of NPP/GPP led to a five-percent decrease of Ra/RE. In all three ecosystems, RE and its components showed similar seasonal dynamics, with a single-peak pattern achieving its maximum midway through the growing season. The ratio of Rh to RE (Rh/RE) also showed a seasonal dynamic which was different among the three ecosystems. In CBS, Rh/RE increased during the first half of the year, reached its peak during the growing season then decreased. However, Rh/RE in HBGC decreased during the first half of the year and increased again later in growing-season. In DHS, Rh/RE was relatively stable at approximately 0.5. Changes in Ra/RE over time were opposite to those in Rh/RE. The annual summed Rh accounted for 60% of the RE in HBGC, suggesting that in this ecosystem, a large proportion of emitted carbon was released by Rh. In CBS and DHS, Rh was only 49% of RE, indicating that the release of carbon through Ra and Rh was nearly the same in these two forest ecosystems. Results indicate that this method, which requires detailed observations of NPP/GPP, can be successfully used to accurately separate RE into Rh and Ra and can provide data necessary for the detailed analysis of the ecosystem carbon cycle.