1958-2008年太白山太白红杉林碳循环模拟

太白红杉(Larix chinensis林主要分布于我国秦岭太白山的林线位置,对气候变化的响应十分敏感.为了定量分析太白山太白红杉林在气候变化背景下的碳循环特征,基于模型(MTCLIM)模拟的温度和降水数据,应用植被动态过程模型(LPJ-GUESS)模拟了太白山南北坡1958-2008年太白红杉林的净初级生产力(NPP)、生物量和净生态系统碳交换量(NEE).结果表明:1)太白红杉和巴山冷杉(Abies fargesii)的NPP和生物量在太白红杉林占有优势,太白红杉的NPP和生物量均大于巴山冷杉.1958-2008年间太白红杉南北坡NPP的平均值为0.38 kgC·m-2·a-1,巴山冷杉为0.25 kgC·m-2,a-1,两者之和占整个太白红杉林NPP的86％;1958-2008年间太白红杉南北坡生物量的平均值为2.91 kgC/m2,巴山冷杉为2.02 kgC/m2,两者之和占太白红杉林生物量的94％.2)太白红杉和巴山冷杉的NPP均表现为北坡大于南坡,且南北坡均有逐年增加的趋势,北坡的增幅小于南坡,所以太白山南北坡太白红杉林的NPP差异有逐年减少的趋势.3)太白红杉生物量的年际波动较大,南北坡呈交替上升趋势,南坡的平均值(2.94 kgC/m2)大于北坡(2.89 kgC/m2).巴山冷杉生物量的年际波动相对较小,北坡生物量水平大于南坡.4)1958-2008年南北坡太白红杉林平均NEE均为-0.023 kgC·m-2·a-1,表现为碳汇.南北坡碳汇水平均呈逐年增加趋势,南坡的增加幅度(0.91 g·m-2·a-1)大于北坡(0.42 g·m-2·a-1).以气候和CO2为驱动因子对太白山太白红杉林的长期碳循环动态做了定量分析,从机理上揭示气候变化与生态系统碳循环的关系,还需要做进一步的野外观测和控制实验研究.

Simulation of the carbon cycle of Larix chinensis forest during 1958 and 2008 at Taibai Mountain, China

The terrestrial ecosystem carbon cycle, an important component of the global carbon cycle, has significant impacts on the composition of atmospheric greenhouse gases (GHGs) and global climate change. Quantitative analysis, which provides knowledge of the terrestrial ecosystem carbon cycle, is not only a prerequisite for accurately predicting regional and global climate; it also provides a scientific basis from which governments can develop programs in response to global change. The major goal of this study is to quantify the carbon cycle of the Larix chinensis forest at Taibai Mountain, Shaanxi, China, which experienced significant climate change during the time period from 1958 to 2008. Process-based models are useful tools for predicting changes to the long-term ecosystem carbon cycle that is influenced by climate change. We quantitatively investigated the carbon cycle of the modeled area by using a process-based model, LPJ-GUESS, using climatic data from the Mountain Microclimate Simulation Model (MTCLIM) and CO₂ concentration data to drive the model. Net primary productivity (NPP), biomass and net ecosystem carbon exchange (NEE) are the major outputs of the LPJ-GUESS model we used in this study. The NPP and biomass of L. chinensis and Abies fargesii were large in the L. chinensis forest, and both NPP and biomass of L. chinensis were larger than A. fargesii. The average NPP of L. chinensis and A. fargesii during 1958 and 2008 were 0.38 kgC·m^-2·a^-1 and 0.25 kgC·m^-2·a^-1, respectively. The sum of the two species' NPP accounted for 86% of the biomass in L. chinensis forest. The average biomass of L. chinensis and A. fargesii during 1958 and 2008 were 2.91 kgC/m² and 2.02 kgC/m², respectively. The sum of the two species' biomass was 94 percent of the NPP in L. chinensis forest. A. fargesii occupied the lower slope of the L. chinensis forest because of its altitudinal limitation, and the upper elevation forest was pure L. chinensis forest. Both L. chinensis and A. fargesii had larger NPP on the northern slope of Taibai Mountain than on the southern slope. Both slopes experienced increasing NPP of the two species over time, and the increase of the northern slope was smaller than the southern slope, so the difference of the L. chinensis forest's NPP between the northern and southern slope was decreasing over the 51-year study period. Biomass of L. chinensis experienced inter-annual fluctuations during the 1958-2008 study period and increased alternatively between the northern and southern slope. The mean biomass on the southern slope between 1958 and 2008 (2.94 kgC/m²) was greater than the northern slope (2.89 kgC/m²). Biomass of A. fargesii, which always occupied a larger part on the northern slope during the 51-year study period, had fewer inter-annual fluctuations compared with L. chinensis. The modeled value of NEE, whose average was -0.023 kgC·m^-2·a^-1, showed that L. chinensis forest has been a carbon sink over the 51 years studied. There was no significant difference in average NEE between the northern and southern slope. Both slopes showed increasing carbon sink functioning, with an annual increase of 0.91 gC·m^-2·a^-1 on the southern slope and 0.42 gC·m^-2·a^-1 on the northern slope. This long-term simulation of the L. chinensis forest driven by climatic data and CO₂ concentration was only a preliminary quantitative study of the carbon cycle dynamics. Additional field observations and manipulative experiments are needed to reveal the relationships between climate change and the ecosystem carbon cycle.