东北东部森林生态系统土壤碳贮量和碳通量

Soil carbon storage and flux of temperate forest ecosystems in northeastern China

土壤碳是高纬度地区森林生态系统最大的碳库,是森林生态系统碳循环的极其重要组分.研究了东北东部典型的6种次生林生态系统(天然蒙古栎林、杨桦林、杂木林、硬阔叶林、红松人工林和落叶松人工林)的土壤碳动态,包括(1)量化土壤有机碳(SOC)含量、碳密度及周转时间,(2)比较不同森林生态系统的土壤表面CO2通量(Rs)年通量差异,(3)建立Rs年通量及其分量与SOC的量化关系.研究结果表明:阔叶天然次生林和针叶人工林的SOC含量变化范围分别为52.63～66.29 g·kg-1和42.15～49.15g·kg-1;平均SOC密度分别为15.57和17.16 kg·m-2;平均SOC周转时间分别为32a和48a.各个生态系统的Rs依次为杂木林951 gC·m-2·a-1、硬阔叶林892 gC·m-2·a-1、杨桦林812 gC·m-2·a-1、蒙古栎林678gC·m-2·a-1、红松林596 gC·m-2·a-1和落叶松林451 gC·m-2·a-1.Rs年通量及其分量(土壤异养呼吸和自养呼吸)与SOC含量呈显著的正相关,但其相关程度因土层不同而异(R2=0.747～0.933).同一生态系统中,SOC含量随土深增加而降低,而SOC密度和SOC周转时间随深度增加而增大.采用统一规范的研究方法,获取大量有代表性的森林生态系统土壤碳贮量和Rs的实测数据,是减少区域尺度碳平衡研究中不确定性的不可缺少的研究内容.

Soil carbon, a key component of ecosystem carbon budgets, is the largest carbon pool of forest ecosystems in high latitude regions. Temperate forests occupy a large area in northeastern China where effects of projected climatic warming on terrestrial ecosystems are significant. However, few data on soil carbon budgets are available for these forests. In this paper, we studied the soil carbon dynamics of six representative types of temperate secondary forest ecosystems in northeast China, which were oak forest dominated by Quercus mongolica, poplar-birch forest dominated by Populous davidiana and Betula platyphylla, mixed forest without dominant tree species, hardwood forest dominated by Fraxinus mandshurica, Juglans mandshurica, and Phellodendron amurense, Korean pine plantation dominated by Pinus koraiensis, and Dahurian larch plantation dominated by Larix gmelinii. Our specific objectives were to （1） quantify soil organic carbon （SOC） contents and turnover time for the six forest ecosystems, and （2） compare the annual flux of soil surface CO2 flux （Rs） for the ecosystems, and （3） establish quantitative relationship between Rs and SOC. The experimental design included six forest ecosystem types, three random replicate plots each ecosystem type. In each plot, we dug three soil pits and measured SOC content and density. We measured Rs with a LI-6400 infrared gas analyzer, and partitioned autotrophic and heterotrophic respiration in the Rs using a trenched-plot approach. The SOC content for the broadleaved secondary forests and coniferous plantations was 52. 63- 66.29 g · kg^-1 and 42.15~49.15 g · kg^-1, respectively; the mean SOC density was 15.57 and 17.16 kg·m^-2, respectively; and the mean SOC turnover time was 32 and 48 years, respectively. The Rs for the mixed stand, hardwood stand, poplar-birch stand, Mongolian oak stand, Korean pine plantation, and Dahurian larch plantation was 951g·m^-2·a^-1, 892g·m^-2·a^-1, 812g·m^-2·a^-1, 678g·m^-2·a^-1, 596g·m^-2·a^-1, and 451g·m^-2·a^-1, respectively. The Rs and its components （soil autotrophic and heterotrophic respiration） were positively correlated to SOC content, and the significance level of the correlation depended on soil horizons （R^2=0.747-0. 933）. The SOC content decreased with soil depth in a specific forest ecosystem, whereas the SOC density and turnover time increased with soil depth. The large spatial variation in SOC and Rs among forest ecosystems and soil profile horizons within a specific ecosystem suggested that measurements of forest soil carbon storage and flux using standardized approaches be critical for reducing uncertainties in regional-scale carbon budget studies.