Carbon fluxes and their response to environmental variables in a Dahurian larch forest ecosystem in northeast China

东北落叶松林生态系统碳通量及其对环境因子的响应(英文)

The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g.m^-2.month ^-1 in June 2004 （simplified expression of g （carbon）.m^-2.month^-1） and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g-m^-2.a^-1 （simplified expression of g （carbon）.m^-2.a^-1） during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit （VPD） and temperature. Under humid conditions （VPD 〈 1.0 kPa）, the gross ecosystem production （GEP） increased with increasing temperature. But the net ecosystem production （NEP） showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment （VPD 〉 1.0 kPa）, the GEP decreased with the increasing VPD at a rate of 3.0 μmol.m^-2.s^-1kPa -1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol.m^-2.s-1.kPa^-1. Under humid conditions （VPD 〈 1.0 kPa）, both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range.

本研究首次运用涡度相关技术对落叶松人工林生态系统的碳收支进行了长期连续观测(从20004年5月到2005年4月)。结果表明,落叶松生态系统的碳收支具有明显的季节性变化和日变化,在非生长季(从2004年10月中旬到2005年的4月)生态系统向大气释放CO2,生态系统碳收支没有明显的日变化;但在生长季(从5月到10月上旬)生态系统则从大气中强烈吸收CO2,碳收支日变化强烈,基本上是白天吸收,夜间放出二氧化碳,但在阴雨天,即使是白天生态系统也可能向大气中释放二氧化碳,成为碳源。落叶松林的净生态系统碳吸收量从5月初开始逐渐增高,在6月份达到最高值(112g-m-2-month-1),而后逐渐降低,到10月中旬则完全转化为碳源。该落叶松人工林生态系统每年可从大气中净吸收146g-m-2-a-1,与日本北海道地区的落叶松林碳吸收能力(141g-m-2-a-1)相近,但远远高出西伯利亚(90g-m-2-a-1)和蒙古(85g-m-2-a-1)地区落叶松林的碳吸收能力。该落叶松林生态系统的光合过程受到饱和差(VPD)和温度的影响很大。我们发现1.0kPa是影响生态系统光合能力的干燥和湿润环境的一个标志性分界值。在湿润环境条件下(VPD<1.0kPa),生态系统的总生产力(GEP)随着温度升高而增大,但是生态系统的净生产力(NEP)几乎不随温度发生变化,这是由于温度增高产生的GEP增量被呼吸增量所抵消的缘故。但在干燥环境条件下(VPD>1.0kPa),GEP则随着VPD增加以3.0μmol-m-2-s-1-kPa-1的速度降低,与此同时,由于气温与VPD线性正相关,VPD的增加总是伴随着温度升高,因而增加了生态系统的呼吸量,结果导致净生态系统的碳吸收速率随着VPD增高以5.2μmol-m-2-s-1-kPa-1速度显著降低。在湿润条件下(VPD<1.0kPa),GEP和NEP都明显受到低温的影响,但是对高温不敏感,这主要是由于当地所观测到的高温值仍未超出落叶松的最适温度范围的缘故。图7表3参40。