Measuring forest floor CO2 fluxes in a Douglas-fir forest
Measuring forest floor CO2 fluxes in a Douglas-fir forest
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DOI：
10.1016/s0168-1923(01)00294-5
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发表时间：
2002-02-28
影响因子：
6.2
通讯作者：
Morgenstern, K
中科院分区：
文献类型：
--
作者：
Drewitt, GB;Black, TA;Morgenstern, K
在加拿大不列颠哥伦比亚省坎贝尔河附近的一片沿海温带花旗松森林的林地地表测量了二氧化碳交换。2000年4月至12月期间，使用自动化箱式系统在六个地点进行了连续测量。通过使箱内顶部空间的空气循环经过一个采样歧管组件和一台闭路红外气体分析仪，每半小时测量一次通量。在不同箱式测量地点之间，所测最大二氧化碳通量的差异系数接近3，而在两个箱式测量地点观测到的最高日平均通量偶尔会达到接近15微摩尔碳/平方米·秒的值。一般来说，在测量期间通量介于2到10微摩尔碳/平方米·秒之间。林地地表的二氧化碳通量与土壤温度密切相关，与5厘米深处的温度相关性最高。一个简单的依赖温度的指数模型与夜间通量拟合后显示，在一年中较温暖的时段，Q₁₀值处于2 - 3的正常范围，但在较冷时期为4 - 5。在六个箱式测量地点中的四个，苔藓光合作用可忽略不计，而在其他地点，它使白天每半小时的净二氧化碳通量减少了约25%。土壤湿度对林地地表二氧化碳通量影响极小。观测到箱式通量与土壤温度之间的年度关系存在滞后现象。据估计，六个箱式测量地点的净交换量为每年1920 ± 530克碳/平方米，较高的估计值超过了在该地点使用全年冠层上方涡动相关法对生态系统呼吸的测量值。这种差异归因于箱式测量数量不足，无法可靠地估计该地点土壤二氧化碳通量的空间平均值，以及涡动协方差呼吸测量的不确定性。（C）2002爱思唯尔科学出版社。保留所有权利。
CO2 exchange was measured on the forest floor of a coastal temperate Douglas-fir forest located near Campbell River, British Columbia, Canada. Continuous measurements were obtained at six locations using an automated chamber system between April and December, 2000. Fluxes were measured every half hour by circulating chamber headspace air through a sampling manifold assembly and a closed-path infrared gas analyzer. Maximum CO2 fluxes measured varied by a factor of almost 3 between the chamber locations, while the highest daily average fluxes observed at two chamber locations occasionally reached values near 15 mumol C m(-2) s(-1). Generally, fluxes ranged between 2 and 10 mumol C m(-2) s(-1) during the measurement period. CO2 flux from the forest floor was strongly related to soil temperature with the highest correlation found with 5 cm depth temperature. A simple temperature dependent exponential model fit to the nighttime fluxes revealed Q(10) values in the normal range of 2-3 during the warmer parts of the year, but values of 4-5 during cooler periods. Moss photosynthesis was negligible in four of the six chambers, while at the other locations, it reduced daytime half-hourly net CO2 flux by about 25%. Soil moisture had very little effect on forest floor CO2 flux. Hysteresis in the annual relationship between chamber fluxes and soil temperatures was observed. Net exchange from the six chambers was estimated to be 1920 +/- 530 g C m(-2) per year, the higher estimates exceeding measurement of ecosystem respiration using year-round eddy correlation above the canopy at this site. This discrepancy is attributed to the inadequate number of chambers to obtain a reliable estimate of the spatial average soil CO2 flux at the site and uncertainty in the eddy covariance respiration measurements. (C) 2002 Elsevier Science B.V. All rights reserved.