Hanson P J, Wullschleger S D, Bohlman S A, Todd D E
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6034, USA.
Tree Physiol. 1993 Jul;13(1):1-15. doi: 10.1093/treephys/13.1.1.
Forest floor CO(2) efflux (FF(cer)) is an important component of global carbon budgets, but the spatial variability of forest floor respiration within a forest type is not well documented. Measurements of FF(cer) were initiated in mid-March of 1991 and continued at biweekly to monthly intervals until mid-November. Observations were made at 45 sites along topographic gradients of the Walker Branch Watershed, Tennessee including northeast and southwest facing slopes, valley-bottoms, and exposed ridge-top locations. The FF(cer) measurements were made with a portable gas-exchange system, and all observations were accompanied by soil temperature and soil water content measurements. As expected, FF(cer) exhibited a distinct seasonal trend following patterns of soil temperature, but soil water content and the volume percent of the soil's coarse fraction were also correlated with observed rates. Over the entire measurement period, FF(cer) ranged from a typical minimum of 0.8 micro mol m(-2) s(-1) to an average maximum near 5.7 micro mol m(-2) s(-1). No significant differences in FF(cer) were observed among the ridge-top and slope positions, but FF(cer) in the valley-bottom locations was lower on several occasions. An empirical model of FF(cer) based on these observations is suggested for application to whole-stand estimates of forest carbon sequestration.
林地二氧化碳通量（FF(cer)）是全球碳收支的一个重要组成部分，但同一森林类型内林地呼吸作用的空间变异性尚无充分记录。FF(cer)的测量始于1991年3月中旬，以两周至一个月的间隔持续进行，直至11月中旬。在田纳西州沃克分支流域沿地形梯度的45个地点进行了观测，包括东北和西南向的斜坡、谷底以及暴露的山脊顶部位置。FF(cer)的测量使用便携式气体交换系统，所有观测均伴有土壤温度和土壤含水量的测量。正如预期的那样，FF(cer)呈现出随土壤温度模式变化的明显季节性趋势，但土壤含水量和土壤粗颗粒的体积百分比也与观测速率相关。在整个测量期间，FF(cer)范围从典型的最小值0.8微摩尔·米-2·秒-1到接近5.7微摩尔·米-2·秒-1的平均最大值。在山脊顶部和斜坡位置之间未观察到FF(cer)的显著差异，但谷底位置的FF(cer)在某些情况下较低。基于这些观测结果提出了一个FF(cer)的经验模型，用于应用于森林碳固存的全林分估计。
