Cavaleri Molly A, Oberbauer Steven F, Ryan Michael G
Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA.
Plant Cell Environ. 2008 Apr;31(4):473-83. doi: 10.1111/j.1365-3040.2008.01775.x. Epub 2008 Jan 29.
Foliar respiration is a major component of ecosystem respiration, yet extrapolations are often uncertain in tropical forests because of indirect estimates of leaf area index (LAI). A portable tower was used to directly measure LAI and night-time foliar respiration from 52 vertical transects throughout an old-growth tropical rain forest in Costa Rica. In this study, we (1) explored the effects of structural, functional and environmental variables on foliar respiration; (2) extrapolated foliar respiration to the ecosystem; and (3) estimated ecosystem respiration. Foliar respiration temperature response was constant within plant functional group, and foliar morphology drove much of the within-canopy variability in respiration and foliar nutrients. Foliar respiration per unit ground area was 3.5 +/- 0.2 micromol CO2 m(-2) s(-1), and ecosystem respiration was 9.4 +/- 0.5 micromol CO2 m(-2) s(-1)[soil = 41%; foliage = 37%; woody = 14%; coarse woody debris (CWD) = 7%]. When modelled with El Niño Southern Oscillation (ENSO) year temperatures, foliar respiration was 9% greater than when modelled with temperatures from a normal year, which is in the range of carbon sink versus source behaviour for this forest. Our ecosystem respiration estimate from component fluxes was 33% greater than night-time net ecosystem exchange for the same forest, suggesting that studies reporting a large carbon sink for tropical rain forests based solely on eddy flux measurements may be in error.
叶呼吸是生态系统呼吸的主要组成部分，但由于叶面积指数（LAI）的间接估计，在热带森林中进行推断往往存在不确定性。在哥斯达黎加的一片原始热带雨林中，使用便携式塔从52个垂直样带直接测量了叶面积指数和夜间叶呼吸。在本研究中，我们（1）探讨了结构、功能和环境变量对叶呼吸的影响；（2）将叶呼吸外推到生态系统；（3）估计了生态系统呼吸。植物功能组内叶呼吸温度响应是恒定的，叶形态驱动了冠层内呼吸和叶养分的大部分变异性。单位地面面积的叶呼吸为3.5±0.2 μmol CO₂ m⁻² s⁻¹，生态系统呼吸为9.4±0.5 μmol CO₂ m⁻² s⁻¹[土壤 = 41%；树叶 = 37%；木质 = 14%；粗木质残体（CWD） = 7%]。当用厄尔尼诺南方涛动（ENSO）年温度进行模拟时，叶呼吸比用正常年份温度模拟时大9%，这处于该森林碳汇与碳源行为的范围内。我们根据组分通量估计的生态系统呼吸比同一森林夜间净生态系统交换大33%，这表明仅基于涡度通量测量报告热带雨林有大量碳汇的研究可能存在误差。
