Zeller K F, Nikolov N T
USDA Forest Service, Rocky Mountain Research Station, 240 W. Prospect, Ft. Collins, CO 80526, USA.
Environ Pollut. 2000 Jan;107(1):1-20. doi: 10.1016/s0269-7491(99)00156-6.
Assessing the long-term exchange of trace gases and energy between terrestrial ecosystems and the atmosphere is an important priority of the current climate change research. In this regard, it is particularly significant to provide valid data on simultaneous fluxes of carbon, water vapor and pollutants over representative ecosystems. Eddy covariance measurements and model analyses of such combined fluxes over a subalpine coniferous forest in southern Wyoming (USA) are presented. While the exchange of water vapor and ozone are successfully measured by the eddy covariance system, fluxes of carbon dioxide (CO(2)) are uncertain. This is established by comparing measured fluxes with simulations produced by a detailed biophysical model (FORFLUX). The bias in CO(2) flux measurements is partially attributed to below-canopy advection caused by a complex terrain. We emphasize the difficulty of obtaining continuous long-term flux data in mountainous areas by direct measurements. Instrumental records are combined with simulation models as a feasible approach to assess seasonal and annual ecosystem exchange of carbon, water and ozone in alpine environments. The viability of this approach is demonstrated by: (1) showing the ability of the FORFLUX model to predict observed fluxes over a 9-day period in the summer of 1996; and (2) applying the model to estimate seasonal dynamics and annual totals of ozone deposition and carbon, and water vapor exchange at our study site. Estimated fluxes above this subalpine ecosystem in 1996 are: 195 g C m(-2) year(-1) net ecosystem production, 277 g C m(-2) year(-1) net primary production, 535 mm year(-1) total evapo-transpiration, 174 mm year(-1) canopy transpiration, 2.9 g m(-2) year(-1) total ozone deposition, and 1.72 g O(3) m(-2) year(-1) plant ozone uptake via leaf stomata. Given the large portion of non-stomatal ozone uptake (i.e. 41% of the total annual flux) predicted for this site, we suggest that future research of pollution-vegetation interactions should relate plant response to actively assimilated ozone by foliage rather than to total deposition. In this regard, we propose the Physiological Ozone Uptake Per Unit of Leaf Area (POUPULA) as a practical index for quantifying vegetation vulnerability to ozone damage. We estimate POUPULA to be 0.614 g O(3) m(-2) leaf area year(-1) at our subalpine site in 1996.
评估陆地生态系统与大气之间痕量气体和能量的长期交换是当前气候变化研究的一个重要优先事项。在这方面，提供有关代表性生态系统中碳、水汽和污染物同时通量的有效数据尤为重要。本文介绍了在美国怀俄明州南部一个亚高山针叶林上对这种组合通量进行的涡度协方差测量和模型分析。虽然涡度协方差系统成功测量了水汽和臭氧的交换，但二氧化碳（CO₂）通量不确定。这是通过将测量通量与详细生物物理模型（FORFLUX）产生的模拟结果进行比较确立的。CO₂通量测量中的偏差部分归因于复杂地形导致的冠层以下平流。我们强调在山区通过直接测量获取连续长期通量数据的困难。仪器记录与模拟模型相结合是评估高山环境中碳、水和臭氧的季节性和年度生态系统交换的一种可行方法。这种方法的可行性通过以下方式得到证明：（1）展示FORFLUX模型在1996年夏季9天内预测观测通量的能力；（2）应用该模型估算我们研究地点的臭氧沉降、碳和水汽交换的季节动态和年度总量。1996年该亚高山生态系统上方的估算通量为：净生态系统生产力195 g C m⁻² 年⁻¹, 净初级生产力277 g C m⁻² 年⁻¹, 总蒸散量535 mm 年⁻¹, 冠层蒸腾量174 mm 年⁻¹, 总臭氧沉降量2.9 g m⁻² 年⁻¹, 以及通过叶片气孔植物对臭氧的吸收量1.72 g O₃ m⁻² 年⁻¹。鉴于该地点预测的非气孔臭氧吸收占很大比例（即占年通量总量的41%），我们建议未来关于污染 - 植被相互作用的研究应将植物响应与叶片主动同化的臭氧相关联，而不是与总沉降相关联。在这方面，我们提出单位叶面积生理臭氧吸收量（POUPULA）作为量化植被对臭氧损害脆弱性的一个实用指标。我们估算出1996年我们亚高山地点的POUPULA为0.614 g O₃ m⁻² 叶面积 年⁻¹。
