Estimation of vegetation photosynthetic capacity from space-based measurements of chlorophyll fluorescence for terrestrial biosphere models
Estimation of vegetation photosynthetic capacity from space-based measurements of chlorophyll fluorescence for terrestrial biosphere models
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DOI：
10.1111/gcb.12664
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发表时间：
2014-12-01
影响因子：
11.6
通讯作者：
Koehler, Philipp
中科院分区：
文献类型：
--
作者：
Zhang, Yongguang;Guanter, Luis;Koehler, Philipp
陆地生物圈模型的光合作用模拟通常基于Farquhar模型，其中最大羧化速率（V-cmax）是光合能力的关键控制参数。尽管已知V-cmax在空间和时间上对环境控制的响应有很大的变化，但它通常在与植物功能类型相关的表格值的模型中被参数化。遥感可用于产生空间连续和时间分辨的光合效率视图，但传统的基于光谱反射率的植被观测缺乏与植物光化学过程的直接联系。另外，最近对太阳诱导的叶绿素荧光（SIF）的空间测量可以为光合作用模拟提供观测约束。研究表明，空间上的冠层SIF对生态系统水平的V-cmax非常敏感，并提出了一种利用SIF数据反演V-cmax的方法。利用土壤-冠层光合和能量观测（SCOPE）平衡模型，推导了季节V-cmax与SIF之间的经验关系，并利用该关系求解了反演问题。我们在美国中西部六个农业通量塔站点使用基于空间的SIF检索来评估我们的V-cmax估计方法。我们的V-cmax估算值与玉米和大豆植物的文献值(平均值分别为37和101molm（-2)s(-1)）一致，并显示出合理的季节模式。通过与固定V-cmax值的模拟对比，验证了更新后的季节变化V-cmax参数化对模拟总初级生产力（GPP）的影响。对通量塔观测结果的验证表明，当使用SIF的时间分辨V-cmax估计时，GPP和光能利用效率的模拟显著改善，GPP比较的R-2从0.85增加到0.93，光能利用效率从0.44增加到0.83。我们的研究结果支持使用基于空间的SIF数据作为光合能力的代理，并提出了全球的、时间分辨的V-cmax估计的潜力。
Photosynthesis simulations by terrestrial biosphere models are usually based on the Farquhar's model, in which the maximum rate of carboxylation (V-cmax) is a key control parameter of photosynthetic capacity. Even though V-cmax is known to vary substantially in space and time in response to environmental controls, it is typically parameterized in models with tabulated values associated to plant functional types. Remote sensing can be used to produce a spatially continuous and temporally resolved view on photosynthetic efficiency, but traditional vegetation observations based on spectral reflectance lack a direct link to plant photochemical processes. Alternatively, recent space-borne measurements of sun-induced chlorophyll fluorescence (SIF) can offer an observational constraint on photosynthesis simulations. Here, we show that top-of-canopy SIF measurements from space are sensitive to V-cmax at the ecosystem level, and present an approach to invert V-cmax from SIF data. We use the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) balance model to derive empirical relationships between seasonal V-cmax and SIF which are used to solve the inverse problem. We evaluate our V-cmax estimation method at six agricultural flux tower sites in the midwestern US using spaced-based SIF retrievals. Our V-cmax estimates agree well with literature values for corn and soybean plants (average values of 37 and 101molm(-2)s(-1), respectively) and show plausible seasonal patterns. The effect of the updated seasonally varying V-cmax parameterization on simulated gross primary productivity (GPP) is tested by comparing to simulations with fixed V-cmax values. Validation against flux tower observations demonstrate that simulations of GPP and light use efficiency improve significantly when our time-resolved V-cmax estimates from SIF are used, with R-2 for GPP comparisons increasing from 0.85 to 0.93, and for light use efficiency from 0.44 to 0.83. Our results support the use of space-based SIF data as a proxy for photosynthetic capacity and suggest the potential for global, time-resolved estimates of V-cmax.