Vegetation phenology regulates ecosystem carbon, water, and energy fluxes, as well as biosphere-atmosphere feedbacks. Currently, vegetation indices and carbon fluxes have been incorporated in models for predicting vegetation phenology, hydrological processes have not yet been used despite significant interactions between climate, phenology, and hydrology. The evaporative fraction (EF) and Bowen ratio are key parameters for characterizing hydrological drought and estimating evapotranspiration. Here we use long-term records of eddy covariance fluxes from seven temperate ecosystems (eight vegetation types) in the ChinaFLUX to assess how well EF and the reciprocal of Bowen ratio (1/β) predict phenological parameters. The start, peak, end, and length of the growing season were estimated for each site and year. Across the eight vegetation types, there was a strong correlation between the multi-year averages of the phenological parameters derived from EF and 1/β and those from gross primary production (R2 range: 0.78 – 0.99). However, the strength of the relationship between hydrological and photosynthetic phenology (as measured by R2) decreased as the aridity index increased. This was likely attributable to differences in hydrological processes and photosynthesis responses to drought events. Our results demonstrate that EF and 1/β are good spatial predictors of photosynthetic phenology. However, this relationship did not apply to mesic sites where carbon and water were not as tightly coupled as those in arid sites. We expand the application of eddy covariance in exploring “functional phenology” of vegetation from carbon fluxes to water and energy fluxes. Because numerous meteorological and hydrological stations are equipped with the Bowen ratio system, the hydrological phenology algorithm proposed in this study may be applied widely in future vegetation phenology studies.

中文翻译：

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从水文过程评估植被物候的新指标：与光合物候学的比较


植被物候调节生态系统的碳、水和能量通量，以及生物圈-大气反馈。目前，植被指数和碳通量已被纳入预测植被物候的模型中，尽管气候、物候和水文之间存在显着的相互作用，但水文过程尚未被使用。蒸发分数 （EF） 和 Bowen 比是表征水文干旱和估计蒸散量的关键参数。在这里，我们使用 ChinaFLUX 中来自 7 个温带生态系统（8 种植被类型）的涡度相关通量的长期记录来评估 EF 和 Bowen 比的倒数 （1/β） 对物候参数的预测能力。估计每个地点和年份的生长季节的开始、高峰、结束和长度。在八种植被类型中，EF 和 1/β 得出的物候参数的多年平均值与来自总初级生产（R2 范围：0.78 – 0.99）的物候参数之间存在很强的相关性。然而，随着干旱指数的增加，水文物候和光合物候学（用 R2 测量）之间的关系强度降低。这可能是由于水文过程和光合作用对干旱事件的响应的差异。我们的结果表明，EF 和 1/β 是光合物候的良好空间预测因子。然而，这种关系不适用于碳和水不像干旱地区那样紧密耦合的中部地区。我们扩展了涡度相关差在探索植被的“功能物候”中的应用，从碳通量到水和能量通量。 由于许多气象和水文站都配备了 Bowen 比值系统，因此本研究提出的水文物候算法可能在未来的植被物候研究中得到广泛应用。