Bridging the Flux Gap: Sap Flow Measurements Reveal Species-Specific Patterns of Water Use in a Tallgrass Prairie
Bridging the Flux Gap: Sap Flow Measurements Reveal Species-Specific Patterns of Water Use in a Tallgrass Prairie
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DOI：
10.1029/2019jg005446
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发表时间：
2020-02-01
影响因子：
3.7
通讯作者：
Nippert, Jesse B.
中科院分区：
文献类型：
--
作者：
O'Keefe, Kimberly;Bell, David M.;Nippert, Jesse B.
预测草原植被类型变化(即木本植物入侵)后的水文后果，需要了解草原群落中优势物种在高时空分辨率下的水通量动态。然而，草原通量通常是在树叶或景观尺度上测量的，这限制了我们预测单个物种如何影响生态系统通量变化的能力。我们使用外部热平衡树液流量传感器和分层贝叶斯状态空间建模方法来弥合这一“通量差距”，并估计普通高粱草原物种的连续物种水平的水分通量。具体地说，我们问了以下问题：(1)木本植物和草本植物之间的昼夜水分通量有什么不同？(2)木本植物和草本植物对昼夜水分通量的环境驱动因素有多敏感？我们重点介绍了三个结果：(1)该草原的主要木本植物入侵植物--山茱萸在冠层水平上表现出最大的水分损失；(2)夜间蒸腾是该生态系统损失的水分的很大组成部分，主要由C-4草和山茱萸驱动；(3)冠层蒸腾对环境驱动因素的敏感性因植物功能类型和整个24小时的周期而异。我们的数据揭示了关于高草草原木本植物与草本植物的用水策略以及持续的木本植物入侵的潜在水文后果的重要见解。我们认为，随着时间的推移，在木本植物中观察到的高静态通量速率可能会耗尽深水储存，潜在地在经历木本植物入侵的草原上造成水文赤字，并随之而来增加这些生态系统对干旱的脆弱性。由于木本植物使用水分的方式(例如，速率、土壤吸收深度和活动时间)与草本植物不同，木本植物的入侵可能会潜在地改变草原的水循环。为了了解草原水分利用如何随着持续的木本植物入侵而变化，我们测量了北美草原上常见植物的连续失水率。我们发现，随着时间的推移，这片草原上主要的入侵灌木比草或野花消耗更多的水。此外，与野花相比，这种灌木和草在夜间使用了大量的水。最后，我们发现不同的天气条件对木本植物、草和野花利用水分的方式有不同的影响。我们认为，木本植物的入侵可能会减少草地中储存的水量，这可能会改变未来草地植物的组成。关键点：在这一草原上，主要的木本植物入侵者--山茱萸--表现出最大的冠层水平的水分损失，夜间蒸腾是该生态系统中损失的水分的一大部分，主要由C-4草和鸡冠草驱动。冠层蒸腾对环境驱动因素的敏感性因植物功能类型和整个24小时的周期而不同
Predicting the hydrological consequences following changes in grassland vegetation type (i.e., woody encroachment) requires an understanding of water flux dynamics at high spatiotemporal resolution for predominant species within grassland communities. However, grassland fluxes are typically measured at the leaf or landscape scale, which inhibits our ability to predict how individual species contribute to changing ecosystem fluxes. We used external heat balance sap flow sensors and a hierarchical Bayesian state-space modeling approach to bridge this "flux gap" and estimate continuous species-level water flux in common tallgrass prairie species. Specifically, we asked the following: (1) How do diurnal and nocturnal water fluxes differ among woody and herbaceous plants? (2) How sensitive are woody and herbaceous species to environmental drivers of diurnal and nocturnal water flux? We highlight three results: (1) Cornus drummondii, the primary woody encroacher in this grassland, exhibited the greatest canopy-level water loss; (2) nocturnal transpiration was a large component of the water lost in this ecosystem and was driven primarily by C-4 grasses and C. drummondii; and (3) the sensitivity of canopy transpiration to environmental drivers varies among plant functional types and throughout a 24-hr period. Our data reveal important insights regarding the water use strategies of woody versus herbaceous species in tallgrass prairies and about the potential hydrological consequences of ongoing woody encroachment. We suggest that the high, static flux rates observed in woody species will likely deplete deep water stores over time, potentially creating hydrological deficits in grasslands experiencing woody encroachment and concomitantly increasing the vulnerability of these ecosystems to drought.Plain Language Summary Woody encroachment, the process through which woody plants (trees and shrubs) replace grasses and wildflowers in grassland ecosystems, is occurring globally. Because woody plants use water differently (e.g., rates, soil depths of uptake, and time periods of activity) than grasses, woody encroachment could potentially change the water cycle in grasslands. In order to understand how grassland water use might change with ongoing woody encroachment, we measured continuous rates of water loss in common plant species in a North American grassland. We found that the main encroaching shrub in this grassland used more water over time than grasses or wildflowers. Additionally, this shrub and grasses used a large amount of water at night compared to wildflowers. Finally, we found that different weather conditions had different impacts on how water was used by woody plants, grasses, and wildflowers. We suggest that woody encroachment might reduce the amount of water stored in grasslands, which could alter the composition of grassland plants in the future.Key PointsCornus drummondii, the primary woody encroacher in this grassland, exhibited the greatest canopy-level water loss Nocturnal transpiration was a large component of the water lost in this ecosystem and was driven primarily by C-4 grasses and C. drummondii The sensitivity of canopy transpiration to environmental drivers varies among plant functional types and throughout a 24-hr period