By examining the derivation of Penn-Monteith-like equations for estimating evapotranspiration, one can uncover valuable insights into plant functionality. In essence, equations talk. For a more comprehensive and in-depth exploration of this topic, refer to this erlier post.
In our collaborative work with Concetta D'Amato for the WATERSTEM project, we encountered the initial constraint of transpiration imposed by the hydraulic conductance of the stem-root system. Through our research, inspired by Manzoni et al. [2013], we discovered that the sigmoidal form of conductivity leads to an optimum for transpiration. We attempted to reproduce this phenomenon using the data provided by Kroeber et al. [2-13]. After considerable effort, we successfully generated the gray curve in the Figure, which exhibits a peak just before -4 MPa and enables too high transpiration.
However, we realized that the soil resistance was missing from our analysis. To address this, we incorporated the conductivity of a Silt Loam soil using the van Genuchten Mualem parameterization. The resulting brownish curves serve as evidence that the soil plays a crucial role, as anticipated by Carminati and Javaux [2020]. It is important to note that these curves depict the limits imposed by the soil and stem, which determine the potential sapflow rates, but do not reflect the constraints imposed by plant physiology. To account for plant physiology, we introduced the stomatal resistance, represented by the three dashed curves under different working hypotheses whose parameterization was taken from Daly et al. [2004]. The red points in the Figure represent the plant's working points (although the coupling with the atmospheric boundary layer is not depicted). One notable aspect of the Figure is that at typical soil suctions, the sapflow curves appear relatively flat, and the working points result in relatively constant sapflow despite variations in xylem/leaves pressure. The complete story will soon be available in Concetta's Ph.D. thesis, and the detailed process of creating the Figure can be found in its supplemental material notebooks.
References
Carminati, Andrea, and Mathieu Javaux. 2020. “Soil Rather Than Xylem Vulnerability Controls Stomatal Response to Drought.” Trends in Plant Science 25 (9): 868–80. https://doi.org/10.1016/j.tplants.2020.04.003.
Daly, Edoardo, Amilcare Porporato, and Ignacio Rodriguez-Iturbe. 2004. “Coupled Dynamics of Photosynthesis, Transpiration, and Soil Water Balance. Part I: Upscaling from Hourly to Daily Level.” Journal of Hydrometeorology 5 (3): 546–58. https://doi.org/10.1175/1525-7541(2004)005<0546:cdopta>2.0.co;2.
Kröber, Wenzel, Shouren Zhang, Merten Ehmig, and Helge Bruelheide. 2014. “Linking Xylem Hydraulic Conductivity and Vulnerability to the Leaf Economics Spectrum—A Cross-Species Study of 39 Evergreen and Deciduous Broadleaved Subtropical Tree Species.” PloS One 9 (11): e109211. https://doi.org/10.1371/journal.pone.0109211.
Manzoni, Stefano, Giulia Vico, Gabriel Katul, Sari Palmroth, Robert B. Jackson, and Amilcare Porporato. 2013. “Hydraulic Limits on Maximum Plant Transpiration and the Emergence of the Safety-Efficiency Trade-Off.” The New Phytologist 198 (1): 169–78. https://doi.org/10.1111/nph.12126.
A consistent part of root zone and surface water evaporates and returns to the atmosphere to eventually form clouds and precipitation again. The process follows quite complicate routes and is different when happening from liquid surfaces, soil or vegetation (and BTW animals). In this group of lectures we try to figure out the physical mechanisms that act in the process and give some hint on methods to estimate evaporation and transpiration with physically based models.
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| Courtesy of Luca Chisté (http://www.lucachiste.it/) |
Dennis Baldocchi (GS) is a myth for me, for his knowledge of the processes and issues related to the soil atmosphere interactions, for the wide range of materials he shared with the community and for his efforts in the FLUXNET. So it was a great pleasure when I heard that he accepted to give a talk to our class (held by Mirco Rodeghiero, GS) "Biosphere Atmosphere and Climate Interactions" of the Master in Environmental Meteorology. His talk was very dense and illuminating and, fortunately, he agreed with us to share the videos that are presented here below.
Evaporation and transpiration are the topics more discussed in this blog, due to the interests I grew in the last few years (almost without publishing). However, I believe I collected enough information to be able to summarize a new view on these processes. Certainly shared with others, but not so widely shared, and not already present in other posts of this blog. In this presentation, that I shrinked in less than half an hour, I tried to summarize part of my current knowledge. For complimentary information, please see the lectures I gave at the GEOframe Winter School, or during the class of hydrology I do.
Land-Vegetation-Atmosphere interactions are an exciting field of Hydrology. Within our system GEOframe, one branch of work is improving the physics of GEOtop and this talk shows some of the work we made to this goal. Lysimiter GEO builds a virtual lysimiter and modeling infiltration and energy transfer in soil and evaporation and transpiration. The infiltration is modeled by the component WHETGEO 1D (Water, HEat and Transport in GEOframe) that integrates the 1D Richards developed by Niccolò Tubini. The evaporation and Transpiration are modeled by the GEOframe component Prospero developed by Michele Bottazzi in his Ph.D. Thesis. Lysimeter GEO, however, was completed by Concetta D'Amato who is pursuing her Ph.D. on these topics within the PRIN project WATZON.By clicking on the Figure below you can access the slides.
The work of Concetta D’Amato Ph.D. started with joining together a reasonable evapotranspiration model with a solid infiltration model building a virtual lysimeter.
