28 Jan 2022
28 Jan 2022
Status: this preprint is currently under review for the journal BG.

Exploring the role of bedrock representation on plant transpiration response during dry periods at four forested sites in Europe

César Dionisio Jiménez-Rodríguez, Mauro Sulis, and Stanislaus Schymanski César Dionisio Jiménez-Rodríguez et al.
  • Environmental Research and Innovation (ERIN) Department, Luxembourg Institute of Science and Technology (LIST), Belvaux, L-4422, Luxembourg

Abstract. Forest transpiration is controlled by the atmospheric water demand, potentially constrained by soil moisture availability, and regulated by plant physiological properties. During summer periods, soil moisture availability at sites with thin soils can be limited, forcing the plants to access moisture stored in the weathered bedrock. Land surface models (LSMs) have considerably evolved in the description of the physical processes related to vegetation water use but the effects of bedrock position and water uptake from fractured bedrock has not received much attention. In this study, the Community Land Model version 5.0 (CLM 5) is implemented at four forested sites with relatively shallow bedrock and located across an environmental gradient in Europe. Three different bedrock configurations (i.e., default, deeper, and fractured) are applied to evaluate if the omission of water uptake from weathered bedrock could explain some model deficiencies with respect to the simulation of seasonal transpiration patterns. Sap flow measurements are used to benchmark the response of these three bedrock configurations. It was found that the simulated transpiration response of the default model configuration is strongly limited by soil moisture availability at sites with extended dry seasons. Under these climate conditions, the implementation of an alternative (i.e., deeper and fractured) bedrock configuration resulted in a better agreement between modeled and measured transpiration. At the site with a continental climate, the default model configuration accurately reproduced the magnitude and temporal patterns of the measured transpiration. The implementation of the alternative bedrock configurations at this site provided more realistic water potentials in plant tissues but negatively affects the modeled transpiration during the summer period. Finally, all three bedrock configurations did not show differences in terms of water potentials, fluxes, and performances on the more northern and colder site exhibiting a transition between oceanic and continental climate. Model performances at this site are low, with a clear overestimation of transpiration compared to sap flow data. The results of this study call for increased efforts into better representing lithological controls on plant water uptake in LSMs.

César Dionisio Jiménez-Rodríguez et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-311', Anonymous Referee #1, 05 Feb 2022
    • AC1: 'Reply on RC1', César Dionisio Jiménez-Rodríguez, 15 Mar 2022
  • RC2: 'Comment on bg-2021-311', Anonymous Referee #2, 25 Mar 2022
    • AC2: 'Reply on RC2', César Dionisio Jiménez-Rodríguez, 04 Apr 2022

César Dionisio Jiménez-Rodríguez et al.

César Dionisio Jiménez-Rodríguez et al.


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Short summary
The vegetation often uses more water than the stored in the soil, forcing them to access the rocks beneath to fulfill their water needs. However, the numerical representation of this process is usually overlooked by Land Surface Models. In this work, we mimicked the effect of fractured rocks beneath four forested sites in Europe. We observed the positive impact of these rocks on the modeled plant transpiration when compared with the measured water use of the selected forests during summertime.