| | 20 | == 15/03/2018 and 16/03/2018 Coordination between plant hydraulics and photosynthesis == |
| | 21 | The meeting consisted of three parts spread over two days: |
| | 22 | (1) A presentation of the interplay between xylem, phloem, sugar sinks and photosynthesis by Teemu Hölttä [attachment:"Holtta_presentation.pdf" slides]. The models discussed by Teemu have been published in Niikinmaa et al 2013 and Hölttä et al 2016. |
| | 23 | (2) Angi Mauranen introduced the general framework as well as a series of analytical solutions to calculate stomatal conductance while accounting for the hydraulic architecture of tall vegetation (Dewar et al 2017) [attachment:"Mauranen_presentation.pdf" slides]. During the subsequent discussion Sebastiaan Luyssaert presented the expectations the ORCHIDEE-team has in terms of its photosynthesis model [attachment:"Luyssaert_presentation.pdf" slides] and Thomas Janssen presented the results of a literature study on stomatal functioning in the Amazon [attachment:"Janssen_presentation.pdf" slides]. |
| | 24 | (3) During the final session the group discussed how to proceed working on this topic without formal funding for this work. |
| | 25 | |
| | 26 | '''Participated in the discussions''': Marc Peaucelle (remotely), Kim Naudts (remotely), Aude Valade (remotely), Emilie Joetzer (remotely), Timo Vessala, Yann Saumon, Angi Mauranen, Teemu Hölttä, Nicolas Viovy, Daniel Goll, Fabienne Maignan, Philippe Peylin, Thomas Janssens, Sebastiaan Luyssaert (minutes) |
| | 27 | |
| | 28 | '''Conclusions''': The attention for plant hydraulic architecture in Earth system modelling is increasing. Photosynthesis models has been high on the agenda for a long time resulting in a steady flow of new model developments. Coordination of light and CO2 limitation in photosynthesis has received quite some attention recently and bears the promise to simulate, rather than prescribe, several of the key parameters of the current photosynthesis models. Given the physiological coupling between photosynthesis and transpiration, models accounting for the coordination between photosynthesis and within-plant water transport are a logic advancement. |
| | 29 | |
| | 30 | At present the dynamic model by Niikinmaa et al 2013 is among the most complete representations of the coupling between plant hydraulics, photosynthesis and plant growth. The model is computationally very demanding. Assuming steady state, a simplified version of the model was published by Hölttä et al 2106. This version accounts for xylem, phloem, sugar sinks and photosynthesis but no longer accounts for cavitation and water storage. The analytical solutions further reduce the number of processes that are accounted for but would overcome the need to recalculate gs in case there is plant water stress. The analytical solution retained the physical basis of the parameters as in the steady-state model but basically accounts for the upward water flow through plant hydraulic architecture. Accounting for hydraulic architecture of vegetation requires that the different vegetation components have dimensions (height, diameter, ...) as is the case in ORCHIDEE-CN-CAN. As such it was thought that in terms of functionality the analytical solution would add little to the functionality currently present in ORCHIDEE-CN-CAN. On the other hand, adding the analytical solution would require a lot of changes to the current trunk. |
| | 31 | |
| | 32 | '''Long-term goal''': coupling a unified photosynthesis model accounting for coordination/co-limitation with a closed within-plant water cycle with the aim to better account for the short term responses of photosynthesis to drought, the long-term changes in water use efficiency, as well as the source-sink dynamics which are currently poorly represented in most land surface models. A balanced representation of these processes would require a dynamic approach towards simulating the root profile as well as an investment on how to make best use of the interplay between soil water in the 11-layer hydrology and the root profile. |
| | 33 | |
| | 34 | '''Draft roadmap to achieve this long-term goal''': |
| | 35 | - Marc keeps working on the coordination, it would be good to study how easily this new approach could be added to either ORCHIDEE, ORCHIDEE-CN, ORCHIDEE-MICT or ORCHIDEE-CN-CAN. |
| | 36 | - Aude’s Marie Curie fellowship partly overlaps with the long-term objectives (i.e., adding water storage, adding dynamic roots, testing the analytical solution) |
| | 37 | - Thomas PhD’s study could be steered towards overlapping with the long-term objectives (i.e., rather than moving parts of ORCHIDEE into his Python code of Teemu’s steady state model, the missing parts of Teemu’s model could be integrated in ORCHIDEE) |
| | 38 | - Fabienne is interested in photosynthesis and showed interest in contributing to this work |
| | 39 | - If some progress is made in the coming 10 months, we should apply for funding dedicated to supporting Finnish-French collaboration through exchange visits and workshops. |
| | 40 | - Kim offered Angi some help with the nuts and bolts of JSBACH |
| | 41 | - Sebastiaan would like to prepare a scheme showing whether and how the different components of the steady-state model are currently formalized in ORCHIDEE-CN-CAN. |
| | 42 | - A shared folder containing the presentations and key papers was established access can be requested through Sebastiaan. |
| | 43 | |
