The interrelation of carbon and water balance in beech-dominated forests - from leaf level water use efficiency to stand and area scale assessments
Zusammenfassung der Projektergebnisse
In order to assess the interrelation between the carbon and water balance in beech dominated forests across scales we carried out a research program consisting of four independent but complementing work packages dealing with: 1) Drought adaptation at the leaf level: Water use efficiency, mesophyll conductance and photosynthetic carbon isotope discrimination; 2) Carbon transport and the interaction between water and carbon balance at the tree level; 3) Water and carbon balance at the tree and stand level: Retrospective analysis of stable isotopes in tree rings, 4) Tree water and carbon balance model; and 5) Transferring physiological information from the point to area scale - Isoscapes and geospatial modelling of stable isotope ratios. Our main findings were that, changes in mesophyll conductance (g m) were significantly correlated with the drought-induced change in water use efficiency (WUE), thus proving the importance of g m in optimizing resource use under water restriction. Thus on the leaf level not only stomatal conductance but additionally mesophyll conductance is a means for plants to adapt their balance of water use vs. carbon uptake. When moving to the whole tree scale we could show that moderate "realistic" drought slows down the transfer of recent assimilates below ground but it is likely that the uncoupling between assimilation and below ground processes is less dramatic as assumed earlier. It is probably more important to consider storage and remobilization processes - which might be also affected by the tree water balance - when tracing the fate of carbon not only below ground but also into the tree ring archive. Only when the coupling or decoupling between leaf level isotopic signals and the tree ring is understood this archive can be fully exploited for the retrospective analysis of the tree`s physiological response to environmental drivers. Moving from the tree to the stand level we applied the single-tree xylem water flow model (XWF). We could show that with species-specific model parameterization and precise terrestrial laser scan-based stand characterization, the XWF model is applicable to various sites and tree species and is a promising tool for predicting the possible water supply limitations of pure and mixed forest stands. Scaling up the stand level balance between assimilation and stomatal conductance to the area scale by applying intrinsic water use efficiency data obtained from TM 13 C measurements and forest inventory data, we could point to the importance of biodiversity in Germany’s beech dominated forests for their water supply especially under drought conditions.
Projektbezogene Publikationen (Auswahl)
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2011. Diel variations in the carbon isotope composition of respired CO2 and associated carbon sources: a review of dynamics and mechanisms. Biogeosciences, Vol. 8.2011, issue 9, pp. 2437-2459.
Werner C, Gessler A.
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2011. The Long way down – are carbon and oxygen isotope signals in the tree ring uncoupled from canopy physiological processes? Tree Physiology, Vol. 31. 2011, Issue 10, pp. 1088-1102.
Offermann C., Ferrio J.P., Holst J., Grote R., Siegwolf R., Kayler Z., Gessler A.
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2012. The Péclet effect on leaf water enrichment correlates with leaf hydraulic conductance and Mesophyll conductance for CO2. Plant, Cell & Environment, Vol. 35. 2012, Issue 3, pp. 611–625.
Ferrio J.P., Pou A., Florez-Sarasa I., Gessler A., Kodama N., Flexas J., Ribas-Carbo M.
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2013. Simulation of stand transpiration based on a xylem water flow model for individual trees. Agricultural and Forest Meteorology, Vol. 182–183. 2013, pp. 31–42.
Hentschel R., Bittner S., Janott, M., Biernath C., Holst J., Ferrio J.P., Gessler A., Priesack E.
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2013. The oxygen isotope enrichment of leaf-exported assimilates - does it always reflect lamina leaf water enrichment?
New Phytologist, Vol. 200. 2013, Issue 1, pp. 144–157.
Gessler A., Brandes E., Keitel C., Boda S., Kayler Z.E., Granier A., Barbour M., Farquhar G.D., Treydte K.
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2014. Drought response of mesophyll conductance in forest understory species - Impacts on water use efficiency and interactions with leaf water movement. Physiologia Plantarum, Vol. 152. 2014, Issue 1, pp. 98–114.
Hommel R, Siegwolf R., Saurer M, Farquhar GD, Kayler Z, Ferrio JP Gessler A.
