Coupling soil hydraulics to stomatal conductance; a mechanism for modelling the impacts of drought on forest gas exchange.
Rosie
Alice
Fisher, University of Edinburgh, rosie.fisher@ed.ac.uk
Mathew
Williams, University of Edinburgh, mat.williams@ed.ac.uk
Antônio
Carlos Lôla da
Costa, Universidade Federal do Para, lola@ufpa.br
Maria
de Lourdes Pinheiro
Ruivo, Museu Paraense Emilio Goeldi, ruivo@museu-goeldi.br
Patrick
Meir, University of Edinburgh, pmeir@ed.ac.uk
(Presenting)
At our throughfall exclusion experiment at Caxiuanã (Para), we are investigating how forest gas exchange responds to drought stress. We have artificially reduced the soil water content, and are observing how the sapflow, leaf physiology, tree dynamics and soil respiration change as the drought progresses. Substantial reductions in sapflow have been measured at our droughted site compared to the control site. In order to apply what we have learnt about the behaviour of the drought tolerance of the Caxiuanã forest to other area of Amazonia, or to alternative droughting scenarios, it is necessary to integrate our new understanding of drought physiology into a simulation model.
The majority of soil-vegetation-atmosphere-transfer models express drought induced stomatal closure as a simple function of soil water content or potential, the parameters of which are generally poorly known. Our goal is to remove the need for this empiricism by explicitly simulating the movement of water through the soil and plant to the leaf, and optimising the stomatal conductance such that the plant maximises photosynthesis rates whilst avoiding desiccation.
To parameterise our soil-plant-atmosphere model (SPA), we collected data on soil hydraulic properties, LAI, root biomass profiles, and photosynthetic capacity. The model was validated against sapflow, soil moisture, and leaf physiology data. We found that the key factor driving reductions in forest gas exchange in the dry season is soil hydraulic resistance, however, measurements of soil hydraulic resistance are extremely uncommon in Amazonia, and we conclude that a survey of soil hydraulics is necessary to identify areas of Amazonia most vulnerable to climate drying.
Submetido por Rosie Alice Fisher em 18-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)