HR: 10:55h
AN: H52C-03 INVITED     [Abstracts]
TI: Transpiration as the Leak in a Carbon Factory: A Model of Self-Optimising Vegetation
AU: * Sivapalan, M
EM: sivapala@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Departments of Geography and Civil and Environmental Engineering, 220 Davenport Hall, 607 S. Mathews Avenue, Urbana, IL 61801 United States
AU: Schymanski, S J
EM: schymans@cwr.uwa.edu.au
AF: University of Western Australia, School of Water Research, 35 Stirling Highway, Crawley, WA 6009 Australia
AU: Roderick, M L
EM: Michael.Roderick@anu.edu.au
AF: Australian National University, CRC for Greenhouse Accounting, Research School of Biological Sciences, GPO Box 475, Canberra, ACT 2601 Australia
AB: "Only now it occurred to me that plants are not water pumps but carbon factories" (Anonymous Hydrologist). When thinking of plants as `water pumps', we are led to the conclusion that vegetation would tend to maximise the total amount of transpiration while minimising the occurrence probability of periods without adequate water availability (`stress'). However, this does not do adequate justice to the fact that plants owe their existence to photosynthesis, and can thrive perfectly well even when the relative humidity of the air is very high and transpiration is almost negligible. In this paper, we present a model in which the maximisation of net CO2 uptake rather than maximisation of water use or minimisation of `stress' is assumed to be the driving force behind natural selection. Transpiration is the inevitable consequence of CO2 uptake from the atmosphere and water uptake from the soil incurs construction and maintenance costs of a root system, so that water use strategies become a consequence of the maximisation of net CO2 uptake and `stress' becomes an obsolete feature. We will demonstrate that a simple model based on ecological optimality is capable of reproducing some vegetation and water balance dynamics without any prior knowledge about the vegetation on a particular site. The model is based on a physical water balance model by Reggiani et al. (2000), an ecophysiological gas exchange and photosynthesis model (Cowan and Farquhar 1977; von Caemmerer 2000), and the hypothesis that natural selection leads to a vegetation type that optimally uses available resources to maximise its `net carbon profit' (the net tradeoff between carbon acquired by photosynthesis and carbon spent on maintenance of the organs involved in its uptake). While, at this early stage of its development, the site properties such as soil type and depth, topography and climate still have to be prescribed, the model creates the `optimal' dynamically adjusting vegetation for the particular site and calculates the water- and CO2- fluxes between soil, watershed boundaries, vegetation and atmosphere. Cowan, I. R. and G. D. Farquhar (1977). Stomatal Function in Relation to Leaf Metabolism and Environment. Integration of activity in the higher plant. D. H. Jennings. Cambridge, Cambridge University Press: 471-505. Reggiani, P., M. Sivapalan, et al. (2000). Conservation equations governing hillslope responses: Exploring the physical basis of water balance. Water Resources Research 36(7): 1845-1863. von Caemmerer, S. (2000). Biochemical Models of Leaf Photosynthesis. Collingwood, CSIRO Publishing.
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1836 Hydrological cycles and budgets (1218, 1655)
DE: 1852 Plant uptake
DE: 1874 Ungaged basins
SC: Hydrology [H]
MN: Fall Meeting 2005