COMPUTER-SIMULATIONS AS A TOOL FOR UNDERSTANDING THE EVOLUTION OF WATER TRANSPORT-SYSTEMS IN LAND PLANTS - A REVIEW AND NEW DATA

The analyses of the form-function relationship in plant water transpor t systems are severely restricted due to several factors: (1) It is al most impossible to directly observe the water flow in single component s of the xylem: tracheids or vessels. (2) The water relations of tissu es or whole plant organs are difficult to measure experimentally. (3) Systematic comparative studies of various xylem constructions are seve rely hampered by individual variations in morphology as well as by the complex pattern of physiological reactions of living plants. (4) Fina lly, direct experimental work on fossil plants is obviously impossible . Here, numerical modelling is provided as an alternative to experimen tal studies. Computer simulations have the following advantages and po ssibilities. (1) The different levels of xylem organization, conduits or conducting bundles and systems of conducting bundles, can be modell ed by appropriate physical models. (2) Systematic parameter variations are easily accomplished. The consideration of arbitrary architectures is possible and, thus, a direct comparison of various xylem architect ures. (3) High resolution results on the spatial as well as the tempor al level can be obtained. (4) The evolutionary process can be simulate d with the approach of synergetics (a mathematical theory which descri bes self organization processes) allowing form-function relationships to be tested. In this paper some numerical studies of the water transp ort properties of telomes with various stele types to provide a functi onal explanation for observed patterns of stelar evolution are present ed. It is demonstrated that water transporting function is the crucial factor in the evolution of the various stales. Three geometric parame ters which determine the water transport performance and the water tra nsport efficiency of transpiring plant axes are identified, These geom etric parameters provide the basis for a functional explanation of the evolution of the stale. Using the approach of phenomenological synerg etics the stelar evolution itself is simulated as system state transit ions induced by water supply demands of the axis. (C) 1998 Elsevier Sc ience B.V. AU rights reserved.