A Limiting Factor
Published on Plants in Action (http://plantsinaction.science.uq.edu.au/edition1) Home > Printer-friendly > Printer-friendly Chapter 15 - Water: a limiting factor [1] A superb stand of flooded gums, (Eucalyptus grandis) near Coffs Habour, northern New South Wales, 'each tall because of each' (Les Murray (1991), Collected Poems) (Photograph by Ken Eldridge, supplied by Peter Burgess, CSIRO Forestry and Forest Products) With perspective phrasing, Les Murray (1991) summarises structural aspects of a gum forest as: 'Flooded gums on creek ground, each tall because of each' and on conceptualising water relations, 'Foliage builds like a layering splash: ground water drily upheld in edge-on, wax rolled, gall-puckered leaves upon leaves. The shoal life of parrots up there.' (Les Murray, Collected Poems, 1991) Introduction Life-giving water molecules, fundamental to our biosphere, are as remarkable as they are abundant. Hydrogen bonds, enhanced by dipole forces, confer extraordinary physical properties on liquid water that would not be expected from atomic structure alone. Water has the strongest surface tension, biggest specific heat, largest latent heat of vaporisation and, with the exception of mercury, the best thermal conductivity of any known natural liquid. A high specific grav-ity is linked to a high specific heat, and very few natural substances require 1 calorie to increase the temperature of 1 gram by 1ºC. Similarly, a high heat of vaporisation means that 500 calories are required to convert 1 gram of water from liquid to vapour at 100ºC. This huge energy requirement (latent heat of vaporisation, Section 14.5) ties up much heat so that massive bodies of water contribute to climatic stability, while tiny bodies of water are significant for heat budgets of organisms.
[Show full text]