Soil plant atmosphere continuum
- Soil plant atmosphere continuum
The Soil-Plant-Atmosphere Continuum (SPAC) is the pathway for water moving from soil through the plant-animals to the atmosphere.
The transport of water along this pathway occurs in components only as separate defined and differently between a scientific discipline in the environment:
* soil physics characterizes soil water in terms of tension,
* plant physiology characterizes plant water in terms of "diffusion pressure deficit",
* meteorology uses vapour pressure or relative humidity to characterize atmospheric water, and
* medicine uses physiology with essential processes in all forms of life - as human excretion.
SPAC integrates the some components and is defined as a:
...concept recognising that the field with all its components (soil, plant, animals and the ambient atmosphere taken together) constitutes a physically integrated, dynamic system in which the various flow processes involving energy and matter occur simultaneously and independently like links in the chain. [ John R. Philip (1966). Plant water relations: some physical aspects. Annu. Rev. Plant Physiol. 17, 245–268.]
This continuum hypothesis characterises the state of water in different components of the SPAC as expressions of the energy level or water potential of each. Modelling of water transport between components relies on SPAC, as do studies of water potential gradients between segments.References
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