Soil-plant-atmosphere continuum

The soil-plant-atmosphere continuum (SPAC) is the pathway for water moving from soil through plants to the atmosphere.

Continuum in the description highlights the continuous nature of water connection through the pathway.

[1] As water vapour transpires out of the leaf, further water molecules evaporate off the surface of mesophyll cells to replace the lost molecules since water in the air inside leaves is maintained at saturation vapour pressure.

The transport of water along this pathway occurs in components, variously defined among scientific disciplines: SPAC integrates these 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.

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Arbitrary numbers picked to represent decreasing water potentials from the soil, through the plant, to the atmosphere. This shows the net movement of water down its potential energy gradient, from highest water potential in the soil to lowest water potential in the air. [ 1 ]