Summary:

### Vegetation Water Potential

The article discusses how the Plant Hydraulics Simulator (PHS) model explicitly represents the water potential of different plant components, including roots, stems, shaded leaves, and sunlit leaves. This water potential (ψ) is a vector that satisfies the continuity between the non-linear vegetation water supply and demand.

The key points are:

1. PHS iteratively finds the vegetation water potentials (ψ) that match the supply and demand equations [(2.11.24)](#equation-11-302).

2. The demand terms (transpiration) are decreasing functions of absolute leaf water potential, as higher water stress reduces transpiration.

3. The supply terms are increasing functions of absolute leaf water potential, as higher water potential gradients increase water supply.

4. PHS uses a Newton's method approach to solve for the vegetation water potentials that satisfy the continuity between water supply and demand.

The article provides the mathematical expressions for the vegetation water potential vector [(2.11.23)](#equation-11-301) and the plant water transport equations [(2.11.24)](#equation-11-302).