Fig. 3: Predicted photosynthetic responses to progressive soil drought closely match observations.

Matches are shown here for two Eucalyptus species from contrasting climates, and corresponding matches for all 18 species are shown in Supplementary Fig. 1. a–f, Predicted responses (lines) and observed responses (points) to decreasing soil water potential (ψ_s, measured as predawn leaf water potential): assimilation rate A (a), stomatal conductance g_s (b), leaf-internal-to-external CO₂ ratio χ (c), soil-to-leaf water-potential difference Δψ (d), carboxylation capacity V_cmax (e) and electron-transport capacity J_max (f). Eucalyptus pilularis (blue lines and squares) typically occupies warm and humid coastal areas in eastern Australia, whereas Eucalyptus populnea (green lines and triangles) typically occupies semi-arid interior regions of eastern Australia. Since both species were grown in the same greenhouse during the experiment, their contrasting responses reveal genetic adaptations to their native environments. For both species, progressive drought was experimentally induced over 12 d, resulting in a fast instantaneous response of stomatal conductance in combination with a slow acclimating response of photosynthetic capacity. Our model predictions readily account for both responses.