Fig. 3: Soil texture shapes the relative importance of VPD and soil moisture.

a–d, Soil texture drives the relative importance of VPD versus the soil moisture (θ) limitation of ecosystem fluxes (that is, the downregulation of g_c from its maximum g_cmax) and involves implications of future climate on terrestrial ecosystems (Fig. 4). Ecosystems in fine-textured soils (that is, clays (b,d)) are expected to be comparatively more sensitive to VPD than those in coarse soils (that is, sands (a,c)), while ecosystems in coarse-textured soils are expected to be comparatively more sensitive to soil drying than in fine soils because critical soil water potentials (ψ_soil) are more negative (note the 10-fold different x-axis limit in a,b), and the g_c downregulation is more gradual (softer colour transitions), in fine- than in coarse-textured soils. e,f, The evaporative fraction (EF) from eddy covariance data shows different responses to the two environmental drivers, θ and VPD, for the two contrasting soil textures (sand (e) and clay (f) sites, median of five FN sites). The evaporative fraction declines in both soil textures within a narrow range of soil moisture, but more sharply and at lower absolute water contents in the sand sites than in the clay sites. The simulations of transpiration rate as a function of VPD and θ (red line) agree well with the observed decline in the evaporative fraction around θ_crit. The inset plots show the median relative sensitivity of evaporative fraction to VPD and θ, confirming the stronger relative contribution of soil hydraulic limitation in coarse-textured compared to fine-textured soils.