Global diurnal and nocturnal parameters of stomatal conductance in woody plants and major crops

Aim: Stomata regulate CO2 uptake, water-vapour loss and uptake of gaseous pollutants. Jarvis-type models that apply multiple-constraint functions are commonly used to estimate stomatal conductance (g(s)), but most parameters for plant functional types (PFTs) have been estimated using limited information. We refined the data set of key components of the g(s) response to environmental factors in global PFTs. Location: Global. Time period: Data published in 1973-2015. Major taxa studied: Woody plants and major crops (rice, wheat and maize). Methods: We reviewed 235 publications of field-observed g(s) for the parameterization of Jarvis-type models in global PFTs. The relationships between stomatal parameters and climatic factors [mean annual air temperature (MAT) and mean annual precipitation (MAP)] were assessed. Results: We found that maximal stomatal conductance (g(max)) in global woody plants was correlated with MAP rather than with MAT. The g(max) of woody plants on average increased from 0.18 to 0.26mol/m(2)/s with an increase in MAP from 0 to 2,000 mm. Models, however, can use a single g(max) across major crops (0.44 mol/m(2)/s). We propose similar stomatal responses to light for C-3 crops and woody plants, but C-4 crops should use a higher light saturation point of g(s). Stomatal sensitivity to vapour-pressure deficit (VPD) was similar across forest PFTs and crops, although desert shrubs had a relatively low sensitivity of stomata to VPD. The optimal temperature for g(s) increased by 1 degrees C for every 3.0 degrees C of MAT. Stomatal sensitivity to predawn water potential was reduced in hot and dry climate. The fraction of nighttime conductance to g(max) (0.14 for forest trees, 0.28 for desert shrubs and 0.13 for crops) should be incorporated into the models. Main conclusions: This analysis of global g(s) data provides a new summary of g(s) responses and will contribute to modelling studies for plant-atmosphere gas exchange and land-surface energy partitioning.