RELATIONSHIPS AMONG MAXIMUM STOMATAL CONDUCTANCE, ECOSYSTEM SURFACE CONDUCTANCE, CARBON ASSIMILATION RATE, AND PLANT NITROGEN NUTRITION: A Global Ecology Scaling Exercise

Abstract

This review provides a theoretical framework and global maps for relations between nitrogen-(N)-nutrition and stomatal conductance, gs' at the leaf scale and flUXe!1 of water vapor and carbon dioxide at the canopy scale. This theory defines the boundaries for observed rates of maximum surface conductance, Gsmax, and its relation to leaf area index, A, within a range of observed max­ imum stomatal conductances. gsmax. Soil evaporation compensates for the reduced contribution of plants to total ecosystem water loss at A < 4. Thus, Gsmax is fairly independent of changes in A for a broad range of vegetation types. The variation of Gsmax within these boundaries can be explained by effects of plant nutrition on stomatal conductance via effects on assimilation. Relations are established for the main global vegetation types among (i) maximum stomatal conductance and leaf nitrogen concentrations with a slope of 0.3 mm s-I per mg N g-I, (ii) maximum surface conductance and stomatal conductance with a slope of 3 mm s-I in G per mm S-I in g, and (iii) maximum surface CO2 uptake and surface conductance with a slope of 1 /lmol m-2 s-1 in A per mm S-1 in G. Based on the distribution of leaf nitrogen in different vegetation types, predictions are made for maximum surface conductance and assimilation of carbon dioxide at a global scale. The review provides a basis for modeling and predicting feedforward and feedback effects between terres­ trial vegetation and global climate.