The photosynthesis leaf nitrogen relationship at ambient and elevated atmospheric carbon dioxide: a meta-analysis

Estimation of leaf photosynthetic rate (A) from leaf nitrogen content (N) i s both conceptually and numerically important in models of plant, ecosystem , and biosphere responses to global change. The relationship between A and N has been studied extensively at ambient CO2 but much less at elevated CO2 . This study was designed to (i) assess whether the A-N relationship was mo re similar for species within than between community and vegetation types, and (ii) examine how growth at elevated CO2 affects the A-N relationship. D ata were obtained for 39 C3 species grown at ambient CO2 and 10 C3 species grown at ambient and elevated CO2. A regression model was applied to each s pecies as well as to species pooled within different community and vegetati on types. Cluster analysis of the regression coefficients indicated that sp ecies measured at ambient CO2 did not separate into distinct groups matchin g community or vegetation type. Instead, most community and vegetation type s shared the same general parameter space for regression coefficients. Grow th at elevated CO2 increased photosynthetic nitrogen use efficiency for pin es and deciduous trees. When species were pooled by vegetation type, the A- N relationship for deciduous trees expressed on a leaf-mass basis was not a ltered by elevated CO2, while the intercept increased for pines. When regre ssion coefficients were averaged to give mean responses for different veget ation types, elevated CO2 increased the intercept and the slope for deciduo us trees but increased only the intercept for pines. There were no statisti cal differences between the pines and deciduous trees for the effect of CO2 . Generalizations about the effect of elevated CO2 on the A-N relationship, and differences between pines and deciduous trees will be enhanced as more data become available.