The relationship between photosynthetic capacity (Areaβ’ and leaf nitrogen concentration (N) among all C 3 species can be described roughly with one general equation, yet within that overall pattern species groups or individual species may have markedly different A~a x-N relationships. To determine whether one or several predictive, fundamental Amax-N relationships exist for temperate trees we measured Amax, specific leaf area (SLA) and N in 22 broad-leaved deciduous and 9 needleleaved evergreen tree species in Wisconsin, United States. For broad-leaved deciduous trees, mass-based Area x was highly correlated with leaf N (r2=0.75, P<0.001). For evergreen conifers, mass-based Ama x was also correlated with leaf N (r2=0.59, P<0.001) and the slope of the regression (rate of increase of Ama x per unit increase in N) was lower (P<0.001) by two-thirds than in the broad-leaved species (1.9 vs. 6.4 gmol CO 2 gq N sq), consistent with predictions based on tropical rain forest trees of short vs. long leaf life-span. On an area basis, there was a strong Amax-N correlation among deciduous species (r2=0.78, P<0.001) and no correlation (r2=0.03, P>0.25) in the evergreen conifers. Compared to deciduous trees at a common leaf N (mass or area basis), evergreen trees had lower Ama x and SLA. For all data pooled, both leaf N and Area x on a mass basis were correlated (r2-~0.6) with SLA; in contrast, area-based leaf N scaled tightly with SLA (r2=0.81), but area-based Area x did not (r2=0.06) because of low Ama x per unit N in the evergreen conifers. Multiple regression analysis of all data pooled showed that both N (mass or area basis) and SLA were significantly (P<0.