Fig. 6.

Correlations between the capacities for isoprene emission (I_max) and photosynthetic electron transport [J_max, (a)], and saturating quantum flux density (Q₉₀) for isoprene emission in relation to Q₉₀ for net assimilation (b) and photosynthetic electron transport (c) and in different-aged leaves of hybrid aspen (P. tremula x P. tremuloides). The process capacities are defined by Eq. 2 and the saturating quantum flux density by Eq. 3. Data for all leaf ages pooled in (a), and data for young and mature leaves pooled in (b) and (c) were fitted by linear regressions (symbols as in Fig. 3 and leaf age classes as in Fig. 1, all regressions are significant at P < 0.01). Dashed lines in (b) and (c) denote the 1:1 relationships.