Fluorescence parameters among leaf photosynthesis-related traits are the best proxies for CO2 assimilation in Central Amazon trees

We investigated whether photosynthesis along the vertical profile of tropical forest can be represented by JIP-test parameters derived from the fluorescence induction curve instead of more commonly utilized traits. Photosynthesis-related traits were measured during four seasons in 45 trees along a vertical forest profile in the Central Amazon, and their combined (interspecific) correlations with canopy openness and P Nmax (light-saturated photosynthesis) were examined. P Nmax , canopy openness, the efficiency of electron transport in PSI (IP-phase and RE 0 /ET 0 ), leaf mass per area and leaf phosphorus content had strong positive correlations (r > 0.6). JIP-test parameters related to the final steps of electron transport (IP-phase, RE 0 /ET 0 and PI total ) were good predictors of P Nmax during all seasons, whereas stomatal conductance had the strongest correlation with P Nmax during the dry season. The JIP-test parameters related to PSII efficiency (PI ABS and F V / F M ) were poorly associated with P Nmax . Therefore, the P Nmax variation along the vertical profile of Central Amazonian forest can be represented by JIP-test parameters, especially those related to the final steps of the electron transport chain.