Growth and Leaf Gas Exchange Upregulation by Elevated [CO 2 ] Is Light Dependent in Coffee Plants.

Coffee ( Coffea arabica L.) plants have been assorted as highly suitable to growth at elevated [CO 2 ] (e C a ), although such suitability is hypothesized to decrease under severe shade. We herein examined how the combination of e C a and contrasting irradiance affects growth and photosynthetic performance. Coffee plants were grown in open-top chambers under relatively high light (HL) or low light (LL) (9 or 1 mol photons m -2 day -1 , respectively), and a C a or e C a (437 or 705 μmol mol -1 , respectively). Most traits were affected by light and CO 2 , and by their interaction. Relative to a C a , our main findings were (i) a greater stomatal conductance ( g s ) (only at HL) with decreased diffusive limitations to photosynthesis, (ii) greater g s during HL-to-LL transitions, whereas g s was unresponsive to the LL-to-HL transitions irrespective of [CO 2 ], (iii) greater leaf nitrogen pools (only at HL) and higher photosynthetic nitrogen-use efficiency irrespective of light, (iv) lack of photosynthetic acclimation, and (v) greater biomass partitioning to roots and earlier branching. In summary, e C a improved plant growth and photosynthetic performance. Our novel and timely findings suggest that coffee plants are highly suited for a changing climate characterized by a progressive elevation of [CO 2 ], especially if the light is nonlimiting.