Growth and Leaf Gas Exchange Upregulation by Elevated [CO2] Is Light Dependent in Coffee Plants

Coffee (Coffea arabica L.) plants have been assorted as highly suitable to growth at elevated [CO2] (eC(a)), although such suitability is hypothesized to decrease under severe shade. We herein examined how the combination of eC(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 aC(a) or eC(a) (437 or 705 mu mol mol(-1), respectively). Most traits were affected by light and CO2, and by their interaction. Relative to aC(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 gs was unresponsive to the LL-to-HL transitions irrespective of [CO2], (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, eC(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 [CO2], especially if the light is nonlimiting.