Mechanistic insights into the intrinsic drought resilience of Coffea spp. and its reinforcement by elevated air CO2: from water relations to photoprotection and lipid-sugar dynamics.

Drought is a critical climatic constraint to coffee, but its interaction with enhanced atmospheric [CO2] is highly relevant to the crop's sustainability under climate-change scenarios. We explored such interaction through the physiological and biochemical responses of 7-year-old potted plants of two genotypes: Coffea canephora cv. Conilon Clone 153 (CL153) and C. arabica cv. Icatu, grown under well-watered (WW) conditions at ambient [CO2] (aCO2, 380 µL L-1) or elevated [CO2] (eCO2, 700 µL L-1). Plants were gradually exposed to moderate (MWD) and severe (SWD) water deficits, reaching predawn water potentials (Ψpd) between -1.6 and -2.2 MPa (MWD) or ≤ -3.7 MPa (SWD). Under aCO2, both genotypes showed full resilience to MWD. Moreover, Icatu exhibited tolerance to SWD regardless of [CO2], showing stable chronic photoinhibition (PIChr), chlorophyll (Chl) content, and moderate osmotic adjustment from MWD to SWD (mostly related to mannitol buildup). It also showed a broader coordinated response involving enhanced photoprotection (e.g., xanthophylls), the reconfiguration of photosystems (Chl (a/b) decline), and the lipid profile of chloroplast membranes (fatty-acid composition and degree of unsaturation). The latter involved both quantitative (de novo synthesis) and qualitative changes (unsaturation shift, mostly due to an increase in C18:3 and a decline in C16:0), along with an increased C16:1c+t. Notably, eCO2 attenuated the declines in Ψpd and cell turgor under MWD particularly in Icatu, thus preserving growth. As for CL153, several adverse impacts were found in SWD under aCO2 (PIChr, Chl loss, and membrane leakage), which were counteracted by eCO2, highlighting its key role in the acquired resilience of this genotype. Collectively, these findings identify reliable traits underpinning the drought resilience of climate-resilient coffee cultivars.