Zeira, D.;Eisenbach, O.;Harel-Beja, R.;Trainin, T.;Hatib, K.;Terner, L.;Abd-Elhadi, M.;Brukental, H.;Shapira, O.;Zait, Y.;Holland, D.;Shemer, T.

Rising winter temperatures threaten deciduous fruit tree productivity by depleting carbohydrate reserves during dormancy. This study investigated Stem Photosynthetic Capacity (SPC), a rare adaptive trait from wild Prunus arabica , as a mechanism to enhance almond carbon economy. Using extreme segregating groups from the F1 population ( P. dulcis X P. arabica ), we evaluated physiological performance through high-resolution lysimetric and multi-year orchard monitoring. High-SPC [SPC(+)] genotypes maintained significantly greater stem CO 2 assimilation and transpiration during leafless periods compared to low-SPC [SPC(-)] progenies. Over five successive seasons, SPC(+) trees exhibited a 33.3% increase in trunk secondary growth and reached 10% bloom approximately 8 days earlier. Most importantly, the SPC(+) group achieved a 4.6-fold increase in mean kernel yield when compared to SPC(-) group. These findings demonstrate that SPC provides a flexible, supplementary winter carbon source that directly supports both vegetative and reproductive development. Integrating SPC into commercial almond breeding programs may offer a valuable strategy to improve climate resilience and help sustain yields under warming conditions. Highlight Integrating stem photosynthesis into commercial almond hybrids provides a winter carbon source that advances blooming, expands trunk growth by ∼33%, and increases kernel yields by more than 4.5-fold.