Adaptation of cotton bracts to high CO₂

The rapid respiration rate of cotton (Gossypium hirsutum) fruits produces a microenvironment with intercellular CO₂ concentrations of 500–1300 μmol mol^–1, and Hu et al. hypothesize that the adaptations that have evolved in response to this can provide insights relevant to future increases in atmospheric CO₂. They compare morphological and physiological traits of bracts and leaves of cotton, and find that bracts show significantly lower stomatal conductance, which results in a significantly higher water use efficiency. Both gas exchange and protein content show a significantly greater RuBP regeneration/RuBP carboxylation capacity ratio (J_max/V_cmax) in bracts than in leaves, which agrees with theoretical predictions regarding adaptation to elevated CO₂. They conclude that cotton bracts provide readily available material for studying adaptations to elevated CO₂.