Impacts of elevated temperature and CO2 concentration on carbon metabolism in an endangered carnation: Consequences for biomass allocation and flowering

One of the greatest threats to plant function and fitness is global warming, characterised by a combination of increased atmospheric CO₂ concentrations and temperatures. However, their effects on plant physiology, growth, and reproduction remain unclear, particularly for rare species that support vulnerable ecosystem functions. Here, we investigated these effects on leaf and whole-plant functional traits of the rare endangered C₃ species Dianthus inoxianus. Mature plants were grown for 18 weeks in controlled-environment chambers under four environmental scenarios that combined day/night air temperatures (ambient: 25/20 °C or elevated: 29/24 °C) with CO₂ concentrations (400 ppm or 700 ppm). Under elevated temperature, D. inoxianus exhibited impaired photosynthetic capacity but also employed an avoidance strategy by prioritising accelerated reproduction (earlier flowering) and biomass allocation to roots for future resprouting. Elevated CO₂ induced photosynthesis acclimation and biochemical constraints, preventing growth enhancement, but also mitigated the loss of stomatal functionality and carboxylation capacity loss caused by elevated temperature. Although plants sustained gas exchange under combined elevated CO₂ and temperature, assimilation rates decreased. Such a decline, linked to reduced photoprotection capacity and photosystem performance, was accompanied by an advanced onset of flowering and reduced flower production. These changes suggest that the vulnerability of D. inoxianus might increase under climate change, with additional stressors potentially exacerbating photoinhibition. Our findings offer critical insights into the complex relationships between threatened species and their environment, underscoring the need for preventive conservation measures for D. inoxianus to address the challenges posed by more extreme or prolonged environmental stresses.