Carbon assimilation through a vertical light gradient in the canopy of invasive herbs grown under different temperature regimes is determined by leaf and whole-plant architecture.

This study examined the acclimation to temperature of two globally invasive species and , which share the same habitat type but differ in morphology. has long vertical leaves, allowing light penetration through the canopy, while has stems with small horizontal leaves, creating significant self-shading. We aimed to build a physiological understanding of how these two species respond to different growth temperatures with regard to growth and gas exchange-related traits over the canopy. Growth and gas exchange-related traits in response to low (15 °C) and high (25 °C) growth temperature regimes were compared. Plants were grown in growth chambers, and light response curves were measured with infrared gas analysers after 23-33 days at three leaf positions on each plant, following the vertical light gradient through the canopy. After 37 days of growth, above-ground biomass, photosynthetic pigments and leaf N concentration were determined. The maximum photosynthesis rate was lower in lower leaf positions but did not differ significantly between temperatures. photosynthesis decreased with decreasing leaf position, more so than . This was explained by decreasing N and chlorophyll concentrations towards the leaf base in , while pigment concentrations increased towards the lower canopy in Biomass, shoot height and specific leaf area increased with temperature, more so in than in Light response curves revealed that had a higher degree of shade acclimation than , probably due to self-shading in . High temperature decreased C assimilation at the bottom of the canopy in , while C assimilation in was less affected by temperature. As vegetative growth and flowering was stimulated by temperature, the invasive potential of these species is predicted to increase under global warming.