Elevated CO2, Warming and Drought Differentially Impact Reproductive and Vegetative Economic Traits in Two Grassland Species.

Background and aims: Since the Industrial Revolution, rising atmospheric CO₂, warming, and more frequent droughts have significantly impacted ecosystems. While the response of leaf functional traits to these climate change factors have been widely studied, reproductive traits remain relatively understudied, despite their key role in the diversification and distribution of flowering plants. Here, we investigated how elevated CO₂, warming, drought, and their interactions affect floral, leaf and seed traits in two model grassland species. We also examined how these factors influence trait coordination.

Methods: Two common grassland species, Lotus corniculatus and Crepis capillaris, were sampled from a 10-year climate manipulation experiment. We measured resource economic traits related to organ size, construction cost, and dry matter content in both leaves and flowers, along with seed size and number. Univariate and multivariate analyses were used to assess trait responses, and rank-abundance curves were employed to visualize changes in trait coordination across treatments.

Key results: Trait responses to climate change factors varied between species. Drought emerged as the most influential factor, affecting only leaf traits in L. corniculatus, but impacting leaf, floral, and seed traits in C. capillaris. Across both species, climate change conditions increased leaf construction costs and reduced flower size. In addition, it led to larger leaves in L. corniculatus, and fewer seeds in C. capillaris. Under extreme climate change conditions, trait coordination became stronger in both species, although C. capillaris showed no coordination response specifically to drought.

Conclusion: Our results show that floral economic traits, like leaf traits, are responsive to individual and combined effects of climate change factors. This highlights their importance in shaping plant strategies under environmental stress and emphasizes the need to better integrate floral traits into the whole-plant economic framework.