Carbon and Nitrogen Dynamics in Plants Grown at Low CO2 Conditions of the Past

Andre Galvao Duarte, The University of Western Ontario

Abstract

For most of the recent evolutionary history of plants, atmospheric CO₂ concentrations have been far below modern values. However, little is known about how plants grown in a low CO₂ environment balance their carbon demand for growth while meeting their requirement for nitrogen acquisition, the establishment of mycorrhizal fungal associations, and the production of defense compounds. Here, I investigated how low CO₂ affects Elymus canadensis and Picea mariana by comparing their growth at low and current CO₂ concentrations. I found that reduced N availability exacerbated low CO₂ effects on growth, and reduced stomatal index and N isotope composition, indicating that the use of these variables as paleo-indicators can be influenced by N availability. Mycorrhizal association was enhanced in low-CO₂ plants, and increased root N but decreased root δ¹⁵N, which could skew the interpretation of δ¹⁵N when comparing non- and mycorrhizal ancient plant samples. Growth at low CO₂ decreased the formation and size of resin ducts and terpene production, suggesting that plants growing at past CO₂ conditions had reduced capacity to chemically defend against herbivory.