The increase of current atmospheric CO2 and temperature can benefit leaf gas exchanges, carbohydrate content and growth in C4 grass invaders of the Cerrado biome

Abstract

Leaf gas exchanges, carbohydrate metabolism and growth of three Brazilian Cerrado invasive African grasses were evaluated after growing for 75 days under doubled CO₂ concentration and temperature elevated by 3 °C. Results showed that although the species presented photosynthetic C4 metabolism, they all had some kind of positive response to increased CO₂. Urochloa brizantha and Megathyrsus maximus showed increased height for all induced environmental conditions. Urochloa decumbens showed only improvement in water use efficiency (WUE), while U. brizantha showed increased CO₂ assimilation and M. maximus presented higher biomass accumulation under doubled CO₂ concentration. The most significant improvement of increased CO₂ in all three species appears to be the increase in WUE. This improvement probably explains the positive increase of photosynthesis and biomass accumulation presented by U. brizantha and M. maximus, respectively. The increase in temperature affected leaf carbohydrate content of M. maximus by reducing sucrose, glucose and fructose content. These reductions were not related to thermal stress since photosynthesis and growth were not harmed. Cellulose content was not affected in any of the three species, just the lignin content in U. decumbens and M. maximus. All treatments promoted lignin content reduction in U. brizantha, suggesting a delay in leaf maturation of this species. Together, the results indicate that climate change may differentially promote changes in leaf gas exchanges, carbohydrate content and growth in C4 plant species studied and all of them could benefit in some way from these changes, constituting a threat to the native Cerrado biodiversity.

Keywords: C4 metabolism; Photosynthesis; Soluble sugars; Water relations.