Carbon (C) and nitrogen (N) are the two most abundant nutrient elements in plants, and the synergistic and tightly coupled regulation of C and N metabolism plays a crucial role in the adaptation of plants to all kinds of stresses. Freshwater plants, the important primary producers in productive freshwater ecosystems, their growth is frequently limited by the availability of carbon. Comprehensively revealing the regulation of C and N metabolism, as well as their interactions are important and helpful for understanding the adaptation of freshwater plants to lower CO₂ stress. However, the studies on the photosynthetic C and N metabolism response to CO₂ limitation in freshwater plants are fragmented and limited.

Researchers from Wuhan Botanical Garden comprehensively investigated the diel change of photosynthates, soluble proteins, free amino acids, and a comprehensive metabolomics analysis in the freshwater plant Ottelia alismoides to reveal the underlying adaptive mechanism of C-N interactions to different CO₂ environments.

Results showed that when O. alismoides was stressed by low CO₂, crassulacean acid metabolism (CAM) was induced for adapting to the carbon stress. In addition, the metabolomic analysis showed that most intermediates associated with energy metabolism including glycolysis, pentose phosphate pathway (PPP) and tricarboxylic acid (TCA) cycle were increased significantly following low CO₂ stress, which indicated the activation of respiration in low CO₂ treated O. alismoides. Meanwhile, most of the amino acids involved in pathways of glutamate and arginine metabolism, aspartate metabolism, and the branched-chain amino acids (BCAAs) metabolism were significantly promoted under low CO₂.

In conclusion, this study provides valuable insight into the metabolic response of O. alismoides to variable CO₂ based on a conjoint analysis of physiology and metabolomics.

It was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences and the National Natural Science Foundation of China. The results have been published in Frontiers in Plant Science entitled “Carbon and nitrogen metabolic regulation in freshwater plant Ottelia alismoides in response to carbon limitation: A metabolite perspective”.

A summary of the metabolic changes in carbon and nitrogen metabolism in low CO₂ compared to high CO₂ grown Ottelia alismoides (Image by WBG)