CO2 and nitrogen interaction alters root anatomy, morphology, nitrogen partitioning and photosynthetic acclimation of tomato plants

Main conclusionNitrogen and CO2 supply interactively regulate whole plant nitrogen partitioning and root anatomical and morphological development in tomato plants.AbstractNitrogen (N) and carbon (C) are the key elements in plant growth and constitute the majority of plant dry matter. Growing at CO2 enrichment has the potential to stimulate the growth of C-3 plants, however, growth is often limited by N availability. Thus, the interactive effects of CO2 under different N fertilization rates can affect growth, acclimation to elevated CO2, and yield. However, the majority of research in this field has focused on shoot traits, while neglecting plants' hidden half-the roots. We hypothesize that elevated CO2 and low N effects on transpiration will interactively affect root vascular development and plant N partitioning. Here we studied the effects of elevated CO2 and N concentrations on greenhouse-grown tomato plants, a C-3 crop. Our main objective was to determine in what manner the N fertilization rate and elevated CO2 affected root development and nitrogen partitioning among plant organs. Our results indicate that N interacting with the CO2 level affects the development of the root system in terms of the length, anatomy, and partitioning of the N concentration between the roots and shoot. Both CO2 and N concentrations were found to affect xylem size in an opposite manner, elevated CO2 found to repressed, whereas ample N stimulated xylem development. We found that under limiting N and eCO(2), the N% increase in the root, while it decreased in the shoot. Under eCO(2), the root system size increased with a coordinated decrease in root xylem area. We suggest that tomato root response to elevated CO2 depends on N fertilization rates, and that a decrease in xylem size is a possible underlying response that limits nitrogen allocation from the root into the shoot. Additionally, the greater abundance of root amino acids suggests increased root nitrogen metabolism at eCO(2) conditions with ample N.