The effects of elevated CO2 and nitrogen nutrition on root dynamics.

Ambient CO2 concentration is currently 400 μmol mol-1, and projections forecast an increase up to 970 μmol mol-1 by century's end. Elevated CO2 can stimulate C3 plant growth, whereas nitrogen is the main nutrient plants acquire from soils and often limits growth. Plants primarily obtain two nitrogen sources from the soil, ammonium (NH4+) and nitrate (NO3-). At elevated CO2 levels, plant growth and nitrogen metabolism is affected by the nitrogen source. Most research has focused on shoot traits, while neglecting the plants' hidden half, the root. We studied the effects of elevated CO2 and nitrogen source on hydroponically grown tomato plants, a C3 model and crop plant. Our main objective was to determine how the nitrogen source and elevated CO2 affect root development. Our results indicate they affect development in terms of the size and anatomy of different root orders. Specifically, root xylem development was found sensitive to the nitrogen source, whereas NO3--supplied plants displayed greater xylem development compared to their NH4+ counterparts, and also to a lesser extent, to elevated CO2, which we found inhibits this development. Additionally, elevated CO2 decreased root respiration in different root orders exclusively in plants supplied with NH4+as the sole nitrogen source.