The growth of plants in elevated CO2 typically decreases the concentration of nitrogen (%N) in their tissues, especially in shoots, thereby decreasing plant protein content and food quality. Decreases in %N with elevated CO2 are likely caused by several factors, including increased carbohydrate production from photosynthesis and decreased nutrient uptake from decreased stomatal opening and transpiration. We examined if elevated CO2 might also decrease the concentration of major N-uptake proteins in roots, which could then decrease N-uptake rate. We grew tomato and barley plants under current or elevated CO2 (400 or 700 ppm) and high N availability (6mM, NO3 + NH4), or tomato at both low and high N (0.25 or 2.5 mM, NO3 or NH4). Then we quantified the concentration of the major NO3- and NH4-uptake proteins (NRT1 and AMT1), using our own protein-specific antibodies and ELISA.
Results/Conclusions
In general, elevated CO2 increased the concentrations of the major N-uptake proteins per g dry mass and per g of total protein in tomato and barley grown at high N, but decreased concentrations per g root under low N (for both NO3 and NH4). At low NO3, decreases in N-uptake proteins per g root with elevated CO2 occurred despite increases in concentrations per unit total root protein, because of decreases in total protein per g root; the reverse was true for low NH4. Hence, at high N, increases in levels of N-uptake proteins may help plants compensate for other mechanisms that decrease %N under elevated CO2, but at low N, decreases in N-uptake proteins may exacerbate high-CO2-related decreases in %N.