Effect of drought and carbon dioxide on nutrient uptake and levels of nutrient-uptake proteins in roots of barley

Abstract

Premise: Atmospheric carbon dioxide (CO2) concentration is increasing, as is the frequency and duration of drought in some regions. Elevated CO2 can decrease the effects of drought by further decreasing stomatal opening and, hence, water loss from leaves. Both elevated CO2 and drought typically decrease plant nutrient concentration, but their interactive effects on nutrient status and uptake are little studied. We investigated whether elevated CO2 helps negate the decrease in plant nutrient status during drought by upregulating nutrient-uptake proteins in roots. Methods: Barley (Hordeum vulgare) was subjected to current vs. elevated CO2 (400 or 700 ppm) and drought vs. well-watered conditions, after which we measured biomass, tissue nitrogen (N) and phosphorus (P) concentrations (%N and P), N- and P-uptake rates, and the concentration of the major N- and P-uptake proteins in roots. Results: Elevated CO2 decreased the impact of drought on biomass. In contrast, both drought and elevated CO2 decreased %N and %P in most cases, and their effects were additive for shoots. Root N- and P-uptake rates were strongly decreased by drought, but were not significantly affected by CO2. Averaged across treatments, both drought and high CO2 resulted in upregulation of NRT1 (NO3− transporter) and AMT1 (NH4+ transporter) per unit total root protein, while only drought increased PHT1 (P transporter). Conclusions: Elevated CO2 exacerbated decreases in %N and %P, and hence food quality, during drought, despite increases in the concentration of nutrient-uptake proteins in roots, indicating other limitations to nutrient uptake.