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.

Keywords: Gramineae; Poaceae; carbon dioxide; climate change; drought; nutrient uptake; nutrient-uptake protein; roots.