Effect of Drought on Nutrient Uptake and Levels of Nutrient-Uptake Proteins in Roots of Drought-Sensitive and -Tolerant Plants.

Climate models predict a reduction in precipitation and an increase in evapotranspiration rates in many regions of the world in coming decades, resulting in increased drought. In addition to decreasing plant growth and reproduction, drought also decreases the concentration (%) of nitrogen (N) and phosphorous (P) in plant tissues, but the reasons for this decrease are not fully understood. We evaluated the effects of drought stress on nutrient-uptake rate, concentration of nutrient-uptake proteins, and uptake-protein activity in roots, and we determined if the effects differed in drought-tolerant and -susceptible species (Andropogon gerardii, Zea mays, and Hordeum vulgare). Drought was imposed by withholding water, with the rate and severity of drought stress controlled by partial water replacement based on water mass loss and stomatal conductance (to ca. 50% and 75-90% of stomatal closure for mid- and end-of-drought, respectively). Drought slowed growth, yet reduced tissue %N and P, indicating larger effects on nutrient uptake than growth. We show for the first time that despite increased root-to-shoot mass ratio and up-regulation of N- and P-uptake proteins per unit total root protein, N and P uptake rates per g root decreased with drought, in conjunction with decreases in total root protein and either nutrient-uptake proteins per gram root (especially P) or uptake activity per transporter (especially N). Hence, future efforts to improve crop drought tolerance and minimize drought effects on crop nutritional quality should include a focus on maintaining the concentration of total root protein during drought, which will increase levels of nutrient-uptake proteins and nutrient-uptake rate.