Reduction of transpiration and altered nutrient allocation contribute to nutrient decline of crops grown in elevated CO2 concentrations

Abstract

Plants grown in elevated [CO2] have lower protein and mineral concentrations compared with plants grown in ambient [CO2]. Dilution by enhanced production of carbohydrates is a likely cause, but it cannot explain all of the reductions. Two proposed, but untested, hypotheses are that (1) reduced canopy transpiration reduces mass flow of nutrients to the roots thus reducing nutrient uptake and (2) changes in metabolite or enzyme concentrations caused by physiological changes alter requirements for minerals as protein cofactors or in other organic complexes, shifting allocation between tissues and possibly altering uptake. Here, we use the meta-analysis of previous studies in crops to test these hypotheses. Nutrients acquired mostly by mass flow were decreased significantly more by elevated [CO2] than nutrients acquired by diffusion to the roots through the soil, supporting the first hypothesis. Similarly, Mg showed large concentration declines in leaves and wheat stems, but smaller decreases in other tissues. Because chlorophyll requires a large fraction of total plant Mg, and chlorophyll concentration is reduced by growth in elevated [CO2], this supports the second hypothesis. Understanding these mechanisms may guide efforts to improve nutrient content, and allow modeling of nutrient changes and health impacts under future climate change scenarios. Plants grown in elevated [CO2] have lower protein and mineral concentrations compared to plants grown in ambient [CO2], but the mechanisms for this decline have not been fully elucidated. Support for two previously unexamined mechanisms was found: 1) reduced canopy transpiration reduces mass flow of nutrients to the roots, thus reducing nutrient uptake and 2) changes in physiological requirements alter requirements for minerals, shifting allocation between tissues and possibly altering uptake. Copyright © 2013 Blackwell Publishing Ltd 36 3 March 2013 10.1111/pce.12007 Original Articles Original Article © 2012 Blackwell Publishing Ltd.