The effects of rising atmospheric carbon dioxide on shoot-root nitrogen and water signaling.

Hsien Ming Easlon,Arnold J Bloom

doi:10.3389/fpls.2013.00304

Abstract

Terrestrial higher plants are composed of roots and shoots, distinct organs that conduct complementary functions in dissimilar environments. For example, roots are responsible for acquiring water and nutrients such as inorganic nitrogen from the soil, yet shoots consume the majority of these resources. The success of such a relationship depends on excellent root–shoot communications. Increased net photosynthesis and decreased shoot nitrogen and water use at elevated CO2 fundamentally alter these source–sink relations. Lower than predicted productivity gains at elevated CO2 under nitrogen or water stress may indicate shoot–root signaling lacks plasticity to respond to rising atmospheric CO2 concentrations. The following presents recent research results on shoot–root nitrogen and water signaling, emphasizing the influence that rising atmospheric carbon dioxide levels are having on these source–sink interactions.

Highlights

Land plants occupy highly dissimilar aboveground and belowground environments and face the basic allocation dilemma of where to invest resources (Bloom et al, 1985)
The goal of this review is to describe shoot–root signaling for N and water and to examine the observed and predicted responses of these signaling mechanisms to rising atmospheric CO2 concentrations
Slower transpiration minimizes development of leaf water deficit during chilling at elevated CO2 (Boese et al, 1997), which may inhibit root Abscisic acid (ABA) production (Vernieri et al, 2001) that is important for root acclimation to chilling

Summary

INTRODUCTION

Land plants occupy highly dissimilar aboveground and belowground environments and face the basic allocation dilemma of where to invest resources (Bloom et al, 1985). Flowering plants have evolved specific adaptations to this low CO2 environment including increased stomatal density (Beerling and Chaloner, 1993), increased leaf vein density (Boyce and Zwieniecki, 2012), and C4 photosynthesis (Ehleringer et al, 1991) This concentration has increased from 280 to 400 μmol mol−1 since 1800 from the burning of fossil fuels (Whorf and Keeling, 1998) and is projected to reach between 500 and 900 μmol mol−1 by the end of the century (Joos et al, 1999). NITROGEN: COMMUNICATING ROOT AVAILABILITY AND SHOOT DEMAND For most plants, growth and productivity is highly dependent upon N obtained from root absorption of soil inorganic and organic N. Many studies have shown that elevated CO2 stimulates photosynthesis, plant growth, and demand for mineral nutrients

Easlon and Bloom

ROOT TO SHOOT N SIGNALING

CONCLUSION

Bidirectional signal of root or shoot water stress