The Role of Sink Strength and Nitrogen Availability in the Down-Regulation of Photosynthetic Capacity in Field-Grown Nicotiana tabacum L. at Elevated CO2 Concentration.

Ursula M Ruiz-Vera,Donald R Ort,Stephen P Long,Amanda P De Souza

doi:10.3389/fpls.2017.00998

Abstract

Down-regulation of photosynthesis is among the most common responses observed in C3 plants grown under elevated atmospheric CO2 concentration ([CO2]). Down-regulation is often attributed to an insufficient capacity of sink organs to use or store the increased carbohydrate production that results from the stimulation of photosynthesis by elevated [CO2]. Down-regulation can be accentuated by inadequate nitrogen (N) supply, which may limit sink development. While there is strong evidence for down-regulation of photosynthesis at elevated [CO2] in enclosure studies most often involving potted plants, there is little evidence for this when [CO2] is elevated fully under open-air field treatment conditions. To assess the importance of sink strength on the down-regulation of photosynthesis and on the potential of N to mitigate this down-regulation under agriculturally relevant field conditions, two tobacco cultivars (Nicotiana tabacum L. cv. Petit Havana; cv. Mammoth) of strongly contrasting ability to produce the major sink of this crop, leaves, were grown under ambient and elevated [CO2] and with two different N additions in a free air [CO2] (FACE) facility. Photosynthetic down-regulation at elevated [CO2] reached only 9% in cv. Mammoth late in the season likely reflecting sustained sink strength of the rapidly growing plant whereas down-regulation in cv. Petit Havana reached 25%. Increased N supply partially mitigated down-regulation of photosynthesis in cv. Petit Havana and this mitigation was dependent on plant developmental stage. Overall, these field results were consistent with the hypothesis that sustained sink strength, that is the ability to utilize photosynthate, and adequate N supply will allow C3 crops in the field to maintain enhanced photosynthesis and therefore productivity as [CO2] continues to rise.

Highlights

Due to anthropogenic activities, the CO2 concentration ([CO2]) of the atmosphere has risen dramatically since 1750 (IPCC, 2013); currently increasing at annual rate average of 2.1 μmol mol−1 (NOAA, 2016)
This increased potential is seldom fully realized across the growing season due to down-regulation of photosynthesis capacity that occurs when C3 plants are grown at elevated [CO2] (Drake et al, 1997; Moore et al, 1999; Rogers and Humphries, 2000; Ainsworth and Long, 2005; Bernacchi et al, 2005)
There was no effect of high nitrogen treatment (HN) on A, gs, and Ci/Ca in either cultivar (Table S2) with the exception of A on day of the year (DOY) 211 in MM and of Ci/Ca on DOY 211 in Petit Havana (PH), which slightly increased with HN by 6.5 and 4% respectively

Summary

Introduction

The CO2 concentration ([CO2]) of the atmosphere has risen dramatically since 1750 (IPCC, 2013); currently increasing at annual rate average of 2.1 μmol mol−1 (NOAA, 2016). In Free Air CO2 Enrichment (FACE) experiments, elevating the ambient atmospheric [CO2] by 100– 250 μmol mol−1 resulted in an increase in A of 13–46% depending on the level of [CO2] elevation, plant functional group, and interacting environmental factors (Ainsworth and Long, 2005; Leakey et al, 2009) This increased potential is seldom fully realized across the growing season due to down-regulation of photosynthesis capacity that occurs when C3 plants are grown at elevated [CO2] (Drake et al, 1997; Moore et al, 1999; Rogers and Humphries, 2000; Ainsworth and Long, 2005; Bernacchi et al, 2005). Preventing an escalation in the carbon:nitrogen (C:N) ratio may be critical to maintain an equilibrium between production and utilization of carbohydrates and to avoid a state of sink limitation that potentiates downregulation in photosynthesis (Paul and Driscoll, 1997; Leakey et al, 2009)

Methods

Results

Discussion

Conclusion