|De Souza, Amanda|
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2017
Publication Date: 6/17/2017
Citation: Ruiz-Vera, U.M., De Souza, A.P., Long, S.P., Ort, D.R. 2017. The role of sink strength and nitrogen availability in the down-regulation of photosynthetic capacity in field-grown Nicotiana tabacum at elevated CO2 concentration. Frontiers in Plant Science. doi.org/10.3389/fpls.2017.00998. Interpretive Summary: Due to anthropogenic activities, the CO2 concentration of the atmosphere has risen dramatically since 1750 now accumulating at an average annual rate of 2.1 µmol mol-1. For C3 plants, past and future increases [CO2] considerably increase potential net photosynthesis since the current [CO2] of 400 µmol mol-1 is insufficient to saturate photosynthesis and because the oxygenase activity of Rubisco will be competitively inhibited. However, this increased potential is seldom fully realized across the growing season because of down-regulation of photosynthesis capacity that occurs when C3 plants are grown at elevated [CO2]. This study investigates the role that the ability of the developing storage and other tissues has in the mechanism of this down-regulation and if down-regulation is less severe when plants are given ample nitrogen fertilizer. It was discovered that the ability of the plant to use the extra photosynthetic products for growth and storage is essential for plants like tobacco to sustained enhanced photosynthesis when grown at elevated CO2.
Technical Abstract: Down-regulation of photosynthesis is one of the most frequent 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 increase in carbohydrate production in leaves through stimulation of photosynthesis by elevated [CO2]. Down-regulation is suggested to be particularly pronounced when there is inadequate nitrogen (N), which may limit sink development. To assess the importance of sink strength on photosynthetic down-regulation and the potential of N to mitigate down-regulation, two tobacco cultivars (Nicotiana tabacum L. cv. Petit Havana; cv. Mammoth) with distinct growth patterns and sink sizes were grown under ambient and elevated [CO2] and with two different N additions in a free air gas concentration enrichment (FACE) experiment. While Petit Havana cv. flowered and formed branches after flowering, Mammoth cv. did not flower under the prevailing photoperiod of the experiment and continued to grow and develop new leaves. Photosynthetic down-regulation at elevated [CO2] was lower in Mammoth likely reflecting sustained sink strength of the rapidly growing plant whereas down-regulation became stronger in Petit Havana cv. as the season progressed. Increased N partially mitigated down-regulation of photosynthesis in both tobacco cultivars and was dependent on plant developmental stage. Overall the results were consistent with the hypothesis that sustained sink strength, that is the ability to utilize photosynthate, is critical to the ability of C3 plants to maintained enhanced photosynthesis when grown at elevated [CO2 ].