Estimating Photosynthesis and Concurrent Export Rates in C3 and C4 Species at Ambient and Elevated CO21,2

Abstract

The ability of 21 C 3 and C 4 monocot and dicot species to rapidly export newly fixed C in the light at both ambient and enriched CO 2 levels was compared. Photosynthesis and concurrent export rates were estimated during isotopic equilibrium of the transport sugars using a steady-state 14 CO 2 -labeling procedure. At ambient CO 2 photosynthesis and export rates for C 3 species were 5 to 15 and 1 to 10 mol C m ؊2 s ؊1 , respectively, and 20 to 30 and 15 to 22 mol C m ؊2 s ؊1 , respectively, for C 4 species. A linear regression plot of export on photosynthesis rate of all species had a correlation coefficient of 0.87. When concurrent export was expressed as a percentage of photosynthesis, several C 3 dicots that produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C 4 species. At high CO 2 photosynthetic and export rates were only slightly altered in C 4 species, and photosynthesis increased but export rates did not in all C 3 species. The C 3 species that had high efflux rates relative to photosynthesis at ambient CO 2 exported at rates comparable to those of C 4 species on both an absolute basis and as a percentage of photosynthesis. At ambient CO 2 there were strong linear relationships between photosynthesis, sugar synthesis, and concurrent export. However, at high CO 2 the relationships between photosynthesis and export rate and between sugar synthesis and export rate were not as strong because sugars and starch were accumulated.

Regulation of Sucrose Transporters and Phloem Loading in Response to Environmental Cues

“…The export rate of carbohydrates from the leaf depends to a high degree on their production, that is photosynthetic activity, which is influenced by factors such as light and CO 2 availability (Jiao and Grodzinski, 1996;Grodzinski et al, 1998;Amiard et al, 2005;Duan et al, 2014). Here, transfer of plants to an environment with high light (400-800 mmol photons m 22 s 21 ) or low light (,100 mmol photons m 22 s 21 ) was found to not significantly alter the expression of any SUT in species with apoplasmic phloem loading (Fig.…”

Photosynthetic responses of muskmelon (Cucumis melo L.) to photon flux density, leaf temperature and CO2 concentration

“…The organic fertilizer released CO 2 as it decomposed, which elevated the CO 2 concentration in the greenhouse two to five times higher than that measured in open air (Chen 2001;Ma 2001). High CO 2 concentrations, coupled with low light intensities and low temperatures in greenhouses, reduce transport of the photosynthetic assimilates (Grodzinski et al 1998), decrease gas exchange (Cao and Sun 1998), and promote irregular stomatal closure (Peet et at. 1986).…”

Leaf micronutrient concentrations and potential photosynthesis in Ochroma pyramidale established in a degraded land

“…grown in the open, we use C 4 data from herbaceous dicots reported elsewhere (Grodzinski et al, 1998). (Butterfield, 1996).…”