Photosynthetic features of non-Kranz type C versus Kranz type C and C species in subfamily Suaedoideae (Chenopodiaceae).

The objective of this study was to characterise photosynthesis in terrestrial non-Kranz (NK) C species, Bienertia sinuspersici Akhani and Suaeda aralocaspica (Bunge) Freitag & Schütze (formerly Borszczowia aralocaspica), compared with closely related Kranz type C Suaeda eltonica Iljin and Suaeda taxifolia Standley, and C species Suaeda heterophylla Bunge and Suaeda maritima Dumort in subfamily Suaedoideae (Chenopodiaceae). Traditional Kranz type C photosynthesis has several advantages over C photosynthesis under certain environmental conditions by suppressing photorespiration. The different photosynthetic types were evaluated under varying levels of CO and light at 25°C. Both NK and Kranz type species had C type CO compensation points (corrected for dark-type respiration) and half maximum saturation of photosynthesis at similar levels of atmospheric CO (average of 145 µbar for the C species v. 330 µbar CO for C species) characteristic of C photosynthesis. CO saturated rates of photosynthesis per unit chlorophyll was higher in the C (at ~2.5 current ambient CO levels) than the C species, which is likely related to their higher Rubisco content. The amount of Rubisco as a percentage of total protein was similar in NK and Kranz type species (mean 10.2%), but much lower than in the C species (35%). Light saturated rates of CO fixation per unit leaf area at 25°C and 340 µbar CO were higher in the Kranz species and the NK C S. aralocaspica than in the C species. In response to light at 340 µbar CO, there was a difference in rates of photosynthesis per unit Rubisco with NK > Kranz > C species. There were no significant differences between the three photosynthetic types in maximum quantum yields, convexity of light response curves, and light compensation points at 25°C. The water use efficiency (CO fixed per water transpired) at 340 µbar CO, 25°C and 1000 µmol quanta m s was on average 3-fold higher in the C (NK and Kranz) compared with the C species. The results show that the NK species have several C traits like the Kranz type species in subfamily Suaedoideae.