Photosynthetic features of non-Kranz type C4versus Kranz type C4and C3species in subfamily Suaedoideae (Chenopodiaceae).

The objective of this study was to characterise photosynthesis in terrestrial non-Kranz (NK) C4species, Bienertia sinuspersiciAkhani and Suaeda aralocaspica(Bunge) Freitag & Schütze (formerly Borszczowia aralocaspica), compared with closely related Kranz type C4Suaeda eltonicaIljin and Suaeda taxifoliaStandley, and C3species Suaeda heterophyllaBunge and Suaeda maritimaDumort in subfamily Suaedoideae (Chenopodiaceae). Traditional Kranz type C4photosynthesis has several advantages over C3photosynthesis under certain environmental conditions by suppressing photorespiration. The different photosynthetic types were evaluated under varying levels of CO2and light at 25°C. Both NK and Kranz type species had C4type CO2compensation points (corrected for dark-type respiration) and half maximum saturation of photosynthesis at similar levels of atmospheric CO2(average of 145µbar for the C4species v. 330µbar CO2for C3species) characteristic of C4photosynthesis. CO2saturated rates of photosynthesis per unit chlorophyll was higher in the C3(at ~2.5 current ambient CO2levels) than the C4species, 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 C3species (35%). Light saturated rates of CO2fixation per unit leaf area at 25°C and 340µbar CO2were higher in the Kranz species and the NK C4S. aralocaspicathan in the C3species. In response to light at 340µbar CO2, there was a difference in rates of photosynthesis per unit Rubisco with NK>Kranz>C3species. 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 (CO2fixed per water transpired) at 340µbar CO2, 25°C and 1000µmolquantam-2s-1was on average 3-fold higher in the C4(NK and Kranz) compared with the C3species. The results show that the NK species have several C4traits like the Kranz type species in subfamily Suaedoideae. [ABSTRACT FROM AUTHOR]