Photosynthetic features of non-Kranz type C4 versus Kranz type C4 and C3 species in subfamily Suaedoideae (Chenopodiaceae).

Abstract

The objective of this study was to characterise photosynthesis in terrestrial non-Kranz (NK) C4 species, Bienertia sinuspersici Akhani and Suaeda aralocaspica (Bunge) Freitag & Schütze (formerly Borszczowia aralocaspica), compared with closely related Kranz type C4 Suaeda eltonica Iljin and Suaeda taxifolia Standley, and C3 species Suaeda heterophylla Bunge and Suaeda maritima Dumort in subfamily Suaedoideae (Chenopodiaceae). Traditional Kranz type C4 photosynthesis has several advantages over C3 photosynthesis under certain environmental conditions by suppressing photorespiration. The different photosynthetic types were evaluated under varying levels of CO2 and light at 25°C. Both NK and Kranz type species had C4 type CO2 compensation points (corrected for dark-type respiration) and half maximum saturation of photosynthesis at similar levels of atmospheric CO2 (average of 145 µbar for the C4 species v. 330 µbar CO2 for C3 species) characteristic of C4 photosynthesis. CO2 saturated rates of photosynthesis per unit chlorophyll was higher in the C3 (at ~2.5 current ambient CO2 levels) than the C4 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 C3 species (35%). Light saturated rates of CO2 fixation per unit leaf area at 25°C and 340 µbar CO2 were higher in the Kranz species and the NK C4 S. aralocaspica than in the C3 species. In response to light at 340 µbar CO2, there was a difference in rates of photosynthesis per unit Rubisco with NK > Kranz > C3 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 (CO2 fixed per water transpired) at 340 µbar CO2, 25°C and 1000 µmol quanta m-2 s-1 was on average 3-fold higher in the C4 (NK and Kranz) compared with the C3 species. The results show that the NK species have several C4 traits like the Kranz type species in subfamily Suaedoideae.