Diurnal light fitness of the C3 and C4 species from the genus Atriplex under control and drought conditions.

Abstract

The literature showed contradictory results regarding the acclimation of C3 and C4 photosynthesis to low light intensities. Atriplex halimus, A. nummularia (C4, NAD-ME), A. portulacoides and A. prostrata (C3) were exposed to three natural light intensities: full light (FL), medium light (ML) and low light (LL) under control or drought condition. Under control condition, in A. halimus and A. nummularia, photosynthetic rate (A) was proportionally linked to stomatal conductance (g_s). In A. halimus, A and gs peaked at 9:00 and 12:00 at FL only. However, A and gs peaked at 9:00 and 12:00 under FL and ML, respectively, in A. nummularia. The leakage of CO₂ could limit A in the C4 species under lower light intensities. A. halimus reduced g_s and A (a typical NAD-ME strategy) to cope with lower light intensities. However, A. nummularia optimized leaf anatomical features and PEPC/ Rubisco ratio to reduce CO₂ leakage, leading to improved g_s, A and biomass. In contrast, the increase in g_s reflected no increase in A, which could be attributed to the negative effect of low light on the electron transport system in the C3 species. Under drought condition, the performance of the C3 and C4 species was better at ML and LL than that at FL because of enhanced g_s and A. The present study concluded that the C4 species acclimated better to low light intensities than the C3 species. The acclimation of the C4 species was dependent on the species and the soil water content rather than the biochemical subtype.