Erodium oxyrhinchum sustains severe drought stress by maintaining stable photosynthetic electron transport under progressive drought conditions

Drought is a key environmental factor limiting the growth and development of desert plants. In this experiment, we investigated the response of photosynthesis in the ephemeral plant E. oxyrhinchum to progressive drought conditions in its natural habitat. In response to drought stress, the mechanism for photosynthesis regulation in E. oxyrhinchum is switched from stomatal to non-stomatal limitations. One notable characteristic of E. oxyrhinchum is its ability to sustain photosynthesis under severe drought conditions. This is because the transition from stomatal to non-stomatal limitation occurred at a much lower leaf water content (56.51% +/- 8.53%), compared to that in other plant species. With the drought treatment, the net photosynthetic rate was maintained or even increased to a much higher value to that of the control (33.65 +/- 1.72 vs. 17.65 +/- 2.35 mu mol CO2 m-2s-1), which coincided with the increased stomatal conductance. During the entire stomatal limitation to the photosynthesis stage, the maximum photochemical efficiency of photosystem II (Fv/Fm) remained unchanged. Additionally, the prompt Chl a fluorescence induction was stable, which indicated an intact photosystem II structure and a balanced redox state of the plastoquinone pool. The variation partition analysis revealed that the substantial increase in antioxidant activities and sensitive response to nonphotochemical quenching during this stage contributed significantly to maintaining a stable Fv/Fm value. To conclude, we have not only provided novel information regarding the drought-escape E. oxyrhinchum species but also concluded that PSII activity modulates the switch from stomatal to non-stomatal photosynthesis limitation under progressive drought conditions.