Measurement and simulation of photosynthesis-light response process in Artemisia ordosica under water stress.

Artemisia ordosica is the dominant species in arid and semi-arid areas. It is critical for understanding the adaptability of A. ordosica to study its photosynthetic characteristics and light-response process under different soil moisture gradients. Photosynthesis of A. ordosica under five different soil water content (19%, 16%, 12%, 9% and 5%) was measured to explore its photoresponse process under water stress by pot cultivating. Three photoresponse models were used to simulate the photoresponse and characteristic parameters. The results showed that the photosynthetic rate (Pn ) of A. ordosica came down with the decrease of soil water content. When photosynthetically active radiation (PAR) was lower than 1 000 mol/ (m2s), the Pn of 16% water content treatment was higher than that of 19% treatment. Under intense radiation, Pn of 4 water content treatments (19%, 16%, 12% and 9%) maintained the peak level (Pnmax) as PAR increased and photoinhibition was not observed. When PAR exceeded 500mol/ (m2s), the Pn decreased with increasing PAR for the treatment with 5% soil water content , and photosynthesis was inhibited. Three photoresponse models used can well fit the simulation of photoresponse process and characteristic parameters, including apparent quantum efficiency, dark respiration and light compensation point for the treatments with 19%, 16%, 12% and 9% soil water content. However, for the treatment with 5% soil water content, only the rectangle hyperbola revisedmodel can well fit the simulation of photoresponse process and characteristic parameters.