The effects of air exposure on the desiccation rate and photosynthetic activity of Thalassia hemprichii and Enhalus acoroides

The effects of air exposure on the desiccation rate and photosynthetic activity of Thalassia hemprichii and Enhalus acoroides were studied using chlorophyll fluorescence. The desiccation rate of T. hemprichii was higher than that of E. acoroides, while the critical threshold of relative water content (RWCcritical) showed opposite trend. Neither the desiccation rate nor RWCcritical of T. hemprichii was significantly affected by temperature, while the desiccation rate of E. acoroides was affected significantly. For both species, the effective photochemical efficiency of PSII decreased gradually above the RWCcritical, while declined rapidly below the RWCcritical. After initial air exposure, the relative maximum electron transport rate of both seagrasses increased gradually to a maximum and then decreased to initial value near the RWCcritical. Therefore, short-term air exposure above the RWCcritical is beneficial for both seagrasses, and the RWCcritical should be considered when examining the response of seagrass photosynthesis to air exposure and selecting transplantation sites.