Short-term salt spray reveals high salt tolerance in a neotropical orchid species

Salt is a limiting factor of plant growth in natural environments. Although not commonly exposed to salt, epiphytic orchids have some drought-related phenotypical traits that could grant some tolerance to the ionic component of salinity. Epidendrum fulgens Brongn. is a terrestrial orchid with recent epiphytic ancestry and it shares many phenotypic traits with epiphytic orchids. Here we investigated the salinity response of the orchid species E. fulgens by exposing plant stems to varying concentrations of artificial seawater spray (0, 200, 400 and 800 mM Na+). Each plant had four stems, each stem corresponding to a salt treatment. We measured the maximum quantum efficiency of photosystem II (PSII) over 10 days and at the end of this period, we measured the relative water content (RWC), osmotic potential, chlorophyll index, and leaf Na+ concentration. Negative effects of salt were only observed above 400 mM Na+. While stems treated with 800 mM Na+ reduced the osmotic potential, the RWC remained similar to control stems. Unexpectedly, leaf Na+ concentration was similar for salt-treaded and control stems, suggesting that E. fulgens might be able to avoid the leaf absorption of this ion. Therefore, E. fulgens can tolerate salt spray in similar concentrations as the seawater and some of its physiological responses, such as maintaining a high RWC when facing osmotic stress, resemble the response of epiphytic orchids when facing drought stress.

Automated summary

Salt is a limiting factor for plant growth, but epiphytic orchids show some tolerance to salinity. This study found that E. fulgens, a terrestrial orchid with epiphytic ancestry, can tolerate salt spray in concentrations similar to seawater and is able to maintain a high relative water content when facing osmotic stress.