Salt-driven interactions between Pistacia lentiscus and Salsola inermis.

BACKGROUND, AIM, AND SCOPE: It can be learned from the Pistacia spp. germplasm collection (http://www.bgu.ac.il/pistacia) that the growth of Salsola inermis is inhibited in the vicinity of the evergreen Pistacia lentiscus, but not in the surroundings of the deciduous Pistacia atlantica and Pistacia chinensis. Irrigation of trees during the summer months increases soil salinity around the trees. It was therefore hypothesized that inhibition of S. inermis around P. lentiscus is related to depletion of salt in the vicinity of the latter species.
MATERIALS AND METHODS: A multi-approach experimental scheme was carried out which included soil edaphic characterization and germination tests. To test salt tolerance of P. lentiscus, plants were grown in a hydroponic system for a month in medium containing NaCl, while physiological and growth parameters were measured.
RESULTS: Conductivity measurements in summer, during the growth season of S. inermis, indicated that soil salinity beneath deciduous Pistacia trees was significantly higher than that below P. lentiscus. Germination of S. inermis seeds on filter paper moistened with P. lentiscus low-conductivity soil filtrate was twice as high as that of the deciduous trees high-conductivity soil filtrates. Nevertheless, fresh and dry weights of mature S. inermis growing next to P. atlantica and P. chinensis were 2.9 to 4.8 times higher than those of plants growing in the vicinity of P. lentiscus. In a hydroponic system, no significant differences were found in growth parameters and stomatal conductance between P. lentiscus growing in control and salt treatments. It was therefore proposed that salt depletion in the vicinity of P. lentiscus inhibits the growth, but not germination, of S. inermis thus confirming the halophylic characteristics of this plant. DISCUSSION: The nature of Salsola-Pistacia interactions cannot be explained by allelopathic effects; hence, plausible salt-driven interactions were considered. Our data showed that S. inermis accumulated salt and has halophytic characteristics. Interestingly, germination of S. inermis was inhibited in medium containing salt, but the salt was obligatory for further growth, development, and fast biomass production. These results explained the observation of large biomass accumulation in the more saline soil around the deciduous P. atlantica and P. chinensis and the lack of development in the salt-depleted soil around the salt-tolerant accumulator P. lentiscus.
CONCLUSIONS: Soil salinity around Pistacia trees critically affects the growth of S. inermis. Inhibition of S. inermis growth, but not germination, around the evergreen P. lentiscus, stems from the latter's ability to deplete salt from its surroundings. The results indicated that P. lentiscus is able to tolerate and accumulate salt, which we assume contributes to its wide distribution along the Mediterranean coast in Israel. Recommendations and perspectives While the phytoremediation potential of Salsola spp. has been explored to some extent, this of P. lentiscus has not been tested and proven before. The results suggest that the evergreen perennial salt-tolerant P. lentiscus can be recommended for horticulture purposes and soil stabilization in relatively saline environments.