Salt application as an effective measure to control ruderal invaders threatening endangered halophytic plant species

Questions How does salinity affect germination, seedling performance and survival of the critically endangered L imonium barceloi, compared to ruderal species invading its salt marsh habitat? Is salt application an effective management tool for controlling invaders and favouring endangered halophytes? Location Ses F ontanelles, M allorca, B alearic I slands, S pain. Methods The germination of seeds of L . barceloi and nine ruderal species was tested in five salinity levels (0–37 g·L −1 ), and also in freshwater after a pre‐treatment with seawater. The ruderal study species were: A sphodelus fistulosus, A vena barbata , G eranium molle , H ypochoeris achyrophorus , O ryzopsis miliacea , P lantago coronopus, R eichardia picroides, S onchus asper and S onchus tenerrimus . Two salt concentration levels (18 and 37 g·L −1 ) were applied twice monthly, weekly or twice weekly to examine the effect of salt irrigation schemes on the performance and seedling survival of L . barceloi compared to two of the principal species invading these salt marshes, S . tenerrimus and A . fistulosus . Results Germination of L . barceloi and most ruderal species was highest at low salinity (0–8 g·L −1 ). Seeds of L . barceloi, A . fistulosus and S . tenerrimus were also able to germinate at the highest salinity level, in contrast to the other species. Germination in freshwater after seawater pre‐treatment was highest in L . barceloi (72 ± 6%). Seedling performance and survival of A . fistulosus and S . tenerrimus decreased with frequency and concentration of the salt treatment. An application of 37 g·L −1 salt twice a week reduced seedling survival of A . fistulosus and S . tenerrimus by 83.3 and 91.6%, respectively. In contrast, 100% of the L . barceloi seedlings survived and showed similar performance among treatments. Conclusions Limonium barceloi had higher seedling growth and survival than ruderal invaders when salinity levels were high (37 g·L −1 ). Nevertheless, at lower salinity, ruderal species may germinate and grow better and thus salinity level changes may represent a threat to the survival of this critically endangered species. Although further field testing is required, our experiments suggest that salt application could be an effective measure to protect L . barceloi and other endangered halophytic plant species from less salt‐tolerant invaders.