An exotic plant species indirectly facilitates a secondary exotic plant through increased soil salinity

• Published in: Biological invasions 2023-08, Vol.25 (8), p.2599-2611
• Main Authors: De La Cruz, Henry J., Salgado-Luarte, Cristian, Stotz, Gisela C., Gianoli, Ernesto
• Format: Article
• Language: English
• Subjects: Biodiversity; Biodiversity loss; Biomedical and Life Sciences; Competition; Crassulacean acid metabolism; Developmental Biology; Ecology; Freshwater & Marine Ecology; Germination; Halophytes; Introduced plants; Introduced species; Leaf area; Life Sciences; Mesembryanthemum; Mesembryanthemum crystallinum; Mesembryanthemum nodiflorum; Original Paper; Plant Sciences; Plant species; Plants (botany); Saline soils; Salinity; Salinity effects; Salinity tolerance; Salt; Salts; Soil salinity
• ISSN: 1387-3547; 1573-1464
• DOI: 10.1007/s10530-023-03061-z

Indirect facilitation among exotic species may promote their establishment on ecosystems, causing biodiversity losses. However, few experimental studies have identified the mechanisms underlying the indirect facilitation among exotic species. In central-northern Chile, Mesembryanthemum crystallinum (Aizoaceae) is an exotic halophyte that increases soil salinity, while M. nodiflorum is another exotic halophyte –currently less dominant– that often co-occurs with M. crystallinum . In this study, we evaluated the indirect facilitation of M. nodiflorum by M. crystallinum which was mediated by the suppression of salt-susceptible native competitors via increased soil salinity. We further determined the relationship between salt-tolerance traits and the outcome of competitive interactions in saline soil. We included two native Asteraceae plants co-occurring with these Mesembryanthemum species: the –highly probable– salt-susceptible Helenium urmenetae and the salt-tolerant Amblyopappus pusillus . We combined field co-occurrence surveys with greenhouse germination and competition experiments. The Mesembryanthemum species tended to co-occur, which suggests facilitation. Further, the salinity level found under M. crystallinum significantly decreased germination and performance of H. urmenetae , but not of M. nodiflorum and A. pusillus . Accordingly, when in competition, the increased salinity counteracted the negative effect of H. urmenetae on M. nodiflorum biomass, giving M. nodiflorum a competitive advantage. These patterns were associated with decreased specific leaf area and crassulacean acid metabolism expression in M. nodiflorum . In contrast, A. pusillus and M. nodiflorum maintained a neutral interaction regardless of salinity. Overall, our results suggest that M. crystallinum , by increasing soil salinity, may reduce the performance of salt-susceptible competitors, indirectly facilitating the establishment of M. nodiflorum .