The interplay of soil stress and the native Cakile maritima functional response determine the alien invasion success in coastal dunes

Description

Coastal areas are unique ecosystems characterized by strong environmental gradients that determine high plant community diversity. Due to human activities and their interactions with abiotic factors, coastal dunes are among the most invaded habitats worldwide. Many factors can co-occur to drive the invasion process and influence the final invasion success, including biotical interaction with other dune species. In order to curb the invasion of alien plant, it is important to study and understand the interplay between biotic and abiotic factors during the colonization process. Our experiment investigated the cascading effects of soil stress, plant growth, and the functional traits of the key species Cakile maritima, on the plant alien and native plant community abundance and composition. In a barrier island of the Marano and Grado lagoon, Northern Adriatic Sea, we mechanically removed the occurring vegetation in the back dune (simulating an extreme storm event), triggering a new ecological succession. In the site we created a soil stress gradient by altering main soil properties (i.e., salt, nitrogen, and organic matter) with a randomized block design. Soil properties directly affected the plant functional response of C. maritima and the diversity and composition of the whole community, showing contrasting responses for alien and native species. Moreover, the growth and functional response of C. maritima showed a direct effect on native and alien species populations, likely competing with other native species, but only when soil conditions ameliorate, leaving free niches for the alien species colonization. These results showed a direct effect of soil on sand dune plant succession and diversity, but this effect was also indirectly mediated by the key species response. This opens some important considerations for the future management actions, also in the context of the stress gradient hypothesis. This study has provided new information on the mechanisms and processes of biological invasion, highlighting possible soil gradients that could be used as an effective tool to combat biological invasion.

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