Abstract
Plant–plant interactions are among the fundamental processes that shape structure and functioning of arid and semi‐arid plant communities. Despite the large amount of studies that have assessed the relationship between plant–plant interactions (i.e., facilitation and competition) and diversity, often researchers forget a third kind of interaction, known as allelopathy. We examined the effect of plant–plant interactions of three dominant species: the perennial grass Lygeum spartum, the allelopathic dwarf shrub Artemisia herba‐alba, and the nurse shrub Salsola vermiculata, on plant diversity and species composition in a semi‐arid ecosystem in NE Spain. Specifically, we quantified the interaction outcome (IO) based on species co‐occurrence, we analyzed diversity by calculation of the individual species–area relationship (ISAR), and compositional changes by calculation of the Chao‐Jaccard similarity index. We found that S. vermiculata had more positive IO values than L. spartum, and A. herba‐alba had values between them. Lygeum spartum and A. herba‐alba acted as diversity repellers, whereas S. vermiculata acted as a diversity accumulator. As aridity increased, A. herba‐alba transitioned from diversity repeller to neutral and S. vermiculata transitioned from neutral to diversity accumulator, while L. spartum remained as diversity repeller. Artemisia herba‐alba had more perennial grass species in its local neighborhood than expected by the null model, suggesting some tolerance of this group to its “chemical neighbor”. Consequently, species that coexist with A. herba‐alba were very similar among different A. herba‐alba individuals. Our findings highlight the role of the nurse shrub S. vermiculata as ecosystem engineer, creating and maintaining patches of diversity, as well as the complex mechanism that an allelopathic plant may have on diversity and species assemblage. Further research is needed to determine the relative importance of allelopathy and competition in the overall interference of allelopathic plants.
Highlights
The effect of biotic interactions on the structure and diversity of plant communities has been a central topic in ecology for the last half century
We examined the effect of plant–plant interactions of three dominant species: the perennial grass Lygeum spartum, the allelopathic dwarf shrub Artemisia herba-alba, and the nurse shrub Salsola vermiculata, on plant diversity and species composition in a semi-arid ecosystem in NE Spain
Tukey0s post hoc honest significant difference (HSD) test showed that S. vermiculata had a significantly more positive interaction outcome (IO) value than L. spartum, and that A. herba-alba had an intermediate IO value between them (Fig. 2B)
Summary
The effect of biotic interactions on the structure and diversity of plant communities has been a central topic in ecology for the last half century. Only competitive interactions among plants have been considered to drive community structure and diversity (Grime 1973; Huston 1979). In communities from mid- to high-productivity, a decrease in plant diversity was explained by increased competition and the exclusion of species with lower competitive capacity (Grime 1973). In the last years, many studies (Hacker and Gaines 1997; Bruno et al 2003; Brooker et al 2008; McIntire and Fajardo 2014) have recognized the key role of positive interactions driving diversity in plant communities. Positive interactions are crucial for increasing, maintaining, or preventing the loss of species diversity (Hacker and Gaines 1997; Michalet et al 2006; Le Bagousse-Pinguet et al 2014), functional diversity (Scho€b et al 2012; Gross et al 2013), and phylogenetic diversity (Valiente-Banuet and Verdu 2007; Butterfield et al 2013), at the local, and at the regional and global scales (Cavieres et al 2014)
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