Soil heterogeneity tends to promote the growth of naturalized aliens when competing with native plant communities

Abstract

Elton's diversity‐invasibility hypothesis predicts that diverse communities are more resistant against alien invaders. However, observational studies frequently find positive relationships between the numbers of alien and native species. It has been suggested, but rarely tested, that environmental heterogeneity may cause such positive relationships. Here, we experimentally tested the effects of soil heterogeneity and diversity (species richness) on the invasibility of native communities. We first filled mesocosm pots with either a heterogeneous soil, consisting of one patch of sand, one patch of peat and one patch of an equal mixture of both substrates, or a homogeneous soil, consisting of the mixture only. Then, we planted those pots with 29 native communities consisting of one, four or eight species, and invaded them with populations of four individuals of one of five alien species. In the heterogeneous soils, individual alien plants benefited more strongly from the resource‐rich peat soil than the native communities did. Moreover, in the mixture soil of the heterogeneous treatment, individual alien plant over‐proportionally produced more biomass than in the mixture soil of the homogeneous treatment. Consequently, the populations of naturalized alien plants in each pot benefited from heterogeneous soil conditions, and this tended to be particularly the case when a native community was present. The native communities did not respond to soil heterogeneity, but they had a negative effect on the naturalized plants, irrespective of their diversity. Synthesis. Our results indicate that soil heterogeneity might alleviate the competitive effects of native communities on the alien invaders, as the latter took more advantage of the high resource patches than the natives did. The beneficial effect of heterogeneity on invasion success could thus explain why observational studies usually find positive relationships between the numbers of alien and native species.

Drivers of the negative diversity-invasibility relationship: nutrient availablity, allelopathy, soil biota and soil legacy effects

“…For example, separate experiments detected significantly stronger resistance of more diverse native plant communities to growth and reproductive performance of the alien plant invaders Lolium temulentum (Lyons and Schwartz 2001), Cirsium arvense, Plantago major, and Agrostis stolonifera (Levine 2001), Crepis tectorum (Naeem et al 2000), Lolium arundinaceum (Rudgers et al 2005) and Centaurea maculosa (Maron and Marler 2007). By contrast, other experiments did not find significant negative relationship between the diversity of the native plant communities and growth performance of alien plant species (Power and Sánchez Vilas 2020; Wei and van Kleunen 2022). The inconsistencies among the results that tested the diversity-invasibility hypothesis could be due to various factors including heterogeneity in resource conditions among the studies (Davies et al 2005) and effects of microbial mutualists of plants in the invaded communities (Rudgers et al 2005).…”

Disentangling the role of environmental filtering and biotic resistance on alien invasions in a reservoir area

“…This can be explained by the invasibility metrics, the covariation of environmental factors, and study scales (Smith & Cote, 2019). The richness of both native and alien species can covary with abiotic and biotic factors, which may result in a positive diversity‐invasibility relationship and be found particularly at large scales with greater environmental heterogeneity (Davies et al, 2005; Wei & van Kleunen, 2022).…”

Biodiversity increases resistance of grasslands against plant invasions under multiple environmental changes

“…Indeed, many such experiments corroborate the positive relationship between diversity and invasion resistance 19 – 22 . However, there is considerable variability in the strength of the relationship 23 , 24 , and a number of exceptions also occur 25 , 26 . Likely, this variation in the strength of the relationship between diversity and invasion resistance is caused by variations in environmental conditions 27 – 29 .…”