Adding insult to injury: Light competition and allelochemical weapons interact to facilitate grass invasion

Abstract

Biological invasions are a leading ecological issue of the 21st century because of their worldwide contributions to biodiversity loss and degradation of ecosystem services. Answering general questions about the mechanisms facilitating the spread of successful invasives is key to understanding how to manage them moving forward. The success of introduced primary producers has often been attributed to superior competitive ability or to their release from natural enemies that constrained them in their native range. In contrast, nonnative primary producers can successfully invade and establish in new areas by releasing allelochemical compounds into the environment that are toxic to the native flora. The interactive effects of allelopathy and competition remain underexplored. Here, we evaluated the mechanism of invasion by Guinea grass, a globally distributed tallgrass from tropical and subtropical Africa with known allelopathic effects associated with 2-hydroxyphenylacetic acid (2HPAA). We asked if allelopathy and light availability interact to give Guinea grass a competitive advantage during seedling establishment in its introduced range. We used a fully factorial greenhouse experiment in which allelochemical concentrations and light availability treatments were based on empirical measurements of these variables at an invaded site in South Texas. Seedling recruitment and growth were assessed for three native species and for Guinea grass itself. We also described the metabolome (the complete set of small molecules) of an invasive grass for the first time to facilitate a comparison of the effect of the known allelochemical 2HPAA with that of the whole-plant chemical extract. Shading and allelochemistry each reduced recruitment and growth by themselves, and a significant interaction of these stressors exacerbated the negative effects in the shade, resulting in short plants, low biomass, and ultimately decreased seedling recruitment. The whole-plant metabolomic extract had significantly stronger effects than pure 2HPAA, and these negative effects were intensified in

Arthropod associates of Kenyan buffelgrass (Cenchrus ciliaris): a field survey for biological control candidates of a globally important invasive grass

“…Buffelgrass also indirectly alters plant community composition by increasing fire frequency and intensity, replacing fire-sensitive natives (Burquez-Montijo et al 2002). Moreover, buffelgrass root and leaf chemical exudates may deter the germination and growth of natives via allelopathy (Fulbright and Fulbright 1990), similar to other sympatric invasive grasses (Morrison et al 2023). These factors all contribute to establishing a strong priority effect that makes buffelgrass-dominated habitats difficult to restore (Stevens and Fehmi 2011).…”

Systematic reduction of natural enemies and competition across variable precipitation approximates buffelgrass invasiveness (Cenchrus ciliaris) in its native range

“…Higher interspecific competitive ability of nonnative grasses occurs by direct resource competition, apparent (indirect) competition through a loss of natural enemies, and an evolved competitive ability in the absence of native stressors (Callaway et al., 2022; Gioria & Osborne, 2014). Enhanced competitive ability of invasive grasses results in higher growth rates and higher nutrient turnover and can be driven by novel weapons and changes in soil biomes and chemistry (Bowman et al., 2023; Morrison, Rhodes, et al., 2023). This improved productivity also leads to higher propagule pressure and spread.…”