Response of bluebunch wheatgrass to invasion: Differences in competitive ability among invader‐experienced and invader‐naïve populations

Growth Allocation Shifts in the Invasive Hydrilla verticillata Under Interspecific Competition with Native Submerged Macrophytes

Communities with high native species diversity tend to be less susceptible to the establishment of invasive species, especially in studies that test their local impact. This study investigated the impact of competition between native submerged aquatic macrophytes (SAMs) (Egeria najas and Egeria densa) and the exotic Hydrilla verticillata, recognized for its invasive potential in aquatic ecosystems, through a mesocosm experiment conducted over six months. Two treatments were evaluated: the intraspecific competition of H. verticillata and an interspecific competition involving all three species. The plants were cultivated under controlled conditions, with the foliar and subterranean biomass being monitored to analyze resource allocation patterns. The results showed that, under interspecific competition, the mean foliar biomass of H. verticillata was significantly higher compared to the intraspecific treatment, while the subterranean biomass was reduced in the presence of native species. We conclude that native species alter the biomass allocation pattern of the invader, favoring foliar structures over subterranean ones. Among the mechanisms of invasiveness, differential resource allocation represents an important strategy for the adaptation and competitiveness of invasive species influenced by environmental factors and resource competition. These findings contribute to the understanding of competitive interactions in aquatic ecosystems and have implications for the management and control of invasive species, highlighting the importance of promoting native diversity to mitigate invasibility. Future studies should investigate the impacts of reduced subterranean structures on the persistence and spread of submerged invasive species.

Temporal development in the impacts of plant invasions: search for the underlying mechanisms

Many invasive plants have negative impacts on native populations and communities, but there remains much uncertainty about how these impacts develop over time. In this review, I describe the mechanisms that promote the initial dominance of invaders, the characteristics associated with large negative impacts, and present the processes that contribute to changes in invader abundance and impacts over time. Together with ecological processes such as ecosystem engineering or enemy accumulation, I show that temporal variation in impacts can be linked to evolution in both native and invasive species. I also show that multiple processes operating in the same invasion system can jointly shape long-term impacts. Finally, I present the framework of modern coexistence theory as a tool for predicting the effects of invaders on native populations, and how these effects change with processes ongoing within invaded communities.

Older populations of the invader Solidago canadensis exhibit stronger positive plant-soil feedbacks and competitive ability in China

PREMISE

The enemy release hypothesis predicts that release from natural enemies, including soil-borne pathogens, liberates invasive plants from a negative regulating force. Nevertheless, invasive plants may acquire novel enemies and mutualists in the introduced range, which may cause variable effects on invader growth. However, how soil microorganisms may influence competitive ability of invasive plants along invasion chronosequences has been little explored.

METHODS

Using the invasive plant Solidago canadensis, we tested whether longer residence times are associated with stronger negative plant-soil feedbacks and thus weaker competitive abilities at the individual level. We grew S. canadensis individuals from 36 populations with different residence times across southeastern China in competition versus no competition and in three different types of soils: (1) conspecific rhizospheric soils; (2) soils from uninvaded patches; and (3) sterilized soil. For our competitor treatments, we constructed synthetic communities of four native species (Bidens parviflora, Solanum nigrum, Kalimeris indica, and Mosla scabra), which naturally co-occur with Solidago canadensis in the field.

RESULTS

Solidago canadensis populations with longer residence times experienced stronger positive plant-soil feedbacks and had greater competitive responses (i.e., produced greater above-ground biomass and grew taller) in conspecific rhizospheric soils than in sterilized or uninvaded soils. Moreover, S. canadensis from older populations significantly suppressed above-ground biomass of the native communities in rhizospheric and uninvaded soils but not in sterilized soil.

CONCLUSIONS

The present results suggest that older populations of S. canadensis experience stronger positive plant-soil feedbacks, which may enhance their competitive ability against native plant communities.

Native plant species show evolutionary responses to invasion by Parthenium hysterophorus in an African savanna

Invasive plant species often competitively displace native plant species but some populations of native plant species can evolve adaptation to competition from invasive plants and persist in invaded habitats. However, studies are lacking that examine how variation in abiotic conditions in invaded landscapes may affect fitness of native plants that have adapted to compete with invasive plants. I tested whether invasion by Parthenium hysterophorus in Nairobi National Park - Kenya may have selected for native plant individuals with greater competitive ability than conspecific naïve natives in nutrient-rich and mesic soil conditions. I compared vegetative growth and seed yields of invader-experienced and conspecific naïve individuals of seven native species. Invader-experienced natives grew shorter than naïve natives regardless of growth conditions. Nevertheless, the two groups of native plants also exhibited treatment-specific differences in competitive ability against P. hysterophorus. Invader-experienced natives displayed plasticity in seed yield under drought treatment, while naïve natives did not. Moreover, drought treatment enhanced competitive effects of invader-experienced natives on P. hysterophorus, while nutrient enrichment relaxed competitive effects of invader-experienced natives on the invader. The results suggest that P. hysterophorus may have selected for shorter native plant genotypes that also exhibit plasticity in competitive ability under drought conditions.