Aboveground herbivory can promote exotic plant invasion through intra- and interspecific aboveground-belowground interactions.

Aboveground herbivores and soil biota profoundly affect plant invasions. However, how they interactively affect plant invasions through plant-soil feedbacks (PSFs) remains unclear. To explore how herbivory by the introduced beetle Agasicles hygrophila affects Alternanthera philoxeroides invasions in China, we integrated multiyear field surveys and a 2-yr PSF experiment, in which we examined how herbivory affects PSFs on the performance of native and invasive plants and the introduced beetles. Despite increased herbivory from A. hygrophila, A. philoxeroides dominance over co-occurring congeneric native Alternanthera sessilis remained constant from 2014 to 2019. While occurring at lower abundances, A. sessilis experienced similar herbivore damage, suggesting apparent competitive effects. Our experiments revealed that herbivory on A. philoxeroides altered soil microbial communities, prolonged its negative PSF on A. sessilis, and decreased A. hygrophila larvae performance on the next-generation invasive plants. Consequently, A. hygrophila larvae performed better on leaves of natives than those of invasives when grown in soils conditioned by invasive plants defoliated by the introduced beetles. Our findings suggest that aboveground herbivory might promote rather than suppress A. philoxeroides invasion by enhancing its soil-mediated self-reinforcement, providing a novel mechanistic understanding of plant invasions. These findings highlight the need to incorporate an aboveground-belowground perspective during the assessment of potential biocontrol agents.

Latitudinal variation in the diversity and composition of various organisms associated with an exotic plant: the role of climate and plant invasion.

Climate and plant invasion can shape biotic communities at large spatial scales. Yet, how diverse groups of organisms associated with an invasive plant change simultaneously with latitude and the roles of climate and plant invasion remains unclear. We conducted a field survey of plants (native vs exotic), soil fungi (pathogenic, saprotrophic, arbuscular mycorrhiza fungi (AMF) and ectomycorrhizal (EcM) fungi) and arthropods (herbivores, predators and detritivores) associated with the invasive plant Alternanthera philoxeroides at 49 sites spanning 14 latitudinal degrees in China. Results showed that diversity and composition of these functional groups changed differently with latitude, partially due to their specific responses to climate, invasion of A. philoxeroides and other biotic environments. Moreover, A. philoxeroides invasion and/or composition of other plants, rather than climate, predicted the diversity and richness of major functional groups and partly explained variance in composition of putative fungal pathogens. Our results suggest that climate and plant invasion could affect the diversity and composition of diverse groups of organisms simultaneously and their relative importance might vary among functional groups. Thus, it is necessary to explore latitudinal patterns and underlying drivers of diverse groups of organisms simultaneously to improve our ability to predict and mitigate threats posed by plant invasion and climate change.

Plant evolution overwhelms geographical origin in shaping rhizosphere fungi across latitudes.

As the number of non-native invasive species in the world is increasing, there is a pressing need to understand the effects of invasive species on recipient biotic communities to improve our ability to migrate or relieve their potential negative effects on biodiversity and ecosystem functions. Plant invasions have been shown to impose great threats to aboveground biotic communities; however, invasive impacts on soil biota remain ambiguous, partially because of the paucity of studies with a large number of species across biogeographic gradients. Here, we characterized rhizosphere fungal communities of 53 native and invasive plants spanning approximately 1800 km in China, as well as eight pairs of phylogenetically related native versus invasive plants in a greenhouse experiment. The results of both field survey and greenhouse experiment showed that rhizosphere fungal composition was primarily predicted by plant phylogeny (e.g. family and species), and plant geographic origin (native vs. invasive) and abiotic factors had much smaller effects. We detected no differences in the number and relative abundance of total and family/species-specific OTUs (i.e. overall, pathogens and mutualists) associated with these native and invasive plants on average, suggesting novel co-evolution between native soil fungi and these invasive plants. These results suggest that non-native plant invasions had only a weak impact on soil fungi, partially due to stronger controls of plant evolution on rhizosphere fungi and adaptation of native fungi to these invasive species. Interestingly, rhizosphere fungal composition was more variable between invasive plants than between native plants at middle latitudes, potentially creating spatial variations in plant-soil interactions and, in turn, invasion dynamics. These novel findings highlight the importance of integrating phylogenetic and biogeographical approaches to explore invasive effects on native biota.

[Control effects of mowing in combining with planting tree species on Chromolaena odorata in karst region of Guangxi, China].

A field experiment was conducted in 2006-2008 to evaluate the control effects of three mowing frequencies in combining with planting three tree species with three densities on the Chromolaena odorata in southwestern Karst region of Guangxi. In all treatments, the relative coverage, height, density, and aboveground biomass of C. odorata were decreased by 89.7%-99.3%, 41.6% - 81.2%, 61.4% - 83.2% and 91.7% - 97.8%, respectively, and the capitulum number was significantly lesser than that in the control (P<0.05). The control effects on the growth of C. odorata were in the order of mowing frequency > tree species > planting density, and the optimal control mode was mowing twice one year and planting four plants of Delavaya yunnanensis per plot (4 m x 4 m).