Invasive Plant Alternanthera Philoxeroides Research Articles

Aboveground herbivory increases soil nematode abundance of an invasive plant

AbstractAimsPlant invasions have the potential to affect the community structure of soil nematodes, but little is known about whether such effects are mediated by aboveground herbivores since invasive plants are not completely released from herbivores in the introduced range. In this study, we explored how aboveground insect herbivores mediated the effect of invasive plant Alternanthera philoxeroides on soil nematodes and examined the temporal variations of such an herbivory-elicited effect.MethodsWe conducted a greenhouse experiment by applying different herbivory treatments (no insect herbivores, specialist Agasicles hygrophila and generalist Cassida piperata) to potted A. philoxeroides, and then measured the community compositions of soil nematodes in corresponding pots on the 1st, 10th and 20th day after removal of all herbivores. In addition, the carbon content of roots and root exudate of A. philoxeroides were also measured.Important FindingsOur results showed that aboveground herbivory significantly increased the abundance of soil nematodes of A. philoxeroides, likely plant feeder nematodes, after insect herbivores were removed immediately (1st day). However, such impacts waned with time and there was no significant difference at later stages (10th and 20th days). Furthermore, the effects of specialist A. hygrophila and generalist C. piperata herbivory were consistent on the abundance of soil nematodes. Overall, our results suggest that aboveground insect herbivores have the potential to alter the effects of plant invasions on soil nematodes, but such impacts are transient. Furthermore, our study highlighted the importance of integrating the effects of above- and belowground organisms when evaluating the impacts of plant invasions.

Soil resource heterogeneity competitively favors an invasive clonal plant over a native one.

Soil resource heterogeneity can affect plant growth and competitive ability. However, little is known about how soil resource heterogeneity affects competitive interactions between invasive and native plants. We conducted an experiment with an invasive clonal plant Alternanthera philoxeroides and a coexisting native one Alternanthera sessilis. The experiment was a randomized design with three factors, i.e. two species (A. philoxeroides and A. sessilis), two interspecific competition treatments (with and without) and five soil treatments (three homogeneous treatments and two small-scale heterogeneous treatments consisting of two patches of 10cm × 15cm and with different initial planting positions). Irrespective of competition, increasing soil resource availability increased the growth of A. philoxeroides. Increasing soil resource availability alsoincreased the growth of A. sessilis without competition, but had no impact with competition. Irrespective of competition, soil resource heterogeneity increased biomass and ramet production of A. philoxeroides, andsuch effects were independent of initial planting position. For A. sessilis, however, soil resource heterogeneity only increased ramet production when the initial plant was grown in the low-resource patch without competition. Our results suggest that both high soil resource availability and small-scale soil resource heterogeneity can increase the relative competitive ability of the invasive plant A. philoxeroides when grown with its native congener A. sessilis. These findings may partly explain the invasion success of this clonal species in area with high soil resource availability and heterogeneity caused by e.g. nitrogen deposition, fertilization and disturbance.

Herbivory may promote a non-native plant invasion at low but not high latitudes.

The strengths of biotic interactions such as herbivory are expected to decrease with increasing latitude for native species. To what extent this applies to invasive species and what the consequences of this variation are for competition among native and invasive species remain unexplored. Here, herbivore impacts on the invasive plant Alternanthera philoxeroides and its competition with the native congener A. sessilis were estimated across latitudes in China. An common garden experiment spanning ten latitudinal degrees was conducted to test how herbivore impacts on A. philoxeroides and A. sessilis, and competition between them change with latitude. In addition, a field survey was conducted from 21°N to 36.8°N to test whether A. philoxeroides invasiveness changes with latitude in nature as a result of variations in herbivory. In the experiment, A. sessilis cover was significantly higher than A. philoxeroides cover when they competed in the absence of herbivores, but otherwise their cover was comparable at low latitude. However, A. philoxeroides cover was always higher on average than A. sessilis cover at middle latitude. At high latitude, only A. sessilis emerged in the second year. Herbivore abundance decreased with latitude and A. philoxeroides emerged earlier than A. sessilis at middle latitude. In the field survey, the ratio of A. philoxeroides to A. sessilis cover was hump shaped with latitude. These results indicate that herbivory may promote A. philoxeroides invasion only at low latitude by altering the outcome of competition in favour of the invader and point to the importance of other factors, such as earlier emergence, in A. philoxeroides invasion at higher latitudes. These results suggest that the key factors promoting plant invasions might change with latitude, highlighting the importance of teasing apart the roles of multiple factors in plant invasions within a biogeographic framework.

Herbivory and nitrogen availability affect performance of an invader Alternanthera philoxeroides and its native congener A. sessilis

Tolerance to herbivory influences the success of invasive species in introduced ranges, and thus a comparison of the difference in herbivory tolerance between invasive and native species may help to understand the mechanisms of plant invasions. We conducted a greenhouse experiment in Beijing, China to examine effects of aboveground herbivory (by a beetle Agasicles hygrophila or not) and nitrogen availability (high vs. low) on growth and physiology of the invasive plant Alternanthera philoxeroides and its coexisting native congener A. sessilis. Herbivory by A. hygrophila significantly reduced total mass and aboveground development of both plant species, and the negative effects of herbivory on leaf mass, ramet number, and leaf number were more remarkable at the high than at the low nitrogen level. On the other hand, herbivory did not affect root mass and even increased root to shoot ratio of both plant species. The increase in root to shoot ratio and relative ratio of root mass caused by herbivory was also stronger in A. philoxeroides than in A. sessilis. Besides, herbivory exerted neutral or positive effects on the concentrations of starch and total non-structural carbohydrates in stems and roots of A. philoxeroides, but negative effects on the physiological measures of A. sessilis. We conclude that A. philoxeroides may possess a stronger tolerance to herbivory than A. sessilis and that increased resource allocation to roots could potentially contribute to compensatory responses of A. philoxeroides to aboveground herbivory. Our findings also suggest that the control of A. hygrophila may be invalid in belowground invasion of A. philoxeroides, and that belowground herbivores should be considered in the future management of invasive species.

Effects of physiological integration on defense strategies against herbivory by the clonal plant Alternanthera philoxeroides

The plant–herbivore interaction is one of the most fundamental interactions in nature. Plants are sessile organisms, and consequently rely on particular strategies to avoid or reduce the negative impact of herbivory. Here, we aimed to determine the defense strategies against insect herbivores in the creeping invasive plant Alternanthera philoxeroides. We tested the defense response of A. philoxeroides to herbivory by a leaf-feeding specialist insect Agasicles hygrophila and a polyphagous sap-feeding insect Planococcus minor. We also tested the mechanisms triggering defense responses of A. philoxeroides by including treatments of artificial leaf removal and jasmonic acid application. Furthermore, we examined the effect of physiological integration on these defense strategies. The combination of artificial leaf removal and jasmonic acid application produced a similar effect to that of leaf-feeding by the real herbivore. Physiological integration influenced the defense strategies of A. philoxeroides against herbivores, and increased biomass allocation to aboveground parts in its apical ramets damaged by real herbivores. Our study highlights the importance of physiological integration and modular plasticity for understanding the consequences of herbivory in clonal plants.

Effects of clonal integration and nitrogen supply on responses of a clonal plant to short-term herbivory

Clonal integration, i.e. resource sharing between interconnected ramets, can help clonal plants tolerate abiotic stress. However, few studies have directly examined the ecological significance of clonal integration in the ability of clonal plants to tolerate biotic stress such as herbivory. We grew clonal fragments of an invasive clonal plant Alternanthera philoxeroides, each consisting of an apical part (relatively young) and a basal part (relatively old), at two levels (low and high) of soil nitrogen (N). For each fragment, the apical part was subjected to either no herbivory or herbivory for 2 weeks by a specialist insect, Agasicles hygrophila, and was either connected with or disconnected from the basal part not subjected to herbivory. Herbivory in the apical part severely reduced leaf growth (leaf mass, leaf number or leaf area) and ramet production of both apical and basal parts, and increased root to shoot ratio of the apical part. Irrespective of herbivory and soil N, stem connection between the apical and the basal part decreased root to shoot ratio of the apical part, but did not change its growth measures. Meanwhile, connection increased stem N concentration of the apical part growing under high-N supply and decreased stem carbon (C) concentration of the apical part under low-N supply. By contrast, connection increased root to shoot ratio of the basal part, but reduced its leaf and ramet production. Connection also increased leaf and stem C concentrations of the basal part under low-N supply. Thus, clonal integration can be beneficial for the early development of young A. philoxeroides ramets, but not for their local adaptation to herbivory damage by A. hygrophila.

Allelopathic potential of Phragmites australis extracts on the growth of invasive plant Alternanthera philoxeroides

Allelopathic potential of Phragmites australis extracts on the growth of invasive plant Alternanthera philoxeroides

Direct and legacy effects of herbivory on growth and physiology of a clonal plant

The ability to tolerate novel herbivores is widely considered to influence plant invasion success. For clonal plants that have reduced capacity to evolve in response to novel herbivores, legacy effects of herbivory on parental plants might be translated to offspring ramets, resulting in pre-adaptation to tolerate herbivory for new vegetative growth. Using the invasive clonal plant Alternanthera philoxeroides, we first exposed plants to herbivory by Planococcus minor, a widespread and generalist piercing-sucking insect. Herbivory decreased above- and below-ground plant biomass by approximately 50% with a concomitant 134% increase in root N concentration but no changes in concentrations of soluble sugars, starch or non-structural carbohydrates related to herbivory tolerance. Offspring ramets were then exposed to herbivory by three different herbivore species: (1) P. minor, (2) the specialist leaf-beetle Agasicles hygrophila, and (3) the stenophagous tortoise-beetle Cassida piperata. There was no evidence of interactive effects between herbivory on parental plants and herbivory on offspring plants on growth, biomass allocation patterns, or physiological responses, suggesting that pre-adaptation to herbivory did not occur in A. philoxeroides with these herbivores. There were, however, species-specific herbivore tolerance responses. In the offspring generation, herbivory by A. hygrophila strongly suppressed growth and biomass allocation, but patterns were generally weaker for other herbivores. Tolerance effects could be explained by stimulatory effects of grazing by C. piperata and P. minor on taproot biomass along with idiosyncratic increases of starch and non-structural carbohydrate concentration in some storage organs. Our results highlight the importance of A. hygrophila in controlling the aboveground spread of A. philoxeroides. However, herbivory by other species was largely tolerated and accompanied by increased allocation to underground storage organs and altered physiological reserves, both of which could allow this invasive plant to tolerate herbivory and successfully invade new areas in the face of new herbivore pressure.

Latitudinal variation in soil biota: testing the biotic interaction hypothesis with an invasive plant and a native congener

Soil biota community structure can change with latitude, but the effects of changes on native plants, invasive plants, and their herbivores remain unclear. Here, we examined latitudinal variation in the soil biota community associated with the invasive plant Alternanthera philoxeroides and its native congener A. sessilis, and the effects of soil biota community variation on these plants and the beetle Agasicles hygrophila. We characterized the soil bacterial and fungal communities and root-knot nematodes of plant rhizospheres collected from 22 °N to 36.6 °N in China. Soil biota community structure changed with latitude as a function of climate and soil properties. Root-knot nematode abundance and potential soil fungal pathogen diversity (classified with FUNGuild) decreased with latitude, apparently due to higher soil pH and lower temperatures. A greenhouse experiment and lab bioassay showed native plant mass, seed production, and mass of beetles fed native foliage increased with soil collection latitude. However, there were no latitudinal patterns for the invasive plant. These results suggest that invasive and native plants and, consequently, their herbivores have different responses to latitudinal changes in soil-borne enemies, potentially creating spatial variation in enemy release or biotic resistance. This highlights the importance of linking above- and below-ground multitrophic interactions to explore the role of soil biota in non-native plant invasions with a biogeographic approach.

Evolution of increased intraspecific competitive ability following introduction: The importance of relatedness among genotypes

Abstract A long‐standing explanation for invasion success is that invasive plants could evolve to be more competitive following introduction. This evolution of increased competitive ability (EICA) hypothesis, however, has seldom been tested with regard to intraspecific competition. Given that plants can display different responses to related and unrelated conspecifics, the evolution of intraspecific competitive ability might be specific to genotypes of different relatedness. Here, we grew five native (South American) and five introduced (North American) genotypes of the clonal herbaceous invasive plant Alternanthera philoxeroides alone, with above‐ground competition from kin (the same genotype) or from one of two types of strangers (another genotype from the same range or another genotype from the other range). When grown alone, introduced and native genotypes produced similar total biomass and storage‐root biomass. However, in response to intraspecific competition, introduced genotypes showed increases in total biomass and stem length, and a decrease in specific stem length, whereas native genotypes showed the opposite pattern. When grown with kin instead of strangers, introduced genotypes showed an increase in branch number, whereas native genotypes showed the opposite. Synthesis. Our study provided evidence for evolution of increased intraspecific competitive ability in an invasive plant. We also found, for the first time, that the interactions among kin were likely to shift from competition towards facilitation following introduction.

Tolerance and resistance facilitate the invasion success of Alternanthera philoxeroides in disturbed habitats: A reconsideration of the disturbance hypothesis in the light of phenotypic variation

Disturbance has been considered to exert positive, neutral or negative effects on the invasion of exotic plants. Disturbance may enhance the invasion success of alien invasive species by both increasing their performance and alleviating the harmful effects caused by disturbance via tolerance and resistance, especially in the late phases of the invasion process. However, the tolerance and resistance of invasive plant clonal populations to disturbance has been mostly neglected. In the present study, we explored the phenotypic responses of clonal populations of the invasive plant Alternanthera philoxeroides and three co-occurring non-invasive clonal species, i.e., Alternanthera sessilis, Myriophyllum aquaticum and Jussiaea repens, to different levels of fluctuating flood disturbances using a mesocosm experiment. Different functional traits related to morphology, biomass allocation and physiology were used to evaluate plant performance. We found that A. philoxeroides coped with fluctuating flooding by performing phenotypic maintenance that affected ramet number, stolon length, specific leaf area, leaf mass ratio, chlorophyll content, nitrogen content and non-structural carbohydrate content; additionally, the plant experienced variations in stolon diameter, stolon mass ratio, root mass allocation and maximum fluorescence. In addition, Alternanthera philoxeroides demonstrated several similarities with the three non-invasive species in terms of the observed phenotypic responses to different disturbance statuses. Furthermore, Alternanthera philoxeroides showed respective advantages in tolerance compared to A. sessilis, photosynthetic capacity compared to M. aquaticum and especially J. repens, and resistance to submergence compared to all three non-invasive species. Overall, tolerance and resistance facilitated the successful invasion of A. philoxeroides in disturbed habitats. Furthermore, the native constructive species J. repens was severely harmed by fluctuating flooding; thus, fluctuating flooding could create an empty niche that promotes the expansion of the clonal populations of A. philoxeroides.

Response of soil enzymes and microbial communities to root extracts of the alien Alternanthera philoxeroides

ABSTRACTAlternanthera philoxeroides is an alien invasive species, which can cause substantial damage to the local ecosystem by secreting allelochemicals. The objective of the present study was to appraise the effects of root extracts of the invasive plant Alternanthera philoxeroides on soil enzyme and native microbial community. Urease activity was measured using the phenol sodium hypochlorite colorimetric method, sucrase activity was determined by 3, 5-dinitrosalicylic acid colorimetric method, catalase activity was determined using the KMnO4 titration method and alkaline phosphatase activity was determined by the disodium phenyl phosphate colorimetric method. The soil microbial community was investigated by pyrosequencing of the 16S rRNA gene. Results showed that the alkaline phosphatase, sucrase and urease activities were all significantly lower than that of the control treatment. The structure of the soil microbial community in the treatments with root extracts addition clearly differed from that of the control treatment. The result showed that the relative abundance of microorganism decreased including Burkhholderia, Gp6, Gp1 and Gp4 in the applied treatments at genus level as compared to control treatment. Hence, we inferred that A. philoxeroides could inhibit the growth of native plant species through toxic effects on soil enzyme activities and the microbial community.

Fragmentation of the invasive, clonal plant Alternanthera philoxeroides decreases its growth but not its competitive effect

Clonal integration and fragmentation are potentially competing advantages of clonal growth. Clonal fragmentation can increase the dispersal of ramets, but it prevents physiological integration, which can increase the growth of clones and may increase their competitive effect on other plant species. We tested whether fragmentation can reduce the competitive effect of invasive clonal plants within mixed communities and whether this effect of fragmentation is greater under conditions in which the competitive effect of a clonal plant is greater. We constructed wetland communities each consisting of four common, co-occurring, mainly aquatic plant species under flooded and unflooded conditions, and compared the growth of the species with and without intact or fragmented groups of ramets of the widespread, amphibious, invasive clonal plant Alternanthera philoxeroides. We measured the community-level competitive effect of A. philoxeroides on the four aquatic plant species. Fragmentation reduced mass accumulation of A. philoxeroides, but did not reduce its competitive effect, either under flooded or under unflooded conditions. One explanation is that A. philoxeroides was able to maintain production of new ramets when fragmented. Clonal plants may thus mitigate trade-offs between the potential ecological advantages of physiological integration and fragmentation by maintaining rates of vegetative reproduction after fragmentation, even when total growth is reduced.

Shifts in growth and competitive dominance of the invasive plant Alternanthera philoxeroides under different nitrogen and phosphorus supply

The availability of nitrogen and phosphorus is an important factor determining the growth and competitive dominance of invasive plants. To clarify the influence of nutrient availability on the performance of alien species, we conducted a greenhouse experiment in which the invasive plant Alternanthera philoxeroides was planted as a monoculture or in mixed culture with noninvasive species (Oenanthe javanica or Iris pseudacorus) under combined conditions of various nutrient level (low, medium, and high) and N/P ratio (1, 10, and 100). Nutrient level and N/P ratio both affected the growth of A. philoxeroides and the effects were similar in mixed culture and monoculture. Increased nutrient level significantly increased the total biomass and total stolon length of A. philoxeroides under all N/P ratios. At low nutrient level, N/P ratio had little influence on the total biomass and total stolon length of A. philoxeroides. At medium and high nutrient levels, however, increased N/P ratios inhibited the growth of A. philoxeroides. Nutrient level rather than N/P ratio affected the relative dominance index (RDI) of A. philoxeroides, with increased nutrient levels enhancing the competitive dominance of A. philoxeroides. Furthermore, the RDI of A. philoxeroides in mixed culture with I. pseudacorus was consistently higher than that of A. philoxeroides when grown with O. javanica. Therefore, our results indicate that nutrient enrichment (such as over-fertilization and eutrophication) would aggravate the already serious impact of biological invasions and that the identity of resident plant species might also affect the competitive dominance of exotic plants.

The invasive stoloniferous clonal plant Alternanthera philoxeroides outperforms its co-occurring non-invasive functional counterparts in heterogeneous soil environments - invasion implications.

Environmental heterogeneity is considered to play a defining role in promoting invasion success, and it favours clonal plants. Although clonality has been demonstrated to be correlated with the invasion success of several species of clonal invasive plants in heterogeneous environments, little is known about how the spatial scale of heterogeneity affects their performance. In addition, the factors that distinguish invasive from non-invasive clonal species and that enhance the invasive potential of clonal exotic invaders in heterogeneous environments remain unclear. In this study, we compared several traits of a noxious clonal invasive species, Alternanthera philoxeroides, with its co-occurring non-invasive functional counterparts, the native congener Alternanthera sessilis, the exotic Myriophyllum aquaticum and the native Jussiaea repens, in three manipulative substrates with different soil distribution patterns. We found that the invasive performance of A. philoxeroides was not enhanced by heterogeneity and that it was generally scale independent. However, A. philoxeroides showed some advantages over the three non-invasives with respect to trait values and phenotypic variation. These advantages may enhance the competitive capacity of A. philoxeroides and thus promote its invasion success in heterogeneous environments.

Invasive plant Alternanthera philoxeroides suffers more severe herbivory pressure than native competitors in recipient communities.

Host-enemy interactions are vital mechanisms that explain the success or failure of invasive plants in new ranges. We surveyed the defoliation of invasive Alternanthera philoxeroides and co-occurring native plants on two islands during different seasons over three consecutive years and measured the leaf nitrogen content and the C/N ratio of each plant species. To evaluate the effects of herbivory on A. philoxeroides, an herbivore exclosure experiment was conducted. We found that the mean defoliation of A. philoxeroides was higher than that of native plants, regardless of whether the dominant species was A. philoxeroides or native plants. A. philoxeroides defoliation increased significantly as the months progressed, whereas the defoliation of the total population of native plants was constant. The leaf nitrogen content was positively correlated with defoliation, and it was highest in A. philoxeroides. Additionally, A. philoxeroides in the herbivore exclusion treatment showed an increase in shoot biomass and total shoot length. Our study revealed that native generalist herbivores prefer the invasive plant to the natives because of the higher leaf nitrogen content. These results support the biotic resistance hypothesis, suggesting that native herbivore species can limit the population spread of invasive plants.

Global warming increases the interspecific competitiveness of the invasive plant alligator weed, Alternanthera philoxeroides

Global warming could accelerate the spread of invasive species to higher latitudes and intensify their effects on native species. Here, we report results of two years of field surveys along a latitudinal gradient (21°N to 31°N) in southern China, to determine the species structure of the invasive plant Alternanthera philoxeroides community. We also performed a replacement series experiment (mono and mixed) to evaluate the effects of elevated temperature on the competitiveness of A. philoxeroides with the native co-occurring species Digitaria sanguinalis. In the field survey, we found that the dominance of A. philoxeroides increased with increasing of latitude gradient while cover of D. sanguinalis decreased. In monospecific plantings, artificial warming reduced the length of D. sanguinalis roots. In mixed plantings, warming reduced both A. philoxeroides abundance and D. sanguinalis stem length when A. philoxeroides was more prevalent in the planting. Warming also significantly reduced D. sanguinalis biomass, but increased that of A. philoxeroides. In addition, elevated temperatures significantly reduced the relative yield (RY) of D. sanguinalis, particularly when A. philoxeroides was planted in higher proportion in the plot. These results suggest that the invasiveness of A. philoxeroides increased with increasing latitude, and that warming may increase the effectiveness of its interspecific competition with D. sanguinalis. Hence, under global warming conditions, the harm to native species from A. philoxeroides would increase at higher latitudes. Our findings are critical for predicting the invasiveness of alien species under climate change.

Differences in interactions of aboveground and belowground herbivores on the invasive plant Alternanthera philoxeroides and native host A. sessilis

Plant invasions may result in novel plant-herbivore interactions. However, we know little about whether and how invasive plants can mediate native above- and belowground herbivore interactions. In this study, we conducted greenhouse experiments to examine the interaction between a native defoliating beetle, Cassida piperata, and a native root-knot nematode, Meloidogyne incognita, on the invasive alligator weed, Alternanthera philoxeroides. We also included their native host A. sessilis in the experiments to examine whether the patterns of above- and belowground herbivore interaction vary with host plants (invasive vs. native). We analyzed total carbon and nitrogen in leaves and roots attacked by M. incognita and C. piperata. M. incognita slightly negatively affected feeding by C. piperata on A. philoxeroides, and the leaf area damaged decreased as the number of M. incognita increased. M. incognita had a negative impact on total leaf nitrogen, but had no impact on total leaf carbon. M. incognita egg production on A. philoxeroides roots decreased as the amount of damage caused by C. piperata increased. Herbivory by C. piperata did not affect total root carbon or nitrogen. M. incognita and C. piperata did not affect each other on the native plant A. sessilis. These results suggest that invasive plants can mediate native above- and belowground herbivore interactions. The knowledge of how invasive plants affect those interactions is crucial for better understanding the impacts of biological invasions on native above- and belowground organisms.

Effects of clonal integration on the invasive clonal plant Alternanthera philoxeroides under heterogeneous and homogeneous water availability.

Many notorious invasive plants are clonal, living in heterogeneous or homogeneous habitats. To understand how clonal integration affects the performance of these plants in different habitat conditions, an 8-week greenhouse experiment was conducted: ramet pairs of A. philoxeroides were grown in two habitats, either heterogeneous or homogeneous in water availability, with the stolon connections either severed or kept intact. Under heterogeneous water availability, compared with ramets in homogeneous habitats, clonal integration significantly promoted the growth and photosynthetic performance of water-stressed apical ramets, whereas it only increased the photosynthetic performance but did not affect the growth of water-stressed basal ramets. Moreover, clonal integration markedly increased the root/shoot ratios of ramets grown in habitats with high water supply but decreased it under low water availability. Under homogeneous water availability, stolon connection (clonal integration) did not influence the growth, photosynthetic performance and biomass allocation of water-stressed ramets, but it significantly promoted the growth of well-watered ramets in both apical and basal sections. These findings deepen our understanding of the bidirectional and differentiated (mainly acropetal) clonal integration of A. philoxeroides, suggesting that the invasive plant A. philoxeroides can benefit from clonal integration in both heterogeneous and homogeneous habitats.

Warming benefits a native species competing with an invasive congener in the presence of a biocontrol beetle

Climate warming may affect biological invasions by altering competition between native and non-native species, but these effects may depend on biotic interactions. In field surveys at 33 sites in China along a latitudinal and temperature gradient from 21°N to 30.5°N and a 2-yr field experiment at 30.5°N, we tested the role of the biocontrol beetle Agasicles hygrophila in mediating warming effects on competition between the invasive plant Alternanthera philoxeroides and the native plant Alternanthera sessilis. In surveys, native populations were perennial below 25.8°N but only annual populations were found above 26.5°N where the invader dominated the community. Beetles were present throughout the gradient. Experimental warming (+1.8°C) increased native plant performance directly by shifting its lifecycle from annual to perennial, and indirectly by releasing the native from competition via disproportionate increases in herbivory on the invader. Consequently, warming shifted the plant community from invader-dominated to native-dominated but only in the presence of the beetle. Our results show that herbivores can play a critical role in determining warming effects on plant communities and species invasions. Understanding how biotic interactions shape responses of communities to climate change is crucial for predicting the risk of plant invasions.