Neighboring Plants Research Articles

Plasticity of functional traits of forb species in response to biodiversity

In spite of increasing recognition that intraspecific variation may play an important role for niche differentiation, which is regarded as a promoter of species coexistence, the extent and structure of functional trait variation in response to plant neighbor diversity is poorly understood. We studied the plasticity of functional traits in vegetative and reproductive shoots of 27 non-legume forb species with different growth forms (reptant, rosulate, semirosulate) in experimental grasslands (Jena Experiment) of varying species richness and functional group composition (with and without legumes). Traits related to whole-shoot structure differed strongly among forb species with different growth forms, while leaf traits associated with light acquisition (specific leaf area, foliar δ13C values) and traits associated with nitrogen nutrition (shoot biomass:N ratios, leaf nitrogen concentrations, foliar δ15N values) were highly plastic within forb species. Plant height generally increased with increasing species richness. Plasticities to increased species richness in leaf traits (leaf length, SLA, foliar δ13C) varied among growth forms and depended on developmental stage. The presence of legumes generally increased plastic responses in light-acquisition traits in the same direction as increasing species richness. Greater tissue nitrogen concentrations and unchanged foliar δ15N values of forb species in the presence of legumes suggested that the fertilizing effect of nitrogen-fixing legumes was due to the supply of unconsumed mineral nitrogen. Stronger correlations between trait means and trait plasticities in size-related traits suggested a functional convergence in response to light competition. A more variable spectrum in the plasticities of traits not associated with plant size indicated a greater functional separation among species. Our results suggest that both interspecific differences and intraspecific trait plasticity affect niche partitioning among forb species and are important for their coexistence in multi-species assemblages.

Plant community response to drought-induced canopy defoliation in a Mediterranean Quercus ilex forest

Climate change has increased drought-induced tree die-off in many parts of the world, and future climate models expect a higher recurrence of these perturbations. However, few studies have addressed plant community recovery after drought events, particularly in Mediterranean forests. This study evaluates the consequences of drought-induced die-off of the dominant holm-oak (Quercus ilex) trees on composition, structure and recruitment of the plant community, 6 years after a severe drought episode in Montserrat mountain (Catalonia, NE Spain). We evaluated the relationship of the vegetation response variables to two parameters related to the die-off consequences: canopy openness, as a measure of radiation arriving to ground, and canopy defoliation weighed by plant size, as a measure of drought impact on dominant neighbor plants. We also included in our analyses topographic situation to account for the proximity to ridge summits. Six years after the drought episode, the main findings were as follows: (1) There was a general loss of canopy cover, but Q. ilex still remained as dominant; nevertheless, the small tree Phyllirea latifolia and the shrub Buxus sempervirens tended to increase its relative abundance in the upper vegetation canopy; (2) overall, in open canopy conditions, species richness was higher mostly due to the presence of shade-intolerant herbaceous plants and early successional shrubs, such as Cistus albidus; (3) die-off did not result in increasing recruitment of the dominant species but preexisting Q. ilex sprouts were taller in sites with more open canopy; (4) there was a negative relationship between weighed defoliation and understory height, including Q. ilex sprouts, that can be attributed to large drought impact to both understory and canopy holm-oaks in some microhabitats, such as sites with abundant outcrops. This study highlights the ways in which Q. ilex Mediterranean forests regenerate after drought-induced events of canopy die-off. This regeneration involves changes in community structure and composition involving the increase in species, mostly small shrubs and herbaceous plants, which are able to grow in habitats created by canopy openness, likely becoming dominant in the landscape, as well as the arrival of non-dominant shrubs and short trees to the canopy. Potential shift in vegetation may be facilitated by the lack of increasing recruitment of Q. ilex, but this may be counterbalanced by the ability of holm-oak canopy to resprout and because pre-established saplings grown more with canopy openness. Thus, if tree canopies do not recover in a certain amount of time after the drought episode, then defoliation could lead to permanent changes in diversity and composition of the community.

Neighbour effects of purslane (Portulaca oleracea L.) on Cd bioaccumulation by soybean in saline soil

Bioaccumulation of heavy metals can be affected by various crop-weed interactions in agroecosystems. An experiment was conducted to evaluate the role of belowground interaction of soybean and purslane (Portulaca oleracea L.) weed on cadmium (Cd) uptake and its allocation to soybean grains. The experimental treatments included two cropping systems (mono and mixed culture), two salinity levels (0% and 0.5% NaCl) and three levels of Cd in soil (control; 3 and 6 mg Cd/kg). Results showed that the promoting effect of salinity on Cd uptake by soybean and Cd allocation to grains was enhanced in the presence of purslane compared to the absence of neighbour plant. This could be due to increasing Cd-mobilization within the shared rhizosphere of plants. In the non-saline soil decreasing uptake and grain allocation of Cd in co-planted soybean was associated with enhancing of purslane Cd uptake and the depletion of Cd in soil solution. Therefore, it can be concluded that co-planted purslane can alter the uptake of cadmium to the neighboring soybean plants; its effect may be influenced by soil environmental conditions such as salinity.

Land‐use legacies and present fire regimes interact to mediate herbivory by altering the neighboring plant community

Past and present human activities, such as historic agriculture and fire suppression, are widespread and can create depauperate plant communities. Although many studies show that herbivory on focal plants depends on the density of herbivores or the composition of the surrounding plant community, it is unclear whether anthropogenic changes to plant communities alter herbivory. We tested the hypothesis that human activities that alter the plant community lead to subsequent changes in herbivory. At 20 sites distributed across 80 300 hectares, we conducted a field experiment that manipulated insect herbivore access (full exclosures and pseudo‐exclosures) to four focal plant species in longleaf pine woodlands with different land‐use histories (post‐agricultural sites or non‐agricultural sites) and degrees of fire frequency (frequent and infrequent). Plant cover, particularly herbaceous cover, was lower in post‐agricultural and fire suppressed woodlands. Density of the dominant insect herbivore at our site (grasshoppers) was positively related to plant cover. Herbivore access reduced biomass of the palatable forb Solidago odora in frequently burned post‐agricultural sites and in infrequently burned non‐agricultural woodlands and increased mortality of another forb (Pityopsis graminifolia), but did not affect two other less palatable species (Schizachyrium scoparium and Tephrosia virginiana). Herbivory on S. odora exhibited a hump‐shaped response to plant cover, with low herbivory at low and high levels of plant cover. Herbivore density had a weak negative effect on herbivory. These findings suggest that changes in plant cover related to past and present human activities can modify damage rates on focal S. odora plants by altering grasshopper foraging behavior rather than by altering local grasshopper density. The resulting changes in herbivory may have the potential to limit natural recovery or restoration efforts by reducing the establishment or performance of palatable plant species.

Allelochemicals in the rhizosphere soil of Euphorbia himalayensis.

Weed infestation has been known to cause considerable reductions in crop yields, thereby hindering sustainable agriculture. Many plants in genus Euphorbia affect neighboring plants and other organisms by releasing chemicals into the environment. In view of the serious threat of weeds to agriculture, the allelochemicals of Euphorbia himalayensis and their allelopathic effects were investigated. The extract of root exudates from rhizosphere soil exhibited allelopathic activities against crops (wheat, rape, and lettuce) and grasses (Poa annua, Festuca rubra, and red clover). Bioassay-guided fractionation and isolation from the root extract of E. himalayensis led to the characterization of two ellagic acid derivatives and a jatrophane diterpene, which observably showed phytotoxic activities against lettuce, Festuca arundinacea, and F. rubra. They were further confirmed by ultra-performance liquid chromatography-tandem mass spectrometry to have concentrations of 3.6, 3.8, and 8.99 nmol/g in the rhizospere soil, respectively. Bioassay indicated that the combination of the allelochemicals could be selective plant growth regulator in agriculture.

Role of tussock morphology in providing protection from grazing for neighbouring palatable plants in a semi-arid Mongolian rangeland

Background: Palatable plants in rangelands may be protected from herbivore grazing by the presence of less palatable neighbouring plants. The protective role of benefactor species on palatable species often collapses under heavy grazing, but the underlying mechanism—the relationship between the reduced protective role and grazing damage to benefactor species—remains unclear.Aims: To clarify whether the protection of surrounding palatable species conferred by a less palatable tussock grass (Achnatherum splendens) is reduced under heavy grazing, focusing on the changes to tussock morphology caused by grazing.Methods: In the Mongolian steppe, we measured the morphological traits of A. splendens tussocks, plant density of palatable graminoids and grazing damage in three A. splendens microhabitats (inside, adjacent to, and outside tussocks) under light and heavy grazing areas.Results: A. splendens tussocks had smaller basal area and culm height, and greater culm density under heavy grazing. The densities of palatable graminoids adjacent to and inside tussocks were equal to or lower than those outside, but grazing damage decreased inside tussocks. Additionally, plant establishment inside tussocks was negatively related to A. splendens culm density, probably owing to competition for space within the tussocks.Conclusions: Our results indicate that the collapse of positive grass–grass interactions results from the decline in neighbouring benefactor plants through the morphological changes caused by grazing.

The presence of a below-ground neighbour alters within-plant seed size distribution in Phaseolus vulgaris.

Considerable variation in seed size commonly exists within plants, and is believed to be favoured under natural selection. This study aims to examine the extent to which seed size distribution depends on the presence of competing neighbour plants. Phaseolus vulgaris plants rooting with or without a conspecific neighbour were grown in soil with high or low nutrient availability. Seeds were harvested at the end of the growth cycle, the total nitrogen and phosphorus invested in seed production were measured and within-plant seed size distribution was quantified using a set of statistical descriptors. Exposure to neighbours' roots induced significant changes in seed size distribution. Plants produced proportionally more large seeds and fewer small ones, as reflected by significant increases in minimal seed size, mean seed size, skewness and Lorenz asymmetry coefficient. These effects were different from, and in several cases opposite to, the responses when the soil nutrient level was reduced, and were significant after correction for the amount of resources invested in seed production. Below-ground neighbour presence affects within-plant seed size distribution in P. vulgaris. This effect appears to be non-resource-mediated, i.e. to be independent of neighbour-induced effects on resource availability. It implies that, based on current environmental cues, plants can make an anticipatory adjustment of their investment strategy in offspring as an adaptation to the local environment in the future.

Assembly of root-associated bacteria communities: interactions between abiotic and biotic factors.

Nitrogen (N) deposition in many areas of the world is over an order of magnitude greater than it would be in absence of human activity. We ask how abiotic (N)and biotic (plant host and neighborhood) effects interact to influence root-associated bacterial (RAB)community assembly. Using 454 pyrosequencing, we examined RAB communities from two dominantal pine tundra plants, Geum rossii and Deschampsia cespitosa, under control, N addition and D. cespitosa removal treatments, implemented in a factorial design. We hypothesized that host would have the strongest effect on RAB assembly, followed by N,then neighbor effects.The most dominant phyla were Proteobacteria (mostly Gammaproteobacteria), Actinobacteria,Bacteroidetes and Acidobacteria. We found RAB communities were host specific, with only 17% overlap in operational taxonomic units. Host effects on composition were over twice as strong as Neffects. D. cespitosa RAB diversity declined with N, while G. rossii RAB did not. D. cespitosa removal did not influence G. rossii RAB community composition, but G. rossii RAB diversity declined with N only when D. cespitosa was absent. We conclude that RAB of both hosts are sensitive to N enrichment, and RAB response to N is influenced by host identity and plant neighborhood.

Phytotoxic flavonoids from roots of Stellera chamaejasme L. (Thymelaeaceae)

Allelopathy, the negative effect on plants of chemicals released to the surroundings by a neighboring plant, is an important factor which contributes to the spread of some weeds in plant communities. In this field, Stellera chamaejasme L. (Thymelaeaceae) is one of the most toxic and ecologically-threatening weeds in some of the grasslands of north and west China. Bioassay-guided fractionation of root extracts of this plant led to the isolation of eight flavonoids 1–8, whose structures were elucidated by spectroscopic analysis. All compounds obtained, except 7-methoxylneochaejasmin A (4) and (+)-epiafzelechin (5), showed strong phytotoxic activity against Arabidopsis thaliana seedlings. Seedling growth was reduced by neochamaejasmin B (1), mesoneochamaejasmin A (2), chamaejasmenin C (3), genkwanol A (6), daphnodorin B (7) and dihydrodaphnodorin B (8) with IC50 values of 6.9, 12.1, 43.2, 74.8, 7.1 and 27.3μg/mL, respectively, and all of these compounds disrupted root development. Endogenous auxin levels at the root tips of the A. thaliana DR5::GUS transgenic line were largely reduced by compounds 1, 2 and 6–8, and were increased by compound 4. Moreover, the inhibition rate of A. thaliana auxin transport mutants pin2 and aux1–7 by compounds 1–8 were all lower than the wild type (Col-0). The influence of these compounds on endogenous auxin distribution is thus proposed as a critical factor for the phytotoxic effect. Compounds 1, 2, 4 and 8 were found in soils associated with S. chamaejasme, and these flavonoids also showed phytotoxicity to Clinelymus nutans L., an associated weed of S. chamaejasme. These results indicated that some phytotoxic compounds from roots of S. chamaejasme may be involved in the potential allelopathic behavior of this widespread weed.

Insect herbivores should follow plants escaping their relatives.

Neighboring plants within a local community may be separated by many millions of years of evolutionary history, potentially reducing enemy pressure by insect herbivores. However, it is not known how the evolutionary isolation of a plant affects the fitness of an insect herbivore living on such a plant, especially the herbivore’s enemy pressure. Here, we suggest that evolutionary isolation of host plants may operate similarly as spatial isolation and reduce the enemy pressure per insect herbivore. We investigated the effect of the phylogenetic isolation of host trees on the pressure exerted by specialist and generalist enemies (parasitoids and birds) on ectophagous Lepidoptera and galling Hymenoptera. We found that the phylogenetic isolation of host trees decreases pressure by specialist enemies on these insect herbivores. In Lepidoptera, decreasing enemy pressure resulted from the density dependence of enemy attack, a mechanism often observed in herbivores. In contrast, in galling Hymenoptera, enemy pressure declined with the phylogenetic isolation of host trees per se, as well as with the parallel decline in leaf damage by non-galling insects. Our results suggest that plants that leave their phylogenetic ancestral neighborhood can trigger, partly through simple density-dependency, an enemy release and fitness increase of the few insect herbivores that succeed in tracking these plants.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-014-3026-3) contains supplementary material, which is available to authorized users.

Plant neighbours rather than soil biota determine impact of an alien plant invader

Summary Various factors have been shown contributing to the ecosystem impact of invasive alien plants, but their relative importance remains unclear. We focused on the effects of neighbouring plant community and soil biota as these biotic factors have been repeatedly put forward to explain invasion success (e.g. as components of the novel weapons and of the biotic release hypothesis). To assess their relative importance in explaining the high impact of Centaurea stoebe during the invasion of new sites in the introduced range, we conducted a greenhouse experiment with both European (EU) and North American (NA) tetraploid C. stoebe competing with/without EU vs. NA neighbouring community and with the two neighbouring communities growing without C. stoebe. Plants were grown in sterilized commercial soil inoculated with naïve soil (from rhizosphere of plants other than C. stoebe) originating either from the home EU or the introduced NA range and half of which was sterilized to remove soil biota. In the competition pots, relative competitive ability (difference between the relative growth rates of C. stoebe and neighbouring community) and impact level (biomass of the neighbouring community relative to that in non‐competition pots) of C. stoebe was significantly higher when grown with the NA than with the EU neighbouring community, although growth rates of EU and NA neighbouring communities did not differ in the non‐competition pots. Both soil origin and C. stoebe origin had no effect on these processes. Soil sterilization increased growth of both C. stoebe and neighbouring communities, but had only a moderate effect on impact level and type, and no effect on the relative competitive ability of C. stoebe. These results suggest that during the colonization of new sites in North American grasslands, the impact of C. stoebe is strongly driven by reduced competitive ability of NA neighbours compared with EU neighbours, while altered biotic soil conditions in the introduced range and post‐introduction evolutionary changes in the invader are of less importance. This differential impact appears to be due to inherently different mechanisms underlying the competitive interactions between EU and NA neighbouring communities when grown with C. stoebe.

Ecology of plant volatiles: taking a plant community perspective

Although plants are sessile organisms, they can modulate their phenotype so as to cope with environmental stresses such as herbivore attack and competition with neighbouring plants. Plant-produced volatile compounds mediate various aspects of plant defence. The emission of volatiles has costs and benefits. Research on the role of plant volatiles in defence has focused primarily on the responses of individual plants. However, in nature, plants rarely occur as isolated individuals but are members of plant communities where they compete for resources and exchange information with other plants. In this review, we address the effects of neighbouring plants on plant volatile-mediated defences. We will outline the various roles of volatile compounds in the interactions between plants and other organisms, address the mechanisms of plant neighbour perception in plant communities, and discuss how neighbour detection and volatile signalling are interconnected. Finally, we will outline the most urgent questions to be addressed in the future.

Effects of plant neighborhoods on plant–herbivore interactions: resource dilution and associational effects

Effects of neighboring plants on herbivore damage to a focal plant (associational effects) have been documented in many systems and can lead to either increased or decreased herbivore attack. Mechanistic models that explain the observed variety of herbivore responses to local plant community composition have, however, been lacking. We present a model of herbivore responses to patches that consist of two plant types, where herbivore densities on a focal plant are determined by a combination of patch-finding, within-patch redistribution, and patch-leaving. Our analyses show that the effect of plant neighborhood on herbivores depends both on how plant and herbivore traits combine to affect herbivore movement and on how experimental designs reveal the effects of plant density and plant relative frequency. Associational susceptibility should be the dominant pattern when herbivores have biased landing rates within patches. Other behavioral decision rules lead to mixed responses, but a common pattern is that in mixed patches, one plant type experiences associational resistance while the other plant experiences associational susceptibility. In some cases, the associational effect may shift sign along a gradient of plant frequency, suggesting that future empirical studies should include more than two plant frequencies to detect nonlinearities. Finally, we find that associational susceptibility should be commonly observed in experiments using replacement designs, whereas associational resistance will be the dominant pattern when using additive designs. Consequently, outcomes from one experimental design cannot be directly compared to studies with other designs. Our model can also be translated to other systems with foragers searching for multiple resource types.

Do interactions with neighbours modify the above-ground productivity response to drought? A test with two grassland species

Natural systems are predicted to be exposed to more frequent and more intense drought events in the near future. Plant–plant interactions form an important part of the whole of mechanisms that govern the responses of plant species and communities to drought. The accuracy of predictions on ecosystem functioning would therefore be improved by determining when plant interactions need to be considered and how these interactions can drive species responses. In this study, we assessed the effect of neighbour plants on the drought response of a target plant. Two grassland species (Plantago lanceolata and Lolium perenne) were grown in the presence of either six conspecific or three conspecific and three heterospecific neighbours in sunlit growth chambers. They were subjected to drought by withholding water for 20 days. Regardless of the identity of the target plant, having P. lanceolata as a neighbour increased the susceptibility to negative drought effects on biomass production while L. perenne neighbours buffered the target's drought response. Our results therefore suggest that drought responses depended largely on the identity and the traits of the neighbours. Such findings demonstrate that current models to predict ecosystem functioning may be misleading by not sufficiently taking plant–plant interactions into account.

Chemical Ecology: Body Odor, Behavior, and Body Building

Chemical Ecology: Body Odor, Behavior, and Body Building

Is light interception of understorey species facilitated by light reflection from plant neighbours?

Background: Facilitation is an ecological process that has previously been discussed largely in relation to the modification of abiotic conditions in extreme habitats. Here, we introduce the concept of reflected radiation as a potential facilitation mechanism that may raise the beneficiary’s resource level in light-limited habitats.Objectives: We examined whether plants may be able to use their spatial architecture to increase their light absorption through the use of radiation reflected by their neighbours. We tested if this interaction resulted in increased biomass or leaf area between the respective pairs of species.Methods: We determined the biomass and leaf area of eight common herb-layer species, composed of four grass and four herb species, in a beech forest. Plant three-dimensional architecture was digitised and used to simulate reflected and absorbed radiation between the species in a virtual black box. To accomplish this, a so-called light donor plant (which reflected light from its leaf surfaces) was surrounded by four receptor plants (which absorbed this reflected radiation) at a distance of 10 cm. This was repeated using every combination of the available species. We established a ray-trace simulation, including measured light reflection and transmission rates of leaves that enabled us to quantify the relative light absorption by receptor plants, expressed as brightness per leaf area, and estimated the amount of incoming photons. Furthermore, we calculated Seifan’s importance index as an indicator for the relevance of the postulated facilitation effect on plant biomass and leaf area.Results: The leaves of the species studied reflected ca. 7% of radiation between 400 and 700 nm and 18% between 540 to 650 nm of daily incident photon flux density, corresponding to the accessory pigments’ range of efficacy. An average of 0.19% of radiation reflected by a donor plant reached a receptor plant. The benefits to receptor plants varied significantly with donor identity. Conspecific donors supplied significantly larger benefits for Stellaria, Galium, Brachypodium and Hordelymus, which are rhizomatous plants with short stolons. Clones of these species may be able to increase their daily light intake through absorption of reflected light by 0.2%, 0.5–5.0%, 5.0% and 0.6–11.6%, respectively, depending on the number of donor ramets and on the distance between the donor and receptor ramets. Nonetheless, the estimated conspecific facilitation effects through light reflectance within a single clone did not translate into increased biomass.Conclusion: As light intensity decreases with distance according to Lambert’s law, a significant increase of light intake through neighbours can only be predicted for plants with a high density of donor ramets, such as clonal species having many ramets within a short distance. We suggest that in strongly light-limited habitats there may be an advantage to a clonal growth strategy due to the observed facilitation effect of absorption of reflected radiation. To evaluate the magnitude of this effect, future studies should concentrate on ‘payback times’ of leaves with low light intake to gauge the period of time necessary for one leaf to offset the necessary investment in photosynthetic light capture, calculated as cost-benefit calculation between the cost of the leaf’s production and the net carbon gain realised by it.

Ontogenetic shifts in plant–plant interactions in a rare cycad within angiosperm communities

Gymnosperms and angiosperms can co-occur within the same habitats but key plant traits are thought to give angiosperms an evolutionary competitive advantage in many ecological settings. We studied ontogenetic changes in competitive and facilitative interactions between a rare gymnosperm (Dioon sonorense, our target species) and different plant and abiotic neighbours (conspecific-cycads, heterospecific-angiosperms, or abiotic-rocks) from 2007 to 2010 in an arid environment of northwestern Mexico. We monitored survival and growth of seedlings, juveniles, and adults of the cycad Dioon sonorense to evaluate how cycad survival and relative height growth rate (RHGR) responded to intra- and interspecific competition, canopy openness, and nearest neighbour. We tested spatial associations among D. sonorense life stages and angiosperm species and measured ontogenetic shifts in cycad shade tolerance. Canopy openness decreased cycad survival while intraspecific competition decreased survival and RHGR during early ontogeny. Seedling survival was higher in association with rocks and heterospecific neighbours where intraspecific competition was lower. Shade tolerance decreased with cycad ontogeny reflecting the spatial association of advanced stages with more open canopies. Interspecific facilitation during early ontogeny of our target species may promote its persistence in spite of increasing interspecific competition in later stages. We provide empirical support to the long-standing assumption that marginal rocky habitats serve as refugia from angiosperm competition for slow-growing gymnosperms such as cycads. The lack of knowledge of plant-plant interactions in rare or endangered species may hinder developing efficient conservation strategies (e.g. managing for sustained canopy cover), especially under the ongoing land use and climatic changes.

Cell wall methanol as a signal in plant immunity

Cell wall pectin forms a matrix around the cellulose–xyloglucan network that is composed of rhamnogalacturonan I, rhamnogalacturonan II, and homogalacturonan (HG), a major pectic polymer consisting of α-1,4-linked galacturonic acids. HG is secreted in a highly methyl-esterified form and selectively de-methyl-esterified by pectin methylesterases (PMEs) during cell growth and pathogen attack. The mechanical damage that often precedes the penetration of the leaf by a pathogen promotes the activation of PME, which in turn leads to the emission of methanol (MeOH), an abundant volatile organic compound, which is quickly perceived by the intact leaves of the damaged plant, and the neighboring plants. The exposure to MeOH may result in a “priming” effect on intact leaves, setting the stage for the within-plant, and neighboring plant immunity. The emission of MeOH by a wounded plant enhances the resistance of the non-wounded, neighboring “receiver” plants to bacterial pathogens and promotes cell-to-cell communication that facilitates the spread of viruses in neighboring plants.

Suppression of nativeMelaleuca ericifoliaby the invasivePhragmites australisthrough allelopathic root exudates

Invasive plants are a great threat to the conservation of natural ecosystems and biodiversity. Allelopathy as a mechanism for invasion of plants such as Phragmites australis, one of the most aggressive invaders, has the potential to suppress neighboring plant species. Allelopathic interference, through root exudates of P. australis on native Melaleuca ericifolia, was investigated to find out the underlying invasion mechanisms. Germination and growth effects of P. australis on M. ericifolia were studied in the greenhouse using potting mix both with and without activated carbon, and a combination of single and repeated cuttings of P. australis as the management tool. P. AUSTRALIS had significant negative effects on germination and growth of M. ericifolia by inhibiting germination percentage, maximum root length and plant height, biomass, stem diameter, and number of growth points with little effect on leaf physiology. Activated carbon (AC) in turn moderately counteracted these effects. The cutting of P. australis shoots significantly reduced the suppressive effects on M. ericifolia compared to the addition of AC to soil. Furthermore, significant changes in soil such as pH, electrical conductivity, osmotic potential, phenolics, and dehydrogenase activity were identified among cutting treatments with little variation between AC treatments. The results demonstrated that allelopathy through root exudates of P. australis had relatively low contribution in suppressing M. ericifolia in comparison to other competitive effects. Management tools combining repeated cutting of P. australis shoots with AC treatments may assist partly in the restoration of native ecosystems invaded by P. australis.

Climatic extremes lead to species-specific legume facilitation in an experimental temperate grassland

Background Nitrogen-fixing legumes are key species in grassland ecosystems, as their ability to fix atmospheric nitrogen can facilitate neighboring plants. However, little is known about the fate of this legume effect in the face of extreme weather events, which are increasingly expected to occur. Methods Here, we examined experimentally how the presence of a legume modifies above-ground net primary production (ANPP) and nitrogen supply of neighboring non-legumes under annually recurrent pulsed drought and heavy rainfall events by comparing responses of three key species in European grassland versus without legume presence over 4 years. Results Legume presence facilitated community productivity of neighboring non-legumes under ambient weather conditions and also under experimental heavy rainfall. However, no facilitation of community productivity by the legume was found under experimental drought. Productivity of the three target species responded species-specifically to legume presence under different weather conditions: Holcus lanatus was facilitated only under control conditions, Plantago lanceolata was facilitated only under heavy rainfall, and Arrhenatherum elatius was facilitated irrespective of climate manipulations. The legume effects on δ 15 N, leaf N concentration, and N uptake were also speciesspecific, yet irrespective of the climate manipulations. The data suggest that the missing legume effect on community productivity under the pulsed drought was rather caused by reduced N-uptake of the target species than by reduced N-fixation by the legume. Conclusions In contrast to heavy rain, the presence of a legume could not effectively buffer community ANPP against the negative effects of extreme drought events in an experimental temperate grassland. Facilitation also depends on the key species that are dominating a grassland community.