Plant Competition Research Articles

The impact of cultivation technology elements on the productivity of the soybean (Glycine max (L.) Merr.) variety ‘Hoverla’ in the Prykarpattia region

Purpose. To study the formation of the productivity of the ‘Hoverla’ soybean variety using different elements of cultivation technology. Methods. Field, laboratory, statistical (calculation­comparative, mathematical­statistical). Results. The effectiveness of spring chisel ploughing for the cultivation of the soyabean variety ‘Hoverla’ in the soil and climatic conditions of the Prykarpattia region was established. The positive effect of the studied tillage methods on the phytosanitary condition of the crop was noted. In particular, the combination of autumn ploughing and spring chisel ploughing with the application of N30P30K30 mineral fertiliser and double foliar spraying of crops with a growth regulator led to an increase in the competitiveness of plants against weeds and reduced the number of weeds by 46.2% compared to the control. The implementation of the above measures also contributed to an increase in yield to 2.48 t/ha, or 57.0% on average over three years. At the same time, the yield of forage units and digestible protein increased by 1.35 and 0.3 t/ha respectively. Conclusions. Spring chisel ploughing, together with autumn ploughing and a rational combination of the predecessor’s by­products, the proposed doses of mineral fertiliser and growth regulator in the conditions of the Prykarpattia region, helped to reduce the weediness of crops by 46.2% and increase the yield of the ‘Ho­verla’ soybean variety by 57.0%.

The effect of phosphorus, irradiance and competitor identity on the relative performance of invasive Chromolaena odorata

BackgroundResource competition is an important factor affecting the invasion success of alien plants, and environmental factors influence the competition outcomes between invasive and native plants. In this study, we explore the competitive pattern between invasive Chromolaena odorata and two native plant species under different phosphorus and irradiance levels.ResultsThe final biomass of each plant was regulated by both morphological and physiological traits. Invasive C. odorata did not always perform better than both native plants, and the competitive pattern between C. odorata and native plants was dependent on native competitor identity and environmental conditions. With competition, invasive C. odorata showed higher biomass (over 60%) than native Xanthium sibiricum under all treatments, but only showed higher biomass (about 20%) than native Eupatorium lindleyanum in normal irradiance treatments. The effect of phosphorus on competition depended on the irradiance level. Under normal irradiance, phosphorus addition increased (almost 10 times) the competitive index of invasive C. odorata; however, under shade irradiance, phosphorus addition decreased (40%) the competitive index of C. odorata.ConclusionThese results suggest that phosphorus, irradiance and native plant competitor together influence the relative performance of invasive C. odorata. In shade environment, selecting E. lindleyanum as competitor and increasing phosphorus level is an effective method for controlling the invasion of C. odorata.

A Parasite Plant Promotes the Coexistence of Two Annual Plants.

Consumers can influence the competitive outcomes of prey species in various ways. Modern coexistence theory predicts that consumers can promote prey coexistence by preferably targeting a competitively superior one, thereby reducing fitness differences. However, previous studies yielded mixed conclusions. In this study, we tested the hypothesis that a parasitic annual plant, Cuscuta campestris, facilitates the coexistence of two common annual plants. We performed field surveys and parasitism experiments to parameterize a plant competition dynamics model. The model suggested a competition-defence tradeoff: the legume Lespedeza striata was a better competitor than the grass Setaria faberi, while it was more susceptible to the parasite. Moreover, an empirical host-parasite dynamics model, extended from the plant competition model, predicted their coexistence within broad, biologically reasonable ranges of parameters. This work provides field evidence of the coexisting-promoting role of a parasitic plant, as caused by stabilising feedback between host and parasite densities.

The role of arbuscular mycorrhizal fungi in exotic plant invasion

The invasion success of exotic plants is largely determined by their invasiveness, which is influenced by soil abiotic properties and soil biota. Among these, arbuscular mycorrhiza fungi (AMF) can symbiosis with more than 80% of terrestrial plants and may be crucial to the successful invasion of exotic plants. Although many studies indicated that AMF can enhance the growth and competitiveness of invasive plants, some studies have also reported that AMF does not actually increase the invasiveness of invasive plants, and even inhibits it. This inconsistency is frequently attributed to the interactions between AMF and soil abiotic properties, especially soil nutrients like nitrogen and phosphorus, which significantly affect the symbiotic relationship between AMF and host plants. Here, we summarize the common hypothesis on invasion mechanisms, the relationship between AMF and host plants, the AMF's role in plant invasion, the control of invasiveness by soil abiotic properties, the interaction between AMF and soil abiotic properties, which benefits our understanding for the prevention and control of exotic invasive plants and the remediation of the soil at the invaded site.

Transcriptomic and Phenotypical Analysis of the Physiological Plasticity of Chamaecyparis hodginsii Roots under Different Nutrient Environments and Adjacent Plant Competition.

Chamaecyparis hodginsii seedlings undergo significant changes during growth due to different nutrient environments and adjacent plant competition, which is evident in the physiological plasticity changes in their roots. Therefore, in this experiment, 20 one-year-old elite C. hodginsii family seedlings were selected as the test objects, and the different nutrient environments and adjacent plant competition environments in nature were artificially simulated. Four nutrient environments (N heterogeneous nutrient environment, P heterogeneous nutrient environment, K heterogeneous nutrient environment, and homogeneous environment) and three planting patterns (single plant, conspecific neighbor, and heterospecific neighbor) were set up to determine the differences in root physiological indexes and plasticity of different family seedlings, and the families and treatment combinations with higher comprehensive evaluation were selected. The transcriptome sequencing of fine roots of C. hodginsii under different treatments was performed to analyze the differentially expressed genes. The results showed that the root activity, antioxidant enzyme activity, and nutrient element content of C. hodginsii seedlings in the N and P heterogeneous environments were higher than those in the homogeneous nutrient environment, while there was no significant difference between the K heterogeneous nutrient environment and the homogeneous environment, but MDA content was higher than that in other nutrient environments. The root activity and antioxidant enzyme activity in the competitive patterns were generally higher than those in the single plant and reached the peak in the heterospecific neighbor. The root physiological plasticity index of line 490 was the highest, but the comprehensive evaluation of root physiological indexes of lines 539 and 535 was better. The pattern with the highest comprehensive evaluation score was P heterogeneous nutrient environment × heterospecific neighbor. The effects of the N and P heterogeneous nutrient environments on root transcriptome genes were similar, which significantly increased DNA transcription and regulatory factor activity, while K heterogeneous nutrient environment focused on the regulation of root enzyme activity. The heterogeneous nutrient environment induces the conduction of hormone signals in the roots of C. hodginsii and induces the synthesis of phenylpropanone. The biosynthesis of phenylpropanone in the roots of C. hodginsii will increase significantly under competitive patterns. In summary, the N and P heterogeneous nutrient environments and the heterospecific neighbor can improve the root physiological indexes of C. hodginsii families, and the root physiological indexes of lines 539 and 535 are the best. The nutrient environment and competition pattern mainly affect the root system to transmit hormone signals to regulate enzyme activity.

Phytosociological Study of Weed Communities in Zea Mays Cultivation: Contributions to Sustainable Development Goals (SDG'S) in the Ecuadorian Tropics

Objective: This study investigates the phytosociological characteristics of weed communities associated with Zea mays cultivation in different zones of the Ecuadorian tropics, aiming to identify and classify weeds to develop effective management strategies that enhance productivity while minimizing environmental impacts Theoretical Framework: The research is based on the concept that weeds, or 'noxious weeds,' significantly challenge maize cultivation by competing for essential resources. Theories related to plant competition and agroecosystem sustainability underpin the study Method: The methodology involves a phytosociological survey across five farms in Mocache, Ventanas, and Balzar. Using 45 quadrats of 50 x 50 cm in a zigzag pattern across one-hectare plots, weed species were identified and quantified. Data were analyzed to calculate biodiversity and importance value indices. Results and Discussion: Mocache had the highest weed population, while Balzar exhibited greater species diversity. Similarity indices, including Jaccard and Bray-Curtis, revealed distinct patterns in species distribution and dominance. These findings are discussed in the context of sustainable agriculture, highlighting the implications for weed management and acknowledging potential limitations due to environmental variability. Research Implications: The study provides insights into sustainable weed management in maize agroecosystems, contributing to strategies aligned with SDG 2 (Zero Hunger) and SDG 15 (Life on Land), promoting practices that enhance food security and biodiversity conservation. Originality/Value: This research offers a novel phytosociological analysis of weed communities in tropical maize cultivation, contributing to sustainable agriculture and aligning with global sustainability goals.

Arbuscular mycorrhizal fungi equalize differences in plant fitness and facilitate plant species coexistence through niche differentiation.

Mycorrhizal fungi are essential to the establishment of the vast majority of plant species but are often conceptualized with contradictory roles in plant community assembly. On the one hand, host-specific mycorrhizal fungi may allow a plant to be competitively dominant by enhancing growth. On the other hand, host-specific mycorrhizal fungi with different functional capabilities may increase nutrient niche partitioning, allowing plant species to coexist. Here, to resolve the balance of these two contradictory forces, we used a controlled greenhouse study to manipulate the presence of two main types of mycorrhizal fungus, ectomycorrhizal fungi and arbuscular mycorrhizal fungi, and used a range of conspecific and heterospecific competitor densities to investigate the role of mycorrhizal fungi in plant competition and coexistence. We find that the presence of arbuscular mycorrhizal fungi equalizes fitness differences between plants and stabilizes competition to create conditions for host species coexistence. Our results show how below-ground mutualisms can shift outcomes of plant competition and that a holistic view of plant communities that incorporates their mycorrhizal partners is important in predicting plant community dynamics.

Study of integration processes in the pharmaceutical market in the context of the development of territorial pharmaceutical ecosystems

Introduction. The ecosystem approach to the organization of business processes in the pharmaceutical market meets the prevailing trends, so the growth index of e-commerce in the retail sector of medicines for 5 years amounted to 1.87. The market distribution sector of medicines in the Russian Federation is characterized by a shift in corporate governance towards marketing cooperation based on aggregation electronic trading platforms (AETPS). Development of territorial pharmaceutical ecosystems (TFE) As a new integrative tool for managing the pharmaceutical development – production – distribution cycle, in order to achieve the target model of PHARMA 2030 at the territorial level, it requires the development of regulatory mechanisms for managing the supply of medicines. Objective: characteristics of integration processes in the industrial, wholesale and retail sectors of the pharmaceutical market to assess the potential competitiveness of territorial pharmaceutical ecosystems. Material and methods. The primary data for the analysis were: volumes of wholesale commodity residues of medicines produced in the Ural Federal District (461 registration certificates; proprietary Price and Distribution Test data for 230 trade names of LP EMIS data 2021–2022; Alpharm data 2021–2022; Datainsight 2022. In the course of the study, a structural analysis of the pharmaceutical market, a functional analysis of participants in the pharmaceutical product chain, and a marketing analysis were carried out. Results. It was found that the dynamics of the AETP segment development corresponds to the outstripping growth of highly integrated platforms: the short-term growth index of 5-pl AETP (Uteca) is 164%, 4-pl (Eapteca) is 55%, 3pl-AETP (averaged) is 36.5%. The absence of formal mechanisms of regional protectionism for the sale of finished dosage forms of local manufacturers in the Ural Federal District has been revealed. We have obtained the results of evaluating the effect of ecosystem integration of certain types of pharmaceutical market participants. For manufacturers of medicinal products, it was determined that the median coefficient of penetration of the local assortment of medicinal products into the pharmaceutical market in the context of ATX groups of level 2 is 0.67, which indicates a significant diversification of the assortment portfolio and the possibility of its aggregation without a barrier of internal competition. In the wholesale drugs sector, the potential for saving margins on medicines has been identified when implementing the scenario of localization of supplies in production regions in low and medium-low price ranges (30 – 550 rubles/unit), varying between 53–67%. It was found that the median share of regional distribution in the Ural Federal District (in packages) is 20.72%. It has been established that the Ural Federal District is one of the leaders in terms of the share of omnichannel consumers in the pharmaceutical market (63%), which is a significant incentive for the integration of organizations in the retail sector of the pharmaceutical market into the ecosystem 5pl platform. Conclusion. Situational analysis of the morphology of cooperative interactions in the pharmaceutical market allowed us to identify the prerequisites for the formation of ecosystem-organized management structures in the pharmaceutical market system – territorial pharmaceutical ecosystems. We have systematized incentives for ecosystem determination of medicines supplies, and found that: an additional channel for the market distribution of the industrial range of medicicnes in the Urals is not associated with a barrier to internal competition of pharmaceutical plants; the inclusion of regional suppliers in TFE will allow to form additional competitiveness in the “buyer's market” in conditions of market dominance of federal suppliers; the omnichannel approach to the distribution of the retail range of TFE in pharmacy organizations has a high projected conversion rate. A detailed assessment of integration processes in certain sectors of the pharmaceutical market did not reveal critical barriers to the introduction of TFE.

Plant antagonistic facilitation across environmental gradients: a soil-resource ecosystem engineering model.

Theory questions the persistence of nonreciprocal interactions in which one plant has a positive net effect on a neighbor that, in return, has a negative net impact on its benefactor - a phenomenon known as antagonistic facilitation. We develop a spatially explicit consumer-resource model for belowground plant competition between ecosystem engineers, plants able to mine resources and make them available for any other plant in the community, and exploiters. We use the model to determine in what environmental conditions antagonistic facilitation via soil-resource engineering emerges as an optimal strategy. Antagonistic facilitation emerges in stressful environments where ecosystem engineers' self-benefits from mining resources outweigh the competition with opportunistic neighbors. Among all potential causes of stress considered in the model, the key environmental parameter driving changes in the interaction between plants is the proportion of the resource that becomes readily available for plant consumption in the absence of any mining activity. Our results align with theories of primary succession and the stress gradient hypothesis. However, we find that the total root biomass and its spatial allocation through the root system, often used to measure the sign of the interaction between plants, do not predict facilitation reliably.

Plant competition cues activate a singlet oxygen signaling pathway in Arabidopsis thaliana.

Oxidative stress responses of Arabidopsis to reflected low red to far-red signals (R:FR ≈ 0.3) generated by neighboring weeds or an artificial source of FR light were compared with a weed-free control (R:FR ≈1.6). In the low R:FR treatments, induction of the shade avoidance responses (SAR) coincided with increased leaf production of singlet oxygen (1O2). This 1O2 increase was not due to protochlorophyllide accumulation and did not cause cell death. Chemical treatments, however, with 5-aminolevulinic acid (the precursor of tetrapyrrole biosynthesis) and glutathione (a quinone A reductant) enhanced cell death and growth inhibition. RNA sequencing revealed that transcriptome responses to the reflected low R:FR light treatments minimally resembled previously known Arabidopsis 1O2 generating systems that rapidly generate 1O2 following a dark to light transfer. The upregulation of only a few early 1O2 responsive genes (6 out of 1931) in the reflected low R:FR treatments suggested specificity of the 1O2 signaling. Moreover, increased expression of two enzyme genes, the SULFOTRANSFERASE ST2A (ST2a) and the early 1O2-responsive IAA-LEUCINE RESISTANCE (ILR)-LIKE6 (ILL6), which negatively regulate jasmonate level, suggested that repression of bioactive JAs may promote the shade avoidance (versus defense) and 1O2 acclimation (versus cell death) responses to neighboring weeds.

Root traits and soil legacies drive species competition outcomes

Abstract Plant competition can be affected by plant functional traits but also by differences in fitness mediated by soil microbes. Climatic conditions such as drought further influence plant competition. Yet little is known about how soil microbes and drought interact with plant species that have distinct root traits and how this influences plant competition outcomes. We grew three plant species that co‐occur in temperate grasslands in China (Stipa krylovii, Artemisia frigida, Agropyron cristatum) in monocultures and mixtures and subjected the plant combinations to five soil inocula (root‐associated soil of S. krylovii, A. frigida, A. cristatum, an equal mixture of the three root zone soils and sterilized soil) as well as to a drought treatment. The relative change in plant biomass was used to determine plant competition outcomes. The three species exhibited clear differences in competitive abilities with A. cristatum > S. krylovii > A. frigida, and soil inocula or the drought treatment did not change the order. The relative yield (RY) of plants was affected by soil inocula, drought and plant arrangement. The strongest competitor, A. cristatum, with high total root length, root surface area and root volume experienced more negative biotic feedback, and drought enhanced the magnitude of these negative effects. On the contrary, the most inferior competitor, A. frigida, with high specific root length tended to have neutral or positive biotic feedback, and drought had no effect. Furthermore, the RY and fitness difference (reflected as the competitive ability in the mixture) of the three species were differentially influenced by root traits and plant–soil feedback. RY of A. cristatum could be predicted by the feedback effect in the mixture, and the fitness difference was mainly related to root traits. Both RY and fitness differences of A. frigida (the weakest competitor) could be predicted by root trait differences and feedback effects. Differences in root traits were the best predictors of the intermediate competitor S. krylovii. Our study shows that competition outcomes of co‐existing species depend on root traits and species‐specific PSF effects in mixture. Future work should examine the mechanisms that explain how plant competition and soil microbial heterogeneity act in conjunction with climate change in influencing plant coexistence. Read the free Plain Language Summary for this article on the Journal blog.

Shallow tillage mitigates plant competition by increasing diversity and altering plant community assembly process.

Understanding how human activities affect biodiversity is needed to inform systemic policies and targets for achieving sustainable development goals. Shallow tillage to remove Artemisia ordosica is commonly conducted in the Mu Us Desert. However, the impacts of shallow tillage on plant community species diversity, phylogenetic structure, and community assembly processes remain poorly understood. This study explores the effects of shallow tillage on species diversity including three a-diversity and two b-diversity indicators, as well as phylogenetic structure [phylogenetic diversity (PD), net relatedness index (NRI), and nearest taxon index (NTI)]. Additionally, this research analyzes the effects of shallow tillage on the community assembly process. The results showed that the a-diversity index, b-diversity index, and PD of the shallow tillage (ST) communities were significantly higher than those of the non-shallow tillage (NT) communities, and the phylogenetic structures of both the ST and NT communities tended to be differentiated, with competitive exclusion being the main mechanism of plant assembly. However, shallow tillage increased the relative importance of the stochastic processes dominated by dispersal limitation, mitigating plant competition in the communities. This conclusion was supported by the Raup-Crick difference index-based analysis. Therefore, for the ecological restoration of the Mu Us Desert, species with adaptability and low niche overlap should be selected to increase the utilization efficiency of the environmental resources. The results of this study provide a foundation for policy development for ecosystem management and restoration in the Mu Us Desert.

Plant traits mediate foliar uptake of deposited nitrogen by mature woody plants.

Increased atmospheric nitrogen (N) deposition significantly disturbs ecosystem N cycle. Although foliar interception and uptake of N deposition can provide an important alternative N supply to forest ecosystems, the mechanisms regulating foliar N uptake from wet deposition are not fully understood. Here, we selected 19 woody species with a wide range of plant traits from different functional groups and conducted a 15N isotope labelling experiment through brushing 15NH4 + and 15NO3 - solution on canopy leaves. Our findings demonstrate that leaves can directly absorb N from wet deposition within a few hours. The average leaf 15N recoveries were 10% and 28% under 15NH4 + and 15NO3 - treatments across species, respectively, while twig N recoveries were only 1%-7% of leaf N recoveries. Differences in foliar N uptake efficiency among species were closely associated with leaf traits but were little influenced by meteorological conditions or soil nutrient status. Specifically, plants with higher leaf N concentration, larger specific leaf area and lower wax concentration exhibited higher leaf N recovery. Our results indicated that tree canopies could directly absorb N from atmospheric deposition. We highlight the critical role of leaf traits in determining canopy foliar N uptake, which may consequently influence plant competition under elevated N deposition.

Evolutionary emergence of plant and pollinator polymorphisms in consumer-resource mutualisms

Mutualism is considered a major driver of biodiversity, as it enables extensive codiversification in terrestrial communities. An important case is flowering plants and their pollinators, where convergent selection on plant and pollinator traits is combined with divergent selection to minimize niche overlap within each group. In this article, we study the emergence of polymorphisms in communities structured trophically: plants are the primary producers of resources required by the primary consumers, the servicing pollinators. We model natural selection on traits affecting mutualism between plants and pollinators and competition within these two trophic levels. We show that phenotypic diversification is favored by broad plant niches, suggesting that bottom-up trophic control leads to codiversification. Mutualistic generalism, i.e., tolerance to differences in plant and pollinator traits, promotes a cascade of evolutionary branching favored by bottom-up plant competition dependent on similarity and top-down mutualistic services that broaden plant niches. Our results predict a strong positive correlation between the diversity of plant and pollinator phenotypes, which previous work has partially attributed to the trophic dependence of pollinators on plants.

Multigenerational invasive plant competition causes greater root than shoot trait shifts in a perennial grass

Multigenerational invasive plant competition causes greater root than shoot trait shifts in a perennial grass

Evaluating effectiveness of clonal plant selection of alfalfa (Medicago sativa L.) and sainfoin (Onobrychis viciifolia Scop.) in mixtures: Mean performance and stability in a multi‐environment trial

AbstractAlfalfa (Medicago sativa L.) ‐ grass or alfalfa ‐ sainfoin (Onobrychis viciifolia Scop.) mixtures are commonly used for pastures in western Canada because of their high forage quality and their low risk of causing frothy bloat in grazing animals. However, the proportion of these two legumes declines in mixed forage stands over time. The objective of this study was to evaluate the effectiveness of selecting superior genotypes from clonally propagated alfalfa or sainfoin under plant competition in different growth environments. For this study, around 100 genotypes of each legume were cloned and transplanted into meadow bromegrass (Bromus riparius Relm.) or alfalfa swards at Saskatoon, SK and Lethbridge, AB, Canada in 2017. Genotype‐environment (G x E) interactions of alfalfa and sainfoin genotypes were analysed by an additive main‐effects and multiplicative interaction (AMMI) model. Significant variations in plant height, spring vigour and total dry matter yield (TDM) were observed for both species. Among the measured traits, plant height was a more highly heritable trait (H2 = .16 for alfalfa and H2 = .18 for sainfoin), while TDM was the least heritable (H2 = .08 for alfalfa and H2 = .04 for sainfoin). In the AMMI Analysis of variance for TDM, the genotype explained <12% of the variation for both species, suggesting a direct selection of yield would result in a low genetic gain. The biplot mean performance (Y) x weighted average of absolute scores from the singular value decomposition of the matrix of BLUPs stability index (WAASB) identified several promising genotypes with superior performance and stability across different environments that were selected for producing synthetic lines. However, the synthetic lines of both alfalfa and sainfoin did not consistently exhibit superior performance in mixtures compared to their respective check cultivars.

Ecological restoration combining mowing and competition limits the development of invasive Reynoutria japonica

Limiting the negative effects of an invasive species, such as Reynoutria japonica, has become a challenge for scientists and a necessity for managers. Ecologically relevant, technically feasible, and sustainable control methods must be created to reduce the development or spread of R. japonica in ecosystems. The objective of our study was to investigate how monthly mowing in association with plant competition affects the development of R. japonica over a three-year field experiment. Among the plant traits measured, the height growth of R. japonica was the most affected; it was strongly reduced in the presence of competing plants. Combined mowing and competition with restoration plants negatively affected the growth diameter of R. japonica. Most competitive sown species were well established and complementary in limiting the development of R. japonica. The plant communities showed interannual dynamics in which R. japonica declined progressively. The restoration methodology adopted in this study allows managers to make appropriate decisions to reduce the impact of R. japonica on ecosystems.

Optimal design of circulating water system in pressurized water reactor nuclear power plant

The optimization of the circulating water system of pressurized water reactor nuclear power plants can effectively improve the profit without affecting the primary circuit operation, which is of great significance in enhancing the market competitiveness of nuclear power plants. The circulating water system of the nuclear power plant is modeled, and the circulating water system optimization scheme is formed after the nuclear power unit is reformed from three aspects: condenser heat transfer area, condenser connection mode, and circulating water pump operation mode. The circulating water system optimization calculation is carried out for each scheme by using the minimum annual cost method. Based on the sensitivity analysis of the factors that affect the profits of nuclear power plants, the best circulating water system optimization scheme is finally given for new nuclear power plants and nuclear power plants in operation, which provides a reference for the construction of related nuclear power projects.

Belowground plant competition: uncoupling root response strategies of peas.

Belowground plant competition has been shown to induce varying responses, from increases to decreases in root biomass allocation or in directional root placement. Such inconsistencies could result from the fact that root allocation and directional growth were seldom studied together, even though they might represent different strategies. Moreover, variations in belowground responses might be due to different size hierarchies between plants, but this hypothesis has not been studied previously. In a greenhouse rhizobox experiment, we examined the way both root allocation and directional root placement of Pisum sativum are affected by the size and density of Festuca glauca neighbours, and by nutrient distribution. We found that root allocation of P. sativum increased with the density and size of F. glauca. By contrast, directional root placement was unaffected by neighbour size and increased either towards or away from neighbours when nutrients were patchily or uniformly distributed, respectively. These results demonstrate that directional root placement under competition is contingent on the distribution of soil resources. Interestingly, our results suggest that root allocation and directional placement might be uncoupled strategies that simultaneously provide stress tolerance and spatial responsiveness to neighbours, thus highlighting the importance of measuring both when studying belowground plant competition.

Aboveground versus soil-mediated effects of an invasive grass on fire-dependent forbs in an oak woodland.

Most work on plant competition intensity in general has focused on how aboveground and belowground competition for resources between plants changes with soil resource availability. In contrast, much work on the competitive effects of non-native invasive species on native species has focused on other mechanisms (e.g., allelopathy and microbial changes) and has largely ignored how these effects interact with mechanisms of resource competition along productivity gradients. We examined aboveground effects of an invasive grass, Microstegium vimineum, along with soil differences between invaded and non-invaded areas on two native perennial herbs at a productive and an unproductive oak woodland site in north Mississippi, USA. We transplanted 32 individuals each of Helianthus silphioides and Potentilla simplex from uninvaded areas into natural patches dominated by M. vimineum at each of the sites. Each transplant was randomly assigned to a pot with either native soil or soil from around M. vimineum roots. Aboveground competition was manipulated by securing M. vimineum shoots in a non-shading position around the transplant. We monitored survival of all transplants weekly in the growing seasons of 2020 and 2021. Transplant survival of H. silphioides was lowest in M. vimineum soil at the more productive site when M. vimineum was not pinned back. Transplant survival of P. simplex was lower at the more productive site but was mostly unresponsive to pinning and soil treatments. Synthesis. Our results suggest that soil-mediated legacy effects of an invader may reduce some native species' ability to compete for light at productive sites.