Competitive Species Research Articles

Coexistence of two sympatric predators in a transitional ecosystem under constraining environmental conditions: a perspective from space and habitat use

BackgroundRange expansion of species, a major consequence of climate changes, may alter communities substantially due to competition between expanding and native species.MethodsWe first quantified size differences between an expanding habitat generalist, the red fox (Vulpes vulpes), and a circumpolar habitat specialist, the Arctic foxes (Vulpes lagopus), at the edge of the Arctic, where climate-related changes occur rapidly, to predict the likelihood of the larger competitor escalating interference to intraguild killing. We then used satellite telemetry to evaluate competition in a heterogeneous landscape by examining space use early during the foxes' reproductive period, when resource scarcity, increased-food requirements and spatial constraints likely exacerbate the potential for interference. We used time-LoCoH to quantify space and habitat use, and Minta's index to quantify spatio-temporal interactions between neighbors.ResultsOur morphometric comparison involving 236 foxes found that the potential for escalated interference between these species was high due to intermediate size difference. However, our results from 17 collared foxes suggested that expanding and native competitors may coexist when expanding species occur at low densities. Low home-range overlap between neighbors suggested territoriality and substantial exploitation competition for space. No obvious differential use of areas shared by heterospecific neighbors suggested low interference. If anything, intraspecific competition between red foxes may be stronger than interspecific competition. Red and Arctic foxes used habitat differentially, with near-exclusive use of forest patches by red foxes and marine habitats by Arctic foxes.ConclusionHeterogeneous landscapes may relax interspecific competition between expanding and native species, allowing exclusive use of some resources. Furthermore, the scarcity of habitats favored by expanding species may emphasize intraspecific competition between newcomers over interspecific competition, thus creating the potential for self-limitation of expanding populations. Dominant expanding competitors may benefit from interference, but usually lack adaptations to abiotic conditions at their expansion front, favoring rear-edge subordinate species in exploitation competition. However, due to ongoing climate change, systems are usually not at equilibrium. A spread of habitats and resources favorable to expanding species may promote higher densities of antagonistically dominant newcomers, which may lead to extirpation of native species.

IDENTIFIKASI EKTOPARASIT DAN KOMPETITOR KERANG HIJAU (Perna viridis) YANG DIBUDIDAYAKAN DALAM BAGAN TANCAP DI LAUT JAWA KECAMATAN SIDAYU KABUPATEN GRESIK

The green mussel (Perna viridis) is an important commodity in marine aquaculture. A challenge in green mussel cultivation is the presence of diseases caused by parasites that attach or live on the mussels. This research aims to determine the abundance of ectoparasites and competitors on green mussels in the mentioned waters. The research methods employed both qualitative and quantitative descriptive approaches. The observed research variables included species identification, prevalence and intensity of ectoparasites, as well as diversity and abundance of competitors. The findings revealed the presence of 2 ectoparasite species and 10 competitor species. The highest prevalence of Balanus sp. was recorded in Bagan Tancap I for mussels larger than 4 cm, at 79.6%±6.16 (moderate), while the lowest prevalence was in Bagan Tancap II for mussels smaller than 4 cm, at 33.3%±1.05 (common). The highest intensity of Balanus sp. ectoparasite attacks occurred in Bagan Tancap I for mussels larger than 4 cm, at 7.18 ind/mussel (moderate), and the lowest intensity was in Bagan Tancap II for mussels smaller than 4 cm, at 1.75 ind/mussel (low). The intensity of sea snail egg infestations ranged from 1 to 2 ind/mussel, with no significant difference (P>0.05). The highest competitor abundance was found in Bagan Tancap I with the species Nereis sp., at 0.57 ind/mussel, and the highest competitor diversity was also observed in Bagan Tancap I with the species crab at 36.292 ind/mussel. Considering the prevalence and intensity values of Balanus sp. ectoparasites on green mussels in the waters of the Java Sea in Kecamatan Sidayu, it is still suitable for green mussel cultivation.

Genetic Diversity in Pioneer Ants: The Cardiocondyla shuckardi Group

The myrmicine ant genus Cardiocondyla consists of around 80 species of small, inconspicuous ants, which live mainly in subtropical and tropical Africa, Eurasia, and Australia. Several species have been accidentally introduced to America and have also invaded numerous originally ant-free islands around the world. The diversity of life histories in this genus, with lethally fighting wingless males, dominance hierarchies among queens, and considerable variation in the sociogenetic organization of colonies across species, has made it an interesting model to investigate the evolution and behavioral ecology of reproductive strategies. Taxa of the African Cardiocondyla shuckardi group are of particular interest, as in a phylogeny they lie between facultatively polygynous species with fatal male competition and monogynous species with mutually tolerant males. Studies on male behavior and sociogenetics in C. “venustula,” a widespread member of the C. shuckardi group, showed that males defend small territories inside their subterraneous nests. At the same time, they revealed a surprisingly large variability in mtDNA haplotypes both within and between populations in South Africa, Angola, and Côte d’Ivoire. As the different lineages are very similar in morphology and nuclear markers, more research is needed to clarify the very confused taxonomic situation in this fascinating group of ants.

Effects of Clipping an Invasive Plant Species on the Growth of Planted Plants of Two Co-Occurring Species in a Greenhouse Study.

The restoration of native plants in invaded habitats is constrained with the presence of highly competitive exotic species. Aboveground removal, such as clipping or mowing, of invasive plants is required for successful restoration. The effects of clipping an invasive plant species, Solidago canadensis, grown at five densities (1-5 plants per pot), and planting two co-occurring and competitive species, Sesbania cannabina and Imperata cylindrica, on the growth of both the invasive species and the co-occurring species were investigated in a greenhouse experiment. The established S. canadensis suppressed the growth of planted seedlings with 47.8-94.4% reduction in biomass, with stronger effects at higher densities; clipping significantly reduced 97.5-97.4% of biomass of S. canadensis and ameliorated the suppression effects (with only 8.7-52.7% reduction in biomass of the co-occurring plants), irrespective of density. Both the aboveground and belowground part of S. canadensis contributed to its suppression effects on planted co-occurring species. Seed sowing of co-occurring species reduced the belowground growth, but not the underground growth of S. canadensis. S. cannabina appeared to be more effective at reducing the growth of S. canadensis than I. cylindrica. Therefore, clipping together with planting competitive species that can overcome the belowground priority effects of S. canadensis could be a promising strategy for controlling S. canadensis invasion and restoring native plant communities.

ALS ve ACCase inhibitörü herbisitlere dayanıklı Echinochloa crus-galli'nin entegre mücadelesi

Rice is an important grain crop due to its high domestic consumption and important role in terms of food security globally. Because of the difficulty of crop rotation and fallow-free cultivation in rice production, competitive weed species that have the capacity to reproduce rapidly and are adapted to water have become a problem. The strong negative effects of weeds on rice yield and farm profits have created a demand for cost-effective weed management strategies. As a result of the use of herbicides with the same mode of action for many years, the number and population of weed species resistant to herbicides have increased rapidly. So integrated weed control is the only method and an important solution in managing these weeds that should be developed according to the countries' production systems. Echiochloa crus-galli (Barnyardgrass) is one of the earliest resistant weeds adapted to rice production areas. For effective weed management; it aimed to determine the interaction between the cultivation method, water management and rice varieties (Osmancık, Gönen, Koral). The trials were carried out in Turkiye's Marmara and Black Sea Regions. Experiments were carried out with four replications. The water level (especially the high water level) not only had a highly suppressive effect against weeds but also helped to increase the growth and yield of the rice. The deep and medium water levels increased the rice's tillering number and dry weight. The obtained data revealed that better rice growth and high yield can be achieved by maintaining the water level in rice cultivation areas. The development of competitive and local rice varieties is seen as a viable approach in an integrated herbicide-resistant weed control program.

Impact of resource distributions on the competition of species in stream environment.

Our earlier work in Nguyen et al. (Maximizing metapopulation growth rate and biomass in stream networks. arXiv preprint arXiv:2306.05555 , 2023) shows that concentrating resources on the upstream end tends to maximize the total biomass in a metapopulation model for a stream species. In this paper, we continue our research direction by further considering a Lotka-Volterra competition patch model for two stream species. We show that the species whose resource allocations maximize the total biomass has the competitive advantage.

Persulfate-based remediation of organic-contaminated soil: Insight into the impacts of natural iron ions and humic acids with complexation/redox functionality

The use of persulfate (PDS) for in-situ chemical oxidation of organic contaminants in soils has garnered significant interest. However, the presence of naturally occurring iron-containing substances and humic acid (HA) in environmental compartments can potentially influence the effectiveness of soil remediation. Thus, this study aimed to investigate the role of key functional groups (adjacent phenolic hydroxyl (Ar-OH) and carboxyl groups (-COOH)) in HA that interact with iron. Modified HAs were used to confirm the significance of these moieties in iron interaction. Additionally, the mechanism by which specific functional groups affect Fe complexation and redox was explored through contaminant degradation experiments, pH-dependent investigations, HA by-products analysis, and theoretical calculations using six specific hydroxybenzoic acids as HA model compounds. The results showed a strong positive correlation between accessible Ar-OH and -COOH groups and Fe3+/Fe2+ redox. This was attributed to HA undergoing a conversion process to a semiquinone-containing radical form, followed by a quinone-containing intermediate, while Fe3+ acted as an electron shuttle between HA and PDS, with Fe3+ leaching facilitated by generated H+ ions. Although the stability of HA-Fe3+ complexes with -COOH as the primary binding sites was slightly higher at neutral/alkaline conditions compared to acidic conditions, the buffering properties of the soil and acidification of the PDS solution played a greater role in determining the Ar-OH groups as the primary binding site in most cases. Therefore, the availability of Ar-OH groups on HA created a trade-off between accelerated Fe3+/Fe2+ redox and quenching reactions. Appropriate HA and iron contents were found to favor PDS activation, while excessive HA could lead to intense competition for reactive oxygen species (ROS), inhibiting pollutant degradation in soil. The findings provide valuable insights into the interaction of HA and Fe-containing substances in persulfate oxidation, offering useful information for the development of in-situ remediation strategies for organic-contaminated soil.

Scientists’ Warning: Remove the Barriers to Contraception Access, for Health of Women and the Planet

The human population reached 8 billion in 2022 and is still growing, and will possibly peak at 10.4 billion in 2086. Environmental science mandates that continued growth of the human enterprise on a finite planet is unsustainable and already in overshoot. Indeed, 3 billion is an evidence-based target number, for our species in competition with all non-human life-forms. We must achieve zero population growth and, ultimately, a massive decrease. Commonly, even among environmentalists who are not “population-deniers”, human numbers are seen as a given, to be adapted to rather than influenced or managed. Yet, just and appropriate interventions exist. The fundamental requirement is the empowerment of women, removing the barriers in many settings to their education (including environmental education, and the reproductive ethics of smaller families) and to realistic, voluntary access to contraception. Wherever “reproductive health” includes access to rights-based family planning, this not only promotes the health of the planet but also women’s health through, inter alia, their choice to have fewer and better-spaced children. This is ethical, pragmatic, and cost-effective—a prime example of preventive medicine. Politicians (mostly men) everywhere must embrace this long-term thinking and significantly increase the currently inadequate funding of contraceptive care. Herein is another Scientists’ Warning: there is just one planet for all life.

Distribution of functionally distinct native and non‐indigenous species within marine urban habitats

AbstractAimTrait‐based approaches are powerful to examine the processes associated with biological invasions. Functional comparison among native and non‐indigenous species (NIS) can notably infer whether novel assemblages result from neutral or niche‐based assembly rules. Applying such a framework to biofouling communities, our study aimed to elucidate their distributions within two marine urban habitats (namely floating vs. nonfloating habitats).LocationSoutheast Pacific—Central Chilean coastline.MethodsHere, we examined the distribution of 12 functional traits in fouling communities established on settlement plates, after 3 and 13 months of deployment in the two habitats and across ports in Central Chile. Based upon previously described differences of assemblages and NIS contribution across habitats, we hypothesized that nonindigenous, cryptogenic and native taxon pools would be functionally distinct (and trait biased), and that functional diversity and structure would vary across habitats and successional stages.ResultsOur results show, as anticipated, that nonindigenous (13 taxa), cryptogenic (12) and native (18) taxon pools are functionally distinct, though overlapping in the trait space. Non‐indigenous species are rather related to colonizing traits, while native species are more related to competitive traits. Only one widespread NIS was functionally similar to the late successional and most competitive native species, including taxa elsewhere invasives. Despite differences in taxonomic composition between habitats, we did not observe functional differences between them. In contrast, temporal variations across colonization stages were detected along with an increased contribution in large and long‐lived taxa, together with site‐specific trajectories.Main ConclusionsWe conclude that the functional distinctness among nonindigenous, cryptogenic and native taxa occupying artificial habitats in ports reflects niche‐based processes. Site‐specific trajectories indicate that scale‐dependent assembly processes, such as dispersal and species interactions, are at play.

Environmental fluctuations explain the universal decay of species-abundance correlations with phylogenetic distance

Multiple ecological forces act together to shape the composition of microbial communities. Phyloecology approaches-which combine phylogenetic relationships between species with community ecology-have the potential to disentangle such forces but are often hard to connect with quantitative predictions from theoretical models. On the other hand, macroecology, which focuses on statistical patterns of abundance and diversity, provides natural connections with theoretical models but often neglects interspecific correlations and interactions. Here, we propose a unified framework combining both such approaches to analyze microbial communities. In particular, by using both cross-sectional and longitudinal metagenomic data for species abundances, we reveal the existence of an empirical macroecological law establishing that correlations in species-abundance fluctuations across communities decay from positive to null values as a function of phylogenetic dissimilarity in a consistent manner across ecologically distinct microbiomes. We formulate three variants of a mechanistic model-each relying on alternative ecological forces-that lead to radically different predictions. From these analyses, we conclude that the empirically observed macroecological pattern can be quantitatively explained as a result of shared population-independent fluctuating resources, i.e., environmental filtering and not as a consequence of, e.g., species competition. Finally, we show that the macroecological law is also valid for temporal data of a single community and that the properties of delayed temporal correlations can be reproduced as well by the model with environmental filtering.

The β-Lactamase Activity at the Community Level Confers β-Lactam Resistance to Bloom-Forming Microcystis aeruginosa Cells.

Many freshwater cyanobacteria, including Microcystis aeruginosa, lack several known antibiotic resistance genes; however, both axenic and xenic M. aeruginosa strains exhibited high antibiotic resistance against many antibiotics under our tested concentrations, including colistin, trimethoprim, and kanamycin. Interestingly, axenic PCC7806, although not the xenic NIBR18 and NIBR452 strains, displayed susceptibility to ampicillin and amoxicillin, indicating that the associated bacteria in the phycosphere could confer such antibiotic resistance to xenic strains. Fluorescence and scanning electron microscopic observations revealed their tight association, leading to possible community-level β-lactamase activity. Combinatory treatment of ampicillin with a β-lactamase inhibitor, sulbactam, abolished the ampicillin resistance in the xenic stains. The nitrocefin-based assay confirmed the presence of significant community-level β-lactamase activity. Our tested low ampicillin concentration and high β-lactamase activity could potentially balance the competitive advantage of these dominant species and provide opportunities for the less competitive species, thereby resulting in higher bacterial diversity under ampicillin treatment conditions. Non-PCR-based metagenome data from xenic NIBR18 cultures revealed the dominance of blaOXA-related antibiotic resistance genes followed by other class A β-lactamase genes (AST-1 and FAR-1). Alleviation of ampicillin toxicity could be observed only in axenic PCC7806, which had been cocultured with β-lactamase from other freshwater bacteria. Our study suggested M. aeruginosa develops resistance to old-class β-lactam antibiotics through altruism, where associated bacteria protect axenic M. aeruginosa cells.

Competition Status of Salmonella sp., Shigella sp., and Escherichia coli in Tris Egg Yolk Semen Preservation Medium at Different Experimental Conditions

Competition is a very important fact of microorganisms’ life, with the major goal to gain an advantage in terms of scarce nutrients and limited space. In this study, bacterial competition of Salmonella sp., Shigella sp., and Escherichia coli were assessed in Tris- egg-yolk (TEY) semen preservation medium at two temperature degrees and three periods of incubation (3 h at 37°C, 1 and 7 days at 4°C). The three pathogen species were incubated with an initial bacterial load of 103 CFU/mL. After three hours of incubation at 37°C, there were significant differences (P < 0.05) between the three species; however, Salmonella sp. had the highest CFU/ml compared to the two other pathogen species in bilateral and triple competition. Also after one day of storage at 4°C, a clear dominance of Salmonella sp. was noted, while in contrast, no significant difference (P > 0.05) between E.coli and Shigella sp., was observed in the bilateral and triple competition cases. However, the maximum dominance of Salmonella sp. was observed after 7 days at 4°C, where the bacterial load percentages between all species for the triple competition were 74±5.6/12±5.9/14±6.9 for Salmonella sp., E. coli, and Shigella sp., respectively. In conclusion, regardless of the temperature degrees and the time point of incubation, Salmonella was always able to dominate and compete very effectively compared with the two other bacterial pathogens in the TEY medium. Moreover, 4°C gave clear preference to the survival of salmonella with its clear vitality percentage in this media compared to both E. coli and Shigella sp.

Integrated Control of Echinochloa oryzoides, Echinochloa crus-galli and Cyperus difformis Based on Pre-Sowing Herbicide and Some Herbicide Combinations in Rice

Cosmopolitan weeds are even constant elements where rice cultivation started just a century ago. There are few but important weed species with high adaptation in rice, which requires monoculture production systems and aquatic environment. Rotation difficulty resulted in the proliferation of highly competitive weed species strongly adapted to the aquatic environment. Constant use of herbicides with the same mechanisms of action leads to an evaluation of herbicide-resistant weed population and an increased number of herbicide-resistant populations in Türkiye. Chemical weed control and alternative integrated weed management strategies in rice production systems have significantly evolved throughout the years as well as rice herbicide traits and weed spectrum. The study was carried out in rice fields with resistance problems in two different locations, in the Black Sea and the Marmara Regions. The clamozone 480 EC, oxadiazon 200 CS, glyphosate potassium 441 g/l, glyphosate IPA 360 g/lt +carfentrazone-ethyl 5 g/l, cyhalofop-butyl 200 EC, penoxsulam 25.2 OD +bentazon-sodium 480 SL active ingredients and combinations’ efficacy were investigated on ALS and ACCase inhibitor herbicides resistant Cyperus difformis, Echinochloa oryzoides and Echinochloa crus-galli populations. At the end of the study, it was determined that including pre-sowing herbicides such as clomazone and oxadiazon in the weed control program would help control the ALS and ACCase-resistant this species. Implementing integrated weed management strategies for managing existing herbicide-resistant weeds and reducing future development of herbicide resistance is one of our most influential and economical long-term strategies.

Are rare plant species less resistant than common ones to herbivores? A multi-plant species study using above- and below-ground generalist herbivores.

Rare plant species are suggested to be less resistant to herbivores than common species. Their lower apparency and the fact that they often live in isolated populations, resulting in fewer herbivore encounters, might have led to the evolution of reduced defences. Moreover, their frequent lower levels of genetic diversity compared with common species could negatively affect their resistance against enemies. However, the hypothesis that plant resistance depends on plant regional and local rarity, independently of habitat and competitive and growth strategy, lacks evidence. To test this hypothesis, we assessed the performance and preference of one belowground and three aboveground generalist invertebrate herbivores from different taxonomic groups as indicators of plant resistance. Herbivores were fed a total of 62 regionally and locally rare and common plant species from Switzerland. We accounted for differences in a plant's growth and competitive strategy and habitat resource availability. We found that regionally and locally rare and common plant species did not generally differ in their resistance to most generalist herbivores. However, one herbivore species even performed better and preferred locally and regionally common plant species over rarer ones, indicating that common species are not more resistant, but tend to be less resistant. We also found that all herbivore species consistently performed better on competitive and large plant species, although different herbivore species generally preferred and performed better on different plant species. The latter indicates that the use of generalist herbivores as indicators of plant-resistance levels can be misleading. Synthesis: Our results show that rare plant species are not inherently less resistant than common ones to herbivores. Instead, our results suggest that the ability of plants to allocate resources away from defence towards enhancing their competitive ability might have allowed plants to tolerate herbivory, and to become locally and regionally common.

How to Survive Intensive Harvesting: The High Recruitment Rates of the Precious Mediterranean Red Coral (Corallium rubrum L. 1758)

The recruitment process is a fundamental step in population life cycles that determines survival, population demographic structure, and dynamics. The success of recruitment events repeated over successive years greatly affects the survival of long-lived gorgonian populations. Here, we report the recruitment process of the precious, heavily harvested Mediterranean gorgonian Corallium rubrum (red coral) on both settlement tiles and natural substrates over different Mediterranean areas. Red coral is a gonochoric internal brooder that reproduces in early summer. Lecithotrophic planulae settle 15–30 days after release in semi-dark environments at depths between 15 and 800 m. In autumn, 0.58–0.68 mm-wide recruits can be observed on the vaults of small crevices and caves and on rocky cliffs and boulders. Owing to their small size, there is limited knowledge of C. rubrum recruitment in the field. In this study, we examined the recruitment density and distribution in Canadells (Banyuls sur Mer, France) and Calafuria (Livorno, Italy) and compared these findings with those collected over different Mediterranean areas. Red coral exhibited high recruitment values ranging from 0.43 to 13.19 recruits dm−2. The distribution pattern of recruits, examined at a small spatial scale via nearest-neighbor distance analysis, revealed a significantly higher patch frequency on the natural substrate than on settlement tiles, presumably because of the scarcely available spots of free space on the former substrate, which are crowded by competitor species.

Species diversity and competition have minor effects on the growth response of silver fir, European larch and Douglas fir to drought

With climate change, the frequency and duration of droughts are increasing, strongly impacting forest ecosystems. Therefore, a thorough understanding of the factors influencing tree response to drought is needed. Particularly, it remains unclear how competition and species diversity influence the drought sensitivity of tree species. Thinning (i.e., lowering competition) and mixing species (i.e., increasing diversity) are two common forest management practices that are thought to help forests to cope with droughts. However, their actual effects are still controversial. We sampled and measured tree-ring widths of 401 conifer trees with a wide range of competition and species diversity in their neighborhood across a bioclimatic gradient in Switzerland. Based on mixed-effects models and correlations, we examined the climate sensitivity of silver fir, European larch and Douglas fir and analyzed how competition and species diversity affect their radial growth and drought sensitivity. Silver fir was the least sensitive species to temperature, precipitation, and climatic water balance. When we analyzed the combined effects of the climatic water balance, competition and species diversity on tree radial growth over the past 20 years, we found that competition usually had a negative effect on radial growth of the three species, while species diversity had no effect. However, when focusing on drought resilience, competition had a negative effect for silver fir only, and a more mixed neighborhood enhanced the drought resilience of Douglas fir. Larch showed a higher drought sensitivity than silver fir and Douglas fir. At most sites, radial growth of all species recovered within two years after the severe droughts of 2003 and 2018. Overall, our results suggest that competition and species diversity have minor effects on the drought resilience of silver fir, larch and Douglas fir in Switzerland.

Resource competition can explain simplicity in microbial community assembly

Predicting the composition and diversity of communities is a central goal in ecology. While community assembly is considered hard to predict, laboratory microcosms often follow a simple assembly rule based on the outcome of pairwise competitions. This assembly rule predicts that a species that is excluded by another species in pairwise competition cannot survive in a multispecies community with that species. Despite the empirical success of this bottom-up prediction, its mechanistic origin has remained elusive. In this study, we elucidate how this simple pattern in community assembly can emerge from resource competition. Our geometric analysis of a consumer-resource model shows that trio community assembly is always predictable from pairwise outcomes when one species grows faster than another species on every resource. We also identify all possible trio assembly outcomes under three resources and find that only two outcomes violate the assembly rule. Simulations demonstrate that pairwise competitions accurately predict trio assembly with up to 100 resources and the assembly of larger communities containing up to twelve species. We then further demonstrate accurate quantitative prediction of community composition using the harmonic mean of pairwise fractions. Finally, we show that cross-feeding between species does not decrease assembly rule prediction accuracy. Our findings highlight that simple community assembly can emerge even in ecosystems with complex underlying dynamics.

Responses of different invasive and non-invasive ornamental plants to water stress during seed germination and vegetative growth

Biological invasions represent a major threat to natural ecosystems. A primary source of invasive plants is ornamental horticulture, which selects traits related to invasiveness. This study evaluated the responses to water stress during germination and vegetative growth of six species used as ornamental or medicinal plants. Three of them are recognised as invasive weeds in many world areas. Seeds were exposed to increasing concentrations of polyethylene glycol (PEG) mimicking drought stress, and young plants in the vegetative growth stage were subjected to two levels of water stress. Results indicated that in the absence of stress in control conditions, the most competitive species were those reported as weeds, namely Bidens pilosa L., Oenothera biennis L., and Centaurea cyanus L., the last regarding germination velocity. Under stress, only two species, Limonium sinuatum (L.) Mill. and C. cyanus, maintained germination at –1 MPa osmotic potential, but in the recovery experiment, an osmopriming effect of PEG was observed. The most tolerant species during growth were two natives in the Mediterranean region, L. sinuatum and Lobularia maritima (L.) Desv., both accumulating the highest proline concentrations. The sixth species studied, Echinacea purpurea (L.) Moench., proved to be more susceptible to stress in the two developmental stages. This study reveals that the most significant traits associated with invasiveness were related to germination, especially in the absence of stress.

Integrative taxonomy approach to detect spatial and temporal variability of the Mediterranean benthic communities through artificial substrate units (ASUs)

Monitoring spatial and temporal changes of marine benthic communities using standardized procedures is essential to take necessary steps towards conservation of marine ecosystems. In this study we combined Artificial Substrate Units (ASUs) for sampling of benthic communities, with integrative taxonomy approach that incorporated morphological identification of organisms and COI DNA metabarcoding, to characterize the diversity of communities at three locations across the Central Mediterranean Sea (Livorno and Palinuro, Italy; Rovinj, Croatia) in 2019 and 2020. Significant differences in the communities’ structure were observed both at large spatial scale between sampled locations, and at small spatial scale (less than ten kilometers) between sites. Moreover, significant temporal variability in species richness and structure of benthic assemblages was detected, with higher richness in 2020. Revealed variability can probably be attributed to the peculiar geomorphological, oceanographical, and ecological features of locations, but also to the influence of interplaying local chemical and physical factors and biological processes such as species settlement, competition, and migration that can act at small spatial and temporal scales. The similarity in the species composition and community structure accessed by morphological and metabarcoding approaches was low, with only 16% of the species (out of 133 species identified overall) commonly detected by both approaches. This is mostly both due to a lack of data on COI sequences of numerous benthic invertebrates in the public barcoding databases on the one hand, and difficulties in detecting small and cryptic taxa through morphological analyses on the other. This suggests that combining of two approaches is required to fully describe the biodiversity of benthic assemblages. Finally, comparison of the spatial variability of the benthic communities’ structure with two approaches at different taxonomic levels, indicated that genus and family levels give results that are consistent to those obtained by the species level. This suggests that family level might be satisfactory in monitoring the spatial-temporal variability of Mediterranean hard bottom benthic communities.

Leaf senescence, nitrogen remobilization, and productivity of maize in two semiarid intercropping systems

It is unclear how interspecific resource competition affects crop leaf senescence in association with nitrogen (N) remobilization and overyielding in semiarid intercropping systems. To address this issue, maize intercropped with soybean (weakly competitive species) and wheat (strongly competitive species) was examined across three consecutive years to explore the effects of resource competition on maize relative and absolute yield gain, leaf senescence traits, N remobilization and physiological activities in a typical semiarid site. High yield (171.8 g plant−1), relative yield (0.63) and net effect (0.99 t ha−1) of maize were observed in the maizesoybean intercropping system, while the opposite trend was found in the maizewheat intercropping systems. Overall, maize benefited from intercropping with soybean but was negatively affected by intercropping with wheat. Interestingly, both intercropping systems significantly delayed the onset time of maize leaf senescence by approximately 5–20 days and prolonged the senescence duration by approximately 8–18 days. Intercropping with soybean increased maize leaf dry matter remobilization from 7.3 to 12.5 g per plant−1 and reduced N remobilization from 0.81 to 0.45 g plant−1, respectively. However, when intercropped with wheat, dry matter and N remobilization of maize leaves were decreased, at 4.8 and 0.13 g plant−1, respectively. Therefore, excessive delay and prolonged leaf senescence reduced leaf dry matter translocation and N to the grain which impaired yield formation. Our findings provided novel insights into the physiological mechanism of overyielding from the perspective of leaf senescence traits and remobilization function in the semiarid intercropping systems.