Target Plant Species Research Articles

Mechanical mowing of semi‐natural grasslands compromises soil quality and survival of a conservation target plant species

Mowing is a crucial management strategy for conservation and restoration of semi‐natural grasslands. In the past decades, dominant mowing methods have changed from manual to mechanical, using heavy machines causing soil compaction. Whereas the negative effects of compaction are well understood in agriculture and forestry, they have received little attention so far in nature management. This study aims to investigate the effects of compaction on soil quality, arbuscular mycorrhizal fungal communities, and survival of a target plant species. We subjected seven grasslands to three contrasting mowing types: manual mowing with a brush cutter, softtrack mowing—designed to minimize soil compaction—and tractor mowing. We compared compaction, soil properties, and arbuscular mycorrhizal communities among the types. Additionally, we experimentally subjected intact grassland sods containing Devil's bit scabious (Succisa pratensis Moench), a target species of grassland conservation, to compaction levels corresponding to the three mowing types. Subsequently, we assessed plant survival. We found that soil compaction, soil nutrient availability, and toxic soil elements were significantly higher in the softtrack‐ and tractor‐mown parts of grassland sites compared to the manually mown parts. Also, the arbuscular mycorrhizal community composition differed significantly among mowing types, with the largest differences between “manual” and “tractor.” Succisa pratensis survival significantly decreased by 43 and 71% on the short term and by 71 and 86% on the longer term with increasing compaction. Consequently, mowing‐associated soil compaction compromises nature management targets via at least four mechanisms: nutrient enrichment, soil toxicity, changes in arbuscular mycorrhizal communities, and decreased survival of the target plant species.

Bioinoculation Effect of Frankia sp. and Microbial Bioagents on Growth and Development of Elaeagnus latifolia L. seedlings: An Endangered Plant Species of North East India

Aims: Analyses were done on the role of rhizospheric symbiotic Arbuscular Mycorrhizal (AM) fungus, Non-AM fungus and a bacterium in growth and development of E. latifolia L. seedlings. Study Design and Methodology: The seedlings were inoculated with recognized AM fungal strain (Glomus mosseae, Gm 1), non-AM fungus (Trichoderma harzianum, Th-13) alone and nitrogen fixing bacteria Frankia sp. in combined form (both, dual and triple/ tripartite consortium) and analysed for their effect on growth parameters i.e. increase in length, diameter, circumference, Sturdiness quotient (Sq), Biovolume index (Bi) and Plastochron interval index (Pi) of the target plant species. Results: Qualitative analysis have revealed that the consortium treatment containing Glomus mosseae and Frankia sp. (FS-03) resulted in more increase in the length (7.0 ±0.25 cm), diameter (1.3 ±0.25 cm), circumference while the highest biovolume index was observed in the consortium treatment of Frankia sp. along with Glomus mosseae, Trichoderma harzianum viz. Fs-04 (280.96 ± 20.0) and sturdiness quotient of 0.25 including reduced phyto-mortality and initiating rapid phyllogenesis in inoculated seedlings as compared to control seedlings. In contrast to control seedlings, which are covered in depth in this work, a similar pattern with negligible variance in all analyzed parameters as indicated above were also seen in other alone and combined treatments. Conclusion: As a result, it was shown that both AM alone and consortium inoculations with Frankia sp. increased this plant species' adaptation and resilience.

Investigating the host finding behaviour of the weevil Phytobius vestitus for the biological control of the invasive aquatic weed Myriophyllum aquaticum

Biological control programmes involve pre-release studies that include host range tests to predict likely negative effects on native species. Behavioural responses of potential biological control agents to olfactory signals emitted by target and non-target species provide information on the host-finding and selection behaviour for safer agent selection. The weevil Phytobius vestitus (Coleoptera: Curculionidae) was identified as a potential biological control agent for the sustainable management of the aquatic weed Myriophyllum aquaticum (Haloragaceae). Using olfactometer-based bioassays, we analysed the host-finding and host-selection behaviour of P. vestitus across a variety of plant species closely related to M. aquaticum using a glass olfactometer. We further analysed the volatile organic compounds emitted by the target and non-target plant species to explain the weevil's observed preferences. We demonstrated that P. vestitus was able to recognise and discriminate between eight closely related Haloragaceae plant species and was significantly more attracted to the olfactory cues emitted by the target plant, M. aquaticum, compared to the other plant species. This study provides a first important indication of the specificity of P. vestitus and shows the role of plant chemistry in host selection and the possibility of refining host range assessment for potential biological control agents. However, exhaustive risk assessment for possible release into targeted new environments still requires further investigations.

Designing payload and spaceflight operations for plants from extreme terrestrial environments

Terrestrial plants from the very limits of life are likely to harbor genes that confer an advantage in human space exploration. These plants are seemingly capable of performing mission critical functions in spaceflight and on extraterrestrial farms while informing directed gene manipulation in target plant species. However, their adaptations to physiologically extreme habitats may hinder the efficacy of routine laboratory techniques for model plants. We here present the development of Antarctic moss Ceratodon purpureus payload and flight operations for the ANT1 Radiation Tolerance Experiment with Moss in Orbit on the Space Station (ARTEMOSS) experiment to the International Space Station (ISS) given limited physical space and crew time. We demonstrate that the hydrophobic surface of Antarctic moss impedes chemical tissue fixation and precludes the use of RNAlater coupled with payload hardware deployed in standard plant spaceflight experiments. We show that deep-freezing the moss tissue on Petri plates provides adequate tissue fixation and allows the extraction of high-quality RNA suitable for gene expression profiling. We replaced hardware with stacks of Petri plates housing Antarctic moss and chemical fixation with deep-freezing in a cryogenic GLACIER freezer. Our design can be translated to other plant species to expand current experimentation techniques with plants from extreme terrestrial environments in order to advance human space exploration.

Meiotic behavior and its implications on the reproductive success of Arnebia euchroma (Royle ex Benth.) I.M.Johnst. (Boraginaceae), an important medicinal plant of Trans-Himalaya

The present study reports the chromosome number, meiotic behavior and its relation with pollen fertility and seed set of Arnebia euchroma (Royle ex Benth.) I.M.Johnst. The species shows a chromosome count of 2n = 2x = 14. The meiotic abnormalities such as chromatin stickiness, cytomixis, laggard formation, chromosomal bridges, were also observed in the Pollen Mother Cells (PMCs) of the target plant species. The linear model of regression showed a significant reduction of seed set with increasing meiotic abnormality and correlation analysis highlighted positive relationship between pollen viability and seed set. Meiotic abnormalities within the species hinder its reproductive process, causing a decline in reproductive efficiency. This study highlights the importance of addressing these intrinsic factors in future conservation programs to prevent a decline in the species population in nature.

Conservation implications of seed germination studies of Aquilegia fragrans Benth.: A native and endangered medicinal plant species of Kashmir Himalaya

Insufficient investigation of seed germination studies of threatened plant species creates practical obstacles to their conservation efforts. Here, we investigate the seed germination of Aquilegia fragrans Benth.-an endangered medicinal plant species native to Himalaya. The effects of stratification conditions including time (10, 20, 30, and 40 days), temperature (−4, −10, and −20 °C), and hormone treatments (250 ppm GA3, 30 ppm BAP, and 30 ppm Zeatin) on germination of A. fragrans seeds collected from the alpine belt of Kashmir Himalaya were examined. Seeds of species exhibited non-deep simple morphophysiological dormancy (MPD). Seed germination showed significant differences among the various treatments. It was observed that the application of GA3, zeatin, and BAP significantly improved seed germination as compared with the control. The highest germination percentage (73 ± 1 %) along with maximum germination index (1.05 ± 0.05) was recorded in T30 (Seeds stratified for 30 days at −10 °C and treatment with Zeatin 30 ppm) followed by T19 (seeds stratified at −10 °C for 20 days and treatment with zeatin 30 ppm). The seed germination studies of A. fragrans have not been carried out before, and the information gathered in the present study may prove useful for the conservation of the target plant species. The present study will help in the conservation, sustainable development, and restoration of this prized medicinal plant species.

Dominance of non-wetland-dependent pollinators in a plant community in a small natural wetland in Shimane, Japan.

Many wetland plants rely on insects for pollination. However, studies examining pollinator communities in wetlands remain limited. Some studies conducted in large wetlands (> 10ha) have suggested that wetland-dependent flies, which spend their larval stage in aquatic and semi-aquatic habitats, dominate as pollinators. However, smaller wetlands surrounded by secondary forests are more prevalent in Japan, in which pollinators from the surrounding environment might be important. Additionally, information regarding floral traits that attract specific pollinator groups in wetland communities is scarce. Therefore, this study aimed to understand the characteristics of insect pollinators in a small natural wetland (2.5ha) in Japan. We examined the major pollinator groups visiting 34 plant species and explored the relationship between the flower visitation frequency of each pollinator group and floral traits. Overall, flies were the most dominant pollinators (42%), followed by bees and wasps (33%). Cluster analysis indicated that fly-dominated plants were the most abundant among 14 of the 34 target plant species. However, 85% of the hoverflies, the most abundant flies, and 82% of the bees were non-wetland-dependent species, suggesting that these terrestrial species likely originated from the surrounding environment. Therefore, pollinators from the surrounding environment would be important in small natural wetlands. Flies tend to visit open and white/yellow flowers, whereas bees tended to visit tube-shaped flowers, as in forest and grassland ecosystems. The dominance of flies in small wetlands would be due to the dominance of flowers preferred by flies (e.g., yellow/white flowers) rather than because of their larval habitats.

Relative contribution of canopy and soil effects between plants with different metal tolerance along a metal pollution gradient

Multiple effects, operating either on the long-term (soil-engineering effects) or on the short-term during plant life (microclimate modification or resources pre-emption), can act simultaneously and determine the outcome of plant-plant interactions. These diverse effects have not been disentangled along a gradient of metal/metalloid pollution, although this is crucial for understanding the dominant species turnover along the gradient, and thus the driving processes of facilitation recurrently found in metalliferous ecosystems, which could help improving ecological restoration of these degraded ecosystems.Here, we experimentally assessed different short-term effects of two dominant forbs of highly polluted habitats (Hutchinsia alpina and Arenaria multicaulis, tolerant to metal stress) and two grasses of less polluted habitats (Agrostis capillaris and Festuca rubra, less tolerant to metal stress) on target plant species (the same as the dominant species mentioned above) transplanted along a large metal pollution gradient. Additionally, in highly polluted environments, we differentiated short- from long-term effects of the two metallicolous forbs, which had different abilities to concentrate metals in their leaves.In line with other studies along metal gradients, variation of short-term interactions appeared to follow the Stress Gradient Hypothesis for plants less adapted to metal pollution (p = 0.030), with positive interactions dominating in most severe areas. Regarding long-term effects, the species with highest leaf metal-accumulation showed no negative effect contrary to the Elemental allelopathy Hypothesis. Long-term effects of the species with lower leaf-metal accumulation could not be determined because of the occurrence of an unexpected difference in micro-habitat conditions (soil depth and humidity) for this species along the metal pollution gradient.Increasing short-term facilitation along metal pollution gradients, which confirmed previous studies, is promising for improving conditions and restoring the most polluted environments. However, long-term results stressed the difficulty to quantify these effects given that these areas are highly fragmented and heterogeneous.

Flower-Insect Timed Counts (FIT Count): Protocol Adaptation and Preliminary Results in Brazil

FIT Count (Flower-Insect Timed Counts) is a citizen science initiative that seeks to monitor flower visitation by diverse pollinator groups, including bumblebees, stingless bees, honeybees, flies, hummingbirds, among others. The protocol entails determining a 50 x 50 cm plot area around a target plant species, photographing the plant and conducting a standardized 10-minute survey on this area to estimate the frequency of flower visits by different pollinator groups. Conducting FIT Counts in different habitats and locations produces data on the temporal and spatial dynamics of these interactions (Carvell 2022, UK Pollinator Monitoring Scheme 2018). FIT Count methodology was originally developed by the UK Pollinator Monitoring Scheme (PoMS) and has been used in the United Kingdom since 2017, with over 8,500 counts conducted to date. In 2021, the FIT Count application (app) was launched in the United Kingdom, and became available in Brazil, Chile, Argentina, and some other European countries in 2022. After installation, users may select in which country the observations will be conducted and their preferred language, either English or the main native language of participating countries. The adaptation of the application for use by Brazilian citizen scientists involved not only the translation of the interface, but also relied on the expertise of a local team who helped select which plant species and pollinator groups would be appropriate and representative of biodiversity within the country (Fig. 1). The application is supported by a website that features a dedicated page for each country. Users can download the app on Google Play or App Store (Fig. 2). To allow the participation of non-experts, who generally are not familiar with taxonomy or species identification, the flower visitors are identified in general categories such as bumblebees and carpenter bees (grouped together), flies, and others (see Fig. 1), representing the main functional groups of pollinators. If a flower visitor cannot be identified, it should be classified as "other insect" or marked as "I don't know". Including the possibility of uncertainty in flower visitor identification was a suggestion of the Brazilian team for quality assurance during data collection. Currently, 834 flower visits have been counted by 15 participants, who performed 109 FIT Counts across Brazil as a pilot testing phase of the app. Two training workshops were held to disseminate the app, and an illustrated guide was published to help participants identify flower types and flower visitor groups (Koffler 2022). Nineteen plant species were monitored, but most flower-visits counted were on basil (Ocimum basillicum, n = 47) and false heather (Cuphea hyssopifolia, n = 33). The mean number of flower visitors per FIT Count was 8 (min = 0, max = 45). While most visits were performed by honeybees, participants also recorded visits by beetles, butterflies or moths, small insects, solitary bees, wasps and other insects. Next steps include assessing data quality and promoting strategic partnerships to further disseminate this citizen science initiative. For instance, quality control measures may include assessing whether participants perform the protocol steps according to instructions and whether plants and flower visitors are correctly identified and counted. Also, we are exploring the prospective implementation of the Darwin Core standard (Darwin Core Task Group 2009) along with the Plant-Pollinator Interactions vocabulary (Salim 2022) to standardize data description.

Chemical composition and herbicidal activity of Oregano (Origanum onites) essential oil on weeds and wheat

ABSTRACT Oregano essential oil (EO) is known as one of the EOs with the highest biological activity on target plant species. In this study, the inhibitory effects of different doses of oregano (Origanum onites L.) EO on the germination and seedling growth of some wheat cultivars and some problem weed species in wheat fields was investigated. For this purpose, both laboratory and pot experiments were carried out. Oregano EO obtained by steam distillation method and component analysis was made via GS/MS. Germination tests and pot experiments were carried out under controlled laboratory and greenhouse conditions. In the study, five wheat varieties, four for bread and one for durum, and five different weed species were used. The effects of different doses of oregano EO on the germination rate, viable plant rate, seedling length, and biomass of test plants were analyzed. According to the results, it was observed that oregano EO showed bioactivity on all species and cultivars included in the experiment. In terms of all parameters, it was concluded that wheat varieties showed higher resistance to oregano EO than weed species. These results show that oregano EO can be used to control some weed species that are a problem in wheat.

Effects of herbicides and mulch on the soil carbon, nitrogen, and microbial composition of two revegetated riparian zones over 3 years

PurposeRevegetation of riparian zones is important to improve their soil nitrogen (N) dynamics and to preserve their microbial compositions. However, the success of revegetation projects currently depends on weed control to reduce non-target vegetation competing over nutrients and to ensure the target plant species growth and survival. Different weed control methods affect soil microbial composition and N cycling. However, the long-term effects of herbicides on soil nitrogen (N) pools and microbial community composition remain uncertain even after cessation of the herbicide application.Materials and methodsThis study compared the impacts of different herbicides (Roundup®, BioWeed™, Slasher®, and acetic acid) with mulch on soil N dynamics and microbial community structure 3 years after vegetation establishment (herbicides applied repeatedly in the first 2 years after which no herbicides were applied in the third final year).Results and discussionSoil microbial biomass carbon (MBC) was significantly higher in mulch compared with Roundup®, BioWeed™, Slasher®, and acetic acid at month 26 at the Kandanga site and month 10 at the Pinbarren site. Soil MBC remained significantly higher in mulch compared with Roundup® and BioWeed™, 12 months after the cessation of herbicide application at the Pinbarren site. Soil MBC in the Roundup® and BioWeed™ groups was also lower than the acceptable threshold (160 mg kg−1) at month 34 at the Pinbarren site. Soil NO3−-N was significantly higher in the mulch than the Roundup® at months 22 and 34 after revegetation at the Pinbarren site which could be partly explained by the decreased abundance of the denitrifying bacteria (Candidatus solibacter and C. koribacter). Additionally, both soil bacterial and fungal communities at the Pinbarren site and only fungal community at the Kandanga site were different in the mulch group compared with all other herbicides. The differences persisted 12 months after the cessation of herbicide application at the Pinbarren site.ConclusionOur study suggested that the application of mulch to assist with riparian revegetation would be beneficial for soil microbial functionality. The use of herbicides may have long-lasting effects on soil microbial biomass and diversity and therefore herbicides should be used with caution as part of an integrated land management plan.

Understanding reproductive biology for realization of conservation and sustainable development of Swertia thomsonii C. B. Clarke-an endemic medicinal plant of Western Himalaya

Swertia thomsonii an important medicinal plant of Himalaya is more susceptible to extinction in the scenario of anthropogenic threats and global climate change. Therefore a detailed study on reproductive biology was undertaken for its conservation and sustainable use. The present study was conducted with the aim to understand reproductive strategies, breeding behaviour and pollination ecology of this prized, endemic medicinal plant species. It is a perennial rhizomatous herb growing along an altitudinal gradient of 2550–3400 m a.s.l. The flowering commences from the month of August and continuous till September. The variation in floral traits was observed across the altitudinal gradients, which reflects its phenotypic plasticity in these characters that helps the species to get adapted in different environmental conditions. The pollen viability recorded in three study sites viz. Gulmarg (SS-I), Doodhpathri (SS-II), Pahalgam (SS-III) was 89.83 ± 3.1, 75.86 ± 5 and 84.5 ± 2.5% respectively. Stigma becomes receptive 4–5 days after anthesis and reaches its peak on 6–7th day. The presence of typical floral characteristics such as asynchronous anthesis, conspicuous nectaries, spiny exine of pollen, dichogamy, and herkogamy points towards entomophilous and outcrossing nature. Reproductive indices like outcrossing index (OCI), self-incompatibility index (SI) and selfing rate (S) as well as results of bagging experiments also revealed that the species is self as well as cross-compatible. However, fruit and seed set recorded in insect exclusion experiments confirmed its anemophilous nature and therefore species exhibits an ambophilous mode of pollination. Mixed matting is operative in the target plant species, preferring xenogamy followed by geitonogamy and autogamy. The species is pollinated by specialized pollinators which mostly belong to the Order Hymenoptera. Suitable media for in-vitro pollen germination has also been identified; the knowledge about peak stigma receptivity and pollen germination is indispensable for breeding programmes. Thus the scientific information generated in the present study may prove useful in different breeding programmes and conservation of this valuable plant species.

Syntenic Cell Wall QTLs as Versatile Breeding Tools: Intraspecific Allelic Variability and Predictability of Biomass Quality Loci in Target Plant Species

Syntenic cell wall QTLs (SQTLs) can identify genetic determinants of biomass traits in understudied species based on results from model crops. However, their effective use in plant breeding requires SQTLs to display intraspecific allelic variability and to predict causative loci in other populations/species than the ones used for SQTLs identification. In this study, genome assemblies from different accessions of Arabidopsis, rapeseed, tomato, rice, Brachypodium and maize were used to evaluate the intraspecific variability of SQTLs. In parallel, a genome-wide association study (GWAS) on cell wall quality traits was performed in miscanthus to verify the colocalization between GWAS loci and miscanthus SQTLs. Finally, an analogous approach was applied on a set of switchgrass cell wall QTLs retrieved from the literature. These analyses revealed large SQTLs intraspecific genetic variability, ranging from presence-absence gene variation to SNPs/INDELs and changes in coded proteins. Cell wall genes displaying gene dosage regulation, such as PAL and CAD, displayed presence-absence variation in Brachypodium and rapeseed, while protein INDELs were detected for the Brachypodium homologs of the rice brittle culm-like 8 locus, which may likely impact cell wall quality. Furthermore, SQTLs significantly colocalized with the miscanthus and switchgrass QTLs, with relevant cell wall genes being retained in colocalizing regions. Overall, SQTLs are useful tools to screen germplasm for relevant genes and alleles to improve biomass quality and can increase the efficiency of plant breeding in understudied biomass crops.

Urban grassland restorations have reduced plant fitness but not pollinator limitation

Native grasslands worldwide have been greatly reduced due to anthropogenic activities. Grassland restoration efforts strive to increase biodiversity and ecosystem services of these habitats, but often fall short of management goals. This is especially true for small-scale restoration efforts in urban areas, which face unique challenges including increased surface temperatures, increased pollution, decreased habitat connectivity, and decreased pollinator availability. In 2019–2020, we conducted a seed-addition field experiment in four restoration sites near Louisville, KY USA to examine how urbanization influenced survival, growth, and reproduction of a common native forb, Chamaecrista fasciculata. We also conducted observations twice per week to characterize the active pollinator community in each site. We found that plants in urban restoration sites had reduced growth, flowering period, and reproduction compared to those in rural restoration sites. However, pollination rates (visits/flower) in urban sites did not differ from those in rural sites, and urban sites even tended to have greater pollinator effectiveness (seeds/flower) than rural sites. Our results suggest that pollination services are adequate in urban restorations, but that other factors associated with urbanization, such as increased drought stress, can reduce growth and fitness of native plants. Further work is needed to better characterize environmental stresses associated with urban grassland restoration in order to minimize fitness effects on target plant species.

Growth-survival trade-offs and the restoration of non-forested open ecosystems

The growth-survival trade-off has been extensively documented for phanerophyte species, whereas there is little evidence for non-phanerophyte species. However, information on the growth-survival trade-offs in non-phanerophyte species could be of great use in non-forested open ecosystem restoration by providing insights for plant production and transplantation, thus impacting the planning of cost-effective restoration actions. In this study, we explored the relationship between growth and survival of individual plants of non-phanerophyte species used in a coastal dune restoration project, and we investigated whether plant functional traits explained patterns of trade-off between growth and survival. We monitored 355 individual plants of 13 perennial non-phanerophyte species belonging to foredune and transition dune communities every 30 days after planting and calculated relative growth and survival rates. In addition, we regressed the relationship between growth and survival on values of leaf and floral traits. We found that, besides being a widely recognised axis of life history variation in phanerophyte species, the growth-survival trade-off can also be observed in perennial non-phanerophyte species. Species of different coastal dune communities (i.e., foredune vs. transition dune communities) differed with respect to the growth-survival trade-off, with plant species of foredune communities exhibiting higher growth but lower survival rates than plant species of transition dune communities. Leaf dry matter content and mean number of floral displays explained species position on the growth-survival trade-off axis; species with relatively high growth and low survival rates exhibited an acquisitive strategy, with low values of leaf dry matter content, but also a low sexual reproductive effort, as revealed by low number of floral displays. In contrast, plant species with relatively low growth and high survival rates exhibited a conservative strategy but also high sexual reproductive effort, suggesting that trade-offs occur in resource allocation among vegetative and reproductive plant structures. The trade-off we found between growth and survival in perennial non-phanerophyte species provides useful insights for planning cost-effective ecosystem restoration actions of non-forested open ecosystems, especially when the actions are nature-based and involve planting individual plants. The results of this study suggest that individual plant production for coastal dune restoration should disproportionately target plant species of foredune communities because they have low survival rates associated with low sexual reproductive effort. Planning plant production based on ecological knowledge of plant species’ growth and survival after planting in the field could help achieve restoration goals while meeting project cost-effectiveness requirements.

Live under strong power: A third plant species alters interspecific interactions between two plant species

Organisms from higher tropical levels (e.g., herbivores) can mediate indirect competitive interactions between two target plant species, but such apparent competition may also be mediated by a third plant species and thus may vary depending on the size and competitive ability of the target plant species and the third plant species. We set up an outdoor experiment with four aquatic plant species with similar niches but differing greatly in size, i.e., Lemna minor (the smallest), Spirodela polyrhiza (the second smallest), Salvinia natans (the second largest) and Pistia stratiotes (the largest). We grew L. minor and S. polyrhiza alone or in mixture and in the absence of any third plant species, in the presence of a small, third species S. natans or in the presence of a large, third species P. stratiotes. In the absence of the third species or in the presence of S. natans, the growth of L. minor was greatly inhibited by S. polyrhiza, but in the presence of P. stratiotes, the inhibiting effects of S. polyrhiza disappeared completely and the growth of L. minor greatly increased. By contrast, the presence of L. minor had no effect on the growth of S. polyrhiza, and this effect did not depend on the presence or absence of the third plant species, although the presence of the third species, particularly P. stratiotes, decreased its growth. We conclude that the presence of a third plant species can regulate plant-plant interactions, but such an impact depends on the size and competitive ability of the competing species as well as the third species. Our findings highlight the role of complexity in plant-plant interactions, and suggest that apparent competition between plants can also occur at the same trophic level. These results have important implications for the explanations of species coexistence and biodiversity maintenance.

Efficacy of metallic nanoparticles in attenuating the accumulation and toxicity of chromium in plants: Current knowledge and future perspectives

Nanoparticles have emerged as cutting-edge technology for the improvement of crops yield and safe cultivation of agricultural plants, especially in peripheral areas impaired with toxic heavy metals including chromium (Cr). The uncontrolled release of Cr mainly from anthropogenic factors is substantially polluting the surrounding environment, thereby extensively accumulated in soil-plant system. The excessive Cr-accretion in plant tissues disturbed the morph-physiological, biochemical, cellular, metabolic and molecular processes, and impaired the plants functionality. Therefore, it is obligatory to restrict the accumulation and toxic effects of Cr in plant organs. Recent studies on metallic nanoparticles (MNPs) such as iron oxide, silicon dioxide, copper oxide and zinc oxide have approved their efficacy as potent pool to curb the Cr-induced phytotoxicities and improved the plant tolerance. MNPs attenuated the bioaccumulation and phytotoxicity of Cr by utilizing key mechanisms such as improved photosynthetic machinery, regulation of cellular metabolites, greater chelation capacity to bind with Cr, release of corresponding metallic ions, upsurge in the uptake of essential nutrients, activation of antioxidants (enzymatic and non-enzymatic), reduction in oxidative stress, and cellular injuries, thus improvement in plant growth performances. We have briefly discussed the current knowledge and research gaps in existing literature along with possible recommendations for future research. Overall, Cr-detoxification by MNPs may depends upon the target plant species, Cr speciation, plant growth stages (seedling, vegetative and ripening etc.), treatment methods (foliar spray, seed priming and nutrient solution etc.), type, size, dose and coating of applied MNPs, and conditions (hydroponic and soil environment etc.). This review would help plant scientists to develop MNPs based strategies such as nano-fertilizers to alleviate the Cr-accumulation and its toxic impacts. This may leads to safe and healthy food production. The review outcomes can provide new horizons for research in the applications of MNPs for the sustainable agriculture.

Pollinator distribution in patches of suitable habitat depends more on patch isolation than on floral abundance

Intrinsic complexity of real-world systems makes particularly difficult to decipher which factors influence the dispersal of pollinators in the landscape matrix and their distribution amongst patches of suitable habitat. Saltmarshes are an ideal and naturally simplified landscape to study the ability of different groups of pollinators to disperse across a landscape matrix, as they consist of a matrix of flooded areas surrounding patches of suitable habitat with different degrees of isolation from the mainland and different levels of floral abundance. We hypothesise that pollinator distribution to flowering plants depends more on patch isolation than on floral abundance, with pollinator richness and visitation rates to flowering plants decreasing with increasing distance from the mainland. To this end, we established 60 permanent plots at varying distances from the mainland and monitored pollinator visitation to entomophilous plants. We also quantified the reproductive success of entomophilous species in the surveyed plots by calculating fruit set. We found that the pollinator community of saltmarshes consisted only of flying pollinators with good dispersal abilities, while we recorded no flightless pollinator species. Both pollinator richness and visitation rate decreased with increasing distance of patches of suitable habitat from the mainland, affecting reproductive success of a non-autogamous entomophilous species. Interestingly, floral abundance did not affect pollinator richness and visitation rate to flowering plants, nor did it affect reproductive success of target plant species. In saltmarshes, the pollinator distribution depends more on patch distance from the mainland than on floral abundance. Our results suggest that the presence of patches of suitable habitat in a landscape matrix does not necessarily ensure the maintenance of pollinators. Rather, our results suggest that suitable habitat isolation is the critical factor in pollinator dispersal and distribution that should be considered to improve landscape matrix permeability to pollinators.

Small-volume additions of forest topsoil improve root symbiont colonization and seedling growth in mine reclamation

Beneficial soil microbes, such as mycorrhizal fungi and nitrogen-fixing bacteria, can improve plant nutrient acquisition and increase plant resilience to stressors. Yet, the waste materials left behind following major disturbances, such as mining, have negligible biological activity and fresh topsoil availability for reclamation is often limited. We tested if small-volume additions of native forest topsoil can improve early seedling survival and growth, and promote colonization of beneficial root symbionts. In a greenhouse experiment, we grew seedlings representing different functional groups in tailings and glacial-till overburden from the Mount Polley Mine, Canada. We applied 5 % (38 mL) and 25 % (188 mL) forest-soil additions for comparison with tailings/overburden controls and reference forest soil. The experiment was replicated with sterilized soil to isolate the biological effects of the forest soil from the physical and chemical effects. Willow (Salix scouleriana) and spruce (Picea engelmannii x glauca) seedling survival and growth increased with proportion of forest soil, which corresponded with increased ectomycorrhizal fungal colonization. Forest soil additions benefited seedlings grown in both overburden and tailings, with ~200 mL (25 %) forest soil additions generally supporting initial seedling growth comparable to seedlings grown in reference forest soil. Alder (Alnus viridis) showed minimal benefit from forest soil additions, likely due to a lack of nitrogen-fixing bacteria in the forest soil, highlighting the importance of matching the plant and microbial communities of the soil donor site with the target plant species. Differential results among plant species in sterilized soil indicated that plants exhibiting greater dependence on microbial symbionts (spruce and alder), benefited from the biological component of the inoculum, while willow, an early successional species with low mycorrhizal dependence, benefited from the physical and chemical properties of the forest soil. This research showed that targeted additions of small volumes of topsoil from native ecosystems can improve initial seedling survival and growth, and promote recovery of limiting soil microbial communities, making it a promising approach for mine reclamation when topsoil availability is limited.

Research progress on nurse effects of shrubs in ecological restoration

Shrubs are the major components of vegetation in arid and semi-arid areas, and play a pivotal role in maintaining ecosystem stability and function. The nurse effects of shrubs can help with the regeneration of native target plant species by alleviating the adverse influences that limit their growth and reproduction in degraded habitats. We summarized the main research results and application of shrub nurse effects in the last 20 years. We discussed several facilitation mechanisms of nurse shrubs, including microhabitat amelioration, fertile island formation, defense and resistance against herbivores, introduction of beneficial microorganism and propagule propagation or preservation, as well as changes in the patterns of interspecific competitive networks. Key factors affecting nurse effects were analyzed, including abiotic environments, biological disturbances, plant life history as well as growth and reproductive strategies. Prospects for future research were also considered from the aspects of improving theore-tical mechanisms of nurse effects by shrubs and building models involved in multiple plant species interaction affec-ted by multifactors.