Seedling Establishment Research Articles

Seeds vs. Seedlings: The Long-Term Success of Seeds Versus Seedlings in the Restoration of the Federally Endangered Baptisia arachnifera (Fabaceae) During Experimental Planting

The use of seeds versus seedlings may yield different restoration trajectories depending on seed germination (=seedling emergence) success in the of restoration plantings versus seedling establishment. Effective restoration and sustainable population dynamics will require both for long-term persistence. This study compared seed germination in both greenhouse and natural conditions, examining the growth, survival, and reproduction of seedlings from seeds and transplants of a federally endangered perennial, Baptisia arachnifera W.H. Duncan (Fabaceae), in Georgia, USA. Under greenhouse conditions, seed germination is rapid and yields 68% germination across a variety of conditions. In field germination trials, seedling emergence is moderate (20%), but survival, growth, and reproduction are low. Over an 18-yr period (2004–2022) at a restoration planting site in Lowndes County, Georgia, USA, survival, growth, and reproduction were much higher for plants established from seedlings versus plants established from seeds. While dormant plants and seeds are not harmed by winter burns, seedlings derived from both seeds and seedlings are negatively impacted by growing season burns. Restoration efforts in this species should focus on germinating seeds in greenhouses and the effective establishment and management of seedlings, not using seeds directly for restoration efforts.

Germination Strategies and Seed Quality of Colobanthus quitensis: Implications for Sustainable Antarctic Ecosystems and Ex Situ Plant Conservation

The conservation of the Antarctic ecosystem is linked to scientific and tourism activities. The Colección Activa de Plantas Vasculares Antárticas at the Universidad de Concepción aims to help conserve the region’s vascular flora to support scientific research while minimizing anthropogenic pressure on natural ecosystems. Colobanthus quitensis is the only native dicotyledonous plant native to Antarctica and, as an extremophilic plant, is capable of withstanding extreme abiotic conditions. This species has potentially important use as a biological model to study the physiological deterioration of dormant seeds and other traits, some of which may contribute to vegetation development in Antarctica. Although studies have addressed the reproduction and germination of C. quitensis, there is no recent synthesis of information regarding its reproductive biology and seed traits that could support its conservation. This work synthesizes and critically analyzes the current knowledge of C. quitensis reproduction in natural and controlled environments, identifying factors that contribute to the decline in seed quality. We propose that growth conditions, seed morphology, and interactions with endophytic fungi influence germination and seedling establishment. We also highlight critical knowledge gaps that must be addressed to better understand the species’ phenology, the impact of biotic and abiotic factors on its development, strategies for seed conservation, and biotechnological applications.

Invaders break assembly rules to beat the natives: how cheatgrass cheats

Understanding how some introduced plants achieve invasive status while most simply become naturalized is a fundamental question in invasion ecology. Traditional approaches comparing native and introduced plants have linked ruderal traits such as annual life history, high fecundity, and rapid growth rates to invasiveness. However, they do not explain why other introduced species bearing similar traits fail to become invasive, possibly because generic comparisons ignore local processes that drive community assembly. Herein, we contrasted native and introduced annuals in the context of local successional processes to elucidate how introduced annual bromes like cheatgrass (Bromus tectorum) overtake perennial grasslands in the intermountain western United States. We created disturbed plots and seeded them first with annuals representing natives, naturalized species, or invasive bromes. We then seeded plots with native perennial community dominants to examine how the different annuals influenced succession. Native annuals established transient populations that facilitated perennial establishment compared to unseeded controls, enabling the shift to perennial dominance. Naturalized annuals mirrored the natives, but invasive annuals maintained robust populations at high biomass that inhibited perennial establishment and impeded succession. Mechanistically, invasive annuals reduced soil moisture and elevated plant biomass, litter, and soil N. However, only litter abundance correlated with perennial seedling recruitment across treatments. Overall, litter showed a unimodal relationship wherein lower litter abundance associated with native and naturalized annuals appeared to facilitate perennial seedling establishment while higher litter levels generated by invasives appeared to suppress perennial establishment and inhibit succession. Additional experiments provided little support for the roles of pathogen spill-over or plant-soil feedbacks favoring the introduced bromes. The domination of perennial grasslands by annual bromes may be driven by litter buildup that allows these introduced plants to break local succession rules by acting as both early seral and climax species. Traits like litter accumulation may strongly influence invasion outcomes but are indistinguishable using trait comparisons lacking community context.

Seed priming with ascorbic acid and spermidine regulated auxin biosynthesis to promote root growth of rice under drought stress

IntroductionDrought stress severely hampers seedling growth and root architecture, resulting in yield penalties. Seed priming is a promising approach to tolerate drought stress for stand establishment and root development.MethodsHere, various seed priming treatments, viz., hydro priming, ascorbic acid priming (AsA), and spermidine priming (Spd), were adopted concerning root morphological, physiological, microstructural, and molecular studies under drought stress on rice variety Hanyou 73.Results and discussionResults demonstrated that drought severely suppressed seedling establishment, while AsA or Spd priming effectively alleviated the inhibitory effects of drought stress, and significantly increased shoot length (24.5-27.9%), root length (34.6-38.8%), shoot dry weight (56.1-97.1%), root dry weight (39.6-40.6%), total root length (47.0-57.8%), surface area (77.0-84.9%), root volume (106.5-109.8%), average diameter (16.4-19.7%), and root tips (46.8-61.1%); meanwhile, priming with AsA or Spd alleviated microscopic and ultrastructural damage from root cell, and improved root activity (183.8-192.0%). The mitigating effects of AsA or Spd priming on drought stress were primarily responsible for decreasing the accumulation of reactive oxygen species by increasing antioxidants activities and osmoprotectants contents, which reduced oxidative stress and osmotic cell potential and facilitated improved water and nutrients absorption in roots. Additionally, seed priming with AsA or Spd substantially improved auxin synthesis by upregulating of OsYUC7, OsYUC11 and, OsCOW1 expression. However, there were certain differences in the defense responses of plants and mechanisms of reducing the damage of drought stress after seed treatment with AsA or Spd. Under stress conditions, AsA had a greater impact on improving the fresh and dry weight of aboveground parts, while Spd affected the concentration of total sugar and total protein in plants. Likewise, the degree of oxidative damage was lowered, and POD and CAT activities were elevated due to Spd priming under water-deficient conditions.

Invasive shrubs amplify seasonal granivory, revealing optimal windows for seed survival following invasive shrub removal

AbstractInvasive shrubs dramatically reduce the biodiversity of native plants, making invaded areas important targets of conservation and restoration. Adding seeds of native plant species, in addition to the removal of invasive plants, is a potentially promising means for restoration of native plant communities. However, because seed survival may vary among seasons, it is essential to understand temporal patterns of seed survival. For example, dense habitats created by invasive shrubs exhibit seasonal changes in structure and food resources that could create seasonal variation in seed survival by altering the activity and abundance of native seed‐eating rodents. Despite the potential for invasive shrubs to generate seasonal changes in granivory, we lack experimental studies to evaluate changes in granivory caused by invasive plants over a full year. We mechanically removed the widespread invasive species common buckthorn (Rhamnus cathartica) from half of 14 sites (20 × 20 m) in a deciduous oak‐maple forest to track rodent and arthropod granivory of three native tree species, basswood (Tilia americana), black cherry (Prunus serotina), and sugar maple (Acer saccharum), and the invasive shrub R. cathartica over a year. Our results reveal that the effect of invasive shrubs on granivory changed across seasons. Seeds in invaded habitats experienced, on average, 25.9% higher seed removal than seeds in areas with R. cathartica removed, with the largest difference in removal occurring in winter. Seed removal was almost entirely due to rodent granivores that removed seeds at similar rates among species. These results indicate that, following removal of invasive shrubs, sowing seeds in winter may optimize seedling establishment by minimizing granivory. Our findings further reinforce the importance of removing invasive shrubs as an important restoration tool because invasions may amplify granivory throughout the year. Understanding the mechanisms that could be affecting seasonal granivory within invaded systems, the important role of rodent granivores, and the similarities in seed consumption between native and nonnative seeds is critical for continual conservation and restoration efforts aimed at promoting forest regeneration.

Effect of harvest stage, provenance and selected chemical treatments on the seed germination and seedling establishment of Trichilia emetica (Natal mahogany)

Effect of harvest stage, provenance and selected chemical treatments on the seed germination and seedling establishment of <i>Trichilia emetica</i> (Natal mahogany)

Redox Control of Seed Germination is Mediated by the Crosstalk of Nitric Oxide and Reactive Oxygen Species.

Significance: Seed germination and seedling establishment are characterized by changes in the intracellular redox state modulated by accelerated production of nitric oxide (NO) and reactive oxygen species (ROS). Redox regulation and enhanced accumulation of NO and ROS, approaching excessively high levels during seed imbibition, are critically important for breaking endodormancy and inducing germination. Recent Advances: Upon depletion of oxygen under the seed coat, NO is produced anaerobically in the reductive pathway associated mainly with mitochondria, and it participates in the energy metabolism of the seed until radicle protrusion. NO turnover involves nitrate reduction to nitrite in the cytosol, nitrite reduction to NO in mitochondria, and NO oxygenation in the cytosol in the reaction involving the hypoxically induced class 1 phytoglobin. In postgerminative degradation of seed tissues, NO and ROS are involved in redox signaling via post-translational modification of proteins and mediation of phytohormonal responses. Critical Issues: The crosstalk between the cellular redox potential, NO, ROS, and phytohormones integrates major physiological processes related to seed germination. Intensive accumulation of NO and ROS during imbibition is critically important for breaking seed dormancy. Upon oxygen depletion, NO and other nitrous oxides (NOx) are produced anaerobically and support energy metabolism prior to radicle protrusion. Future Directions: The turnover of NOx and ROS is determined by the intracellular redox balance, and it self-controls redox and energy levels upon germination. The particular details, regulation of this process, and its physiological significance remain to be established. Antioxid. Redox Signal. 00, 000-000.

Spatiotemporal bifurcation of HY5-mediated blue-light signaling regulates wood development during secondary growth

Plants have evolved photoreceptors to optimize their development during primary growth, including germination, hypocotyl elongation, cotyledon opening, and root growth, allowing them to adapt to challenging light conditions. The light signaling transduction pathway during seedling establishment has been extensively studied, but little molecular evidence is available for light-regulated secondary growth, and how light regulates cambium-derived tissue production remains largely unexplored. Here, we show that CRYPTOCHROME (CRY)-dependent blue light signaling and the subsequent attenuation of ELONGATED HYPOCOTYL 5 (HY5) movement to hypocotyls are key inducers of xylem fiber differentiation in Arabidopsis thaliana. Using grafted chimeric plants and hypocotyl-specific transcriptome sequencing of light signaling mutants under controlled light conditions, we demonstrate that the perception of blue light by CRYs in shoots drives secondary cell wall (SCW) deposition at xylem fiber cells during the secondary growth of hypocotyls. We propose that HY5 is a blue light–responsive mobile protein that inhibits xylem fiber formation via direct transcriptional repression of NAC SECONDARY WALL THICKENING PROMOTING 3 ( NST3 ). CRYs retain HY5 in the nucleus, impede its long-distance transport from leaf to hypocotyl, and they initiate NST3- driven SCW gene expression, thereby triggering xylem fiber production. Our findings shed light on the long-range CRYs-HY5-NST3 signaling cascade that shapes xylem fiber development, highlighting the activity of HY5 as a transcriptional repressor during secondary growth.

Stem Cutting, Rooting, and Shoot Growth Potentials of Some Hedge Plant Species as Influenced by Number of Nodes

Root and shoot initiation, as well as seedling growth after planting a stem cutting, is critical for ensuring seedling establishment. This study was carried out at the Department of Horticulture Nursery, Federal University of Agriculture Abeokuta, Nigeria, to examine early rooting and shoot development of landscape hedge plants during propagation with respect to the number of nodes per cutting. Species used were Duranta repense Linn., Duranta erecta Linn., Variegated Duranta erecta Linn., Ficus retusa Linn., Ixora coccinea Linn., Acalypha inferno Linn., Acalypha wilkesiana Mull. Arg. Hamelia patense Jacq., Boungainvillea glabra Wild. and Alternanthra dentata Scheygr. Stem cuttings of each of the ten species with 2, 3 and 5 nodes constituted the treatments arranged in Completely Randomized Design with three replicates. Time of root and shoot emergence, rooting percentage observed daily from one day after planting (DAP), number of leaves, seedling height, number of sprouted cuttings were measured weekly from 2 weeks after planting (WAP) and stem girth (at 15cm seedling height) 4 WAP. Fresh root and fresh shoot biomass were measured at 16 WAP. The result revealed that the number of nodes per cutting and the plant species had significant effects on the time to root, shoot initiation, cutting height, and number of leaves, stem girth, fresh root and shoot biomass. Duranta species performed best for all of these parameters while Bougainvillea glabra produced the lowest shoot biomass. Days to shoot initiation was not significantly different (p≤0.05) across the number of nodes for all species, ranging between 8 and 10 days after planting (DAP). Time to root was also similar regardless of the number of nodes across species with all species rooting at a range of 14-28 DAP. All the species used in this study, except Ficus retusa can be classified as easy to propagate because of their early root formation and relatively fast shoot initiation, indicating their potential suitability for use as hedge plants.

The RALF1-FERONIA complex phosphorylates FREE1 to attenuate abscisic acid signaling during seedling establishment.

The receptor-like kinase FERONIA (FER), together with its ligand rapid alkalinization factor 1 (RALF1) peptide, plays a crucial role in regulating stress responses, including its involvement in modulating abscisic acid (ABA) signaling. FER has been shown to activate ABA Insensitive 2 (ABI2) in the cytoplasm, leading to the suppression of ABA signaling. However, its regulation of nucleus events in the ABA response remains unclear. FREE1, identified as a plant-specific component of the endosomal sorting complex required for transport (ESCRT) in eukaryotes, serves as an important negative regulator in ABA signaling. In this study, we elucidate that upon RALF1 treatment, FER phosphorylates FREE1, promoting the accumulation of FREE1 protein in the nucleus in Arabidopsis (Arabidopsis thaliana). Consequently, FREE1 suppresses ABA sensitivity by inhibiting the expression of ABA-response genes. Mutating the six identified phosphorylation sites on FREE1, mediated by FER, to non-phosphorylable residues results in reduced nucleus localization of FREE1 and increased hypersensitivity to ABA. Our data also show that these six phosphorylation sites are likely involved in regulating plant survival under salt stress. Collectively, our study not only unveils an additional function of FER in attenuating ABA signaling in the nucleus but also provides a possible insight into the role of the RALF1-FER-FREE1 module in coordinating plant growth and salt stress tolerance.

Advancements in Seed Treatment Methods and Storage Techniques of Marigold Seeds: An Overview

Floriculture plays a pivotal role in boosting national economies by driving foreign exchange revenues. However, current productivity levels in floriculture, particularly in marigold (Tagetes spp.), are insufficient to meet the escalating global demand for ornamental flowers. Marigold, being one of the most commercially significant crops in this sector, requires improved seed quality to achieve optimal performance and higher yields. Major constraints, such as the limited availability of high-quality seeds, and the rapid decline in seed viability during storage, continue to hamper productivity. Additionally, conventional seed treatment practices and storage methods often fail to sustain seed vigour and germination rates over extended periods. This review offers an in-depth analysis of the latest advancements in seed treatment technologies and storage practices to enhance germination, disease resistance, and seedling establishment. By integrating the insights from seed treatments and post-harvest storage of seeds, this review paper addresses key challenges faced by the floriculture industry and aligns with the growing global demand for high-quality floral crops.

Testing the effects of seed pellet composition to aid in semiarid restoration seeding

Restoring and revegetating semiarid regions with native perennial grasses is an extremely difficult task, often unsuccessful due to harsh abiotic conditions. We conducted studies evaluating the use of seed pellets to improve restoration seeding success in controlled and field environments. In a controlled setting, we evaluated the impacts of clay volume, pellet size, and watering rate on seedling establishment and pellet disintegration. The amount of clay, size of pellets, and watering rate were varied in a full factorial design. Seedlings emerged from 40% of the pellets. Clay content did not impact seedling emergence, but larger pellets (2.5 cm) were more likely to produce seedlings. However, when smaller pellets (1.5 cm) produced seedlings, a higher proportion emerged (15 vs. 9%). In the field, we compared seedling establishment monthly, overall summer recruitment, and disintegration of seed pellets made with 10% and 55% clay to broadcast seed and a non‐seeded control using a randomized design. Seedling emergence was higher for both the 10% (1.4 seedlings) and 55% clay pellets (1.0 seedling) than the control treatments (0.5 seedlings), and also higher for the 10% clay pellets than broadcast treatments (0.8 seedlings). Additionally, we found that seedling establishment and recruitment were unaffected by pellet disintegration. End‐of‐season recruitment was higher in 10% clay pellets (2.6 seedlings) than in 55% clay pellets (1.2 seedlings) and control treatments (1.0 seedling). We also found that 2.5 cm pellets had slightly higher recruitment, indicating that larger pellets may be more suited to seedling survival in semiarid environments.

Fruit traits of different variants of Zanthoxylum planispinum var. dingtanensis in the karst plateau valley area of Guizhou Province, Southwest China.

Many studies have shown that seed traits, which are among the most important plant traits, can be inherited stably, a finding which is of great value for the improvement of seed germination, seed propagation, seedling establishment, plant breeding, and ecological restoration. The differences in phenotype and nutritional traits and their interactions in Zanthoxylum planispinum var. dingtanensis were ascertained, and the nutrient input rule and the strategy of resource balancing were analyzed in order to provide a scientific basis for the screening of improved variants of the test plant. The nutrient distribution with in the tissues of Z. planispinum var. dingtanensis fruit was that the pericarp had adequate concentrations of N and P concentrations and the seed was also sufficient in P, but low in N concentration. Inorganic nutrients were particularly invested in the pericarp, while organic nutrients are more likely to be stored in the seed. In the economic spectrum of seed traits, the large leaf Zanthoxylum variant represented the low-investment economic type, the tufted leaf Zanthoxylum variant represented the high-investment luxury type, and the safflower Zanthoxylum and acutifoliate leaf Zanthoxylum variants represented transitional types. Inorganic nutrients were more invested in the pericarp to produce secondary metabolites, while organic nutrients are more likely to be stored in the seed to ensure seed germination and seedling establishment in order to achieve inheritance. The variants of Z. planispinum var. dingtanensis differ in terms of resource allocation and balance, which could be further exploited through combining characters in breeding programs.

Active restoration increases tree species richness and recruitment of large-seeded taxa after 16-18 years.

Tropical forest restoration presents a potential lifeline to mitigate climate change and biodiversity crises in the Anthropocene. Yet, the extent to which human interventions, such as tree planting, accelerate the recovery of mature functioning ecosystems or redirect successional trajectories toward novel states remains uncertain due to a lack of long-term experiments. In 2004-2006, we established three 0.25-ha plots at 10 sites in southern Costa Rica to test three forest restoration approaches: natural regeneration (no planting), applied nucleation (planting in patches), and plantation (full planting). In a comprehensive survey after 16-18 years of recovery, we censused >80,000 seedlings, saplings, and trees from at least 255 species across 26 restoration plots (nine natural regeneration, nine applied nucleation, eight plantation) and six adjacent reference forests to evaluate treatment effects on recruitment patterns and community composition. Both applied nucleation and plantation treatments resulted in significantly elevated seedling and sapling establishment and more predictable community composition compared with natural regeneration. Similarity of vegetation composition to reference forest tended to scale positively with treatment planting intensity. Later-successional species with seeds ≥5 mm had significantly greater seedling and sapling abundance in the two planted treatments, and plantation showed similar recruitment densities of large-seeded (≥10 mm) species to reference forest. Plantation tended toward a lower abundance of early-successional recruits than applied nucleation. Trees (≥5 cm dbh) in all restoration treatments continued to be dominated by a few early-successional species and originally transplanted individuals. Seedling recruits of planted taxa were more abundant in applied nucleation than the other treatments though few transitioned into the sapling layer. Overall, our findings show that active tree planting accelerates the establishment of later-successional trees compared with natural regeneration after nearly two decades. While the apparent advantages of higher density tree planting on dispersal and understory establishment of larger seeded, later-successional species recruitment is notable, more time is needed to assess whether these differences will persist and transition to the more rapid development of a mature later-successional canopy. Our results underscore the need for ecological restoration planning and monitoring that targets biodiversity recovery over multiple decades.

Influence of post-vegetative foliar application of nitrogen and selenium on micrometeorological parameters, phenology, and yield of wheat (Triticum aestivum L.)

Excessive and continuous use of commercial-grade fertilizers in large quantities during the post-Green Revolution era has led to significant environmental impacts, besides escalating the cost of production in staple crops. Such over-reliance on chemical fertilizers in intensive agriculture and a limited focus on balanced nutrient management have led to an increase in micronutrient deficiency in the sub-tropical part of India. This micronutrient deficiency leads to stunted growth, poor flowering, and reduced grain and fruit formation, directly impacting overall crop productivity. Hence, the introduction of nano form of fertilizers and integration of them with bulk/commercial form will help in improving the nutrient use efficiency, reduce production costs vis-a-vis enhancement in the plant growth, and yield more effectively than the traditional fertilizers. Proper nutrient management promotes healthy development at each stage, from seedling establishment to maturation and ripening, ensuring optimal yields and quality. Hence, fertilization directly and profoundly impacts the phonological stages of the crops. In this respect, a field experiment was conducted at Ludhiana and Fatehgarh Sahib, Punjab, India, during the rabi season of 2021-22. The experiment was laid out in a Randomized Completely Block Design (RCBD) with four replications and 11 treatments. Besides an absolute control where no fertilizer was applied (T1), ten other treatments were commonly fertilized with the recommended dose of fertilizers (RDF), i.e., 125 kg N and 62.5 kg P2O5 ha-1). The treatment varied in applying bulk and nano N (6% urea) and Se (15 ppm) at reproductive phases. The normalized difference vegetation index (NDVI) score and chlorophyll index improved with foliar spray of both bulk and nano urea forms alone or in combination with Se (bulk or nano). The effect of foliar sprays of urea and selenium, either in bulk or nano form, alone or in combination, was insignificant. The reproductive stages, viz. heading, grain filling, and physiological maturity, are prolonged with late season spray of 6% bulk or nano urea alone or in addition to bulk or nano selenium. Maximum days to grain filling was in a foliar spray of nano urea 6% along with nano selenium 15 ppm, further leading to higher grain and biological yield.

Influence of seed-applied biostimulants on soybean germination and early seedling growth under low and high temperature stress

AbstractBiostimulants are environment-friendly agricultural inputs that can improve plant health and yield potential under environmental stressors. Soybeans subjected to extreme temperatures during the growing seasons impacts plant health and performance. Uniform emergence and vigorous seedling establishment are the two traits during the early season that directly correlate with the final yield and are sensitive to abiotic stress. This study tested the effectiveness of seed-applied biostimulants in improving seed germination and emergence traits under different temperatures, low (15 °C, LT), optimum (25 °C, OT), and high (35 °C, HT), using three phenotyping methods such as the paper roll, growth pouch, and soil-based pot culture. Germination, emergence, and seedling growth were significantly accelerated under OT and HT compared to LT in both biostimulant-treated and untreated seeds. While seeds treated with biostimulants exhibited minor differences in germination, emergence, and growth traits under LT and HT compared to the OT. In the soil-based pot culture experiment, humic and fulvic acid-containing treatments extended the time to 50% emergence under LT. This delay was associated with a 13% increase in seedling biomass. A bacillus containing biostimulant improved seedling vigor by 7% under LT compared to untreated check. Notably, biostimulants containing bacterial strains, fulvic acid, and humic acid were found to have a role in reducing time to germination or emergence and enhancing seedling growth. However, the results obtained from different phenotyping methods were inconsistent, suggesting that the effects of biostimulants on germination and growth parameters may be more targeted rather than broad-spectrum. Future research is necessary to optimize application rates and fully explore their potential to mitigate the effects of stressors during the growing season.

Effects of vegetative ground cover on seedling establishment of the invasive liana old man’s beard (Clematis vitalba)

Abstract Opportunistic use of limited resources is often attributed to invasive species, and as a mature vine, old man’s beard (Clematis vitalba L.) is known to have devastating negative impacts on the trees it colonizes. No previous experimental studies have been published on how easily C. vitalba seedlings can colonize ground covered by other established vegetation. This species has had an increasing presence in forestry blocks and riparian zones in New Zealand, both of which usually maintain some grass cover. To determine the importance of vegetative ground cover for preventing ingress of new C. vitalba plants, this study looked at seedling emergence through the soil and establishment of C. vitalba within four different levels of grassy cover at three sites: (1) ground kept bare after vegetation removal; (2) ground bare at C. vitalba seed sowing, but thereafter allowed to recover; (3) vegetative cover trimmed to 4 cm high at C. vitalba sowing, and then allowed to recover; and (4) unmanaged vegetation. At the highest level of vegetation density (unmanaged vegetation), no C. vitalba seedlings were ever detected throughout a 1-yr monitoring period. At lower ground cover densities, poor seedling emergence was observed, with a maximum of 36% of seeds sown in bare plots producing a seedling. Also, seedlings did not survive past 1 yr, except in bare plots or in plots where vegetation grew sparsely. However, seedlings that did survive began producing multiple stems within 6 mo of emergence. These results indicate that obstacles to seedling emergence and poor development at the young seedling stage when vegetative cover is dense severely limit C. vitalba’s chances to invade new sites via seed. Yet some successful seedling recruitment does occur due to the magnitude of the propagule pressure on the landscape and the difficulty of maintaining high-density ground cover across large areas throughout the year.

A systematic review of nurse objects as safe sites for seedling establishment and implications for restoration.

Direct human activity and global climatic changes are threatening the existence of many vegetated habitats. Seedling establishment, one of the riskiest plant life stages, must be successful for such habitats to persist. The establishment of seedlings is known to be enhanced by nurse effects, but most studies to date have looked at the nursing effects of plants while sidelining inanimate objects. Nevertheless, nurse objects can support seedling establishment via diverse mechanisms such as moderating abiotic stresses like extreme temperatures and drought, reducing negative biological interactions such as herbivory while enhancing positive processes like seed dispersal, and providing protection from physical disturbances such as trampling and fire. The robust nature of nurse objects highlights their potential in habitat restoration. The addition of nurse objects allows a simple, single-effort rehabilitation strategy that can later draw on natural seed dispersal and establishment. By achieving a better understanding of the processes in which nurse objects are involved we should be able to better predict vegetation dynamics and manipulate them to minimize adverse processes and support regeneration in natural habitats.

Determination of Median Lethal Dose and Effects of Gamma Radiation on Seed Germination in Viola cornuta L.

Effects of cobalt-60 gamma irradiation on seed germination and seedling survival of 7 cultivars of Viola cornuta L. were investigated. The results revealed that low doses of gamma radiation at 100 Gray (Gy) significantly stimulated germination in ‘Deep Blue Blotch’ and ‘Clear Purple’ and slightly enhanced germination in ‘Clear Yellow’ and ‘Victoriana’. In contrast, higher doses (&gt; 400 Gy) significantly decreased germination across all cultivars. No germination was observed at 1,000 Gy in the ‘Deep Blue Blotch’ cultivar. Analysis of mean germination time (MGT) and coefficient of velocity of germination (CVG) showed delays in germination and decreased germination velocity with increasing irradiation dose. The seedling survival percentage also decreased with higher radiation doses, indicating sublethal effects on seedling establishment. The lethal dose for 50 % mortality (LD50) values ranged from 320 to 495 Gy for the Bel Viso series and from 430 to 640 Gy for the Grandissimo series. Our findings highlight the dose-dependent effects of gamma irradiation on seed germination and seedling survival and provide insights into irradiation tolerance and susceptibility among cultivars. Understanding these responses is crucial for optimizing irradiation-induced mutagenesis strategies and developing plant selection plans for crop improvement. HIGHLIGHTS Low cobalt-60 gamma radiation doses at 100 Gray (Gy) stimulated seed germination in Viola for ‘Victoriana’, ‘Deep Blue Blotch’, ‘Clear Yellow’ and ‘Clear Purple’ cultivars whereas higher doses (&gt; 400 Gy) decreased germination across all 7 cultivars. Mean germination time (MGT) increases and coefficient of velocity of germination (CVG) decreases with higher gamma radiation doses, indicating delayed and slower germination. Seedling survival percentages decline significantly with increasing radiation dose, highlighting sublethal effects on seedling development. GRAPHICAL ABSTRACT

Will climate change constrain the altitudinal range of threatened species? Experimental evidence from a biodiversity hotspot.

A fundamental goal in ecology and evolution is to explain the factors that shape species' abundance and range limits. Evaluating the performance of early life-stages across an altitudinal gradient can be valuable for understanding what factors shape range limits and for predicting how plant species may respond to climate change. To experimentally evaluate the presence of local adaptation in a threatened palm (Euterpe edulis) at early life-stages, we reciprocally sowed seeds at two contrasting elevations. In addition, to evaluate the effect of seed predation on E. edulis seed germination and seedling establishment, seed addition experiments were conducted at three different elevations. Our results showed no evidence of local adaptation in the early life-stages for the two E. edulis populations. We observed lower germination and seedling performance of both E. edulis populations at the low-elevation site. The exclusion of seed predation increased seedling establishment across all elevations. Seed predation and dry soil conditions were the main factors that constrained seedling establishment at the upper altitudinal limit and at the lower elevation, respectively. Climate change in the study area will result in warmer and drier environmental conditions. The lack of local adaptation and the lower performance of both E. edulis populations in warm and dry conditions, combined with a higher seed predation at the upper altitudinal limit, might cause an altitudinal range contraction, increasing the vulnerability of this threatened species to climate change.