Influence Seedling Establishment Research Articles

Impact of salvage logging on short-term natural regeneration in montane forests of the Alps after large windthrow events

Wind disturbances are one of the main drivers of forest dynamics in Europe, shaping forest stands and modifying the ecosystem services provisioning. Salvage logging is often most common strategy adopted after a high-severity disturbance in managed stands. Understanding natural regeneration dynamics including their interaction with the logging operations, is crucial to understand how forests will be changing under a climate with increasing variability and to design adequate adaptive post-disturbance management strategies. In this study, we focused on 148 stands damaged by storm Vaia (2018). The aim was to analyze natural regeneration dynamics under different logging systems and to investigate influences of site characteristics and disturbance legacies on sapling growth and seedling emergence. The sampling protocol consisted of one transect per stand, perpendicular to one of the intact forest edges, and with a length of 80 m. Along the transect, we collected soil cover, natural seedling and sapling stem density, and deadwood quantity in four sample plots of 3 m radius each at distances of 0, 20, 40, and 80 meters from the edge (592 plots in total). Regeneration species composition was mainly driven by previous stand composition, with some exceptions depending on seed dispersal strategy. Distance from the edge significantly influenced seedlings and saplings occurrence in large gaps and affected the browsing damage percentage, together with deadwood presence. According to GLM’s models, distance from the edge, elevation, and logging methods influenced seedling establishment. At the same time, species characteristics, edge structure, deadwood and logging damages significantly influenced pre-storm seedlings and saplings presence and health. In conclusion site factors, disturbance legacies, and logging strategies are key points to consider in post-disturbance management for a fast forest recovery.

Seed physiological traits and environmental factors influence seedling establishment of vegetable soybean (Glycine max L.).

Edamame (Glycine max (L.) Merr.), a specialty soybean prized for its nutritional value and taste, has witnessed a surge in demand within the U.S. However, subpar seedling stands have hindered its production potential, necessitating increased inputs for farmers. This study aims to uncover potential physiological factors contributing to low seedling emergence in edamame. We conducted comprehensive assessments on thirteen prominent edamame genotypes alongside two food-grade and two grain-type soybean genotypes, focusing on germination and emergence speed in both laboratory and field settings. Additionally, we employed single electrical conductivity tests and identified and quantified seed leachate components to distinguish among soybean types. Furthermore, using a LabField™ simulation table, we examined seed emergence across a wide soil temperature range (5°C to 45°C) for edamame and other soybean types. All seeds were produced under the same environmental conditions, harvested in Fall 2020, and stored under uniform conditions to minimize quality variations. Our findings revealed minimal divergence in emergence percentages among the seventeen genotypes, with over 95% germination and emergence in laboratory conditions and over 70% emergence in the field. Nonetheless, edamame genotypes typically exhibited slower germination speeds and higher leachate exudates containing higher soluble sugars and amino acids. Seed size did not significantly impact total emergence but was negatively correlated with germination and emergence speed, although this effect could be mitigated under complex field conditions. Furthermore, this study proposed differences that distinguish edamame from other soybean types regarding ideal and base temperatures, as well as thermal time. The finds offer valuable insights into edamame establishment, potentially paving the way for supporting local edamame production in the U.S.

N6-benzyladenine (BAP)-Based Seed Preconditioning Enhances the Shoot Regeneration of Seedling-Derived Explants for Subsequent Indirect Gene Transfer in Soybeans (Glycine max [L.] Merrill.)

This study evaluated the effects of N6-benzyladenine (BAP) seed preconditioning and seedling-derived explants on in vitro plant regeneration potential in soybeans (Glycine max [L.] Merrill.). The findings showed that seed preconditioning with 2.55 mg/L BAP prior to germination significantly influenced seedling establishment and the development of shoots, shoot elongation, and rooting on MS media supplemented with BAP and TDZ, compared to the negative (MS-NC) and positive (MS-NP) controls. The results also showed significant differences based on the genotypes, with Dundee recording 91.0% germination over a minimum of 5 days, compared to 74.2% with Peking, followed by 87.5% and 80.0% overall shoot induction frequency in these genotypes, respectively. Regenerated shoots were successfully elongated on MS medium supplemented with 0.5 mg/L BAP plus 0.6 mg/L GA3 and rooted on hormone-free medium, for 3‒4 weeks, and then hardened in the acclimatization growth room under elevated light levels. Overall, this study revealed that BAP preconditioning of seeds enhances the frequency of bud initiation and shoot proliferation, mostly in whole-seedling and cotyledonary node explants subcultured on MS-E and MS-A media supplemented with BAP in combination with TDZ.

Positive and negative plant−plant interactions influence seedling establishment at both high and low elevations

Deciphering how plants interact with each other across environmental gradients is important to understand plant community assembly, as well as potential future plant responses to environmental change. Plant−plant interactions are expected to shift from predominantly negative (i.e. competition) to predominantly positive (i.e. facilitation) along gradients of environmental severity. However, most experiments examine the net effects of interactions by growing plants in either the presence or absence of neighbours, thereby neglecting the interplay of both negative and positive effects acting simultaneously within communities. To partially unravel these effects, we tested how the seedling establishment of 10 mountain grassland plants varied in the presence versus absence of plant communities at two sites along an elevation gradient. We created a third experimental treatment (using plastic plant mats to mimic surrounding vegetation) that retained the main hypothesised benefits of plant neighbours (microsite amelioration), while reducing a key negative effect (competition for soil resources). In contrast to our expectations, we found evidence for net positive effects of vegetation at the low elevation site, and net negative effects at the high elevation site. Interestingly, the negative effects of plant neighbours at high elevation were driven by high establishment rates of low elevation grasses in bare soil plots. At both sites, establishment rates were highest in artificial vegetation (after excluding two low elevation grasses at the high elevation site), indicating that positive effects of above-ground vegetation are partially offset by their negative effects. Our results demonstrate that both competition and facilitation act jointly to affect community structure across environmental gradients, while emphasising that competition can be strong also at higher elevations in temperate mountain regions. Consequently, plant−plant interactions are likely to influence the establishment of new, and persistence of resident, species in mountain plant communities as environments change.

Consumers and nutrients alter colonization of an old field community independently and by distinct mechanisms

Abstract As communities assemble, species establishment can be driven by multiple factors. Two such factors, nutrients and consumers, are predicted to interact, but few studies have explored whether this interaction results from synergistically altering the same biotic and abiotic mediators or complementarily altering different mediators. To test this, I added seeds of multiple native species to old field communities in which I experimentally manipulated soil nutrients, leaf litter and consumers (insect herbivores and fungal pathogens). Using Bayesian hierarchical modelling, I evaluated the degree to which changes in light and water availability, fungal disease and insect herbivory, and community functional composition influenced seedling establishment and the richness of colonizing species and were driven by experimental treatments. I then examined whether nutrients, litter and consumers interactively determined the success of colonizing species with different resource allocation strategies. Contrary to expectation, nutrient addition and consumer exclusion reduced, and litter removal increased, seedling establishment and colonizer richness independently and via different pathways. Also contrary to expectation, seedling resource allocation strategy did not interact with nutrient addition and consumer exclusion to alter establishment success. Rather, as community damage (foliar fungal disease + insect herbivory) increased, seedlings with high % leaf nitrogen (a proxy for an acquisitive resource allocation strategy) become increasingly disadvantaged relative to seedlings with low % leaf nitrogen (a proxy for a conservative resource allocation strategy). Synthesis: These results indicate that seedling establishment is unlikely to be interactively impacted by nutrients and consumers (fungal pathogens + insect herbivores) because these two drivers act on different environmental pathways to influence community assembly.

The effects of herbivory, land-use and climate change on seedling establishment in southern Africa

In intact ecosystems, factors such as herbivory and light and water availability affect seedling establishment. Land-use change and climate change are now affecting forests globally, influencing seedling establishment directly via changes in light availability and precipitation and indirectly by affecting herbivory. The present study evaluated the ecological complexity of seedling establishment in response to interactions between these factors. The growth and survival of a pioneer species and two later successional species were measured in a factorial experiment testing the effects of land-use change, water availability, and herbivory. The study was conducted on Mt. Gorongosa in central Mozambique, a protected area that is experiencing high levels of land-use change and is in need of forest restoration. The pioneer species, Erythrina lysistemon, gained the most height in undisturbed, shaded environments where it invested resources in accessing light. Erythrina lysistemon grew the most in diameter in open areas. Khaya anthotheca, a later successional species, gained more biomass in disturbed, high light areas. The growth of Millettia stuhlmannii, another later successional species, was not affected by light. Drought conditions reduced survival of the later successional species, while flooding limited the survival of the pioneer species. Herbivory increased in disturbed areas and was negatively correlated with E. lysistemon root biomass. In summary, this study indicates land-use change and climate change may alter seedling establishment and community composition. Restoration efforts should focus on increasing seedling survival because although survival is limited in disturbed sites, seedlings that do survive grow successfully.

Reviving Mung Bean Seeds: The Impact of Hydro Priming and Heat Shock on Germination Rates

Seed germination is a crucial stage of plant growth that can enhance yield by influencing seedling establishment. The speed and success of germination are key factors that determine the final yield of plants. This research aimed to investigate how hydro priming and heat shock affect the germination properties of green mung bean through a factorial experiment conducted in a completely randomized design with three replications at Parwan University's agronomic laboratory in 2022. The experimental treatments consisted of two temperature levels (35 and 25°C) and three moisture levels (8.5%, 10%, and 11.5%), with four categories of treatment: hydro prim, 30°C shock, 40°C shock, and control. Germination percentage, germination speed, seedling length, and dry weight were measured in the experiment. The results indicated that the triple interaction of temperature, moisture, and treatment was significant only for the germination speed trait at a 5% level. The main effect of temperature and the dual interaction of moisture and treatment at a 1% level were significant for stem length and dry weight. Additionally, the dual interaction between temperature, treatment, and temperature moisture level of 1 and 5% were significant for germination percentage, respectively. Moreover, the study found that hydro priming and thermal flushing treatment frequently improved seed storage capacity. Therefore, the study suggests that hydro priming and heat shock treatments can enhance seed germination and vigor, especially for seed lots stored under unfavorable conditions.

Seed Traits Research Is on the Rise: A Bibliometric Analysis from 1991–2020

Seed traits (ST) influence seedling establishment, population dynamics, community composition and ecosystem function and reflect the adaptability of plants and the environmental conditions they experienced. There has been a historical and global accumulation of studies on ST, but with few pertaining to visual and quantitative analyses. To understand the trends in the field of ST research in the past 30 years, we conducted a bibliometric analysis based on the Science Citation Index-Expanded (SCI-E) database. The analysis provided annual publications, time trends for keywords, the most productive journals, authors, institutions and countries, and a comprehensive overview of the ST field. Our results showed that in the past 30 years, the number of publications in ST research has increased at an average annual growth rate of 9.1%, while the average number of citations per paper per year showed a rapid increase–slow increase–decrease trend. Keyword analysis showed that “germination” was the most popular research section. Crop Science ranked first among the top journals and Theoretical and Applied Genetics had greater influence in this area and more citations than other journals. The 10 most productive institutions were mostly located in the United States, China and Australia. Furthermore, the three countries also had the largest number of publications and citations. Our analysis showed that the research interests in ST have evolved from genetics and agricultural science to ecological research over the last thirty years; as more fields embrace ST research, there are opportunities for international and interdisciplinary collaborations, cooperative institutions and new advances in the field.

Seed and seedling predation by vertebrates mediates the effects of adult trees in two temperate tree species.

Specialised natural enemies can locally suppress seeds and seedlings near conspecific adults more than far from them. Whilst this is thought to facilitate species coexistence, the relative contribution of multiple enemies to whether heterospecific seeds and seedlings rather than conspecifics perform better beneath a particular adult species remains less clear, especially in regions with spatially extensive monodominant stands. We designed a field exclusion experiment to separate the effects of fungi, insects and vertebrates on the seedling establishment and early survival of two temperate tree species, Fagus sylvatica and Picea abies, in the adult tree monocultures of these species. Our experiment demonstrates the key role of vertebrates in mediating the effects of adult trees on seeds and seedlings. Due to vertebrates and partly insects, Fagus sylvatica seedlings survived worse beneath conspecific than heterospecific adults and were also outperformed by Picea abies seedlings beneath their own adults. Picea abies seedling establishment was higher beneath conspecific than heterospecific adults, but Fagus sylvatica seedlings outperformed them beneath their own adults. The impact of enemies onPicea abiesestablishment beneath conspecific adults was less clear. Fungi did not influence seedling establishment and survival. Our findings highlight the need to compare enemy impacts on each seedling species beneath conspecific and heterospecific adults with their impacts on conspecific and heterospecific seedlings beneath a particular adult species. Such evaluations can shed more light on the role of enemies in tree communities by identifying the plant-enemy interactions that facilitate species coexistence and those that promote species monodominance.

24-epibrassinolide confers tolerance against deep-seeding stress in Zea mays L. coleoptile development by phytohormones signaling transduction and their interaction network

ABSTRACT Coleoptile/mesocotyl elongation influence seedling emergence and establishment, is major causes of maize deep-seeding tolerance (DST). Detailed analyses on molecular basis underlying their elongation mediated by brassinosteroid under deep-seeding stress (DSS) could provide meaningful information for key factors controlling their elongation. Here we monitored transcriptome and phytohormones changes specifically in elongating coleoptile/mesocotyl in response to DSS and 24-epibrassinolide (EBR)-signaling. Phenotypically, contrasting maize evolved variant organs to positively respond to DST, longer coleoptile/mesocoty of K12/W64A was a desirable organ for seedling under DSS. Applied-EBR improved maize DST, and their coleoptiles/mesocotyls were further elongated. 15,607/20,491 differentially expressed genes (DEGs) were identified in W64A/K12 coleoptile, KEGG analysis showed plant hormone signal transduction, starch and sucrose metabolism, valine, leucine, and isoleucine degradation were critical processes of coleoptile elongation under DSS and EBR signaling, further highly interconnected network maps including 79/142 DEGs for phytohormones were generated. Consistent with these DEGs expression, interactions, and transport, IAA, GA3, ABA, and Cis-ZT were significantly reduced while EBR, Trans-ZT, JA, and SA were clearly increased in coleoptile under DSS and EBR-signaling. These results enrich our knowledge about the genes and phytohormones regulating coleoptile elongation in maize, and help improve future studies on corresponding genes and develop varieties with DST.

Biogeomorphological processes and structures facilitate seedling establishment and distribution of annual plants: Implications for coastal restoration

Biogeomorphological processes and structures (BPS) can affect plant growth and community structure and promote landscape complexity in ecosystems. However, there is a lack of understanding of how BPS facilitates seedling establishment and distribution of annual plants and promotes the success of coastal restoration. We studied the relationships between seedling establishment of a native annual plant species (Suaeda salsa) and BPS resulting from crabs and plants in a middle elevation salt marsh with moderate tides (where inhabited generally high density of plants and crabs) in the Yellow River Delta of China. While there were many crabs but fewer plants in lower elevation areas with more frequent and stronger tides; and in higher elevation areas with weaker tides there were both fewer crabs and plants. Investigations and field manipulation experiments of microtopography, crabs and plants were conducted to determine if and how these BPS influenced seedling establishment and distribution under tidal influence in the middle elevation salt marshes. Results demonstrated that biogeomorphological structures, mainly concave hollows generated by crab burrowing and concave hollows around plant roots and stems under tidal influence, were associated with the trapping of seeds and influenced the establishment and distribution of seedlings. Additionally, upon senescence, maternal plants with unreleased seeds lodged on the ground and influenced seed retention and seedling establishment. The artificial concave hollows that were created experimentally also trapped many seeds and facilitated seedling establishment. Experimental plantings and creation of artificial hollow microtopography attracted crabs that created burrows, resulting in a positive feedback on seedling establishment. We used information obtained from the experimental component of the study to conduct a hollow microtopography manipulation to successfully restore degraded salt marshes. Understanding the associations between seedling establishment and biogeomorphological processes provides important insights for the utilization of natural or human ecosystem engineering to restore coastal vegetation ecosystems.

The role of sexual reproduction in the maintenance of established Zostera marina meadows

Abstract For clonal plants, the role of sexual reproduction in the maintenance of populations can vary widely. Some species are dependent on repeated seedling recruitment. For other species, interactions between adults and seedlings within existing populations can affect seedling survival and limit sexual reproduction in existing populations. Genetic studies of seagrass populations increasingly suggest sexual reproduction is important for the resilience and stability of their populations, but as of yet little observational data support these findings. Because seagrass populations provide important ecosystem services and are threatened with increasing anthropogenic impacts, understanding their reliance on sexual reproduction is evolutionarily and ecologically important. The goals of this study were to determine (a) whether seedlings of a marine angiosperm, Zostera marina, establish and recruit within existing Z. marina meadows and (b) whether interactions between seedlings and surrounding adult shoots influence the survival of established seedlings. To meet these goals, surveys estimated seedling establishment and tracked seedling survival within multiple populations. Manipulative experiments then tested the impact of neighbouring adult shoots on seedling survival and the overall trajectory of experimental plots with and without sexual reproduction. A 3‐year survey identified established seedlings within Z. marina meadows each year. Additionally, concurrent seed addition experiments indicated seed supply could influence seedling establishment rates. A survey tracking the survival of tagged seedlings, as well as the height and density of surrounding adult shoots, showed adult shoots may negatively impact seedling survival. Experiments then demonstrated that seedlings without neighbouring shoots survived longer than those with neighbouring shoots. Lastly, two transplant garden experiments comparing the survival of plots with and without seeds highlighted that seedling recruitment is likely most important to maintain bottom cover where disturbances generate gaps in the adult population. Synthesis. This study demonstrates that seedlings do establish within existing seagrass meadows, and that some survive to recruit into the adult population. Competition with existing vegetation, however, can be a factor compromising seedling survival. Sexual reproduction may thus most likely occur in, and be most important for, clonal plant populations that experience seasonal disturbance.

Effects of Soil Microbes on Functional Traits of Loblolly Pine (Pinus taeda) Seedling Families From Contrasting Climates.

Examining factors that influence seedling establishment is essential for predicting the impacts of climate change on tree species’ distributions. Seedlings originating from contrasting climates differentially express functional traits related to water and nutrient uptake and drought resistance that reflect their climate of origin and influence their responses to drought. Soil microbes may improve seedling establishment because they can enhance water and nutrient uptake and drought resistance. However, the relative influence of soil microbes on the expression of these functional traits between seedling families or populations from contrasting climates is unknown. To determine if soil microbes may differentially alter functional traits to enhance water and nutrient uptake and drought resistance between dry and wet families, seeds of loblolly pine families from the driest and wettest ends of its geographic range (dry, wet) were planted in sterilized sand (controls) or in sterilized sand inoculated with a soil microbial community (inoculated). Functional traits related to seedling establishment (germination), water and nutrient uptake and C allocation (root:shoot biomass ratio, root exudate concentration, leaf C:N, leaf N isotope composition (δ15N)), and drought resistance (turgor loss point, leaf carbon isotope composition (δ13C)) were measured. Then, plants were exposed to a drought treatment and possible shifts in photosynthetic performance were monitored using chlorophyll fluorescence. Inoculated plants exhibited significantly greater germination than controls regardless of family. The inoculation treatment significantly increased root:shoot biomass ratio in the wet family but not in the dry family, suggesting soil microbes alter functional traits that improve water and nutrient uptake more so in a family originating from a wetter climate than in a family originating from a drier climate. Microbial effects on photosynthetic performance during drought also differed between families, as photosynthetic performance of the dry inoculated group declined fastest. Regardless of treatment, the dry family exhibited a greater root:shoot biomass ratio, root exudate concentration, and leaf δ15N than the wet family. This indicates that the dry family allocated more resources belowground than the wet and the two family may have used different sources of plant available N, which may be related to their contrasting climates of origin and influence their drought resistance. Examination of variation in impacts of soil microbes on seedling physiology improves efforts to enhance seedling establishment and beneficial plant-microbe interactions under climate change.

Bacterial communities differ between plant species and soil type, and differentially influence seedling establishment on serpentine soils

Root-associated microbial communities influence plant phenotype, growth and local abundance, yet the factors that structure these microbial communities are still poorly understood. California landscapes contain serpentine soils, which are nutrient-poor and high in heavy metals, and distinct from neighboring soils making them ideal for studying the factors that structure root microbiomes and their functions. Here, we surveyed the rhizoplane of serpentine-indifferent plants, which grow on and off serpentine soil, to determine the relative influence of plant identity and soil chemistry on rhizoplane microbial community structure using 16S rRNA metabarcoding. Additionally, we experimentally examined if serpentine vs. non-serpentine microorganisms differentially affected plant growth in serpentine soil. Rhizoplane bacterial communities differed among plant species, soil types, and the interaction between them in both the field and experimental soils. In the experiment, soil microbial community source influenced seedling survival, but plant growth phenotypes were largely invariant to microbial community with a few exceptions. Rhizosplane bacterial species composition differed between plant species and soil types, and Amplicon Sequence Variants (ASVs) from the phyla Acidobacteria and Proteobacteria (Genus: Microvirga) were characteristic of serpentine soils. While soil microbial community composition influenced seedling survival in the current study, further study is required to disentangle the role of microbial associations and plant tolerance to serpentine.

Topography regulates edaphic suitability for seedling establishment associated with tidal elevation in coastal salt marshes

Spatial patterns of seedling establishment have been shown to be greatly affected by topographic heterogeneity. Addressing the effect of different topographic structures on seedling establishment is critical for understanding the complexity and variation of plant distribution and dynamics in coastal salt marshes. However, it is far from clear how species populations respond to differences in topography at different tidal zones. Here, we conducted an extensive survey across tidal zones to identify associations between abundance of the halophyte species Suaeda salsa (L.) Pall. with topographic heterogeneity. Furthermore, we manipulated topographic structures to produce flat, hollow and hummock surfaces, to explore the mechanism of responses of seedling establishment to topography across tidal zones. Our results showed that topographic differences of only a few centimeters were enough to influence seedling establishment by affecting seed retention and post-retention soil conditions. The hollow surfaces trapped more seeds than did flat or hummock surfaces in high-elevation marsh and supratidal zones. Under frequent inundation by tides in low-elevation marsh, the flat surfaces had the most favorable conditions for seed anchorage. Differences in duration of tidal water retention caused by topography resulted in different soil conditions. One explanation for the low seedling emergence of S. salsa in hollows in low- and middle-elevation marsh zones was that the lack of oxygen penetration into the soil in the hollows inhibited survival of seedlings, while hummocks and flat surfaces in supratidal zones was against inundated conditions, increasing the drought and salinity stresses on seed germination. Our results suggested that increased heterogeneous topography facilitated halophyte establishment in salt marshes, and that the structure of topography most suitable for seedling establishment differed among the various marsh zones. Hollows in high-elevation marsh and supratidal zones, or flat surfaces and hummocks in low- and middle-elevation marsh zones provided better habitats for S. salsa seedlings, providing important information with which to design and build heterogeneous topography to achieve successful halophyte establishment in plant restoration exercises.

Determinants and correlates of above-ground biomass in a secondary hillside rainforest in Central Vietnam

Despite inception of carbon-conservation forestry programs, information about total above-ground woody biomass (TAGB) in Vietnamese secondary lowland rainforests is still scarce. We elucidated major factors influencing local variation of TAGB within an anthropogenically modified hillside forest in Thừa Thien-Huế Province. On forty 400 m2 sized plots all tree species were recorded, and their biomass was calculated using allometric equations. In addition, bio-physical parameters relating to terrain and soils were measured. Effects of bio-physical variables on forest TAGB were assessed using multivariate regression methods. Forest TAGB (average 117 Mg ha−1) was primarily explained by forest structural variables, i.e. tree densities and average heights, in particular presence of large trees. TAGB was largely determined by the biomass of a few species which dominated different forest parts (ridges or hill base); TAGB was hardly influenced by species diversity. Many dominant trees were light-demanding species; these were characterised by scarce rejuvenation and high tree mortality. Bio-physical patterns indicated that previous logging impacts persisted and continued to influence seedling establishment, sapling growth/survival, and—ultimately—species composition. Nutrient patterns were mostly explained by interactions with certain tree species and tree foliage cover, as modulated by terrain and logging impacts. Development trajectories of TAGB over the next 10–20 years could not be predicted easily since (1) many functionally important late-succession species (e.g. dipterocarps) were very scarce; (2) the sizes of initially established light-demanding species appeared to meet limits, including increasing tree mortality; and (3) rejuvenation and species succession differed locally and proceeded along largely unpredictable pathways. Some suggestions for further research are made.

Mechanisms of influence of invasive grass litter on germination and growth of coexisting species in California

In grasslands, litter has been recognized as an important factor promoting grass persistence and the suppression of forbs. The invasive European annual grass Bromus diandrus (ripgut brome) is widespread throughout California, where it produces a persistent and thick litter layer. The native grass, Stipa pulchra, is also common in some grassland settings and can also produce persistent litter, yet it is typically associated with more forbs. Very little is known about the mechanisms through which these two common grass species influence seedling establishment of both exotic invasive and native herbs. Here, we evaluated the effect of B. diandrus and S. pulchra litter on seedling establishment of two invasive (the grass B. diandrus and the forb Centaurea melitensis) and two native (the grass S. pulchra, and the forb Clarkia purpurea) herbaceous plants in a greenhouse setting. Our results showed that B. diandrus litter cover hindered seedling establishment of the four species tested, but that the degree and mechanism of inhibition was dependent on which species was tested, life form (e.g. monocot/dicot) and seed size. Seedling emergence of the two forb species was more vulnerable to litter cover than either grass species and both forbs had smaller seed size. After germination, only seedling biomass of B. diandrus itself was reduced by litter (both B. diandrus and S. pulchra). We found no significant effects of leachate of either grass species on seedling emergence of any species, while a high concentration of B. diandrus leachates inhibited root growth of all species including B. diandrus seedlings. Stipa pulchra litter leachates did not affect S. pulchra or C. melitensis seedlings although it did suppress B. diandrus and C. purpurea seedling growth. Our findings provide direct experimental evidence for the mechanism of effect of litter on these coexisting invasive and native species. Such evidence helps advance our understanding of role of B. diandrus and S. pulchra litter in California grassland.

Regeneration processes on coarse woody debris in mixed forests: do tree germinants and seedlings have species‐specific responses when grown on coarse woody debris?

Summary Tree regeneration on coarse woody debris (CWD) is considered to be one the most ecologically valuable aspects of CWD in forest systems. However, most studies have focused solely on uncovering the differences in establishment and growth on CWD (regarded as a homogeneous substrate) in comparison with the forest floor. Our study concentrates on the underlying mechanisms of germinant and seedling colonization patterns and demographic responses relative to various properties of CWD. We analysed the effects of CWD properties (decay class, form, species and diameter) on: (i) germinant and seedling annual counts; (ii) annual germinant and seedling survival; and (iii) seedling growth and height. Our study comprised three species (beech, fir and spruce) over 7‐year span in two old‐growth stands in the Western Carpathians, and employed generalized linear models and mixed models to test for differences between species. CWD properties affected regeneration at the germination stage. There were some demographic differences between species relative to CWD properties. Decay class had the most pronounced effect on beech, not only on its establishment but also survival and growth. Beech and spruce established and survived in higher densities on beech CWD, while their height growth was enhanced on conifer‐derived CWD, particularly on spruce CWD. Stumps enhanced establishment of all species and survival of conifer seedlings. Synthesis. Our study shows that CWD properties do influence seedling establishment, growth, height distribution and survival. Moreover, there may be trade‐offs between seedling growth and survival among tree species growing on different species of CWD. This highlights the need to include CWD heterogeneity as a factor that can affect the role of CWD in regeneration in forest ecosystems.

Light availability drives tree seedling success in a subtropical coastal dune forest in South Africa

In subtropical coastal dune forests of South Africa, the microenvironment of tree seedlings is largely influenced by a pervasive understorey woody herb, Isoglossa woodii. We examined whether the additional shading by I. woodii explains the competitive response of tree seedlings from these forests. Seedlings of four common mid- to late-successional tree species (Diospyros natalensis, Euclea racemosa, Sideroxylon inerme and Apodytes dimidiata) were grown at three densities of I. woodii in a common garden experiment under greenhouse conditions. The seedlings were grown at 1.6% and 13.5% of full sunlight and supplied with 1% and 10% nitrogen in half-strength Hoagland's nutrient solution. Total biomass and biomass allocation parameters were used to measure the competitive response of the seedlings. Seedlings attained maximum biomass at high light and high nutrient levels and showed species- and light-specific responses to biomass of I. woodii neighbours. Seedlings' allocation to roots increased with increasing light levels but decreased at higher nutrient levels. The leaf mass fraction (LMF) response to light and nutrient levels was opposite to that shown by root allocation. Specific leaf area (SLA) and leaf area ratio (LAR) decreased with increasing light conditions but were not responsive to manipulation of nutrients. The presence of I. woodii neighbours reduced LMF whilst the responses of SLA to neighbours depended on the light level and species. Leaf trait responses to manipulation of light conditions, I. woodii neighbour density and soil nutrient concentration are complex but overall demonstrate an overwhelming role of light in influencing seedling establishment in coastal dune forests. The competitive response of these seedlings to low irradiance reiterates the notion of phenotypic clustering at the seedling stage amongst shade tolerant tree species, which promotes seedling persistence and gradual transition into the tree layer. Our results highlight the role of additional understorey shading by the herb stratum in influencing tree recruitment dynamics and ultimately tree community structure in many of Africa's tropical lowland forests.

Above- and below-ground effects of plant diversity depend on species origin: an experimental test with multiple invaders.

Although many plant communities are invaded by multiple nonnative species, we have limited information on how a species' origin affects ecosystem function. We tested how differences in species richness and origin affect productivity and seedling establishment. We created phylogenetically paired native and nonnative plant communities in a glasshouse experiment to test diversity-productivity relationships and responsible mechanisms (i.e. selection or complementarity effects). Additionally, we tested how productivity and associated mechanisms influenced seedling establishment. We used diversity-interaction models to describe how species' interactions influenced diversity-productivity relationships. Communities with more species had higher total biomass than did monoculture communities, but native and nonnative communities diverged in root:shoot ratios and the mechanism responsible for increased productivity: positive selection effect in nonnative communities and positive complementarity effect in native communities. Seedling establishment was 46% lower in nonnative than in native communities and was correlated with the average selection effect. Interspecific interactions contributed to productivity patterns, but the specific types of interactions differed between native and nonnative communities. These results reinforce findings that the diversity-productivity mechanisms in native and nonnative communities differ and are the first to show that these mechanisms can influence seedling establishment and that different types of interactions influence diversity-productivity relationships.