Facilitate Seedling Establishment Research Articles

Drainage-Improved Sediment Strength Enhances Saltmarsh Seedling Establishment Chance

Identify critical factors driving seedling establishment is essential for saltmarsh restoration. Recent studies highlight drainage can facilitate seedling establishment for different saltmarsh species, yet the underling mechanism remains largely unknown. By a manipulative mesocosm experiment with contrasting sediment drainage treatments, we investigated the impacts of drainage onSpartina anglicaseedlings survival, growth and stability. Surprisingly, neitherS. anglicaseedling survival nor seedling growth were observed to be directly promoted by well drained treatment. However, the critical erosion depth (maximum erosion tolerance) ofS. anglicaseedlings was found to positively correlate with seedling root length. Measurements on the sediment properties revealed that drainage increased the critical shear strength of sediments with lower water content and higher dry bulk density. These findings indicate that, by dewatering, drainage aids to sediment consolidation and critical shear strength, and thereby facilitate seedling establishment in tempering sediment dynamics. The latter is supported by a field study, in which we found that the magnitude of the sediment dynamics on two tidal flats were positively related to water content of sediment. Overall, present study suggests that drainage could be a key factor that determines seedling stability during the critical windows of opportunity for seedling establishment, and that it could be integrated into future designs for saltmarsh restoration to enhance establishment success.

Spatial distribution of spore banks of ectomycorrhizal fungus, Rhizopogon togasawarius, at Pseudotsuga japonica forest boundaries

ABSTRACT Ectomycorrhizal (EcM) fungal spore banks can facilitate seedling establishment where compatible host tree species are absent. Although Rhizopogon togasawarius spore banks play an important role in the early establishment stage of endangered Japanese Douglas-fir (Pseudotsuga japonica) seedlings, the dispersal ecology of this EcM fungus is poorly understood. The objective of this study was to clarify the spatial distribution and dispersal distance of R. togasawarius spore banks that extend inside and outside extant P. japonica forests. We evaluated R. togasawarius spore banks in five remnant forests and neighboring arbuscular mycorrhizal artificial plantations using Douglas-fir (P. menziesii) seedling bioassays. Forty-five to ninety-five surface soils were collected along lines of increasing distance from P. japonica forests to neighboring plantations. In each forest, 60%–84% of the soils collected inside or within 50 m of forest boundaries of P. japonica forests harbored R. togasawarius spore banks. The occurrence of R. togasawarius decreased significantly with increasing distance from the forest boundaries. Moreover, R. togasawarius was detected in samples several hundred meters away from forest boundaries. These results suggest that R. togasawarius has a dispersal capacity to extend the range of the spore banks outside the forest of host trees.

Directed endozoochorous dispersal by scavengers facilitate sexual reproduction in otherwise clonal plants at cadaver sites.

The regeneration niche of many plant species involves spatially and temporally unpredictable disturbances, called recruitment windows of opportunity. However, even species with clear dispersal adaptations such as fleshy berries may not successfully reach such elusive regeneration microsites. Ericaceous, berry‐producing species in the northern hemisphere demonstrate this dispersal limitation. They are said to display a reproductive paradox owing to their lack of regeneration in apparently suitable microsites despite considerable investment in producing large quantities of berries.Cadavers generate vegetation‐denuded and nutrient‐rich disturbances termed cadaver decomposition islands (CDIs). Cadavers attract facultative scavengers with considerable capacity for endozoochorous seed dispersal. We hypothesize that CDIs facilitate recruitment in berry‐producing ericaceous species due to endozoochorous dispersal directed toward favorable microsites with low competition.We examined seedling establishment within a permanent, semi‐regular 10 × 10 m grid across an ungulate mass die‐off on the Hardangervidda plateau in southeastern Norway. Competing models regarding the relative importance of factors governing recruitment were evaluated, specifically cadaver location (elevated seed rain) and microsite conditions (competition).We found that CDIs did facilitate seedling establishment, as cadaver density was the best predictor of seedling distribution. Other important factors governing seedling establishment such as percentage cover of soil and vascular plants alone were inadequate to explain seedling establishment. Synthesis: This study provides a novel understanding of sexual reproduction in species with cryptic generative reproduction. The directed nature of endozoochorous dispersal combined with long‐distance dispersal abilities of medium to large vertebrate scavengers toward cadavers allows plants to exploit the advantageous but ephemeral resource provided by CDIs.

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.

Which generative reproduction characteristics determine successful establishment of the subalpine shrub Pinus mugo?

AbstractQuestionsShrub expansion in arctic, alpine and subalpine areas has been occurring recently due to warming, land abandonment and increasing nitrogen deposition. However, shrub expansion is strongly affected by largely unknown site‐specific regeneration patterns. We evaluated the importance of seed production, suitable microsite availability and seedling survival for seedling establishment of the subalpine conifer shrub Pinus mugo.LocationHrubý Jeseník Mts., Czech Republic (50° N, 17° E).MethodsWe collected data on: (a) seed quantity and quality; (b) seedling microsite preferences; and (c) seedling survival during initial ontogenetic stages. From 2006 to 2016 we assessed cone production annually and tested seed viability every second year. Microsite preferences were analyzed for 650 seedlings at six sites. The following microsite characteristics were recorded for 1‐m2 around each seedling: percentage of bare surface; surrounding plant species cover; surface shape; and organic horizon thickness. Additionally, distance and direction to the nearest adult pine were recorded. Finally, we tested survival of 200 newly established seedlings in relation to microsite type.ResultsSeed source and viability were not critical factors for seedling establishment. Far more important was the presence of suitable bare‐surface microhabitats with thin or no organic layer near mature pine stands. Vegetation communities dominated by Avenella flexuosa and Nardus stricta facilitated seedling establishment; communities dominated by Vaccinium myrtillus showed strong competitive effects on seedlings. Vegetation's effect on seedling establishment was closely related to disturbance regime, which influences vegetation type. Seedling mortality was highest in the first year of life irrespective of microsite vegetation type. Highest mortality was associated with open mineral‐soil microsites, while microsites with dense herbaceous vegetation showed the lowest.ConclusionsPotential Pinus mugo expansion will occur in close proximity to existing mature stands, and its intensity will be strongly modified by site‐specific density of suitable microsites and/or dominant species of host communities.

Does slow and steady win the race? Root growth dynamics of Arabidopsis halleri ecotypes in soils with varying trace metal element contamination

Hyperaccumulating plants possess complex traits, allowing them to thrive in soils with high concentrations of trace metal elements (TME). Accordingly, their TME hypertolerance and hyperaccumulation capacities have been intensely studied from physiological, evolutionary, and ecological perspectives. Little is known, however, about their root system development in TME enriched vs natural soils. We assessed temporal and quantitative changes in root systems of the model species Arabidopsis halleri, using a novel combination of root phenotyping in rhizoboxes and multitemporal digital imaging. We continuously monitored root growth of two non-metallicolous and two metallicolous populations in different substrate treatments, including homogeneous and horizontal layer applications of metalliferous and non-metalliferous soils. Non-metallicolous plants on non-metalliferous soils produced deep-reaching and wide roots, whereas metallicolous plants on metalliferous soil had smaller roots. This pattern was reversed when transplanting seedlings to foreign substrates, indicating that environment rather than ecotype determines root growth in A. halleri. Dampened root development in metalliferous and favored root proliferation in non-metalliferous soils indicate cost of tolerance and TME foraging, respectively. Importantly, root propagation into metalliferous soil was strongly promoted by a non-metalliferous “capping” layer that facilitated initial plant development. Hence, growing on non-polluted substrate in the early stage provides plants with a robust and optimal root system that facilitates seedling establishment and subsequent development under TME enriched conditions. These findings improve our understanding of plant performance in metalliferous environments and can help refine management practices for the sustainable reclamation of degraded lands.

Arbuscular mycorrhizal symbiosis and achene mucilage have independent functions in seedling growth of a desert shrub

Arbuscular mycorrhizal (AM) symbiosis can play a role in improving seedling establishment in deserts, and it has been suggested that achene mucilage facilitates seedling establishment in sandy deserts and that mucilage biodegradation products may improve seedling growth. We aimed to determine if AM symbiosis interacts with achene mucilage in regulating seedling growth in sand dunes. Up to 20 A M fungal taxa colonized Artemisia sphaerocephala roots in the field, and mycorrhizal frequency and colonization intensity exhibited seasonal dynamics. In the greenhouse, total biomass of AM fungal-colonized plants decreased, whereas the root/shoot ratio increased. AM symbiosis resulted in increased concentrations of nutrients and chlorophyll and decreased concentrations of salicylic acid (SA) and abscisic acid (ABA). Achene mucilage had a weaker effect on biomass and on nutrient, chlorophyll, and phytohormone concentration than did AM symbiosis. We suggest that AM symbiosis and achene mucilage act independently in enhancing seedling establishment in sandy deserts.

SPATIAL DISTRIBUTION AND ASSOCIATION WITH NURSE PLANTS OF THE BISHOP'S MITER CACTUS ASTROPHYTUM MYRIOSTIGMA IN THE CHIHUAHUAN DESERT

Nurse-protege interactions facilitate seedling establishment of many cacti species and might promote spatial aggregation of plants. In June 2014, we analyzed the spatial distribution pattern with Ripley's K-function and the possible association of Astrophytum myriostigma with nurse plants in two populations (Rioverde and Pozas, San Luis Potosi, Mexico). We estimated canopy cover of perennial plant species with a logarithmic scale method and determined the association, size, and orientation of A. myriostigma in relation to nurse plants. Astrophytum myriostigma had an aggregated distribution pattern; approximately 50% were associated with nurse plants at Rioverde and 63% at Pozas, with Hechtia glomerata (Bromeliaceae) being the main nurse plant species in both populations. Cacti associated with nurse plants at Pozas were larger than those not associated, and they did not have any significant orientation in relation to the nurse plant crown. In contrast, the size of associated and nonassociated cacti at Rioverde was similar, but they were established significantly more frequently under the north side of the nurse plant. The association of A. myriostigma with nurse plants is facultative, through either nurse plant protection or open spaces, likely related with abiotic nurses. Understanding nurse plant associations will help target key species for conservation and identify the most likely associations to increase the survival of reintroduced individuals.

Above-Ground Dimensions and Acclimation Explain Variation in Drought Mortality of Scots Pine Seedlings from Various Provenances.

Seedling establishment is a critical part of the life cycle, thus seedling survival might be even more important for forest persistence under recent and future climate change. Scots pine forests have been disproportionally more affected by climate change triggered forest-dieback. Nevertheless, some Scots pine provenances might prove resilient to future drought events because of the species’ large distributional range, genetic diversity, and adaptation potential. However, there is a lack of knowledge on provenance-specific survival under severe drought events and on how acclimation alters survival rates in Scots pine seedlings. We therefore conducted two drought-induced mortality experiments with potted Scots pine seedlings in a greenhouse. In the first experiment, 760 three-year-old seedlings from 12 different provenances of the south-western distribution range were subjected to the same treatment followed by the mortality experiment in 2014. In the second experiment, we addressed the question of whether acclimation to re-occurring drought stress events and to elevated temperature might decrease mortality rates. Thus, 139 four-year-old seedlings from France, Germany, and Poland were subjected to different temperature regimes (2012–2014) and drought treatments (2013–2014) before the mortality experiment in 2015. Provenances clearly differed in their hazard of drought-induced mortality, which was only partly related to the climate of their origin. Drought acclimation decreased the hazard of drought-induced mortality. Above-ground dry weight and height were the main determinants for the hazard of mortality, i.e., heavier and taller seedlings were more prone to mortality. Consequently, Scots pine seedlings exhibit a considerable provenance-specific acclimation potential against drought mortality and the selection of suitable provenances might thus facilitate seedling establishment and the persistence of Scots pine forest.

毛乌素沙地优势灌丛对两种松树幼苗的保育作用

PDF HTML阅读 XML下载 导出引用 引用提醒 毛乌素沙地优势灌丛对两种松树幼苗的保育作用 DOI: 10.5846/stxb201505271061 作者: 作者单位: 陕西师范大学生命科学学院;榆林学院生命科学学院,陕西师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 陕西省教育厅专项科研计划资助项目（09JK839）；榆林市科技计划资助项目（2015CXY-03） Nurse effects of dominant shrubs on the seedlings of two Pinus species in the mu us sandy land in Northwest China Author: Affiliation: College of Life Sciences, Shaanxi Normal University;College of Life Sciences, Yulin University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:选择毛乌素沙地优势灌丛柠条（Caragana intermedia）、紫穗槐（Amorpha fruticosa）和沙柳（Salix psammophila）作为保育植物，选择2年生油松（Pinus tabulaeformis）和樟子松（Pinus sylvestris）幼苗作为目标植物，将其分别种植在开阔地、柠条、紫穗槐和沙柳4种微生境下，连续3a监测油松和樟子松幼苗的存活和生长动态，从而确定毛乌素沙地优势灌丛是否对植物幼苗的定居有促进作用。结果表明：柠条、紫穗槐和沙柳冠层下光照强度、大气温度和土壤温度都显著低于开阔地，致使土壤湿度增高，油松幼苗总存活率均显著高于开阔地，而樟子松幼苗总存活率仅紫穗槐冠层下显著高于开阔地（P < 0.05）。紫穗槐冠层下油松和樟子松幼苗总存活率均最高（P < 0.05），外来种紫穗槐可选为保育植物。保育灌丛下松树幼苗的主枝生长良好，并未受到抑制，但第1年主枝生长长度最小。光照强度和土壤湿度是决定主枝生长长度的重要因素。保育灌丛高度和冠幅面积与油松和樟子松幼苗存活率呈显著正相关（P < 0.05）。固氮灌丛（紫穗槐和柠条）对松树幼苗存活有持续的促进作用，但柠条冠幅结构紧密，可能因为对光的竞争，减弱了促进作用。沙柳灌丛下松树幼苗的存活率较低。油松幼苗具有一定程度的耐阴性，樟子松幼苗喜光性强，保育灌丛下油松幼苗存活率显著高于樟子松幼苗（P < 0.05）。总的来说，保育灌丛对松树幼苗的定居有促进作用，保育植物技术可作为一种有效的恢复措施，应用在毛乌素沙地的植被恢复中来。但是，保育灌丛的选择要考虑是本土种或外来种，以及灌丛的高度、冠幅大小、冠幅结构和化学效应，恢复物种的选择要考虑其自身的生物学特性及其与保育植物的相互作用。 Abstract:Over-grazing, mining, and inappropriate agricultural management practices combined with repeated drought events in the Mu Us sandy land in northern part of Shaanxi, Northwest China, have caused severe desertification. This landscape-scale degradation has significantly declined the possibility of natural ecosystem recovery. These conditions warrant ecological restoration of these areas to allow the re-development of sustainable ecosystems. Seedling establishment is the most crucial stage in a restoration project. In the Mu Us sandy land, restoration efforts might have been largely limited owing to the soil moisture deficiency, temperature fluctuations, high light intensities, low soil fertility, competition, allelopathy, herbivory, and wind. Several restoration techniques have long been used to alleviate these problems; however, their application has been restricted by low seedling and plant survival as well as high cost. Thus, developing novel, low-cost, and efficient restoration techniques is necessary. Plant-plant interaction effects provided by nurse plants can significantly increase or decrease the seed germination rates and establishment of seedlings under their canopies. Therefore, this study primarily aimed to determine the ability of shrubs to be used as a restoration tool in the Mu Us sandy land. Two-year-old seedlings of Pinus tabulaeformis and Pinus sylvestris were planted under the canopies of three shrub species (Caragana intermedia, Amorpha fruticosa, and Salix psammophila) or in open areas with no shrubs as a control; the objective was to determine whether the presence of shrubs facilitated the establishment of pine seedlings, which was assessed three times over three consecutive growing seasons, in the Mu Us sandy land. The height and canopy spatial area of shrubs were measured. The microclimate conditions (light intensity, air and soil temperatures, as well as soil moisture) were recorded in the four microhabitats, that is, under the canopy of each of the three shrubs and in areas without the shrubs (control). The near-surface light intensity as well as air and soil temperatures were lower under the shrubs, which led to higher soil moisture; because of these conditions, the survival rates of P. tabulaeformis seedlings growing under the canopy of the shrub species were higher than those of the seedlings growing in the control area (P < 0.05). However, the survival rates of P. sylvestris seedlings were higher only under the canopy of A. fruticosa (P < 0.05). The survival rates of P. tabulaeformis and P. sylvestris seedlings were the highest under the canopy of A. fruticosa (P < 0.05). Thus, the exotic species, A. fruticosa, could be used successfully as a nurse plant. Increased plant height and canopy area of nurse shrubs might improve the establishment of pine seedlings. The leguminous shrubs (C. intermedia and A. fruticosa) showed continuous facilitation of seedling establishment during moderate drought stress (summers of 2012, 2013, and 2014), but the presence of a dense and small shrub, C. intermedia, reduced the rate of seedling establishment possibly because of the competition for light. In 2012, S. psammophila also facilitated seedling establishment, but an unknown effect led to a high mortality rate for seedlings growing under their canopy. A noteworthy finding was that the growth of the two pine species was not inhibited when they were planted under the three shrubs. Pine seedlings had the shortest leader shoot lengths in 2012, with light intensity and soil moisture as important factors that controlled their length. The shade-tolerant species, P. tabulaeformis, had a higher seedling survival rate than that of P. sylvestris. In conclusion, nurse-shrub facilitation can be used as an effective restoration strategy in the Mu Us sandy land. However, the successful use of shrubs as nurse plants depends on their origin and morphological characteristics and ecological effects; the selection of target species depends on their tolerance of shade and their interaction with nurse plants. 参考文献 相似文献 引证文献

Genetic variation facilitates seedling establishment but not population growth rate of a perennial invader.

Assessing the demographic consequences of genetic variation is fundamental to invasion biology. However, genetic and demographic approaches are rarely combined to explore the effects of genetic variation on invasive populations in natural environments. This study combined population genetics, demographic data and a greenhouse experiment to investigate the consequences of genetic variation for the population fitness of the perennial, invasive herb Lupinus polyphyllus. Genetic and demographic data were collected from 37 L. polyphyllus populations representing different latitudes in Finland, and genetic variation was characterized based on 13 microsatellite loci. Associations between genetic variation and population size, population density, latitude and habitat were investigated. Genetic variation was then explored in relation to four fitness components (establishment, survival, growth, fecundity) measured at the population level, and the long-term population growth rate (λ). For a subset of populations genetic variation was also examined in relation to the temporal variability of λ. A further assessment was made of the role of natural selection in the observed variation of certain fitness components among populations under greenhouse conditions. It was found that genetic variation correlated positively with population size, particularly at higher latitudes, and differed among habitat types. Average seedling establishment per population increased with genetic variation in the field, but not under greenhouse conditions. Quantitative genetic divergence (Q(ST)) based on seedling establishment in the greenhouse was smaller than allelic genetic divergence (F'(ST)), indicating that unifying selection has a prominent role in this fitness component. Genetic variation was not associated with average survival, growth or fecundity measured at the population level, λ or its variability. The study suggests that although genetic variation may facilitate plant invasions by increasing seedling establishment, it may not necessarily affect the long-term population growth rate. Therefore, established invasions may be able to grow equally well regardless of their genetic diversity.

Rodent mounds facilitate shrubs and shrubs inhibit seedlings in the Mojave Desert, USA

The habitat immediately around long-lived desert shrubs often provides a favorable environment (‘fertile island’) for annual plants and shrub seedling establishment. However, adult shrubs can also compete with shrub seedlings. Part of the fertile island effect is due to rodent burrowing and seed caching but less is known about the effect of rodent mounds on short- and long-term desert shrub demography. We demonstrate that the indirect influences of rodent mounds on soil fertility and permeability create conditions favorable for adult shrubs, enhancing shrub size, density, and local species diversity in a nearly monospecific community of Coleogyne ramosissima in the Mojave Desert, in the southwestern USA. Shrubs facilitate seedling establishment but shrub canopies and fertile islands are not favorable for seedling survival. Occasional success of seedlings growing in open areas on mounds (where seedling densities are lowest) appear to have the biggest effect on long-term shrub demography of the dominant shrub, C. ramosissima, and, by inference, on other species of shrubs that are found only on mounds.

The effect of herbivores on genotypic diversity in a clonal aquatic plant

In clonal plants, vegetative parts may outcompete seeds in the absence of disturbance, limiting the build‐up of genotypic diversity through repeated seedling recruitment (RSR). Herbivory may provide disturbance and trigger establishment of strong colonizers (seeds) at the expense of strong competitors (clonal propagules). In the clonal aquatic fennel pondweed Potamogeton pectinatus, two distinct herbivore guilds may modify the dynamics of propagation. In winter, Bewick's swans may deplete patches of tubers, promoting seedling establishment in spring. In summer, seed consumption by waterfowl can reduce the density of viable seeds but grazing may also reduce tuber production and hence facilitate seedling establishment. This study is among the first to experimentally test herbivore impact on plant genotypic diversity. We assess the separate and combined effects of both herbivore guilds on genotypic diversity and structure of fennel pondweed beds. Using microsatellites, we genotyped P. pectinatus from an exclosure experiment and assessed the contribution of herbivory, dispersal and sexual reproduction to the population genetic structure. Despite the predominance of clonal propagation in P. pectinatus, we found considerable genotypic diversity. Within the experimental blocks, kinship among genets decreased with geographic distance, clearly identifying a role for RSR in the maintenance of genotypic diversity within the fennel pondweed beds. However, over a period of five years, none of the herbivory treatments affected genotypic diversity. Hence, sexual reproduction on a local scale is important in this putatively clonal plant and possibly sufficient to ensure a relatively high genotypic diversity even in the absence of herbivores. Although we cannot preclude a role of herbivory in shaping genotypic diversity of a clonal plant, after five years of exclusion of the two investigated herbivore guilds no measurable effect on genotypic diversity was detected.

Direct and indirect effects of tree canopy facilitation in the recruitment of Mediterranean oaks

Summary Tree recruitment in Mediterranean ecosystems is strongly limited at the seedling stage by drought. Increasing evidence shows the critical positive role of the canopy nurse effect on seedling survival which results from direct and indirect, positive and negative interactions between species. Most studies, however, have only focused on the effects of tree canopy on water and light, ignoring other critical factors affecting seedling regeneration, such as canopy effects on high temperatures and the competing herb biomass. Here, we evaluate how tree canopy cover and removal of herbs affect the survival and growth of seedlings of two dominant Mediterranean Quercus species during a 3‐year study. We use an integrated model that combines several data sets to quantify and predict regeneration dynamics along environmental gradients of soil moisture, temperature and light. Low soil moisture, increased soil temperature and herb biomass negatively affected seedling survival of both Quercus species. Seedling growth was positively associated with increasing soil moisture and light. Although tree canopy cover directly facilitated seedling survival in both Quercus species, it also negatively affected herb biomass and thus indirectly facilitated the survival of Quercus suber, but not of Quercus ilex seedlings at low levels of soil moisture. Overall, tree canopies increased seedling survival but not growth during the establishment phase, mainly by ameliorating the effects of low soil moisture and high temperatures. Tree canopy indirectly facilitated survival of Q. suber seedlings by negatively affecting the competing herb layer. Synthesis and applications. To improve tree recruitment and conserve Mediterranean Quercus woodlands, the removal of herbs should be integrated into management plans for dry habitats. Interactions between abiotic and biotic factors may also effect the regeneration of these tree species. In particular, a healthy tree canopy will become important for providing conditions to facilitate seedling establishment if these habitats become drier and warmer, as predicted by some climate change scenarios.

Arbuscular mycorrhizal fungi affect seedling recruitment: a potential mechanism by which N deposition favors the dominance of grasses over forbs

Nitrogen (N) deposition usually alters plant community structure and reduces plant biodiversity in grasslands. Seedling recruitment is essential for maintaining species richness and determines plant community composition. Arbuscular mycorrhizal fungi (AMF) are widespread symbiotic fungi and could facilitate seedling establishment. Here we conducted an experiment to address whether the influence of AMF on seedling recruitment depends on N addition and plant species. Leymus chinensis were cultivated for 5 months in the microcosms that were inoculated with or without AMF at five N addition rates. Seeds of three main species (two C3 grasses and one non-N2-fixing forb) of the Eurasian steppe were sown to the 5-month-old microcosms. Seedling establishment was estimated by shoot biomass, N and P contents 7 weeks after seedling germination. AMF promoted seedlings recruitment of two C3 grasses at addition rates above 0.5 g N m−2. In contrast, seedling recruitment of the non-N2-fixing forb was increased by AMF at addition rates below 0.5 g N m−2 but was decreased above 2.5 g N m−2. These results partly explain why N addition favored the dominance of grasses over forbs in perennial grassland communities. Our study indicates that AMF have the potential to influence plant community composition by mediating revegetation in the face of N deposition.

Spatio-temporal variation in contrasting effects of resident vegetation on establishment, growth and reproduction of dry grassland plants: implications for seed addition experiments.

Successful establishment of plants is limited by both biotic and abiotic conditions and their interactions. Seedling establishment is also used as a direct measure of habitat suitability, but transient changes in vegetation might provide windows of opportunity allowing plant species to colonize sites which otherwise appear unsuitable. We aimed to study spatio-temporal variability in the effects of resident vegetation on establishment, growth and reproduction of dry grassland species in abandoned arable fields representing potentially suitable habitats. Seeds were sown in disturbed (bare of vegetation and roots) and undisturbed plots in three fields abandoned in the last 20 years. To assess the effects of temporal variation on plant establishment, we initiated our experiments in two years (2007 and 2008). Seventeen out of the 35 sown species flowered within two years after sowing, while three species completely failed to become established. The vegetation in the undisturbed plots facilitated seedling establishment only in the year with low spring precipitation, and the effect did not hold for all species. In contrast, growth and flowering rate were consistently much greater in the disturbed plots, but the effect size differed between the fields and years of sowing. We show that colonization is more successful when site opening by disturbance coincide with other suitable conditions such as weather or soil characteristics. Seasonal variability involved in our study emphasizes the necessity of temporal replication of sowing experiments. Studies assessing habitat suitability by seed sowing should either involve both vegetation removal treatments and untreated plots or follow the gradient of vegetation cover. We strongly recommend following the numbers of established individuals, their sizes and reproductive success when assessing habitat suitability by seed sowing since one can gain completely different results in different phases of plant life cycle.

Germination Success and Seedling Development of Argania spinosa under Different Climatic Conditions and Browsing Intensity

The present study assesses whether the germination and establishment success of Argania spinosa seeds are affected by the environmental conditions under which the mother plant has grown. Seeds from three populations with different climatic conditions and herbivory intensity were collected and sown in the laboratory after different treatments. Our study suggests that the seed germination process and initial stages of seedling growth are adaptive. Seeds from the population of Agadir with the highest herbivory pressure and high air relative humidity in summer (due to the proximity to the sea) were stimulated by acid treatment, and showed a lower root/stem ratio, which allows them to take advantage of the atmospheric water resources. Seeds from the Mountain population, where the most arid environmental conditions were found, produced early-germinating seeds with the highest root/stem ratio that would facilitate seedling establishment when the harshest environmental conditions appear in summer.

Differential seedling establishment of woody plants along a tree density gradient in Neotropical savannas

Summary Seedling dynamics are crucial for understanding spatial plant distribution patterns, yet little is known about seedling establishment in Neotropical savannas because empirical studies at the community level are scarce. Over 2 years, we studied the recruitment and survival of an initial seedling assemblage and three cohorts of recruits of woody plants within 216 plots of 1 m2 located along a tree density gradient in the savannas of central Brazil. These savannas differ in tree density and canopy cover, from closed (high canopy cover) to open savannas (low canopy cover), and are located along shallow topographic gradients. We measured community‐wide seedling limitation (i.e. proportion of 1‐m2 plots without seedlings of any woody species), photosynthetic photon flux density, litter cover, soil moisture and soil nutrients in each savanna type. Because closed savannas had lower PPFD and higher leaf litter cover than open savannas, we evaluated the effects of light level and litter cover on seedling emergence of nine dominant savanna woody species under controlled conditions in a glasshouse. Density, recruitment and survival of seedlings decreased over time because of mortality in all savanna types, but they were consistently higher in closed than in open savannas. Community‐wide seedling limitation was significantly lower in closed (0.16 ± 0.03) than in open (0.30 ± 0.05) savannas. In the glasshouse, high litter cover and very low light levels reduced seedling emergence of most species, suggesting an adaptation to delay seed germination until the wet season when soil water availability is high and leaf litter rapidly decomposes. Synthesis: In Neotropical savannas, tree canopy cover facilitates seedling establishment of woody species by reducing stressful environmental conditions. In particular, low irradiance and high litter cover in closed savannas enhance the recruitment and survival of woody seedlings relative to open savannas by reducing soil water deficits and increasing nutrient availability in the upper soil layers. The higher seedling limitation of tree species in open than in closed savannas contributes to maintain relatively different balances between trees and herbaceous plants along topographic gradients in Neotropical savannas and helps to explain spatial distribution patterns of woody species in these ecosystems.

Facilitation by tussock‐forming species on seedling establishment collapses in an extreme drought year in a post‐mined Sphagnum peatland

AbstractQuestionsDoes the facilitation of herbaceous species seedling establishment by tussock‐forming species collapse in an extreme drought year? Do different germination phenologies, between the seedling species, influence the variation in facilitation?LocationA post‐mined Sphagnum peatland at Sarobetsu mire, Hokkaido, northern Japan.MethodsThe effects of tussock‐forming species, as potential facilitators, on seedling emergence and survival of five perennial herbs were examined during a 4‐yr seedling monitoring, which included an extreme drought. The general effects of tussocks on each seedling species during annual variations were simultaneously assessed using hierarchical Bayesian analysis. To examine the stress limiting seedling establishment, which was ameliorated by the tussocks, micro‐environments (i.e. light, temperature, water content and erosion) altered by morphological traits of the tussocks with litter cover were compared to those in open areas.ResultsIn general, tussocks facilitated seedling establishment of all species through a positive effect on emergence and no effect on survival; however, the facilitative effect declined for several species in an extreme drought year. Peat erosion was the limiting stress on seedling establishment in normal years, however, peat water content also limited seedling establishment in a drought year. During the drought year, the positive effect of tussocks on seedling emergence for species that germinated before or during the drought was weakened for one species, and a negative effect on seedling survival emerged in another species. In contrast, species that germinated after the drought did not exhibit annual variation in the effects of tussocks on seedling emergence and survival.ConclusionsOur results illustrate that collapse of facilitation arises under extremely severe conditions through addition of infrequently occurring stress (drought) on frequently occurring stress (peat erosion). Variation in seedling emergence and survival of the five study species in response to severe drought suggests that species‐specific traits must be considered when assessing how facilitation varies temporally. Further, these findings suggest that facilitation in temporally varying environments can drive plant community composition and dynamics.

Positive feedbacks amplify rates of woody encroachment in mesic tallgrass prairie

Over the last century, many grasslands worldwide have transitioned from a graminoid to a tree/shrub-dominated state in a short period of time, a phenomenon referred to as woody encroachment. Positive feedbacks and bi-stability are thought to be important drivers of woody encroachment, but there is little empirical evidence to suggest that positive feedbacks accelerate the woody encroachment of mesic grasslands. In mesic tallgrass prairie, shrub establishment does not directly facilitate seedling establishment. Yet, shrub establishment may facilitate the clonal spread of existing shrubs into nearby patches, because clonal reproduction might circumvent barriers that typically limit woody seedlings. Our results show that when Cornus drummondii (the predominate encroacher of mesic tallgrass prairie) extends rhizomatous stems into open grasslands, these stems use the same deep soil water sources as mature stems—thereby avoiding competition with grasses and gaining access to a reliable water source. In addition...