Successful Seedling Establishment Research Articles

Decoupling the Effects of Fire and Dry Season Drought on Seedling Establishment Success of Tree Functional Types in Humid Savannas

Background: In the seasonal tropics, fire generally occurs in the dry season. Consequently, the effects of fire and dry season drought on seedling establishment of different tree functional types are correlated. Therefore, factors that are more important for tree recruitment in forest-savanna ecotones are still poorly understood. Methods: We studied seedling establishment success of seven tropical tree species (of forest and forest-savanna transition origins) in a common garden experiment using combinations of dry season (irrigation vs no-irrigation) and fire (burning vs no-burning). Results: We found that burning caused a significant decline in survival of forest species, but not of forest-savanna transition species. The combination of burning without dry season irrigation (which typifies dry season fire) had the largest overall effect on survival, mass and height of plants. The separate effect of burning was larger than that of dry season drought. Seedling size at the onset of the dry season significantly predicted root starch content and, hence, dry season survival probability of forest-savanna transition species, but not of forest species. Dry season irrigation increased post-fire survival of forest-savanna transition species, but not of forest species, possibly linked to differences in resprout capacity and root starch reserves. Conclusion: Our work shows that fire and dry season drought produce a stronger negative effect together, than their separate effects on seedling establishment particularly of forest species. This provides a mechanistic explanation for the existence of forest-savanna transition species in fire-prone humid savannas. Implications for Conservation: The mosaic of forest, transitional and savanna vegetation within the forest-savanna ecotone reflects the influences of fire and dry season drought. Any changes in these elements will influence vegetation dynamics within the forest-savanna ecotone.

Unconventional Germination in Terrestrial Plants: A Counterintuitive Case in Desiccation-Sensitive Garcinia aristata (Clusiaceae) Seeds Showing Seedling Growth Without Roots.

Unconventional germination, wherein shoots emerge and establish true leaves before the root emerges, is only found in Zosteraceae. In Garcinia, germination proceeds with the primary root emerging, followed by shoot emergence on the opposite side, but before leaf differentiation, adventitious roots emerge at the base of the shoots. However, germination and survival mechanisms in several Garcinia species are still unclear. We subjected freshly collected G. aristata seeds to an imbibition test, and germination was evaluated at various temperatures and light conditions. Desiccation sensitivity assessments were made at different stages of drying. The effect of natural drying (ambient storage) on germination was assessed by leaving the seeds outside in natural conditions. Seeds of G. aristata with a moisture content (MC) of 67% had more than 95% germination only at 25 and 25/30 °C both in light/dark and darkness, but at 25/40 °C only 10% germinated. In 4% of the seeds, germination incepted with primary shoot emergence, and a secondary (adventitious) root emerged just before leaf differentiation. More than 95% of the seeds germinated with only a secondary root and shoot emerging concurrently. Drying fresh seeds above silica gel to 30% MC resulted in complete viability loss. Seeds stored at ambient conditions germinated without external water, and had no primary or secondary root, and the emerging shoot continued to grow into seedlings. A root develops in these seeds only when water becomes available. G. aristata seeds are desiccation-sensitive and non-dormant. When no external water is available, G. aristata seeds can germinate with shoots and establish seedlings. This is the first report on germination and successful seedling establishment without roots in Garcinia.

Shoot and root dendroanalysis of Ulmus pumila 10 years after outplanting in the Mongolian semi-arid steppe reveals a short-term developmental pattern enhanced by watering

An accurate investigation is needed to determine if the selected location, the tree species, and the applied treatments can support a successful seedling establishment and outplanting performance to ensure the success of large-scale tree-planting initiatives. To shed light on the growth pattern of the trees used in the Green Belt Project plantations in the Mongolian steppe, we analysed the biomass allocation in the stem and roots of Ulmus pumila in terms of ring width, considering different management techniques involving irrigation and fertilisation. We found that the root and shoot ring width of U. pumila followed a bell-shaped curve and reached maximum values after three or four years from seedling outplanting. Moreover, our data confirm that increasing watering regimes may enhance plant growth, especially the root system, while fertilisation did not show a positive effect independently of the fertilisation type (i.e. NPK and compost). Our data allowed us to develop a predictive regression model that could be used with other species and in different environmental conditions to forecast stem and root tree growth and to simulate afforestation performances in different climatic conditions.

Mycorrhizal fungi as critical biotic filters for tree seedling establishment during species range expansions

AbstractGlobal warming has been shifting climatic envelopes of many tree species to higher latitudes and elevations across the globe; however, unsuitable soil biota may inhibit tree migrations into these areas of suitable climate. Specifically, the role of mycorrhizal fungi in facilitating tree seedling establishment beyond natural species range limits has not been fully explored within forest ecosystems. We used three experiments to isolate and quantify the effects of mycorrhizal colonization and common mycorrhizal networks (CMN) on tree seedling survival and growth across (within and beyond) the elevational ranges of two dominant tree species in northeastern North America, which were associated with either arbuscular mycorrhiza (AMF, Acer saccharum) or ectomycorrhiza (EMF, Fagus grandifolia). In order to quantify the influence of mycorrhiza on seedling establishment independent of soil chemistry and climate, we grew seedlings in soils from within and beyond our study species ranges in a greenhouse experiment (GE) as well as in the field using a soil translocation experiment (STE) and another field experiment manipulating seedling connections to potential CMNs (CMNE). Root length colonized, seedling survival and growth, foliar nutrients, and the presence of potential root pathogens were examined as metrics influencing plant performance across species' ranges. Mycorrhizal inoculum from within species ranges, but not from outside, increased seedling survival and growth in a greenhouse setting; however, only seedling survival, and not growth, was significantly improved in field studies. Sustained potential connectivity to AMF networks increased seedling survival across the entire elevational range of A. saccharum. Although seedlings disconnected from a potential CMN did not suffer decreased foliar nutrient levels compared with connected seedlings, disconnected AM seedlings, but not EM seedlings, had significantly higher aluminum concentrations and more potential pathogens present. Our results indicate that mycorrhizal fungi may facilitate tree seedling establishment beyond species range boundaries in this forested ecosystem and that the magnitude of this effect is modulated by the dominant mycorrhizal type present (i.e., AM vs. EM). Thus, despite changing climate conditions beyond species ranges, a lack of suitable mutualists can still limit successful seedling establishment and stall adaptive climate‐induced shifts in tree species distributions.

From Waste to Plant Production: Cattle Dung Compost as an Alternative Nursery Substrate to Commercial Peat for Producing Lettuce Plants

The limited availability of peat-based substrates, a nonrenewable resource, and the negative environmental impacts associated with their extraction require the conservation of this resource. We assessed the use of cattle dung compost as a stand-alone nursery substrate, replacing peat substrate for the production of lettuce (Lactuca sativa L.) seedlings. A completely randomized design was employed, using cattle dung compost (C) and commercial peat (P, control treatment) in various combinations (100% P; 25% C/75% P; 50% C/50% P; 75% C/25% P; 100% C) to assess their effects on different growth parameters of lettuce. Twenty-eight parameters (e.g., seed germination, seedling survival, diameter, height, biomass growth) were assessed, corresponding to the time when the seedlings are transplanted. All treatments achieved 100% seed germination and seedling survival; indicating the successful establishment of lettuce seedlings across all tested substrates. However, seedling growth was found to be significantly influenced by substrate type. Seedling diameter was significantly increased by 10.8% in the 50% C/50% P substrate, while seedling height was significantly increased by 7.7, 6.8, and nearly 10%, respectively, within the 25% C/75% P, 50% C/50% P and 100% C substrates, relative to the control. Other substrate treatments were not significant. Similar or significantly higher values than the control were also observed for biomass growth under the tested substrates, indicating the beneficial effect of cattle dung on the initial growth of plants during the nursery phase. Cattle dung compost, used as a growing substrate, demonstrated similar or superior results to commercial peat, suggesting its potential as a viable alternative potting medium for sustainable horticulture.

Intense light and conspecific density increase seedling mortality across age groups in a typhoon‐disturbed tropical forest

AbstractQuestionsMaintaining forest species diversity, regenerative function and ecosystem resilience begins with successful seedling establishment. Despite their critical role, seedlings face the highest mortality risks among plant life‐history stages. Our research aims to answer the following questions: In a tropical forest disturbed by typhoons, what is the median survival time for seedlings, to what extent do light levels contribute to mortality risks and what are the crucial mortality risks across seedling age groups?LocationA tropical mountain zonal foothill evergreen broad‐leaved forest in Nanjenshan Nature Reserve, Taiwan, frequently visited by typhoons.MethodsWe investigated woody seedlings in 75 quadrats (each 1 m × 1 m) every 3 months from October 2009 to January 2018, spanning 8.3 years with 34 censuses. We used the Kaplan–Meier method to estimate seedlings’ median survival time and Generalized Linear Models to identify mortality risk factors for all seedlings and those that persisted beyond the median survival time.ResultsThe median survival time for all seedlings was 0.5 years, ranging from 0.25 years for shade‐intolerant species to 1.25 years for shade‐tolerant species. Seedlings germinated in high‐light microhabitats and high conspecific seedling density exhibited higher mortality probabilities, regardless of age.ConclusionsThis study reveals the short survival time and key mortality risks of seedlings in a typhoon‐disturbed forest. The negative impact of light levels on seedling survival highlights the potential consequences of increased light levels resulting from typhoon disturbances in the study region.

Voice from both sides: a molecular dialogue between transcriptional activators and repressors in seed-to-seedling transition and crop adaptation.

High-quality seeds provide valuable nutrients to human society and ensure successful seedling establishment. During maturation, seeds accumulate storage compounds that are required to sustain seedling growth during germination. This review focuses on the epigenetic repression of the embryonic and seed maturation programs in seedlings. We begin with an extensive overview of mutants affecting these processes, illustrating the roles of core proteins and accessory components in the epigenetic machinery by comparing mutants at both phenotypic and molecular levels. We highlight how omics assays help uncover target-specific functional specialization and coordination among various epigenetic mechanisms. Furthermore, we provide an in-depth discussion on the Seed dormancy 4 (Sdr4) transcriptional corepressor family, comparing and contrasting their regulation of seed germination in the dicotyledonous species Arabidopsis and two monocotyledonous crops, rice and wheat. Finally, we compare the similarities in the activation and repression of the embryonic and seed maturation programs through a shared set of cis-regulatory elements and discuss the challenges in applying knowledge largely gained in model species to crops.

Variation in the role of the flag‐leaf in reproductive effort of semiarid rangeland bunchgrasses

AbstractUnderstanding the mechanisms underlying viable seed production of perennial bunchgrasses is critical to improving restoration and conservation success in Great Basin sagebrush steppe rangelands. We studied the effects of pre‐ and post‐anthesis flag‐leaf removal and post‐anthesis seed‐head shading on reproductive effort in two important rangeland restoration species, the exotic crested wheatgrass (Agropyron cristatum) and native squirreltail (Elymus elymoides). Flag‐leaf removal had distinct, species‐specific effects on seed filling. Pre‐anthesis flag‐leaf removal in crested wheatgrass reduced the proportion of filled seeds, while post‐anthesis removal did not. In contrast, squirreltail increased filled seed proportions regardless of flag‐leaf removal timing. Neither flag‐leaf removal treatment affected seed quality, as quantified by seed‐specific mass (in grams per square meter), which significantly reduced with seed‐head shading in both species. Seed‐head shading reduced total propagule production (unfilled + filled seeds) in crested wheatgrass but increased it in squirreltail, possibly due to our shading method protecting from seed‐head herbivory or high‐light stress. Flag‐leaf removal in the squirreltail also induced a negative shading effect on filled seed area, mass, and specific mass. These findings suggest flag leaves can modulate reproductive effort outside of seed provisioning, either by maintaining pre‐fertilized seed viability, as in crested wheatgrass, or acting as a competitive sink to the fully emerged seed‐head, as in squirreltail. Moreover, this study demonstrates photosynthetic activity by the seed‐head itself is critical to the expression of seed quality traits important to seedling establishment success of semiarid perennial bunchgrasses.

Effect of acorn fall phenology on seedling establishment success in two mediterranean oak species. Implications facing climate change

This study focuses on the effect of differences in acorn dropping time on seedling establishment in two abundant Mediterranean oak species: Quercus ilex subsp. ballota and Q. suber. These species show extended seed dropping seasons (i.e., 4 to 5 months) and the fallen acorns thus experience variable conditions, including differences in climate and microclimate, as well as differences in biological interactions (mainly pre- and post-dispersal predation by insect larvae and rodents, respectively). We conducted two field experiments and a field survey on acorn infection by insect larvae and analysed the ability of early and late dropped acorns to achieve success (i.e., remaining healthy, germinating, and emerging as seedlings). The results indicated that pre- and post-dispersal predation of propagules changed over time. However, these factors had low effect on final seedling success. In opposition, warmer (i.e., autumn) conditions at acorn dropping and sowing time decreased seedling establishment in Q. suber, likely by a lack of cold stratification, while the conditions had no effect on Q. ilex subsp. ballota seedlings. We conclude that climate warming can selectively decrease the number of seedlings that are established in late springtime, before the onset of the characteristic Mediterranean summertime drought, thus negatively affecting the population dynamic in these species, which exhibit a high level of physiological dormancy as they depend on cold conditions to maximise acorn germination and epicotyl emergence.

Seed functional traits as predictors of seedling establishment success in Brazilian tropical forest restoration

AbstractSeveral ecological filters in deforested and degraded areas reduce seedling emergence and establishment and hinder ecological restoration by direct seeding. Understanding whether functional traits are related to a species' capacity to overcome these filters and predict their field performance might improve the success of direct seeding techniques for ecological restoration. We assessed eight seed functional traits of tropical tree species, seeking those that best explained their establishment success in direct seeding restoration projects. We analyzed a dataset from 52 studies that tested direct seeding techniques with tree species in Brazil. From each study, we collected the mean establishment percentage for all tree species. Seed mass, cotyledon function, and germination speed were the only functional traits that significantly affected the species establishment percentage in direct seeding restoration projects. Species with larger seeds, storage cotyledons, and faster germination had higher establishment percentages. Choosing species with these functional traits for seed mixes will provide higher establishment percentages and, consequently, improve restoration success by direct seeding techniques.

Selecting Suitable Tree Species for Direct Seeding to Restore Forest Ecosystems in Northern Thailand

To upscale restoration of tropical forest ecosystems, direct seeding—sowing seeds directly into the ground—is potentially a more cost-effective technique than tree planting. However, its success is limited by seed predation, the harshness of environmental conditions on restoration sites and particularly by a lack of information about suitable tree species. Therefore, this study tested the suitability of 23 native forest tree species for direct seeding, to restore a biodiversity-rich, upland, evergreen forest in northern Thailand. Three replicate seed batches of each species were sown randomly in two degraded sites and in a tree nursery under controlled conditions. Seed removal and germination were monitored weekly until no further germination had occurred for more than a month. Subsequently, seedling yield, growth and species performance score were also monitored at appropriate intervals. Nine months after sowing, seed removal differed significantly among species but was generally low, with a cross-species average of 3.4% (±0.5 SE). Seed size was negatively correlated with seed removal. Eight species failed to germinate. Seed germination percentage varied widely among species. Cross-species average germination of the 15 species that germinated was 25% (±6.2 SE). Two species (Adenanthera microsperma and Alangium kurzii) were ranked as having high germination (>50%), five species (Choerospondias axillaris, Spondias pinnata, Diospyros glandulosa, Melia azedarach and Phyllanthus emblica) had medium germination (20–50%) and eight species had low germination (<20%). Following the first dry season, two of the fifteen germinated species failed to establish. Germination and establishment were influenced by seed size, seed storage behavior and successional status. A. microsperma, S. pinnata and C. axillaris are recommended for direct seeding based on their high species performance index values. This study further concluded that selecting desiccation-tolerant seeds, particularly those with medium-to-large sizes, could increase the chances of successful seedling establishment.

Influence of seed mass and shape on light plasticity of germination of alpine plants on the Tibetan Plateau: The role of photoblastic taxa, dispersal ability, and life history

Responses of post-disposal germination to light play a crucial role in shaping germination niches and determining the success of seedling establishment, ultimately impacting species distribution and community composition. Seed traits are pivotal factors that influence species' germination, dispersal, and life history strategies. However, it remains unclear whether the relationship between seed traits and the light plasticity of germination is regulated by factors such as life history, photoblastic taxa, and dispersal ability.We measured the seed shape and seed mass of 114 species on the grasslands of the Tibetan Plateau. Germination experiments were conducted under two light conditions: dark and light. We also classified species based on photoblastic taxa (photostimulation vs. photoinhibition), life history (annual vs. perennial), and dispersal ability (weak vs. strong). Phylogenetic structural equation models (SEM) were used to test the complex relationship between seed traits, life history, dispersal ability, and light plasticity.We found that neither seed mass nor shape differed between the two photoblastic taxa. Species with photostimulation taxa exhibited a greater light plasticity of germination compared with photoinhibition taxa. Non-spherical seeds (elongated or flat) possessed low light plasticity of germination. The relationship between seed mass and germination light plasticity varied in different photoblastic taxa. Specifically, in photostimulation species, increased seed mass was associated with higher light plasticity of germination, whereas in photoinhibition species, an opposite relationship was evident. Moreover, dispersal ability and life history indirectly influenced the light plasticity of germination via seed shape.Our results imply that different combinations of seed traits can shape germination strategies in response to light stimulation, which in turn may influence the germination niches differentiation and species persistence in soil. Furthermore, life history and dispersal ability can indirectly affect the light plasticity of germination, which implies that the reproductive strategy of species to adapt to the environment may be regulated by multi-faceted life history strategies.

Enhancing growth and yield parameters of Sinapis alba through optimized seed priming techniques

AbstractEarly seed germination significantly influences crop growth and production, prompting the exploration of seed priming as a pivotal technique. Despite the acknowledged importance of faster germination and emergence for successful seedling establishment, oilseed crops like Sinapis alba have received limited attention concerning seed priming methods, unlike cereal and grain crops. This study aimed to bridge this gap by subjecting S. alba seeds to six priming treatments: T1 = control, T2 = distilled water, T3 = NaCl (0.5%), T4 = KNO3 (0.5%), T5 = CaCl2 (0.5%), and T6 = Moringa leaf extract at a 1:30 ratio (30 times diluted), to assess their impact on various growth and yield parameters. The data analysis revealed significant effects of seed priming on various parameters, with exceptions in plant height unaffected by seed soaking. Seed priming notably enhanced germination percentage, germination rate index, and seedling vigor index, while reducing mean germination time to emergence significantly. Furthermore, primed seeds exhibited significant increases in seedling fresh and dry weights, crop growth rate, net assimilation rate, root and shoot lengths, leaf area, chlorophyll content, early flowering, branch numbers, pod counts, and 1000‐seed weight compared to non‐primed seeds. The biological yield was relatively higher in treated seeds. Additionally, seed yield and oil content were found to be higher in primed seeds compared to the control. Among the treatments, KNO3 along with Moringa, displayed the most desirable outcomes across overall seedling parameters, suggesting their recommendation for effective priming treatments to improve the growth and yield of S. alba.

Decadal survival of tropical pioneer seeds in the soil seed bank is accompanied by fungal infection and dormancy release

Abstract Pioneer trees require high‐light environments for successful seedling establishment. Consequently, seeds of these species often persist in the soil seed bank (SSB) for periods ranging from several weeks to decades. How they survive despite extensive pressure from seed predators and soil‐borne pathogens remains an intriguing question. This study aims to test the hypotheses that decades‐old seeds collected from the SSB in a lowland tropical forest remain viable by (i) escaping infection by fungi, which are major drivers of seed mortality in tropical soils, and/or (ii) maintaining high levels of seed dormancy and seed coat integrity when compared to inviable seeds. We collected seeds of Trema micrantha and Zanthoxylum ekmanii at Barro Colorado Island, Panama, from sites where adult trees previously occurred in the past 30 years. We used carbon dating to measure seed age and characterized seed coat integrity, seed dormancy and fungal communities. Viable seeds from the SSB ranged in age from 9 to 30 years for T. micrantha, and 5 to 33 years for Z. ekmanii. We found no evidence that decades‐old seeds maintain high levels of seed dormancy or seed coat integrity. Fungi were rarely detected in fresh seeds (no soil contact), but phylogenetically diverse fungi were detected often in seeds from the SSB. Although fungal infections were more commonly detected in inviable seeds than in viable seeds, a lack of differences in fungal diversity and community composition between viable and inviable seeds suggested that viable seeds are not simply excluding fungal species to survive long periods in the SSB. Synthesis. Our findings reveal the importance of a previously understudied aspect of seed survival, where the impact of seed–microbial interactions may be critical to understand long‐term persistence in the SSB. Read the free Plain Language Summary for this article on the Journal blog.

Response of Seedling Growth Characteristics to Seed Size and Cotyledon Damage in Quercus wutaishanica

The successful establishment of seedlings is very important for plant regeneration, but it is vulnerable to many factors at this stage. Cotyledon damage will directly affect the health of seedlings, thus affecting the regeneration of the plant population. However, little is known about the effects of different cotyledon loss degrees of large and small seeds on seedling growth. We investigated the effects of 1/4 (light excision), 1/2 (moderate excision), and complete excision of cotyledons (heavy excision) on the growth characteristics of seedlings germinating from different sizes of seeds. The results showed that (1) shoot height, basal stem diameter, number of leaves, leaf area per plant, specific leaf area, and biomass were significantly higher in large-seeded seedlings than in small-seeded seedlings; (2) slight cotyledon excision had no effect on the biomass of large-seeded seedlings but significantly reduced the biomass of small-seeded seedlings. Our study highlights that large-seeded seedlings are more tolerant than small-seeded seedlings in the early seedling recruitment, suggesting that large-seeded seedlings have a strong fitness for recruitment in young populations of Q. wutaishanica.

Drought-induced photosynthetic decline and recruitment losses are mediated by light microenvironment in Rocky Mountain subalpine forest tree seedlings

Rates of tree mortality continue to rise with climate change, particularly in high elevation subalpine forests. In these systems, which depend on a narrow range of microsite conditions for successful seedling establishment, growing drought frequency and intensity may impose regeneration bottlenecks that further exacerbate population declines. However, it is unclear how regeneration processes tied to species-specific stress tolerances and microsite preferences are affected by varying magnitudes and durations of drought. To simulate moderate (50%) and severe (100% precipitation exclusion) growing-season drought, we installed precipitation exclusion shelters in shade and canopy gap light microenvironments over naturally-regenerating seedlings across a range of size-delimited establishment cohorts spanning first year emergents to large and well-established seedlings of two dominant subalpine forest species – Engelmann spruce (Picea engelmannii Parry ex Engelmann) and subalpine fir (Abies lasiocarpa (Hook) Nutt.). Seedling survival and gas exchange physiology was assessed to test the interacting effects of drought and light microenvironment on seedling performance, with contrasts to each species’ historically preferred microsite under ambient precipitation conditions. Shade partially ameliorated drought effects when precipitation reductions were moderate as illustrated by rates of seedling mortality that were statistically indistinguishable from reference rates for both species, whereas moderate drought in canopy gaps significantly or nearly-significantly increased seedling mortality in several cohorts of both spruce and fir (1.9–2.9 and 2.3–7.5 times greater mortality risk in spruce and fir, respectively). When drought was severe, however, shade induced prolonged net-negative photosynthetic carbon assimilation as low as a −1.5 μmol CO2·m−2·s−1 (growing-season average), which occurred alongside significantly increased mortality in spruce (3.2–9.4 times greater mortality risk). In contrast, mortality was significantly higher in canopy gaps under severe drought for fir (5.5–23.1 times greater mortality risk). Larger seedling size was strongly associated with lower mortality risk and more conservative stomatal behavior (e.g., predominantly <0.1 mol·H2O·m−2·s−1 growing-season averages), illustrating the sensitivity of new seedlings to microsite environments. However, persistent declines in photosynthetic carbon uptake observed across all seedling sizes in shaded microsites suggests the potential for lagged mortality and greater susceptibility to recurring drought even for larger and seemingly well-established seedlings. These results demonstrate how acute, intense droughts may alter historical patterns of spruce-fir seedling regeneration and highlight the importance of maintaining suitable microsites when implementing adaptive management strategies to avoid regeneration bottlenecks in forests that are already vulnerable to accelerating drought-induced mortality.

Roles of pathogens and mycorrhizae in conspecific negative distance dependency and replacement of tree species in a temperate forest

Maintaining and recovering species diversity is one of the main management goals of forest managers. It is thus important to understand the mechanisms that drive species diversity. The mechanism is strongly related to the harsh biological environment surrounding the tree, especially its interaction with natural enemies, and a well-known mechanism is the Janzen-Connell hypothesis. The hypothesis is best understood by evaluating not only conspecific negative distance-dependent (CNDD) seedling mortality but also replacement of conspecific seedlings by heterospecifics. However, it remains unclear how antagonistic pathogens and mutualistic mycorrhizae affect the strength of replacement. A reciprocal seed-sowing experiment was conducted for five tree species with different mycorrhizal types in forest understorey (FU) and gaps (Gap) in a temperate forest. We investigated seedling mass, mortality, mortality agents, and root infection with arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. In both FU and Gap sites, two AM species were attacked by pathogens causing damping-off and leaf diseases more severely beneath conspecific than heterospecific adults, and more severely among conspecifics than heterospecifics of focal adults, resulting in strong CNDD and replacement, whereas seedling mortality in two EM species due to damping-off pathogens and leaf diseases did not differ among treatments, resulting in weak CNDD and replacement. One AM species showed an intermediate trend between two AM species and two EM species. Thus, CNDD and replacement caused by pathogens were positively correlated in FU but not Gap sites. These traits reveal that replacement closely correlated with CNDD play an important role in maintaining species diversity, especially when gaps are absent. This study also suggest that replacement plays an important role in regulating the spatial distribution of individual trees and subsequent relative abundance of tree species, as well as CNDD effects. Forest managers need to consider differences in the strength of CNDD and replacement between mycorrhizal fungi types when attempting to achieve successful seedling establishment after harvesting without compromising species diversity.

COMPARATIVE STUDY OF ROOTSTOCKS AND THEIR EFFECTS ON STIONIC ESTABLISHMENT OF THE MANGO SEEDLINGS

To explore the quality rootstock which impart better stionic establishment of the mango seedlings, we studied the comparative effect of scion and rootstock using three mango scion varieties (Sindhri, Chaunsa and Neelum) grafted on three rootstocks i.e. Ratam, Pado and Sindhri. Parameters including seed germination (%), seedling height (cm), leaves seedling rootstock-1, seedling vigor index (SVI), fresh biomass of shoot and roots (g), dry biomass of shoot and roots (g), chlorophyll content (rg), rootstock diameter (mm), scion diameter (mm), stionic ratio, leaves graft-1 and sturdiness quotient were studied. Results showed the best seed germination (88.33%), seedling vigor index (5158.74), and sturdiness quotient (3.89) in Pado rootstock. However maximum fresh biomass of shoot (20.67 g), fresh biomass of roots (16.2 g), dry biomass of shoot (12.65 g), dry biomass of roots (8.33 g) and scion diameter of the rootstocks were observed in Sindhri rootstocks. Regarding grafting data, the best stionic ratio (0.93) was observed from the scion and rootstock combination of Neelum and Pado rootstock. It was concluded that Pado rootstock performed better in terms of seedling rootstock and for successful stionic establishment of the mango seedlings

Plasticity of maternal environment-dependent expression-QTLs of tomato seeds

Seeds are essential for plant reproduction, survival, and dispersal. Germination ability and successful establishment of young seedlings strongly depend on seed quality and on environmental factors such as nutrient availability. In tomato (Solanum lycopersicum) and many other species, seed quality and seedling establishment characteristics are determined by genetic variation, as well as the maternal environment in which the seeds develop and mature. The genetic contribution to variation in seed and seedling quality traits and environmental responsiveness can be estimated at transcriptome level in the dry seed by mapping genomic loci that affect gene expression (expression QTLs) in contrasting maternal environments. In this study, we applied RNA-sequencing to construct a linkage map and measure gene expression of seeds of a tomato recombinant inbred line (RIL) population derived from a cross between S. lycopersicum (cv. Moneymaker) and S. pimpinellifolium (G1.1554). The seeds matured on plants cultivated under different nutritional environments, i.e., on high phosphorus or low nitrogen. The obtained single-nucleotide polymorphisms (SNPs) were subsequently used to construct a genetic map. We show how the genetic landscape of plasticity in gene regulation in dry seeds is affected by the maternal nutrient environment. The combined information on natural genetic variation mediating (variation in) responsiveness to the environment may contribute to knowledge-based breeding programs aiming to develop crop cultivars that are resilient to stressful environments.

Synergistic use of biochar and the plant growth-promoting rhizobacteria in mitigating drought stress on oak (Quercus brantii Lindl.) seedlings

The successful early establishment of seedlings is a challenging step for the management of forests in semi-arid regions, such as in the oak (Q. brantii) forests in western Iran. To address this challenge, we tested the separate and combined effects of different biofertilizers: we evaluated the influence of the application of biochar and plant growth-promoting rhizobacteria (PGPR) on the growth of oak seedlings subjected to water stress in controlled conditions. Two acorns were sown in a total of 216 pots distributed according to the following treatments: 3 water treatments (100, 75 and 50 % of field capacity), 4 biochar treatments (0, 1, 2 and 3 % of soil weight), 2 PGPR treatments (absence or presence) in 9 replicates. Biochar was derived from mistletoe (Loranthus europaeus), a widespread hemi-parasite plant in the studied oak forests. After emergence, a total of 20 ecophysiological, morphological and growth traits were measured on oak seedlings. We found that the interaction between irrigation, biochar and PGPR significantly influenced the ecophysiological attributes of the seedlings. Comparing application to non-application of PGPR, we found that chlorophyll content, photosynthesis rate and biomass of shoots were respectively increased by 21, 50 and 19 % in the absence of water stress and by 54, 14 and 18 % under severe water stress conditions. Moderate biochar concentrations improved seedling growth and ecophysiological responses whereas the highest concentration of biochar had a detrimental effect. A PLS path model revealed the direct and indirect relationships between the treatments, the seedling morpho-physiological traits and the final variable of interest (total dry biomass). The model explained 78 % of the total variance and showed that the root growth indices (path coefficient = 0.665) had a significant direct effect on oak dry matter whereas this effect was reduced with shoot growth indices. We found that the use of moderate levels of biochar alone or in combination with PGPR can benefit oak seedling development in water-limited conditions but further studies are still needed to test the effectiveness and applicability of these treatments in field conditions.