Developmental pleiotropy of SDP1 from seedling to mature stages in B. napus.

Rapeseed, an important oil crop, relies on robust seedling emergence for optimal yields. Seedling emergence in the field is vulnerable to various factors, among which inadequate self-supply of energy is crucial to limiting seedling growth in early stage. SUGAR-DEPENDENT1 (SDP1) initiates triacylglycerol (TAG) degradation, yet its detailed function has not been determined in B. napus. Here, we focused on the effects of plant growth during whole growth stages and energy mobilization during seedling establishment by mutation in BnSDP1. Protein sequence alignment and haplotypic analysis revealed the conservation of SDP1 among species, with a favorable haplotype enhancing oil content. Investigation of agronomic traits indicated bnsdp1 had a minor impact on vegetative growth and no obvious developmental defects when compared with wild type (WT) across growth stages. The seed oil content was improved by 2.0-2.37% in bnsdp1 lines, with slight reductions in silique length and seed number per silique. Furthermore, bnsdp1 resulted in lower seedling emergence, characterized by a shrunken hypocotyl and poor photosynthetic capacity in the early stages. Additionally, impaired seedling growth, especially in yellow seedlings, was not fully rescued in medium supplemented with exogenous sucrose. The limited lipid turnover in bnsdp1 was accompanied by induced amino acid degradation and PPDK-dependent gluconeogenesis pathway. Analysis of the metabolites in cotyledons revealed active amino acid metabolism and suppressed lipid degradation, consistent with the RNA-seq results. Finally, we proposed strategies for applying BnSDP1 in molecular breeding. Our study provides theoretical guidance for understanding trade-off between oil accumulation and seedling energy mobilization in B. napus.

Water restriction alters seed bank traits and ecology in Atlantic Forest seasonal forests under climate change.

The soil seed bank (SSB) is one of the key mechanisms that ensure the perpetuity of forests, but how will it behave in the scenarios projected for the future climate? Faced with this main question, still little explored in seasonal tropical forests, this study evaluated the germination, ecological attributes, and functional traits of the SSB in a seasonal forest in the Atlantic Forest. Forty-eight composite samples of the SSB were collected from 12 plots, distributed across four treatments, each with 12 replicates. The samples were placed in two climate-controlled greenhouses, establishing two environments of controlled climatic conditions, both with two levels of water, as follows: Cur: current scenario without water restriction; Cur_WR: current scenario with water restriction; RCP8.5: future scenario without water restriction; RCP8.5_WR: future scenario with water restriction. The germinants were identified, and their ecological attributes and functional traits were obtained. Leaf area and biomass production, differences in abundance, richness, and diversity were evaluated, along with analysis of variance to assess the interaction between water levels and scenarios. All ecological attributes and functional traits evaluated drastically decreased in the future projection with water restriction, with this restriction being the main component influencing this response. The increased temperature in the future scenario significantly raised water consumption compared to the current scenario. However, persistent water restrictions in the future could undermine the resilience of seasonal forests, hindering seed germination in the soil. Richness and abundance were also adversely affected by water scarcity in the future scenario, revealing a low tolerance to the projected prolonged drought. These changes found in the results could alter the overall structure of seasonal forests in the future, as well as result in the loss of the regeneration potential of the SSB due to decreased seed viability and increased seedling mortality.

Resumo O banco de sementes do solo (SSB) é um dos principais mecanismos que garantem a perpetuidade das florestas, mas como ele se comportará nos cenários projetados para o clima futuro? Diante dessa questão principal, ainda pouco explorada em florestas tropicais sazonais, este estudo avaliou a germinação, atributos ecológicos e traços funcionais do SSB em uma floresta sazonal na Mata Atlântica. Quarenta e oito amostras compostas do SSB foram coletadas de 12 parcelas, distribuídas em quatro tratamentos, cada uma com 12 réplicas. As amostras foram colocadas em duas estufas com controle climático, estabelecendo dois ambientes de condições climáticas controladas, ambos com dois níveis de água, conforme segue: Cur: cenário atual sem restrição hídrica; Cur_WR: cenário atual com restrição hídrica; RCP8.5: cenário futuro sem restrição hídrica; RCP8.5_WR: cenário futuro com restrição hídrica. Os germinantes foram identificados e seus atributos ecológicos e traços funcionais foram obtidos. Área foliar e produção de biomassa, diferenças na abundância, riqueza e diversidade foram avaliadas, juntamente com análise de variância para avaliar a interação entre níveis de água e cenários. Todos os atributos ecológicos e traços funcionais avaliados diminuíram drasticamente na projeção futura com restrição hídrica, sendo essa restrição o principal componente influenciando essa resposta. O aumento da temperatura no cenário futuro elevou significativamente o consumo de água em comparação com o cenário atual. No entanto, a restrição hídrica persistente no futuro pode comprometer a resiliência das florestas sazonais, dificultando a germinação de sementes no solo. Riqueza e abundância também foram adversamente afetadas pela escassez de água no cenário futuro, revelando uma baixa tolerância à seca prolongada projetada. Essas mudanças encontradas nos resultados podem alterar a estrutura geral das florestas sazonais no futuro, além de resultar na perda do potencial de regeneração do SSB devido à diminuição da viabilidade das sementes e ao aumento da mortalidade das plântulas.

Enhancing iron content and growth of cucumber seedlings with MgFe-LDHs under low-temperature stress.

The development of cost-effective and eco-friendly fertilizers is crucial for enhancing iron (Fe) uptake in crops and can help alleviate dietary Fe deficiencies, especially in populations with limited access to meat. This study focused on the application of MgFe-layered double hydroxide nanoparticles (MgFe-LDHs) as a potential solution. We successfully synthesized and characterized MgFe-LDHs and observed that 1-10 mg/L MgFe-LDHs improved cucumber seed germination and water uptake. Notably, the application of 10 mg/L MgFe-LDHs to roots significantly increased the seedling emergence rate and growth under low-temperature stress. The application of 10 mg/L MgFe-LDHs during sowing increased the root length, lateral root number, root fresh weight, aboveground fresh weight, and hypocotyl length under low-temperature stress. A comprehensive analysis integrating plant physiology, nutrition, and transcriptomics suggested that MgFe-LDHs improve cold tolerance by upregulating SA to stimulate CsFAD3 expression, elevating GA3 levels for enhanced nitrogen metabolism and protein synthesis, and reducing levels of ABA and JA to support seedling emergence rate and growth, along with increasing the expression and activity of peroxidase genes. SEM and FTIR further confirmed the adsorption of MgFe-LDHs onto the root hairs in the mature zone of the root apex. Remarkably, MgFe-LDHs application led to a 46% increase (p < 0.05) in the Fe content within cucumber seedlings, a phenomenon not observed with comparable iron salt solutions, suggesting that the nanocrystalline nature of MgFe-LDHs enhances their absorption efficiency in plants. Additionally, MgFe-LDHs significantly increased the nitrogen (N) content of the seedlings by 12% (p < 0.05), promoting nitrogen fixation in the cucumber seedlings. These results pave the way for the development and use of LDH-based Fe fertilizers.

Seeding alpine grasses in low altitude region increases global warming potential during early seedling growth.

Introduction of alpine grasses to low altitude regions has long been a crucial strategy for enriching germplasm diversity, cultivating and acclimating high-quality species, enhancing ecosystem resilience and adaptability, as well as facilitating ecosystem restoration. However, there is an urgent need to investigate the impacts of planting Gramineae seeds on greenhouse gas (GHG) emissions, particularly during the critical stage of early plant growth. In this study, four species of grass seeds (Stipa breviflora, Poa pratensis, Achnatherum splendens, Elymus nutans) were collected from 19 high-altitude regions surrounding the Qinghai-Tibet Plateau and sown at low-altitude. Measurements of GHG emissions at early seedling growth in the mesocosm experiment using static chamber method showed a strong increase in the cumulative emissions of CO2 (5.71%-9.19%) and N2O (11.36%-13.64%) (p < 0.05), as well as an elevated CH4 uptake (2.75%-5.50%) in sites where the four grass species were introduced, compared to bare soil. Consequently, there was a substantial rise in global warming potential (13.87%-16.33%) (p < 0.05) at grass-introduced sites. Redundancy analysis showed that seed traits, plant biomass, and seedling emergence percentage were the main driving biotic factors of three GHGs fluxes. Our study unveils the potential risk of escalating GHG emissions induced by introducing high altitude grasses to low altitude bare soil, elucidating the mechanism through linking seed traits with seedling establishment and environmental feedback. Furthermore, this offers a new perspective for assessing the impact of grass introduction on ecological environment of introduced site.

Effects of fall-spring cement applications on soil physico-mechanical quality of seed bed and seedling emergence.

The physico-mechanical quality of the seed bed is extremely important not only for the soil air-water dynamics, but also for the germination, seedling emergence, and development of the plants. The crust layer formed after precipitation and irrigation in soils with poor structural properties is among the most important indicators of the lower seedbed quality. While there are different applications to increase the physico-mechanical quality of the seedbed, there are also cement applications that provide rapid aggregate formation and stability. The effects of cement application on the soil mechanical quality and seedling emergence of clay textured soil with poor structural characteristics were investigated in the present study. For this purpose, a total of 36 small plots with a size of 2.4 m2 were created. Cement was applied at 0.25-0.5-1 and 2% doses to 18 plots in the fall period, and to the other 18 plots in the spring period. After the treatment, soil samples were taken for analysis before the planting period and the number of seedling emergence was determined by planting the bean plant during the planting period. According to the results of the study, it was found that cement applied in two periods caused an increase in soil aggregate stability, decreased penetration resistance, modulus of rupture, and dispersion rate, and increased water holding capacity to a limited extent. On the other hand, cement application also had positive impacts on the emergence of the bean plant. The 1% dose of the spring application of cement was more effective on the determined soil structural characteristics and seedling emergence.

Integrating demographic niches and black spruce range expansion at subarctic treelines.

When investigating relationships between species' niches and distributions, niches can be divided demographically, resulting in unique niches for different life stages. This approach can identify changing substrate requirements throughout a species' life cycle. Using non-metric multidimensional scaling, we quantified microsite conditions associated with successful recruitment in the tundra landscape and successful seed production amongst adult trees of black spruce (Picea mariana) at subarctic treeline in Yukon, Canada to assess how life stage-specific requirements may impact the distribution of this widespread boreal tree species. Treeline ecotones in this region showed high heterogeneity in tundra microsites available for establishment. Black spruce exhibited changing microsite associations from germination to reproductive maturity, which were mainly driven by changes in plant community and soil moisture. These associations limit the microsites where individuals can establish and reproduce to a subset available within the heterogeneous landscape. Overall, we suggest that (1) substrates suitable for early recruitment are limited at the range edge; and (2) reproductive adults have a narrow niche, limiting successful seed production in adults and forming sink populations where suitable conditions are limited. Our multivariate assessment of microsite suitability can provide valuable insights into the spatial distribution of a species throughout its life cycle and identify life stage-specific constraints to range expansion.

Effect of environmental factors on seed germination and seedling emergence of Viola prionantha, a cleistogamous plant.

Environmental conditions during seed development and maturation can affect seed traits and germination behavior, yet systematic research on the effects of seed maturation time on seed traits, germination behavior and seedling emergence of cleistogamy plants is lacking. Here, we determined the difference in phenotypic characteristics of CH and CL (namely CL1, CL2 and CL3 based on maturation time, respectively) fruits/seeds that were collected from Viola prionantha Bunge, a cleistogamous perennial plant, and evaluated the effects of various environmental factors on seed germination and seedling emergence. The fruit mass, width, seed number per fruit and mean seed mass of CL1 and CL3 were greater than that of CH and CL2, while seed setting of CH was lower than that of CL1, CL2 and CL3. Germination of CH, CL1, CL2, and CL3 seeds was < 10% in the dark at 15/5 and 20/10 â„ƒ, whereas germination (0%-99.2%) of CH, CL1, CL2, and CL3 seeds changed significantly under light conditions. In contrast, more than 71% (from 71.7 to 94.2%) germination of both CH, CL1, CL2 and CL3 seeds occurred under both light/dark conditions and continuous darkness at 30/20 â„ƒ. Germination of CH, CL1, CL2 and CL3 seeds was sensitive to osmotic potential, but CL1 seeds were more resistant to osmotic stress, compared with CH, CL2 and CL3. Seedling emergence of CH seeds was more than 67% (from 67.8 to 73.3%) at a burial depth of 0 cm-2 cm, while all types of CL seeds were below 15% at a burial depth of 2 cm. Information gathered from this study indicates that CH and CL seeds of V. prionantha were different in fruit size, seed mass, thermoperiod and photoperiod sensitivity, osmotic potential tolerance and seedling emergence, especially, maturation time significantly affect phenotypic characteristics and germination behavior of CL seeds matured at different periods. These results indicate that V. prionantha adapts to unpredictable environmental conditions by developing a variety of adaptation strategies, and ensures the survival and reproduction of the populations.

Germination and Growth of Plasma-Treated Maize Seeds Planted in Fields and Exposed to Realistic Environmental Conditions.

In this study, we applied an inductively coupled, radio frequency oxygen plasma to maize seeds and investigated its effects on seedling emergence, plant number at tasseling, and crop yield of maize in realistic field conditions. Maize seeds of seven different hybrids were treated over two harvest years. In addition to plasma-treated seeds, a control sample, fungicide-treated seeds, an eco-layer, and a plasma and eco-layer combination, were planted. Seedling emergence, plant number at tasseling (plants/m2), and yield (kg/ha), were recorded. In the first harvest year, results were negatively affected by the presence of an insect pest. In the second harvest year, plant number and yield results were more uniform. In both years, for two and three hybrids, respectively, the highest yield arose from plants from plasma-treated seeds, but the differences were only partially significant. Considering our results, plasma treatment of maize seeds appears to have a positive effect on the yield of the plant.

A quantitative analysis of temperature-dependent seasonal dormancy cycling in buried Arabidopsis thaliana seeds can predict seedling emergence in a global warming scenario.

Understanding how the environment regulates seed-bank dormancy changes is essential for forecasting seedling emergence in actual and future climatic scenarios, and to interpret studies of dormancy mechanisms at physiological and molecular levels. Here, we used a population threshold modelling approach to analyse dormancy changes through variations in the thermal range permissive for germination in buried seeds of Arabidopsis thaliana Cvi, a winter annual ecotype. Results showed that changes in dormancy level were mainly associated with variations in the higher limit of the thermal range permissive for germination. Changes in this limit were positively related to soil temperature during dormancy release and induction, and could be predicted using thermal time. From this, we developed a temperature-driven simulation to predict the fraction of the seed bank able to germinate in a realistic global warming scenario that approximated seedling emergence timing. Simulations predicted, in accordance with seedling emergence observed in the field, an increase in the fraction of the seed bank able to emerge as a result of global warming. In addition, our results suggest that buried seeds perceive changes in the variability of the mean daily soil temperature as the signal to change between dormancy release and induction according to the seasons.

Competition induces negative conspecific allelopathic effects on seedling recruitment.

BACKGROUND AND AIMS: Some plant species suppress competitors through release of chemical compounds into the environment. As the production of allelochemicals may be costly, it would be beneficial if their production would only be induced when plants experience competition. We tested whether two plant species that frequently co-occur show evidence for induced allelopathy in response to intra- and interspecific competition. METHODS: We used the annual forb Crepidiastrum sonchifolium and the perennial forb Achyranthes bidentata, which are native to China and predominantly occur in ruderal communities, as focal species. We first grew the species without competition, with intraspecific competition and in competition with each other. We chemically analysed aqueous extracts made from these plants to test for evidence that the competition treatments affected the metabolomic profiles of the species. We then tested the effects of the aqueous extracts on seed germination and seedling growth of both plant species. KEY RESULTS: Metabolomic analysis revealed that competition treatments modified the chemical profiles of the two study species. The root lengths of A. bidentata and C. sonchifolium seedlings were reduced by the aqueous plant extracts. For seedling root length of A. bidentata, heterospecific allelopathy was more negative than conspecific allelopathy, but for germination of C. sonchifolium seeds, the reverse was true. Moreover, conspecific allelopathic effects on germination of A. bidentata seeds and on seedling root length of both species were most negative when the aqueous extracts were made from plants that had experienced competition. In the case of seedling root length of A. bidentata, this effect was most negative when the plants had experienced interspecific instead of intraspecific competition. CONCLUSIONS: We showed that plants change their metabolomic profiles in response to competition, and that this correlated with allelopathic inhibition of conspecific seed germination and seedling growth. We suggest that autoallelopathy for seed germination could function as a mechanism to avoid strong competition by keeping the seeds in a dormant state.

Recruitment of pioneer trees with physically dormant seeds under climate change: the case of Vachellia pennatula (Fabaceae) in semiarid environments of Mexico.

Most tree species native to arid and semiarid ecosystems produce seeds with physical dormancy, which have impermeable coats that protect them from desiccation and prevent germination when the environmental conditions are unfavorable for seedling establishment. This dormancy mechanism may confer some degree of tolerance to seeds facing warmer and drier conditions, as those expected in several regions of the world because of climate change. Scarification of these seeds (removal of protective coats) is required for stimulating germination and seedling development. However, as scarification exposes seeds to the external environmental conditions, it can promote desiccation and viability loss in the future. To test these hypotheses, we performed field experiments and sowed scarified and unscarified seeds of a pioneer tree native to semiarid ecosystems of Mesoamerica (Vachellia pennatula) under the current climate and simulated climate change conditions. The experiments were conducted at abandoned fields using open-top chambers to increase temperature and rainout shelters to reduce rainfall. We measured microenvironmental conditions within the experimental plots and monitored seedling emergence and survival during a year. Air temperature and rainfall in climate change simulations approached the values expected for the period 2041-2080. Seedling emergence rates under these climatic conditions were lower than under the current climate. Nevertheless, emergence rates in climate change simulations were even lower for scarified than for unscarified seeds, while the converse occurred under the current climate. On the other hand, although survival rates in climate change simulations were lower than under the current climate, no effects of the scarification treatment were found. In this way, our study suggests that climate change will impair the recruitment of pioneer trees in semiarid environments, even if they produce seeds with physical dormancy, but also indicates that these negative effects will be stronger if seeds are scarified.

Changes in phenological events in response to a global warming scenario reveal greater adaptability of winter annual compared with summer annual arabidopsis ecotypes.

BACKGROUND AND AIMS: The impact of global warming on life cycle timing is uncertain. We investigated changes in life cycle timing in a global warming scenario. We compared Arabidopsis thaliana ecotypes adapted to the warm/dry Cape Verdi Islands (Cvi), Macaronesia, and the cool/wet climate of the Burren (Bur), Ireland, Northern Europe. These are obligate winter and summer annuals, respectively. METHODS: Using a global warming scenario predicting a 4 °C temperature rise from 2011 to approx. 2080, we produced F1 seeds at each end of a thermogradient tunnel. Each F1 cohort (cool and warm) then produced F2 seeds at both ends of the thermal gradient in winter and summer annual life cycles. F2 seeds from the winter life cycle were buried at three positions along the gradient to determine the impact of temperature on seedling emergence in a simulated winter life cycle. KEY RESULTS: In a winter life cycle, increasing temperatures advanced flowering time by 10.1 d °C-1 in the winter annual and 4.9 d °C-1 in the summer annual. Plant size and seed yield responded positively to global warming in both ecotypes. In a winter life cycle, the impact of increasing temperature on seedling emergence timing was positive in the winter annual, but negative in the summer annual. Global warming reduced summer annual plant size and seed yield in a summer life cycle. CONCLUSIONS: Seedling emergence timing observed in the north European summer annual ecotype may exacerbate the negative impact of predicted increased spring and summer temperatures on their establishment and reproductive performance. In contrast, seedling establishment of the Macaronesian winter annual may benefit from higher soil temperatures that will delay emergence until autumn, but which also facilitates earlier spring flowering and consequent avoidance of high summer temperatures. Such plasticity gives winter annual arabidopsis ecotypes a distinct advantage over summer annuals in expected global warming scenarios. This highlights the importance of variation in the timing of seedling establishment in understanding plant species responses to anthropogenic climate change.

Revisiting Sustainability of Fungicide Seed Treatments for Field Crops.

The use of fungicide seed treatment (FST) is a very common practice worldwide. The purported effectiveness of many fungicides in providing broad-spectrum and systemic control of important diseases and the perception that FST reduces overall pesticide use, hence lowering environmental impacts, have greatly promoted the use of FST in the last five decades. Since there have been rapid advancements in the types, formulations, and application methods for seed treatments, there is a need to re-evaluate the benefits versus the risks of FST as a practice. While the use of seeds treated with neonicotinoid insecticides has come under scrutiny due to concern over potential nontarget effects, there are knowledge gaps on potential negative impacts of FST on operators' (those who apply, handle, and use treated seeds) health and nontarget soil organisms (both macro- and microorganisms). Here we review existing knowledge on key fungicides used for seed treatments, benefits and risks related to FST, and propose recommendations to increase benefits and limit risks related to the use of FST. We found FST is applied to almost 100% of sown seeds for the most important arable crops worldwide. Fungicides belonging to 10 chemical families and with one or several types of mobility (contact, locally systemic, and xylem mobile) are used for seed treatment, although the majority are xylem mobile. Seed treatments are applied by the seed distributor, the seed company, and the farmer, although the proportion of seed lots treated by these three groups vary from one crop to another. The average quantity of fungicide active ingredient (a.i.) applied via seed treatment depends on the crop species, environment(s) into which seed is planted, and regional or local regulations. Cost-effectiveness, protection of the seed and seedlings from pathogens up to 4-5 weeks from sowing, user friendliness, and lower impact on human health and nontarget soil organisms compared with foliar spray and broadcast application techniques, are among the most claimed benefits attributed to FST. In contrast, inconsistent economic benefits, development of resistance by soilborne pathogens to many fungicides, exposure risks to operators, and negative impacts on nontarget soil organisms are the key identified risks related to FST. We propose eight recommendations to reduce risks related to FST and to increase their benefits.

Predicting the seedling emergence time of sugar beet (Beta vulgaris) using beta models.

Soil temperature, texture, water content and sowing depth are effective factors on the estimation of emergence time. This research aimed to test the Beta model for its adequacy in predicting the time of emergence for sugar beet. The Beta growth model as a phenological model have been used for evaluating the time of seedling emergences under both controlled environments in laboratory and field conditions. An experiment was conducted both in the laboratory with five soil textures, three sowing depths, five soil water contents and ten constant soil temperatures, under field conditions on five sowing dates (20 February, 28 March, 19 April, 10 May, and 31 May) and three sowing depths. The results demonstrated that the Beta model can predict the time of emergence. Based on the root mean square error (RMSE), the time of emergence estimated by the Beta model was in high agreement with the time of emergence measured in the laboratory. Estimation accuracy was reduced slightly by the Beta model under field conditions. The accuracy of the Beta model was influenced by the sowing date under field conditions. So, on the first and second sowing dates (with low air temperature), the estimation of time of emergence by the model was lower and on the fourth and the fifth sowing date (with warmer air temperature), was more than the duration measured. Estimation accuracy was increased by the Beta model under field conditions using soil temperature. In conclusion, the Beta model can predict the time to emergence of sugar beet seedlings in different levels of soil texture and soil water content under field conditions, and with that, the proper planting date for sugar beet seeds to overcome weeds in different soil water content can be predicted.

Seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence on desert sand dunes.

Seedling emergence is a critical stage in the establishment of desert plants. Soil microbes participate in plant growth and development, but information is lacking with regard to the role of microbes on seedling emergence. We applied the biocides (captan and streptomycin) to assess how seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence of Artemisia sphaerocephala on the desert sand dune. Fungal and bacterial community composition and diversity and fungal-bacterial interactions were changed by both captan and streptomycin. Mucilage increased soil enzyme activities and fungal-bacterial interactions. Highest seedling emergence occurred under streptomycin and mucilage treatment. Members of the phyla Firmicutes and Glomeromycota were the keystone species that improved A. sphaerocephala seedling emergence, by increasing resistance of young seedlings to drought and pathogen. Seed mucilage directly improved seedling emergence and indirectly interacted with the soil microbial community through strengthening fungal-bacterial interactions and providing favourable environment for soil enzymes to affect seedling emergence. Our study provides a comprehensive understanding of the regulatory mechanisms by which soil microbial community and seed mucilage interactively promote successful establishment of populations of desert plants on the barren and stressful sand dune.

Seed supply limits seedling recruitment of Eucalyptus miniata: interactions between seed predation by ants and fire in the Australian seasonal tropics.

Seed predation can cause substantial seed losses and influence plant population dynamics, but the impact depends on the extent to which populations are limited by seed availability or favorable microsites for recruitment. Harvester ants are the dominant post-dispersal seed predators in Australia's tropical savannas, and their abundance and foraging efficiency, as well as the availability of seed and microsites, are affected by fire history. We undertook a predator-exclusion experiment to examine the interactive effects of fire history (no fire compared with annual burning over 5 years) and seed predation by ants on seedling establishment of the dominant savanna tree, Eucalyptus miniata, in northern Australia. Despite its large seed size, the rate of removal (~ 20-60%) was similar or higher than typically reported for eucalypts, although it was lower than that recorded for the smaller seeds of the co-occurring E. tetrodonta. Seed predation rates were twice as high in annually burnt compared to unburnt sites, but there was no significant difference in the proportion of seedlings that emerged from the initial seed available. Seedling emergence in both regimes was low, representing < 7% of seed available after harvesting. About one-third of emergent seedlings were still alive during the middle of the following dry season. Our results indicate that seedling recruitment in E. miniata is limited by both seed supply and microsite availability. However, seed predation by ants reduces the likelihood of seedling establishment from low to virtually zero, which suggests that it plays a potentially important role in the population dynamics of savanna eucalypts.

Is Plant Fitness Proportional to Seed Set? An Experiment and a Spatial Model.

Individual differences in fecundity often serve as proxies for differences in overall fitness, especially when it is difficult to track the fate of an individual's offspring to reproductive maturity. Using fecundity may be biased, however, if density-dependent interactions between siblings affect survival and reproduction of offspring from high- and low-fecundity parents differently. To test for such density-dependent effects in plants, we sowed seeds of the wildflower Ipomopsis aggregata (scarlet gilia) to mimic partially overlapping seed shadows of pairs of plants, one of which produced twice as many seeds. We tested for differences in offspring success using a genetic marker to track offspring to flowering multiple years later. Without density dependence, the high-fecundity parent should produce twice as many surviving offspring. We also developed a model that considered the geometry of seed shadows and assumed limited survivors so that the number of juvenile recruits is proportional to the area. Rather than a ratio of 2∶1 offspring success from high- versus low-fecundity parents, our model predicted a ratio of 1.42∶1, which would translate into weaker selection. Empirical ratios of juvenile offspring and of flowers produced conformed well to the model's prediction. Extending the model shows how spatial relationships of parents and seed dispersal patterns modify inferences about relative fitness based solely on fecundity.

Contribution by vertebrates to seed dispersal effectiveness in the Galápagos Islands: a community-wide approach.

Seed dispersal and seedling recruitment are crucial phases in the life cycle of all spermatophyte plants. The net contribution of seed dispersers to plant establishment is known as seed dispersal effectiveness (SDE) and is defined as the product of a quantitative (number of seeds dispersed) and a qualitative (probability of recruitment) component. In Galápagos, we studied the direct contribution to SDE (number of seeds dispersed and effect on seedling emergence) provided by the five island groups of frugivores (giant tortoises, lizards, medium-sized passerine birds, small non-finch passerine birds, and finches) in the two main habitats in this archipelago: the lowland and the highland zones, and found 16 vertebrate species dispersing 58 plant species. Data on frequency of occurrence of seeds in droppings and number of seeds dispersed per unit area produced contrasting patterns of seed dispersal. Based on the former, giant tortoises and medium-sized passerines were the most important seed dispersers. However, based on the latter, small non-finch passerines were the most important dispersers, followed by finches and medium-sized passerines. The effect of disperser gut passage on seedling emergence varied greatly depending on both the disperser and the plant species. Although the contribution to SDE provided by different disperser guilds changed across plant species, medium-sized passerines (e.g., mockingbirds) provided a higher contribution to SDE than lava lizards in 10 out of 16 plant species analysed, whereas lava lizards provided a higher contribution to SDE than birds in five plant species. While both the quantitative and qualitative components addressed are important, our data suggests that the former is a better predictor of SDE in the Galápagos archipelago.

Physico-chemical changes in karkade (Hibiscus sabdariffa L.) seedlings responding to salt stress.

Salinity is one of the major abiotic stress factors affecting series of morphological, physiological, metabolic and molecular changes in plant growth. The effect of different concentrations (0, 25, 50, 100 and 150 mM) of NaCl on the vegetative growth and some physiological parameters of karkade (Hibiscus sabdariffa var. sabdariffa) seedling were investigated. NaCl affected the germination rate, delayed emergence and retarded vegetative growth of seedlings. The length of seedling as well as the leaf area was significantly reduced. The fresh weight remained lower in NaCl treated seedlings compared to control. NaCl at 100 and 150 mM concentrations had significant effect on the dry matter contents of the treated seedlings. The chloroplast pigments in the treated seedlings were affected, suggesting that the NaCl had a significant effect on the chlorophyll and carotenoid biosynthesis. The results showed that the salt treatments induced an increase in proline concentration of the seedlings. The osmotic potential (ψs) of NaCl treated seedlings decreased with increasing NaCl concentrations. Salt treatments resulted in dramatic quantitative reduction in the total sterol percent compared with control ones. Salt stress resulted in increase and decrease of Na+ and K+ ions, respectively. NaCl salinity increased lipid peroxidation. SDS-PAGE was used to evaluate protein pattern after applying salt stress. High molecular weight proteins were intensified, while low molecular weight proteins were faint. NaCl at 100 and 150 mM concentration distinguished with new protein bands. Salt stress induced a new peroxidase bands and increased the band intensity, indicating the protective role of peroxidase enzyme.