Seedling Establishment Rate Research Articles

Promoting effect of Manila clam Ruditapes philippinarum (Adams & Reeve, 1850) on the establishment of eelgrass Zostera marina L. seedlings

It is necessary to restore the declined eelgrass Zostera marina L. beds which have multiple functions. The utilization of seedlings to recover eelgrass beds can maintain the genetic eelgrass diversity; however, the seedling establishment rate that is affected by many habitat factors is very low. Manila clam Ruditapes philippinarum (Adams & Reeve, 1850) transform habitats through several ways. Thus, it is inferred that the clam affects the establishment of eelgrass seedlings in multiple ways, and the seedling establishment rate of eelgrass might not simply increase or decrease under the presence of clams. To verify this hypothesis, a five-month clam-mediated seedling establishment experiment was conducted. The contents of total nitrogen (TN) and exchangeable ammonia NH4-N (Ex-NH) in sediment increased as the clam body size increased, and TN decreased with the increase in clam abundance. There was a positive relationship between the content of organic matter in sediment (OM) and the interaction of body size and abundance of clam. The emergence rate of germinated seeds and the seedling establishment rate increased with increasing clam biomass. They were positively correlated with the interaction of OM and Ex-NH. The seedling establishment rate was negatively correlated with the interaction of water content in sediment (W) and medium diameter of sediment (Ø50), OM and TN. The presence of clams affected the height, chlorophyll b content and superoxide dismutase (SOD) activity of seedlings. The clam body size affected the SOD activity of seedlings by influencing Ex-NH. Thus, the habitat modification of clams with moderate biomass improves the establishment and traits of seedlings in multiple ways. The seedling establishment mediated by Manila clam is useful for eelgrass bed restoration.

Organic fertilizer type and dose affect growth, morphological and physiological parameters, and mineral nutrition of watermelon seedlings.

Organic agriculture has grown rapidly in recent years due to its environmental friendliness, sustainability, and improved farm profitability. Transplants are commonly used for fruits and vegetables to achieve consistent quality, uniformity, and easy field spacing control. The efficacy and optimal amounts of fertilizers for organic transplant production need to be investigated. The effects of three organic fertilizers (Sustane 4-6-4, Nature Safe 7-7-7, and Dramatic 2-4-1) and one conventional fertilizer Peters Professional 20-20-20 (Conventional) with four doses (nitrogen (N) content was matched among fertilizers in each level, as 0.14 g/L, 0.28 g/L, 0.56 g/L, and 0.84 g/L N, respectively) on watermelon seedlings were compared in this study. The results showed that all organic fertilizer treatments were not significantly different from the Conventional group in terms of watermelon germination. The only exception was the highest dose of Sustane 4-6-4 (0.84 g/L N) which decreased the germination rate and relative emergence index. Generally, growth index, shoot fresh and dry weights, true leaf number, and stem diameter increased as the amount of N increased within each fertilizer type. The best shoot growth was observed in the highest doses of Conventional and Dramatic 2-4-1 treatments (0.84 g/L N). However, Dramatic 2-4-1 treatments resulted in the lowest root growth when compared to other fertilizers at the same N dose. The second highest fertilization dose (0.56 g/L N) of Sustane 4-6-4 had the best root growth according to root fresh weight, root volume, root area, total root length, as well as the numbers of root tip and crossing when compared to other treatments. For seedlings, a well-developed root system can ensure a good seedling establishment and high survival rate under stressful field conditions after transplanting. Thus, Sustane 4-6-4 at 14 g/L (0.56 g/L N) is recommended to produce high-quality organic watermelon seedlings among the treatments applied in this study.

The Arabidopsis katamari2 Mutant Exhibits a Hypersensitive Seedling Arrest Response at the Phase Transition from Heterotrophic to Autotrophic Growth.

Young seedlings use nutrients stored in the seeds to grow and acquire photosynthetic potential. This process, called seedling establishment, involves a developmental phase transition from heterotrophic to autotrophic growth. Some membrane-trafficking mutants of Arabidopsis (Arabidopsis thaliana), such as the katamari2 (kam2) mutant, exhibit growth arrest during seedling development, with a portion of individuals failing to develop true leaves on sucrose-free solid medium. However, the reason for this seedling arrest is unclear. In this study, we show that seedling arrest is a temporal growth arrest response that occurs not only in kam2 but also in wild-type (WT) Arabidopsis; however, the threshold for this response is lower in kam2 than in the WT. A subset of the arrested kam2 seedlings resumed growth after transfer to fresh sucrose-free medium. Growth arrest in kam2 on sucrose-free medium was restored by increasing the gel concentration of the medium or covering the surface of the medium with a perforated plastic sheet. WT Arabidopsis seedlings were also arrested when the gel concentration of sucrose-free medium was reduced. RNA sequencing revealed that transcriptomic changes associated with the rate of seedling establishment were observed as early as 4 d after sowing. Our results suggest that the growth arrest of both kam2 and WT seedlings is an adaptive stress response and is not simply caused by the lack of a carbon source in the medium. This study provides a new perspective on an environmental stress response under unfavorable conditions during the phase transition from heterotrophic to autotrophic growth in Arabidopsis.

Distribution of sexually reproductive eelgrass (Zostera marina) seeds in microhabitats of eelgrass beds in intertidal zones

Eelgrass (Zostera marina) seedling establishment based on the sexually reproductive seed bank depends on habitat factors, and there are different microhabitats in eelgrass beds. Seedling abundance varies with microhabitat. Why is the distribution pattern of seedlings so? Is there an edge effect of eelgrass patches on seedling distribution? To clarify the distribution and variation patterns of ungerminated seeds, germinated seeds and seedlings in microhabitats, field investigations were conducted from December 2020 to April 2021. The density of the total seed bank varied with microhabitat except in March. In April, the density of germinated seed banks in the highland, low-lying area edge and low-lying area was 0.00 ± 0.00, 0.33 ± .33 and 7.44 ± 0.96 seeds.cm−3, respectively, and the density in the low-lying area was higher than that in the other microhabitats. The order of density of the seedling bank was highland < low-lying area edge < low-lying area in April. The relative proportion of germinated seeds in the low-lying area was higher than that in the highland from March to April, during which the increase rate in the seedling bank of the highland was lower than that of other microhabitats. The distribution pattern of eelgrass seeds varies with microhabitat. The change characteristics of germinated seeds or seedling banks are related to microhabitats. There are edge effects of eelgrass patches on the distribution of germinated seeds and seedlings. All these factors contribute to the formation of seedling distribution. Sowing eelgrass seeds in the edge area of a continuously distributed eelgrass bed can promote the seedling establishment rate.

Effect of Manila clam Ruditapes philippinarum on burial depth of eelgrass Zostera marina seeds and sediment porosity

Eelgrass Zostera marina is widely distributed in coastal areas of the Northern Hemisphere; however, its continuous population decline is increasingly serious. Besides exogenous stresses, there are endopathic reasons for the decline, e.g., its seedling establishment rate, which is affected by burial depth of seeds and sediment types, is extremely low. Studies have shown that eelgrass seedlings in bivalve distribution areas are easier to establish. Moreover, large-scale bottom sowing culture for bivalves affects the bulk density of sediments which affects seed germination and seedling establishment of eelgrass. This study sought to examine the relationship between sediment modification induced by Manila clams with different body size and stocking density and the burial depth of eelgrass seeds caused by clams. The porosity of surface sediments varied with Manila clam biomass and was mainly affected by clam body size. Clams with a weight of 2.56 ± 0.12 g created more porosity. Clams with a weight of 3.71 ± 0.10 g caused more porosity than clam with a weight of 7.47 ± 0.22 g did. The sand diving of Manila clams affected the distribution of eelgrass seeds in sediments at different depths. The moderately abundant and large Manila clams promoted the burial depth of eelgrass seeds in sediments, and this effect was more obvious at 1–3 cm near the burial depth of 2 cm which is conducive to germination of eelgrass seeds and seedlings establishment. Thus, based on the bioturbation of Manila clams, the efficiency of sowing methods to restore the eelgrass population can potentially be improved.

Intraspecific variation in native grass seedling plastic trait response to water stress depends on the context of annual grass invasion

Seed selection is critical for successful restoration in semiarid systems. In the Great Basin, drought and annual grass invasion are primary barriers to native perennial seedling establishment. Local seed sourcing is encouraged to overcome drought, as drier populations exhibit drought‐adapted traits. Whether drought‐adapted traits are also beneficial for resisting invasive annual grasses, however, is an outstanding question. Here, we evaluate seedling performance and trait expression of Sandberg bluegrass (Poa secunda), a native perennial grass commonly used in restoration, in a factorial experiment that crossed seed source (five populations collected along an aridity gradient), water treatment (wet and dry), and competition (with and without cheatgrass). Seeds from the wettest site had the highest mean seedling establishment rate and biomass compared to seeds from drier sites. Establishment rate was sensitive to drought but not to cheatgrass competition, whereas biomass was sensitive to both stressors. Watering and competition treatments had a significant interaction effect on seedling trait expression. Specifically, without cheatgrass competition P. secunda exhibited more resource‐conservative traits under drought, such as lower specific leaf area and higher proportion of fine roots, whereas the relationship shifted such that with cheatgrass competition P. secunda exhibited more resource‐acquisitive traits under drought. Plasticity of seedling emergence and root length were negatively correlated with drought tolerance, which suggests no evidence for adaptive plasticity. As trait‐based approaches are increasingly used for seed selection in the Great Basin, our results highlight that the predictive power of traits for drought depends on the context of annual grass invasion.

SES1 is vital for seedling establishment and post-germination growth under high-potassium stress conditions in Arabidopsis thaliana.

The potassium ion (K+) plays an important role in maintaining plant growth and development, while excess potassium in the soil can cause stress to plants. The understanding of the molecular mechanism of plant's response to high KCl stress is still limited. At the seed stage, wild type (WT) and SENSITIVE TO SALT1 (SES1) mutants were exposed to different concentrations of potassium treatments. Tolerance was assayed as we compared their performances under stress using seedling establishment rate and root length. Na+content, K+content, and K+/Na+ ratio were determined using a flame atomic absorption spectrometer. In addition, the expressions of KCl-responding genes and ER stress-related genes were also detected and analyzed using qRT-PCR. SES1 mutants exhibited seedling establishment defects under high potassium concentration conditions and exogenous calcium partially restored the hypersensitivity phenotype of ses1 mutants. The expression of some K+ transporter/channel genes were higher in ses1-2, and the ratio of potassium to sodium (K+/Na+) in ses1-2 roots decreased after KCl treatment compared with WT. Further analysis showed that the ER stress marker genes were dramatically induced by high K+ treatment and much higher expression levels were detected in ses1-2, indicating ses1-2 suffers a more serious ER stress than WT, and ER stress may influence the seedling establishment of ses1-2 under high KCl conditions. These results strongly indicate that SES1 is a potassium tolerance relevant molecule that may be related to maintaining the seedling K+/Na+ balance under high potassium conditions during seedling establishment and post-germination growth. Our results will provide a basis for further studies on the biological roles of SES1 in modulating potassium uptake, transport, and adaptation to stress conditions.

The influence of burial depth on germination and establishment of seeds in chimpanzee faeces, Taï National Park, Côte d’Ivoire

AbstractOne of the many ecosystem services provided by dung beetles is that of secondary seed dispersal. This paper experimentally evaluates the effectiveness of this service using the chimpanzee–dung beetle seed dispersal system in Taï National Park, Côte d’Ivoire. The study focussed on the germination rate and success of four species of seeds contained in the faeces ofPan troglodytes verus: Dacryodes klaineana(Pierre) H.J. Lam,Diospyros manniiHiern,Pycnanthus angolensis(Welw.) Warb., andUapaca guineensisMuell. Arg. For each species, 600 seeds, half from chimpanzee faeces and half from mother trees, were sown in nurseries at depths of 0, 2, 5, 10, and 15 cm (i.e. 120 seeds per depth; 60 from chimp and 60 from mother trees). After germination, only the seeds ofUapaca guineensisandDiospyros manniisown at 2 and 5 cm had a &gt;14% rate (between 14.2 and 30.8%) of germination and seedling establishment, regardless of seed origin. An increase in the depth of seed burial appears to negatively affect the probability of seedling emergence and establishment. This study shows that dung beetles have positive impacts on seed fate. However, for these plant species, the chimpanzee’s role is limited to that of primary seed dispersal.

Harvest and dispersal syndromes influence the probability of tree seedling establishment in the eastern United States

AbstractAimThe goal of this work was to investigate the influence of disturbance, in particular tree harvesting, on seedling establishment rates both within and beyond the range extent of individual species. In addition, we considered how disturbances differentially affect seedling establishment depending on the dispersal syndromes and shade tolerance of species.LocationThis project covers the eastern forests of the USA.Time periodData for this project extend from 1996 to 2019.Major taxa studiedTree species of the eastern USA.MethodsWe used the US Forest Service's Forest Inventory and Analysis (FIA) data for tree species of the eastern USA to investigate the influence of disturbance, the dispersal mechanism and shade tolerance of species on the establishment of seedlings. We ran generalized linear models for seedling presence/absence and the number of seedlings as the response variables. Disturbance categories were no disturbance, natural disturbance, harvest, and both harvest and natural disturbance.ResultsThe probability of seedling establishment increased in response to harvest within FIA plots but not in response to natural disturbances. Harvest increased the probability of seedling presence the most for shade‐intolerant species; however, intermediately shade‐tolerant and ‐intolerant species also increased in harvested plots. Additionally, bird‐dispersed species had a higher probability of colonizing new plots outside their range, in comparison to mammal‐dispersed or wind‐dispersed tree species.Main conclusionsOur results suggest that stand competition is an important limiting factor for seedling establishment in the dense, secondary forests of the eastern USA. Harvesting creates sizeable gaps that promote seedling establishment and species turnover. Harvesting especially facilitates the establishment of tree species with bird dispersal outside of their range. Thus, timber harvesting can be a useful management tool when the goal is to assist range shifts for certain species. We recommend that future research should include harvested plots when looking for evidence of recent tree migration.

An examination of seed germination and seedling growth of Zostera marina for planting-time selection in Rongcheng Bay, Shandong Peninsula, China

This study firstly quantified the responses of seeds of Zostera marina to different planting times (22 September, 5 October, 23 October, 7 November and 20 November in 2015) through a field seed-planting experiment over a two year period. The suitable seed planting time required by the seeds of Z. marina was evaluated. The seedling establishment rate of Z. marina subjected to different planting times ranged from 7% to 55%, with the higher values attained on the treatments of 22 September and 5 October. New plant patches from seed were fully developed and well maintained on the planting time of 22 September, 5 October and 23 October after 2 years following planting. The shoot density under the three treatments ranged from 62 shoots per replicate to 72 shoots per replicate with an average of 67 shoots per replicate in September 2017. According to the propagation assessment and growth analysis, we found that the planting time from mid-September to mid-October may be the optimal time to plant seeds of Z. marina in our experimental site. Our results demonstrate that seed planting time has an important effect on the effectiveness of eelgrass restoration and provide data that could prove helpful in the development of successful eelgrass restoration.

Weed seed mass affects seedling establishment and resource allocation patterns across a cereal rye surface residue gradient

AbstractKnowledge of weed population‐ and community‐level responses to the integration of cover crop surface residues (CCSRs) is vital to understanding their value when integrated into no‐till field crop production systems. Ecological theory suggests that weed seedling survival and resource allocation patterns during the establishment phase should be influenced by the interaction between seed mass and CCSR levels. We conducted a greenhouse experiment to investigate seedling establishment rates and resource allocation patterns in response to increasing CCSR levels across a seed mass gradient, including weed and crop species. The experiment utilised a two‐factor treatment structure, including 10 plant species that varied in seed mass by three orders of magnitude and four cereal rye mulch levels (0, 3360, 6720 and 10,080 kg ha−1). Our results support the hypothesis that the effect of CCSRs on seedling establishment rates is a function of seed mass. Analysis by species showed a decrease in seedling establishment rates of dicotyledon species across all CCSR levels, but this relationship varied among monocotyledon species. CCSR levels were positively correlated with resource allocation to the hypocotyl and specific hypocotyl length of dicotyledon species. Increasing CCSR levels decreased allocation of resources to roots in broadleaved species but did not affect resource allocation patterns in monocotyledon species. We conclude that the combined effects of CCSRs on seedling establishment rates and resource allocation could significantly influence weed population‐ and community‐level dynamics.

ITRAQ-Based Proteomics Investigation of Critical Response Proteins in Embryo and Coleoptile During Rice Anaerobic Germination

Direct-seeding of rice has become popular in recent years due to its low cost and convenience, however, hypoxic condition limits seedling establishment. In this study, weedy rice WR04-6 with high germination ability under anaerobic conditions was used as a gene donor, and we successfully improved the seedling establishment rate of rice cultivar Qishanzhan (QSZ) based on selection of a new rice line R42 from the recombinant inbred line population. R42 inherited high anaerobic germination (AG) ability, and was used for isobaric tags for relative and absolute quantitation (iTRAQ)-based comparative proteomic studies with QSZ to further explore the molecular mechanism of AG. A total of 719 differentially abundant proteins (DAPs) were shared by R42 and QSZ responded to AG, and thus defined as common response DAPs. A total of 300 DAPs that responded to AG were only identified from R42, which were defined as tolerance-specific DAPs. The common response and tolerance-specific DAPs had similar biochemical reaction processes and metabolic pathways in response to anoxic stress, however, they involved different proteins. The tolerance-specific DAPs were involved in amino acid metabolism, starch and sucrose metabolism, tricarboxylic acid cycle pathway, ethylene synthesis pathway, cell wall-associated proteins and activity of active oxygen scavenging enzyme. The in silico protein-protein interactions for the top 60 DAPs indicated that tolerance-specific DAPs had relatively independent protein interaction networks in response to an anoxic environment compared with common response DAPs. The results of physiological indicators showed that α-amylase and superoxide dismutase activities of R42 were significantly increased under anoxic conditions compared with aerobic conditions. Multiple lines of evidence from western blot, physiological analysis and quantitative real-time PCR jointly supported the reliability of proteomics data. In summary, our findings deepened the understanding of the molecular mechanism for the rice response to AG.

Seasonal temperature–moisture interactions limit seedling establishment at upper treeline in the Southern Rockies

AbstractOver recent decades, sharply rising temperatures without an accompanying increase in precipitation have created widespread heat‐induced drought stress, or hotter drought. Tree‐ring reconstructions have discovered significant declines in seedling establishment from hotter drought across montane and subalpine forest belts during this time, yet comparable studies at upper treeline are non‐existent. In this study, we reconstruct annual patterns of seedling establishment at upper treeline in the Southern Rocky Mountains to test the hypotheses that establishment is governed by temperature–moisture interactions and that slope aspect mediates the influence of hotter drought. To test these hypotheses, we destructively sampled seedlings along a network of six study sites to reconstruct annual patterns of establishment on opposite north‐facing and south‐facing slopes. Results from this research can be summarized into two main points with respect to the influence of climate on seedling establishment at upper treeline over approximately the last three decades (1991–2019). First, temperature–moisture interactions throughout the year play a crucial role in facilitating successful seedling establishment. Second, and perhaps most striking, is the complete lack of establishment at all sites over the past decade. This could signify that a threshold has been surpassed and conditions are now beyond the climatic optimum for successful seedling establishment above treeline moving forward. These results expand upon similar findings from forests at lower elevations, introducing the likelihood that seedling establishment along the entire mountain forest belt of the Southern Rocky Mountains is being impacted by hotter drought. This means that any declines in the rate of seedling establishment across montane and subalpine forests will not be offset by increased recruitment at treeline.

Chickpea seed cryostorage alters germinant but not adult plant growth

Food security concerns are emerging in many parts of the world due to climate change, disease, and diminishing areas of arable land. Risks to food security can be alleviated by advances in plant biotechnology such as cryopreservation (usually at −196 °C in liquid nitrogen (LN)). While seed cryopreservation methods are being developed for a number of crop species such as chickpea, the scale at which they are implemented is still limited since the effects of cryostorage on subsequent germination, and plant growth and biochemistry are largely unknown. This short communication describes the early stages of germination, emergence and field performance of plants derived from cryopreserved chickpea seeds. Germination and seedling growth were delayed in seeds exposed to LN. Germination percentage of seeds not exposed to LN was 1.18 fold higher than those immersed in LN (99.9% versus 84.3%). Seedling emergence was 1.24-fold higher in control relative to LN exposed seeds (99.6% versus 80.2%). The enzymes superoxide dismutase and peroxidase showed activities higher in seeds exposed to LN in both cases. Superoxide dismutase specific activity was 1.9 folds increased (0.30 U mg−1 proteins / 0.15 U mg−1 proteins). Peroxidase specific activity was 1.7 folds increased (4.1 U mg−1 proteins / 2.3 U mg−1 proteins). Contrastingly, the total protein level in control seeds was 1.2 fold higher than the LN-exposed seeds (8.98 mg g−1 fresh weight versus 7.54 mg g−1 fresh weight). Electrolyte leakage was higher in seeds exposed to LN (1.9 fold increase; 17.4% versus 9.1%), and in the radicles, plumules, roots and leaves derived from these seeds. Electrolyte leakage in radicles showed 1.8 fold-increase (9.1% / 5.1%) and plumules 1.5 fold-increase at 72 h of germination (9.3% / 6.3%). At 7 d of germination, roots showed 1.4 fold-increase (8.9% / 6.3%) and leaves 1.7 fold-increase (17.3% / 10.2%). When adult plants were compared at harvest (110 days after sowing) in terms of thirteen traits there were no significant differences between those produced from cryopreserved and control seeds. It worth mentioning that these traits included both developmental and biomass/yield-related traits. These results suggest that even though cryostorage may reduce in-field seedling establishment rates by compromising germinability to a small degree, the effects of LN exposure on seed and seedling biochemistry are unlikely to affect subsequent plant yield. This validate the use of cryopreservation for the long term storage of chickpea germplasm.

To grow or not to grow ….

To grow or not to grow ….

Direct seeding reduces the costs of tree planting for forest and savanna restoration

To increase the scale of restoration efforts, it is imperative to develop more cost-efficient methods. Seedling planting is the most common strategy for active restoration in the tropics, but direct seeding is increasingly being used. We estimated the costs of seed production for 50 species of forest and savanna trees in Brazil, the costs for each 1-y-old seedling of 57 species established by direct seeding, and the total costs per area of direct seeding, compared with seedling planting. We recorded the harvesting and processing effort to produce seeds our restoration research project in 2015, 2016, and 2017 in Central Brazil. The cost per 1-y-old seedling was estimated by dividing the market price of a seed by the proportion of successful establishment in the field, plus planting and maintenance costs. Establishment proportion was calculated based on several published and unpublished studies of direct seeding projects in Brazil. To estimate the cost of restoration per area we considered the operational costs and inputs to establish and maintain one hectare for one year. For comparison we used literature data for the costs of nurse-seedling planting. Seed processing is costly, but not always necessary for the success of restoration. The cost of establishing a 1-y-old seedling by direct seeding was cheaper than by nurse-seedling planting for 56 of 57 species. The cost of direct seeding per area is much lower than seedling planting, even considering a low seedling establishment rate. Since direct seeding filters the seed types that can be sowed, integrating direct seeding with sporadic seedling planting can be an efficient strategy when the probability of natural species colonization is low.

RESPONSES OF SOIL WATER‐SALT VARIATION AND COTTON GROWTH TO DRIP IRRIGATION WITH SALINE WATER IN THE LOW PLAIN NEAR THE BOHAI SEA

AbstractTo test the feasibility and sustainability of drip irrigation with saline water in the Low Plain near the Bohai Sea (BHLP) in North China, the effects of drip irrigation using saline water on soil water salt, cotton growth, seed cotton yield and fibre quality were conducted during 2017–2018. Five salinity levels of irrigation water were set up: 1.3, 5.4, 8.8, 12.4 and 15.9 dS m‾¹. Cotton evapotranspiration increased first and then decreased with increasing salinity of irrigation water. Soil ECe within the cotton root zone at each stage increased with greater salinity of irrigation water. After a 2‐year experiment soil desalination occurred in the main root layer (top 0–60 cm soil layer) when water salinity was less than 8.8 dS m‾¹. The significant (p &lt; 0.05) decline of seedling establishment rate and seed cotton yield only occurred in 15.9 dS m‾¹ treatment in 2017 when saline water was drip irrigated right after sowing. Leaf area index and plant height were inhibited when irrigation water salinity was more than 12.4 dS m‾¹ in both years. Additionally, saline water irrigation had little effect on fibre quality. To avoid a secondary salinization risk in this region, water with the salinity level of ≤8.8 dS m‾¹ was recommended under drip irrigation. © 2020 John Wiley &amp; Sons, Ltd.

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

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

Local adaptation constrains drought tolerance in a tropical foundation tree

Abstract Plant species with broad climatic ranges might be more vulnerable to climate change than previously appreciated due to intraspecific variation in climatic stress tolerance. In tropical forests, drought is increasingly frequent and severe, causing widespread declines and altering community dynamics. Yet, little is known about whether foundation tropical trees vary in drought tolerance throughout their distributions, and how intraspecific variation in drought tolerance might contribute to their vulnerability to climate change. We tested for local adaptation in seedling emergence and establishment with a full‐factorial reciprocal transplant experiment including 27 populations and 109,350 seeds along a 3,500 mm precipitation gradient for a widespread tropical foundation tree, Metrosideros polymorpha, in Hawaii. To more precisely relate seedling performance to soil moisture, we conducted a complementary greenhouse experiment to test responses of the same focal populations to simulated drought. In the reciprocal transplant experiment, we observed significant variation among populations and sites in germination and seedling establishment rates. Overall, there was a significant link between historical rainfall of populations and their performance under current rainfall at the study sites consistent with local adaptation. In particular, populations from historically wet sites demonstrated lower germination rates in currently dry sites compared to wet field sites, while populations from historically dry sites germinated well across all sites, with particularly high germination in dry sites. In the greenhouse, seedlings from wet populations survived fewer days without water, and succumbed at wetter soil conditions than populations from historically dry sites, corroborating results from the field experiment. Synthesis. While climate change models project the greatest drying trends for historically dry areas in Hawaii, even moderate drying of wet sites could significantly reduce Metrosideros polymorpha recruitment given the sensitivity of seedlings to very slight changes in water regimes. Thus, although M. polymorpha demonstrates high seedling drought tolerance in some populations, providing evidence of resilience at the species‐scale, there are nonetheless vulnerable populations that will likely decline under climate change. Our approach demonstrates that even trees with high dispersal abilities can show significant clines in drought tolerance, and suggests that similar intraspecific variation might be an important consideration for other tropical foundational tree species.

Mesocotyl elongation, an essential trait for dry-seeded rice (Oryza sativa L.): a review of physiological and genetic basis.

(1) Mesocotyl elongation is responsive to abiotic stresses, such as deep sowing drought, submergence, chilling, and salinity. (2) Humus soil culture with a burial depth of 6cm and at the temperature of 30°C could be the optimum method for mesocotyl length phenotyping, The frequently colocalized quantitative trait loci (QTL) controlling mesocotyl elongation were located on chromosome (3) 1 (RM562-RG146), chromosome 2 (RZ288-RM145), and chromosome 3 (RM426-RM520). Dry direct-seeding is becoming a popular rice cultivation technology in many countries, which reduces water use and labor costs enormously. Meanwhile, direct-seeding rice is also facing the problems of low seedling emergence rate, poor seedling establishment, weed infestation, and high crop lodging rate. To take the full advantages of direct-seeding, both agronomic and genetic solutions are needed. Varieties with optimum mesocotyl length are desired for improving rice seedling emergence rate, particularly under deep sowing and submergence, which is adopted to reduce lodging and increase tolerance to abiotic stresses. In this review, we summarized the physiological and genetic mechanisms of mesocotyl elongation in rice. The elongation of mesocotyl is affected by light, temperature, and water, and, as a result, is responsive to sowing depth, water content, and soil salinity. Plant hormones such as abscisic acid (ABA), brassinosteroid (BR), strigolactones (SLs), cytokinin (CTK), ethylene (ETH), jasmonic acid (JA), gibberellin (GA), and indole-3-acetic acid (IAA) play important roles in regulating mesocotyl elongation. A humus soil culture protocol developed by our team was shown to be a better high-throughput method for measuring mesocotyl length in large scale. Sixty-seven QTL controlling mesocotyl length were reported, which are distributed on all the 12 chromosomes. Twelve chromosomal regions were repeatedly found to have QTL using various mapping populations and methods. These regions should be targeted in future studies to isolate genes and develop markers for molecular breeding. Two genes with very different molecular functions have been cloned, highlighting the genetic complexity of mesocotyl elongation.