Analysis on Factors Affecting Seedling Establishment in Rice

Elongations of coleoptile and mesocotyl are related directly to rice seedling establishment in soil and height of plant is related to lodging in rice production. Twelve typical rice cultivars with different lengths of coleoptile and mesocotyl （long, medium and short） were selected by screening the lengths of coleoptile and mesocotyl in 1500 accessions. The seedling establishments of these typical cultivars were compared under the combinations of different sowing depths and flooding durations, and two semi-dwarf varieties （G140, Zhong 96-21） with good seedling establishments and optimum mesocotyl lengths were found. The length of mesocotyl was completely fitted negative binomial distribution and the length of coleoptile was nearly fitted Iognormal distribution. Analysis of the relationships among mesocotyl, coleoptile, seeding depth, flooding duration, and their interactions to seedling establishment percentage showed that there existed significant relations among mesocotyl, coleoptile, mesocotyl x coleoptile, seeding depth, flooding duration and mesocotyl x sowing depth in the experiment for seedling establishment.

Factors influencing seed reserve utilization during seedling establishment in maize inbred lines

Strong seedlings are essential for high yield.To explore the foundation of strong seedlings,we investigated various factors influencing the conversion and distribution of seed storage reserves during seedling establishment in maize inbred lines.Three maize inbred lines were used to explore the effects of seed size,seed vigor,illumination duration,temperature,water content,and salt concentration of the seedling medium on the utilization of seed storage reserves during seedling establishment.The results showed that the conversion rate of small seeds was 3.69 to 17.71%higher than that of large seeds.Moreover,prolonged illumination time was conducive to the formation of strong seedlings.However,low temperature,drought stress and salt stress reduced the conversion rate of seed storage reserves and increased the root/shoot ratio.These results could be used to guide field management during seedling emergence and develop improved germplasm with a high conversion rate of seed storage reserves.

Identification and fine mapping of quantitative trait loci for seed vigor in germination and seedling establishment in rice

Seed vigor is an index of seed quality that is used to describe the rapid and uniform germination and the establish- ment of strong seedlings in any environmental conditions. Strong seed vigor in low-temperature germination conditions is particularly important in direct-sowing rice production systems. However, seed vigor has not been selected as an important breeding trait in traditional breeding programs due to its quantitative inherence. In this study, we identified and mapped eight quantitative trait loci （QTLs） for seed vigor by using a recombinant inbred population from a cross between rice （Oryza sativa L. ssp. indica） cultivars ZS97 and MH63. Conditional QTL analysis identified qSV-1, qSV-Sb, qSV-6a, qSV- 6b, and qSV-11 influenced seedling establishment and that qSV- 5a, qSV-Sc, and qSV-8 influenced only germination. Of these, qSV-1, qSV-Sb, qSV-6a, qSV-6b, and qSV-8 were low-tempera- ture-specific QTLs. Two major-effective QTLs, qSV-1, and qSV-5cwere narrowed down to 1.13-Mbp and 4oo-kbp genomic regions, respectively. The results provide tightly linked DNA markers for the marker-assistant pyramiding of multiple positive alleles for increased low-temperature germination seed vigor in both normal and environments.

Transcriptional Regulation of Lipid Catabolism during Seedling Establishment

Lipid catabolism in germinating seeds provides energy and substrates for initial seedling growth,but how this process is regulated is not well understood.Here,we show that an AT-hook motif-containing nuclear localized(AHL)protein regulates lipid mobilization and fatty acid p-oxidation during seed germination and seedling establishment.AHL4 was identified to directly interact with the lipid mediator phosphatidic acid(PA).Knockout(KO)of AHL4 enhanced,but overexpression(OE)of AHL4 attenuated,triacylglycerol(TAG)degradation and seedling growth.Normal seedling growth of the OE lines was restored by sucrose supplementation to the growth medium.AHL4-OE seedlings displayed decreased expression of genes involved in TAG hydrolysis and fatty acid oxidation,whereas the opposite was observed in AHL4-KOs.These genes contained AHL4-binding cis elements,and AHL4 was shown to bind to the promoter regions of genes encoding the TAG lipases SDP1 and DALL5 and acyl-thioesterase KAT5.These AHL4-DNA interactions were suppressed by PA species that bound to AHL4.These results indicate that AHL4 suppresses lipid catabolism by repressing the expression of specific genes involved in TAG hydrolysis and fatty acid oxidation,and that PA relieves AHL4-mediated suppression and promotes TAG degradation.Thus,AHL4 and PA together regulate lipid degradation during seed germination and seedling establishment.

Effect of Acorn Burying Depth on Germination, Seedling Emergence and Development of Quercus aliena var. acuteserrata

Acorns of Quercus aliena var. acuteserrata Maxim. are often predated by small mammals and birds in natural forests. These animals not only eat the acorns during the acorn ripening season, but also cache and hoard most of the remaining acorns on the forest floor in the soil for their future use. These buried acorns form the main seed resource for regeneration. Burying depth is potentially important for germination and for seedling development. The effects of burying depth on germination and seedling development in relation to acorn size were studied in an experiment, in which acorns were planted at 6 cm-, 12 cm- and 18 cm-depth. The experimental results showed that fewer acorns germinated as burying depth increased. From the deeply buried acorns fewer seedlings emerged at later time than from those acorns buried less deeply. They appeared to have more difficulties to emerge above-ground than die seedlings from shallowly buried acorns. The deeply buried acorns and their seedlings also appeared to be more susceptible to rot. Acorn size did not significantly affect germination and emergence of the seedlings. As early emerged seedlings had longer developmental periods in their first growing season, and therefore grew better than die late emerged seedlings, seedlings from die shallowly buried acorns took the advantage.

Effects of Trichoderma harzianum YC_(459) and soil types on seed germination and seedling growth in rock slope restoration

We carried out experiments with various concentrations of Trichoderma harzianum YC459 in different soil types(forest soil, mixed soil,merchantable soil, and leaf mold soil) to evaluate its effect on seed germination and seedling establishment of four species(Festuca arundinacea Schreb., Dianthus barbatus var. asiaticus Nakai,Lespedeza cyrtobotrya Miq., and Parthenocissus tricuspidata Planch) for rock slope restoration. We also investigated the use of drilled slanted holes on the rock slopes for seedling establishment. The results showed that T. harzianum concentration had significant effects on seed germination, seedling growth, and seedling survival for all the species with different soil types. Seed germination and survival rates peaked at 5% T. harzianum concentration with leaf mold soil and decreased as T. harzianum concentration increased from 5% to 10%. Seedling survival rates of all four species were generally lowest at 0% T. harzianum concentration in all soil types.The height of F. arundinacea and L. cyrtobotrya peaked at 5% T. harzianum concentration whereas that of D. barbatus and P. tricuspidata peaked at 10%T. harzianum concentration. We concluded that 5% T. harzianum concentration with leaf mold soil is appropriate for seed germination and seedling survival rates of most species, thus enhancing seedling establishment. Practical application of the findings of this study will contribute in the vegetation restoration of steep rocks in mountain environments.

Seed bank and regeneration dynamics of Emmenopterys henryi population on the western side of Wuyi Mountain,South China

Emmenopterys henryi Oliv. (Rubiaceae) is an endangered tree species that is native to China. The wild populations of E. henryi have declined rapidly because of its poor natural regeneration, but the actual regeneration processes are not yet understood. In field tracking surveys and experiments in the Wuyishan Nature Reserve in Southeast China to determine the most important stage that affects the regeneration process, seed bank characteristics, seed germination, and seedling growth dynamics were studied in the typical habitats of E. henryi, Phyllostachys pubescens and broad-leaved forests. Results showed that in both P. pubescens and broad-leaved forests, more than 70% of the E. henryi seeds were distributed in moss and litter layers, and few were found in the soil beneath them. However, seed germination in the soil layer was significantly higher than in the moss and litter layers. Seed density, overall seed quality, and germination rate in the broad-leaved forest were significantly higher than in P. pubescens forest. Seed germination was highest in the microsites around the edge of the crown projection area of E. henryi mother trees. The order of survival rate of the seedlings on different ground surfaces was soil > moss > litter. In both habitats, the average seed density was 24.9 seeds m(-2), and the total germination rate was less than 3.5 parts per thousand. However, seedlings developed from only 1% of the germinated seeds, indicating that the seed germination is the most important stage in the natural regeneration of E. henryi.

Effect of spatial heterogeneity on natural regeneration of Manchurian ash

The spatial patterns of seedlings originating from natural regeneration are often heterogeneous since they are strongly influenced by microsite gradient. We supposed that the patterns of Manchurian ash (Fraxinus mandshurica Rupr.) seedlings, which were originated from natural seed rain, were also spatial heterogeneous in spite of relative homogeneous of planted forest. The tree seedling establishment and growth were monitored in the Forest-experimental-station of Northeast Forestry University during growing season from early May to late September in 1999. The emergence of seedlings began in middle May; but the peak was about in late May. Seedlings were counted in 635 grid cells in late June, there were about 16–30 individuals/m2, but almost all of them died off in late September. The scale and extent of seedling heterogeneity were assessed by semivariogram and fractal dimension. The study showed that over 70% of seedling pattern was spatially autocorrelated, and that the variation caused by random factors was in less than 30%. The spatial dependent scales, both isotropy and anisotropy, were 1.95–2.92 m and 1.83–6.40 m respectively in the research stands. Our hypothesis was supported although there was difference when samples were chose at both different spatial scale and different density stands.

Simultaneous flowering of umbrella bamboo (Fargesia murieliae) at its native home in Central China

Flowering pattern and seedling establishment of umbrella bamboo （Fargesia murieliae （Gamble） Yi） were studied in its native habitat, Mount Shennongjia in Central China. Here in 1996-2000, over 95% of the bamboo plants simultaneously flowered and died, extending from lower elevations to the higher mountains along the altitude and from southwest to northeast along the mountain settings. Bamboo seedlings emerged after the simultaneous flowering, achieving an average density of 5 460 seedlings·m^-2 in the autumn of the year following the flowering. After a high mortality throughout the first winter, bamboo seedlings remained a stable density in following 2-4 years （1130-1230 seedlings·m^-2）. Seedling density positively related to the coverage of parent bamboo, but negatively to the herb layers.

Mangrove forests as a nature-based solution for coastal flood protection:Biophysical and ecological considerations

Nature-based coastal protection is increasingly recognised as a potentially sustainable and cost-effective solution to reduce coastal flood risk.It uses coastal ecosystems such as mangrove forests to create resilient designs for coastal flood protection.However,to use mangroves effectively as a nature-based measure for flood risk reduction,we must understand the biophysical processes that govern risk reduction capacity through mangrove ecosystem size and structure.In this perspective,we evaluate the current state of knowledge on local physical drivers and ecological processes that determine mangrove functioning as part of a nature-based flood defence.We show that the forest properties that comprise coastal flood protection are well-known,but models cannot yet pinpoint how spatial heterogeneity of the forest structure affects the capacity for wave or surge attenuation.Overall,there is relatively good understanding of the ecological processes that drive forest structure and size,but there is a lack of knowledge on how daily bed-level dynamics link to long-term biogeomorphic forest dynamics,and on the role of combined stressors influencing forest retreat.Integrating simulation models of forest structure under changing physical(e.g.due to sea-level change)and ecological drivers with hydrodynamic attenuation models will allow for better projections of long-term natural coastal protection.

Environmentally adaptive reshaping of plant photomorphogenesis by karrikin and strigolactone signaling

Coordinated morphogenic adaptation of growing plants is critical for their survival and propagation under fluctuating environments.Plant morphogenic responses to light and warm temperatures,termed photomorphogenesis and thermomorphogenesis,respectively,have been extensively studied in recent decades.During photomorphogenesis,plants actively reshape their growth and developmental patterns to cope with changes in light regimes.Accordingly,photomorphogenesis is closely associated with diverse growth hormonal cues.Notably,accumulating evidence indicates that light-directed morphogenesis is profoundly affected by two recently identified phytochemicals,karrikins(KARs)and strigolactones(SLs).KARs and SLs are structurally related butenolides acting as signaling molecules during a variety of developmental steps,including seed germination.Their receptors and signaling mediators have been identified,and associated working mechanisms have been explored using gene-deficient mutants in various plant species.Of particular interest is that the KAR and SL signaling pathways play important roles in environmental responses,among which their linkages with photomorphogenesis are most comprehensively studied during seedling establishment.In this review,we focus on how the phytochemical and light signals converge on the optimization of morphogenic fitness.We also discuss molecular mechanisms underlying the signaling crosstalks with an aim of developing potential ways to improve crop productivity under climate changes.

How seed defense and seed abundance predict dispersal and survival patterns in Camellia

Little is known about how seed defense and seed abundance interact with behavioral responses of seed dispersers to predict dispersal and survival dynamics in animal-dispersed plants.By tracking the fate of individual seeds in Camellia stands with high and low seed abundance in Southwest China in 2007,we investigated the dispersal and survival of 2 high-saponin Camellia species(Camellia oleifera and Camellia sinensis and 1 non-saponin species(peanut Arachis hypogaea)as a control.Saponins in Camellia seeds are chemical compounds that act as seed defense.Our results were most consistent with the predictions based on the predator satiation hypothesis and the plant defense hypothesis.At the abundant Camellia stand(predators and dispersers were satiated),more Camellia seeds survived at the source but fewer were hoarded and survived at cache sites.At the sparse Camellia stand(predators and dispersers were not satiated),no Camellia seeds survived at the source,but more Camellia seeds were hoarded and survived at cache sites.Unlike Camellia seeds,no peanuts survived at the source at both stands,while more peanuts were hoarded and then survived at cache sites in the abundant Camellia stand compared to none at the sparse Camellia stand.In addition,the 2 Camellia species showed similar trends for seed fates across different dispersal stages.Our study indicates that the combined effects of seed abundance and seed defense,compared to their separate effects,provide a more accurate prediction for dispersal and survival patterns in animal-dispersed Camellia species.

Mountain invasions on the way:are there climatic constraints for the expansion of alien woody species along an elevation gradient in Argentina?

Aims Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants.Here,we aimed to address whether three major woody invaders of low-mountain areas are constrained to lower altitudes due to climatic restrictions or just by low propagule pressure.We hypothesize that the increasing climatic harshness towards higher altitudes restricts seedling establishment and survival of these woody invaders and thus their potential for altitudinal expansion.Methods The study was carried out in the Sierras Grandes Mountains,Córdoba,central Argentina(32°50′S,64°90′W).We addressed the hypothesis with an experimental approach,dissociating the effect of the environmental gradient from that of propagule pressure,by discarding the influence of seed sources.We translocated seeds of Gleditsia triacanthos L.,Ligustrum lucidum W.T.Aiton.and Pyracantha angustifolia(Franch.)C.K.Schneid.along the altitudinal gradient(from 900 to 2700 m asl).Seven sites were selected along the altitudinal gradient,spaced every 200-400 m.Three plots(4×4 m)were selected within each altitudinal site and excluded from livestock;100 seeds of each species were sown within each plot(6300 seeds in total).Seedling emergence and survival was monitored during two growing seasons and soil temperature and moisture was recorded as well.The field experiment was complemented with lab assays.Important Findings Climate along this altitudinal gradient might be least restrictive at mid elevations,as a result of the intersection between opposite soil temperature and moisture gradients.Sown seeds germinated along the whole altitudinal gradient and seedlings successfully established and over-wintered well above their current altitudinal distribution(up to 2200 m for Ligustrum and 2400 m for Gleditsia and Pyracantha).Additional lab assays confirmed field patterns and gave some insights into contrasting regeneration strategies between these invaders that might help to overcome stochastic environmental constraints in the germination stage.Overall,seedlings of three major woody invaders of low-mountain woodlands can establish and survive at higher elevations than their current distribution.In contrast to natives,they seem to be broad climate tolerators,rather than specialized stress tolerators,capable of germinating and growing across a wide elevational range.While long-term experiments might be necessary to fully address the potentials for altitudinal expansion,out results on early lifecycle stage suggest that the invaders studied here would have mostly a dispersal barrier rather than a climate barrier to establish in the upper belt of the Sierras Grandes.