Response Breadths on Environmental Gradients of Germination and Seedling Growth in Two Dominant Forest Tree Species of Central Himalaya

The responses of Pimis roxburghii (chir pine), an early successionalspecies, andQuercus leucotrichophora(banj oak), a late successionalspecies were compared in terms of seed germination and seedlinggrowth. Seed germination was observed on single-factor gradientsof temperature, water stress, seed desiccation and light, andseedling growth on gradients of shade and soil moisture. Thesuppression of germination caused by continuous dark and far-redwas greater in Pinus than in Quercus. Pinus seed germinationshowed wider response breadth on gradients of water stress andseed desiccation, and narrower response breadth on the gradientof light quality, compared withQuercus. In terms of seedlinggrowth, the response breadth of Pinus was wider on the gradientof soil moisture and narrower on the gradient of shade comparedwith Quercus. Under higher soil moisture stress, the seedlingsof both species attained similar heights, butQuercus seedlingsachieved higher dry weights, a higher root: shoot ratio andlower leaf weight ratio than Pinus.     

PEG模拟干旱胁迫对栓皮栎种子萌发及生长生理的影响

为了阐明栓皮栎种子萌发期对水分胁迫的耐受性,以当年采集的栓皮栎种子为材料,采用培养皿滤纸萌发的方法研究了不同浓度（0%、5%、10%、20%、30%）PEG-6000溶液对其种子萌发、生长、保护酶活性和有机渗透调节物质的影响,并对种子萌发率、胚根生长速率等与PEG浓度进行了回归分析。结果表明:（1）随着干旱胁迫程度的加剧,栓皮栎种子的发芽率、发芽指数、胚根长度、胚根生长速率和活力指数均呈先升高后下降趋势,说明低浓度（5%、10%）PEG胁迫可以促进栓皮栎种子萌发及生长,而高浓度（20%、30%）则具有抑制作用。（2）建立水分胁迫条件下种子萌发率、胚根生长速率等与PEG浓度的回归方程发现,栓皮栎种子在PEG胁迫下的萌发临界值和极限值分别为32.01%和36.99%,胚根生长速率的临界值和极限值分别为30.1%和33.35%。（3）随着PEG浓度的升高,栓皮栎种子中3种保护酶（SOD、POD、CAT）活性和3种有机渗透调节物质（可溶性蛋白、脯氨酸、可溶性糖）含量呈现不同的变化,但均有不同程度升高趋势。由此可见,栓皮栎种子可通过增加保护酶活性和体内渗透调节物质来适应水分胁迫环境,使自身萌发和生长受抑制程度降到最低。     

Dehydrin genes and their expression in recalcitrant oak (<Emphasis Type="Italic">Quercus robur</Emphasis>) embryos

In this work, three dehydrin genes, QrDhn1, QrDhn2, QrDhn3, were isolated from recalcitrant oak (Quercus robur). Their expression pattern was analyzed in both zygotic and somatic embryos as well as in vegetative tissues exposed to different kinds of abiotic stresses including desiccation, osmotic stress, and chilling. The QrDhn1 gene encoding for Y_nSK_n type dehydrin was expressed during later stages of zygotic embryo development but in somatic embryos only when exposed to osmotic or desiccation stress. In contrast, the other two oak dehydrin genes encoding for putative K_n type dehydrins were expressed only in somatic embryos (both not-treated and osmotically stressed) and leaves of oak seedlings exposed to desiccation. Behavior of these genes suggests that different dehydrins are involved in processes of seed maturation and response to altered osmotic (water status) conditions in somatic embryos. Revealing further members of dehydrin gene family in recalcitrant oak might contribute to clarify non-orthodox seed behavior as well as identify mechanisms contributing to desiccation tolerance in plants.     

Mechanisms Involved in Delayed Germination of Quercus nigra L. Seeds

Neither the pericarp nor the seed coat impose significant barriersto passage of water in Quercus nigra seeds. The pericarp eventuallybecomes limiting to continued swelling due to its mechanicalstrength. During stratification trapped gasses escape and continuedswelling of the cotyledons causes expansion of the pericarp.Vigorous acorns need around 105 days of combined stratificationand germination time to reach maximum germination. This additivityphenomenon is true for stratification times between 4 and 10weeks. Delayed germination is caused by at least three factors:(1) Mechanical strength of the pericarp, which was constantduring the observation period of 13 weeks; (2) Chemical inhibitionby the pericarp, which was alleviated by stratification forapproximately 4 weeks; (3) Slowly increasing capacity to imbibewater required for pericarp rupture. This component was apparentlynot dependent on temperature within the range of 5 to 30 °C,and operates during the entire stratification and germinationperiod. Quercus nigra L, water oak, seed germination, pericarp, stratification, dormancy     

Effects of seed mass on seedling height and competition in European white oaks

The relationship between seed size and fitness in plants may depend on offspring density, especially in cases where seed size affects the outcome of competition. We investigated the relationship between seed mass, germination, intraspecific competition and seedling height in a glasshouse experiment on three European white oak species (Quercus robur, Q. petraea, Q. pubescens). Within offspring families, seed mass showed a moderate, but statistically significant effect on seedling height, i.e. seedlings from heavier seeds were slightly taller. In contrast, competition caused pronounced inequality in seedling height in pairs of competing seedlings, but in only 55.2% of all pairs the dominant competitor arose from the heavier seed. It is thus possible that a positive effect of seed mass on seedling growth can be mediated through the density of conspecific seedlings and that heterogeneity in offspring density will contribute to the maintenance of seed mass variation in oak populations.     

Early seedling growth of pine (Pinus densiflora) and oaks (Quercus serrata,Q. mongolica,Q. variabilis) in response to light intensity and soil moisture

In climatic chambers seed germination and seedling growth of Pinus densiflora Sieb. et Zucc., Quercus serrata Thunb., Quercus mongolica Fisch. ex Turcz. and Quercus variablilis Bl. were investigated as functions of light intensity and soil moisture. In Korea these tree species occur widely and form mixed forests with different distributions. Species clearly differed in the pattern of germination and early seedling growth between light and soil treatments. The germination of pine did not differ between the experimental treatments until the breaking of the primary buds. After that, light intensity was the deciding factor for further development. In the most moist treatment (approx. field capacity) growth of the pine seedlings was strongly inhibited. For the three oak species, differences between experimental treatments first occurred after complete formation of primary leaves. Seed development strongly correlated with the weight of the acorn. The large seeded Q. variabilis (acorns with mean weight of 4.7 g) developed faster and reached larger dimensions towards the end of the experiment than Q. mongolica (2.8 g per acorn) and Q. serrata (0.9 g per acorn). Regarding height and biomass growth, the oak species showed a higher shade tolerance than pine. The proleptic shoot growth was clearly influenced by the light intensity. Root formation was favoured by a high exposure to light. In case of the oak species reduction of soil moisture increased the length of primary roots and the number of secondary roots.     

Establishment and growth of Quercus floribunda seedlings after a mast year

Abstract. Population dynamics, mortality factors, growth and dry weight changes in Quercus floribunda seedlings were studied to determine the implication of sun and shade microsites and the role of mast years on regeneration and maintenance of oak forests in Kumaun Himalaya. The number of seedlings was significantly greater at the sun microsites, but seedling survival was not, as ground herbage clearance at sun microsites accounted for 53.5% mortality. Insect herbivores (e.g. acorn worm) were also one of the major mortality factors. At both microsites, most mortality was encountered between June and August. The initial seedling height at sun microsites was significantly lower compared to shade microsites. Seedlings at sun microsites were superior in terms of number of leaves and peak dry weight. Dry mass allocation in seedling components and root:shoot ratio was similar at both microsites. The study shows the importance of sun microsites and of masting in the potential for regeneration and expansion of Q. floribunda forests.     

The Influence of Volatile Substances from Incubated Litter of Pinus radiata on Seed Germination

Vapour from incubated Pinus radiata D. Don litter caused a depressionin the germination of Lolium perenne L. seeds and responsesvarying from stimulation to depression in germination of Trifoliumrepens L. seeds. These effects could be attributed to ethyleneand carbon dioxide. Experiments using ethylene and carbon dioxidesupported this conclusion. Pinus radiata, litter, Lolium perenne, Trifolium repens, seed germination, ethylene, carbon dioxide     

Effects of waterlogging on seed germination of three Mediterranean oak species: Ecological implications

Soil water saturation during prolonged periods of time generates a negative impact on nearly all terrestrial plants. In Mediterranean woodlands, precipitation can be very abundant during the wet season, inducing temporary soil waterlogging, coinciding with the seed dispersal and germination time of many species. We investigated the effects of waterlogging on seed germination and early root growth of three coexisting oak species (Quercus canariensis, Q. suber and Q. pyrenaica), by completely flooding of seeds for various periods of time. The three oak species showed a certain level of tolerance to waterlogging, only being affected those seeds subjected for long periods of submersion (over 30 days). Waterlogging during prolonged periods of time decreased the probability of seed germination in the three oak species, lengthened the time to germination, and hampered root development in two of the studied species. The main differences between oak species occurred in terms of root growth (Q. canariensis being the less affected, and Q. suber the most); these differential responses could be related to a species rank of waterlogging tolerance. Thus inter-specific differences in germination responses to waterlogging could contribute to explain, at least partially, species habitat and distribution patterns across landscapes. Seed mass also played an important role on different aspects of germination, though its relative importance varied as function of species and waterlogging treatment. The tolerance to stress induced by waterlogging increased with seed mass, but only in the case of Q. canariensis.     

Solute accumulation in leaves and roots of woody plants subjected to water stress

Summary Young seedlings of English Oak, Quercus robur L., and Silver Birch, Betula verrucosa Ehrl., were subjected to a number of consecutive periods during which water was withheld. During one 14-day period leaf-and soil-water potentials and leaf- and root-solute potentials of two groups of plants were sampled at noon of each day. One group of plants was watered every day while water was withheld from the other group. Solute accumulation in roots and leaves of oak seedlings subjected to water stress resulted in maintenance of turgor and high leaf conductance as the soil dried. In birch seedlings turgor was only maintained by stomatal closure at high soil water potential.Fourteen consecutive water stress cycles greatly reduced the growth of birch seedlings but had little effect on oak seedlings other than to alter root morphology. Water stress treatment resulted in the production of long thin roots in this plant. Stomatal behaviour in oak and birch seedlings during the 14-week stress period was consistent with observed changes in leaf water and solute potentials. Daily solute accumulation in oak leaves was presumably responsible for the maintenance of plant growth as water potentials fell.     

Canola seed germination and seedling emergence from pre-hydrated and re-dried seeds subjected to salt and water stresses at low temperatures

Low soil temperatures and low water potentials reduce and delay the seed germination of canola (Brassica rapa L., B. napus L.) in western Canada. Germination is also very sensitive to the salinity effects of nitrogen fertiliser placed with the seed, especially when the seed bed is relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10°C subjected to either a water or salt stress were determined. Low water potentials, induced by polyethylene glycol (PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50% germination and emergence of seeds at 10°C. At equal osmotic potentials, Na₂SO₄ was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially alleviated the inhibitory effects of low water potential. Solutions of NaCI produced more abnormal seedlings compared to Na₂SO₄, suggesting that NaCl was more toxic than Na₂SO₄ during seedling development. Pre-hydration and re-drying partially overcame the inhibitory effects of both low water potential and salts on seed germination and seedling emergence at 10°C. The seed treatment increased the germination rate in Petri dishes and seedling emergence from a sandy loam soil. Water potentials or soil water contents required to inhibit 50% germination or emergence at 10°C were lower for treated seeds compared to control seeds. Salt concentrations inhibiting 50% emergence were higher for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was lower than 9% or when the soil was continuously irrigated with salt solutions of 100 mmol kg^-1 of NaCl or 50 mmol kg^-1 of Na₂SO₄. These results suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occur. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, the seed treatment reduced the number of abnormal seedlings.     

Allelopathic effects of interrupted fern on northern red oak seedlings: Amelioration bySuillus luteus L.: Fr.

Summary The allelopathic effects of interrupted fern frond leachates on ectomycorrhizal (inoculated) and nonmycorrhizal (noninoculated) northern red oak (Quercus rubra L.) seedlings were investigated. Container-grown northern red oak was inoculated with vegetative mycelium ofSuillus luteus L. Fr. following acorn germination. Noninoculated control seedlings were also maintained. Seedlings were grown in a glasshouse under full sunlight or shaded (25% of full sunlight) conditions. Leachate or deionized water solutions were applied to seedlings eleven times over a 91-day period to simulate a rainfall induced transfer of allelopathic chemicals from fern fronds to the soil. Fern frond leachates significantly reduced seedling survival, however, inoculated seedlings showed less mortality. Chromium concentrations of pooled lateral root or leaf tissue were comparatively higher in tissues exhibiting greater mortality. Root biomass was reduced by fern fern frond leachate applications. Seedling biomass was not significantly affected by fungal inoculation. Our results confirm previous documentation of the allelopathic potential of ferns, and suggest that ectomycorrhizal fungi may ameliorate allelopathic effects of ferns on northern red oak seedling survival and growth.     

The Effect of Soil Water and Aeration on Seed Germination

The time rate of germination and the final germination percentageof Oryzopsis holciformis decreased with increasing water stress.The optimum matric potential for germination was–0.005bar in coarse sand and –0.5 bar in sandy loam soil. Thisdiscrepancy was explained by changes in the rate of water-supplyto the seed, as determined by the area of contact between seedand germination medium, and by the hydraulic conductivity ofthe medium. At high soil moisture potentials germination also decreased.Such a decrease was not found at equivalent osmotic potentials.It seems that this decrease in germination was brought aboutby the thickening of the water films around the seeds, whichinterfered with oxygen diffusion. This assumption was supportedby determinations with Pt electrodes, and by previous work ongermination at lowered oxygen concentrations.     

The recalcitrant plant species, Castanospermum australe and Trichilia dregeana, differ in their ability to produce dehydrin-related polypeptides during seed maturation and in response to ABA or water-deficit-related stresses

In constrast to seeds of orthodox species, those of recalcitrantspecies do not acquire desiccation tolerance during their developmentand are shed from the parent plant at high water contents. Dehydrinproduction in seeds of recalcitrant species was examined duringdevelopment and germination, in response to abscisic acid (ABA),and following the imposition of various water-deficit-relatedstresses, including desiccation, water stress, high salt, highosmolarity, and low temperature. Two tropical species exhibiteda differential capacity to produce dehydrin-related proteinsduring seed maturation. Dehydrins were present in axes and cotyledonsof Castanospermum australe seeds during mid-maturation and atmaturity. In Trichilia dregeana, no dehydrin-related polypeptideswere detected in the mature seed. During the development ofC. australe seeds, the nature of the dehydrin related polypeptidesaccumulated in the cotyledons and axis changed and new polypeptideswere detected in the mature seeds that were not present duringmid-maturation. The dehydrins present in cotyledons of matureseeds (31, 37 and 40 kDa) were still detectable after germination(i.e. in untreated seedlings). These dehydrins became less abundantin the cotyledons of C. australe seedlings following ABA andall stress treatments except cold, although most of the dehydrinswere still detectable. An exception was the desiccation-treatedseedlings, in which no dehydrins were detected. In the rootsof C. australe seedlings, no dehydrins were found after germinationnor were they induced in the root by ABA or any of the stresstreatments imposed on seedlings. Seedlings of Trichilia dregeanadid not produce dehydrins in the roots or cotyledons when exposedto ABA or water-deficit-related stresses. Key words: Dehydrin, ABA, desiccation, recalcitrant, seed     

Variation in carbon stocks on different slope aspects in seven major forest types of temperate region of Garhwal Himalaya,India

The present study was undertaken in seven major forest types of temperate zone (1500 m a.s.l. to 3100 m a.s.l.) of Garhwal Himalaya to understand the effect of slope aspects on carbon (C) density and make recommendations for forest management based on priorities for C conservation/sequestration. We assessed soil organic carbon (SOC) density, tree density, biomass and soil organic carbon (SOC) on four aspects, viz. north-east (NE), north-west (NW), south-east (SE) and south-west (SW), in forest stands dominated by Abies pindrow, Cedrus deodara, Pinus roxburghii, Cupressus torulosa, Quercus floribunda, Quercus semecarpifolia and Quercus leucotrichophora. TCD ranged between 77.3 CMg ha⁻¹ on SE aspect (Quercus leucotrichophora forest) and 291.6 CMg ha⁻¹ on NE aspect (moist Cedrus deodara forest). SOC varied between 40.3 CMg ha⁻¹ on SW aspect (Himalayan Pinus roxburghii forest) and 177.5 CMg ha⁻¹ on NE aspect (moist Cedrus deodara forest). Total C density (SOC + TCD) ranged between 118.1 CMg ha⁻¹ on SW aspect (Himalayan Pinus roxburghii forest) and 469.1 CMg ha⁻¹ on NE aspect (moist Cedrus deodara forest). SOC and TCD were significantly higher on northern aspects as compared with southern aspects. It is recommended that for C sequestration, the plantation silviculture be exercised on northern aspects, and for C conservation purposes, mature forest stands growing on northern aspects be given priority.     

Effect of Salinity on Germination and Seedling Growth of twoAtriplexspecies (Chenopodiaceae)

Salinity is one of the environmental factors that has a criticalinfluence on the germination of halophyte seeds and plant establishment.Salinity affects imbibition, germination and root elongation.However, the way in which NaCl exerts its influence on thesevital processes, whether it is through an osmotic effect ora specific ion toxicity, is still not resolved. Dimorphic seedsof the halophytesAtriplex prostrataandA. patulawere treatedwith various iso-osmotic solutions of NaCl and polyethyleneglycol (PEG). For each treatment, imbibition, germination rate,percent germination, germination recovery and nuclear area ofroot tip cells were compared. Higher concentrations of NaCl(-1.0 MPa) were more inhibitory to imbibition, germination andseedling root elongation than iso-osmotic PEG solutions. Allseeds recovered from a pre-treatment with -2.0 MPa NaCl andPEG solutions, except large seeds ofA. prostratawhich failedto germinate following transfer from -2.0 MPa NaCl. NaCl causeda greater increase in nuclear volume than iso-osmotic PEG solutions.These data suggest that the influence of NaCl is a combinationof an osmotic effect and a specific ion effect.Copyright 1998Annals of Botany Company Atriplex patula,Atriplex prostrata,cytophotometry, osmotic potential, salinity, seed germination.     

Interspecific Hybridization in the Genus Dioscorea

Interspecific hybridization between Dioscorea alata (2n = 60).D. deltoidea (2n = 20), D. floribunda (2n = 36), D. composita(2n = 36), and D. friedrichsthallii (2n = 36) has revealed levelsof crossability consisting of successful crossing and normalgermination of hybrid seeds, successful crossing but poor germinationof hybrid seeds, crosses not successful due to a pre-fertilizationovular breakdown, and crosses not successful due to post-fertilizationovular breakdown. In general the three Central American species with basic chromosomenumber as 9, namely D. floribunda, D. composita, and D. friedrichsthalliiare cross compatible. In crosses involving D. floribunda withD. composita and D. floribunda with D. friedrichsthallii viablehybrids were obtained. The cross between D. friedrichsthalliiand D. composita is also successful but germination of the hybridseeds is greatly reduced. The cross of D. composita female withthe male D. friedrichsthallii was an exception to the generalcompatibility between these three species. In this cross thefertilized embryo aborted after attaining four-celled stage. The crosses between the two Old World species with basic chromosomenumber as 10, namely D. alata and D. deltoidea with each otherand with the above named three Central American species werenot successful. D. alata had pollen grains which rarely germinated.When D. alata was used as the female parent, the pollen tubesof other species grew down the style but no fertilization tookplace. The reciprocal crosses of D. deltoidea with the CentralAmerican species gave differential results. When D. deltoideawas used as the female parent no fertilization took place. However,when D. deltoidea was used as the male parent the fertilizedembryo aborted after attaining globular stage.     

Endogenous Hormones in Seeds, Germination Behaviour and Early Seedling Characteristics in a Normal and ogura Cytoplasmic Male Sterile Line of Rapeseed (Brassica napus L.)

Endogenous hormones, namely cytokinins (CKs), indole-3-aceticacid (IAA) and abscisic acid (ABA) were quantified by specificenzyme-linked immunosorbent assay (ELISA) in the mature seedof normal (cv. Westar) and ogura (ogu) cytoplasmic male sterile(CMS) lines of rapeseed (Brassica napus L.). Dihydrozeatin (DZ)and dihydrozeatin riboside (DZR) were the major CK base andriboside, respectively, in seeds of both the normal and oguCMS lines. The normal seed had more than 4-fold DZ levels incomparison to that of ogu CMS. On the other hand, the ogu CMSseed had higher levels of CK o-glucosides and CK. nucleotidesthan normal seed. Seeds of the normal line contained 5-foldmore IAA but had one-quarter the level of ABA in comparisonto those of the ogu CMS line. The normal line also had greaterseed diameter and weight than the ogu CMS line and the normalseed germinated earlier than the male sterile seed. DZ (10^–6M) promoted the germination of ogu CMS seeds, but it was notcomparable to that of the normal line. ABA (10^–6 M) inhibitedseed germination of ogu CMS but had little effect on the normalline. The normal seedlings had shorter primary roots, more lateralroots, longer hypocotyls, greater cotyledon fresh weight andhigher chlorophyll levels in comparison to ogu CMS seedlings.Exogenously supplied DZ, IAA and ABA affected the various parametersof both the normal and ogu CMS seedlings, but in most casesdid not fully restore the differences in the two lines. The results presented show that in the ogura cytoplasmic malesterile line of B. napus (1) a number of seed and seedling characteristicsare affected, and (2) the altered seed morphology is accompaniedby changes in the levels of various hormones. Key words: Brassica napus, cytoplasmic male sterility, enzyme-linked immunosorbent assay, hormone, seed germination     

Acorns containing deeper plumule survive better: how white oaks counter embryo excision by rodents

Several squirrel species excise the embryo of acorns of most white oak species to arrest germination for long‐term storage. However, it is not clear how these acorns counter embryo excision and survive in the arms race of coevolution. In this study, we simulated the embryo excision behavior of squirrels by removing 4 mm of cotyledon from the apical end of white oak acorns differing in embryo depths to investigate the effects of embryo excision on acorn germination and seedling performance of white oak species. The embryo depth in the cotyledons was significantly different among white oak acorns, with Quercus mongolica containing the embryo most deeply in the acorns. We found that artificial embryo excision significantly decreased acorn germination rates of Quercus variabilis, Quercus acutissima, Quercus aliena, Quercus aliena var. acutiserrata, Quercus serrata. var. brevipetiolata but not Q. mongolica. Artificial embryo excision exerted significant negative impacts on seedling performance of all oak species except Quercus aliena. Our study demonstrates the role of embryo depth of acorns in countering embryo excision by squirrels and may explain the fact that squirrels do not perform embryo excision in acorns of Q. mongolica with deeper embryos. This apparent adaptation of acorns sheds light on the coevolutionary dynamics between oaks and their seed predators.