Seed size, seedling morphology, and response to deep shade and damage in neotropical rain forest trees

To investigate the existence of coordinated sets of seedling traits adapted to contrasting establishment conditions, we examined evolutionary convergence in seedling traits for 299 French Guianan woody plant species and the stress response in a shadehouse of species representing seed size gradients within five major cotyledon morphology types. The French Guianan woody plant community has larger seeds than other tropical forest communities and the largest proportion of hypogeal cotyledon type (59.2%) reported for tropical forests. Yet the community includes many species with intermediate size seeds that produce seedlings with different cotyledonal morphologies. A split-plot factorial design with two light levels (0.8% and 16.1% PAR) and four damage treatments (control, seed damage, leaf damage, stem damage) was used in the shadehouse experiment. Although larger-seeded species had higher survival and slower growth, these patterns were better explained by cotyledon type than by seed mass. Even larger-seeded species with foliar cotyledons grew faster than species with reserve-type cotyledons, and survival after stem grazing was five times higher in seedlings with hypogeal cotyledons than with epigeal cotyledons. Thus, to predict seedling performance using seed size, seedling morphology must also be considered.     

Importance of animal and plant traits for fruit removal and seedling recruitment in a tropical forest

The traits of animals and plants influence their interaction networks, but the significance of species' traits for the resulting ecosystem functions is poorly understood. A crucial ecosystem function in the tropics is seed dispersal by animals. While the importance of species' traits for structuring plant–frugivore networks is supported by a number of studies, no study has so far identified the functional traits determining the subsequent processes of fruit removal and seedling recruitment. Here, we conducted a comprehensive field study on fruit removal by frugivorous birds and seedling recruitment along an elevational gradient in the Colombian Andes. We measured morphological traits of birds (body mass, bill width, Kipp's index) and plants (plant height, crop mass, fruit width and seed mass) which we expected to be related to fruit removal and seedling recruitment. We tested 1) which bird and plant traits influence fruit removal, and 2) whether network metrics at plant species level, functional identities of frugivores (community‐based mean trait values) and/or plant traits were the main determinants of seedling recruitment. We found that large‐bodied bird species contributed more to fruit removal than small‐bodied bird species and that small‐sized fruits were more frequently removed than large‐sized fruits. Small plant species and plants with heavy seeds recruited more seedlings than did large plants and plants with light seeds. Network metrics and functional identities of seed dispersers were unrelated to seedling recruitment. Our findings have two important implications. First, large birds are functionally more important than small birds in tropical seed‐removal networks. Second, the detected tradeoff between fruit size and seed mass in subsequent recruitment processes suggests that the adaptability of forest plant communities to a loss of large frugivores is limited by life‐history constraints. Hence, the protection of large‐bodied frugivores is of primary importance for the maintenance of diverse tropical plant communities.     

Structure of the zygotic embryos and seedlings of Butia capitata (Arecaceae)

Butia capitata, an endemic palm of the Brazilian savanna threatened by deforestation, demonstrates low germinability due to seed dormancy. The present study characterizes the structure of the zygotic embryo and describes germination and seedling development. Pyrenes were sown into sandy soil substrates to germinate, and their embryos were also cultivated in vitro in MS medium; structural evaluations were made during their development. Seedling growth through the endocarp germ pore culminates in the protrusion of the cotyledonary petiole, with the root and leaf sheaths subsequently being emitted laterally from its extremity. The embryos are composed of the cotyledon (whose proximal third has a haustorial function) and a diminutive embryo axis that is contained within the cotyledonary petiole. The protoderm, ground meristem, and procambium can be observed in their typical positions in the embryo axis and cotyledon. The development of the vegetative axis could be observed on the second day of in vitro cultivation, with elongation of the embryo axis and the beginning of the differentiation of the first eophyll. Elongation of the cotyledonary petiole and the differentiation of the parenchyma and tracheary elements were observed during the second to fifth day. Although the hypocotyl–radicle axis is less differentiated than the plumule, root protrusion occurs on the eighth day, and the leaf sheaths are only emitted between the twelfth and the sixteenth days; the haustorium atrophied during this stage. The embryonic structure of B. capitata does not impose limitations on seed germination as dormancy is of the non-profound physiological type, and the 50 % elongation of the cotyledonary petiole serves as a morphological indicator of germination.     

Differences in the activity and distribution of peroxidases from three different portions of germinating Brassica oleracea seeds

Peroxidase (POD, EC 1.11.1.7) activity, cellular localization and isozyme patterns were investigated in the seed integument, cotyledon and embryo axis of Brassica oleracea cv. Cappuccio during pregermination and seedling growth. Seeds started to germinate after 24 h of imbibition. POD activity was localized in the pigmented layer of the integument and in procambial strands of the cotyledon and embryo axis in the first 24 h of imbibition. It was localized in the integumental cells of palisade, pigmented and aleurone layers and in epidermal, meristematic, procambial cells and xylem elements of the root and hypocotyl after 48 h of imbibition. POD activity increased during germination and early seedling growth: in the integument, it reached a maximum value after 72 h of imbibition, in the embryo axis and cotyledons, it increased up to 144 h of imbibition. The increase in peroxidase activity was accompanied by the appearance of new isozymes correlated with the development of seedling tissues. The isozyme profile was characterized by nine peroxidases: isoperoxidase of 50 kDa peculiar to integuments, that of 150 kDa to cotyledons and that of 82 kDa to the embryo axis. During pregerminative phase isozymes of 84 kDa were detected in the integument and cotyledons, of 48.5 kDa in the embryo axis. After germination, peroxidase activity and the complexity of the isozyme pattern increased, suggesting that they play a relevant role after rupture of the integument.     

The effects of seed size, cotyledon reserves, and herbivory on seedling survival and growth in Quercus rugosa and Q. laurina (Fagaceae)

In a greenhouse experiment, seedling survival of two oak species (Quercus rugosa and Q. laurina) was greatly affected by the excision of cotyledons 1 mo after germination, with a greater impact on Q. laurina. The effect of seed size was also significant for both species, with a positive correlation between seed mass and survival and growth. The effect of cotyledon excision on seedling growth persisted throughout the first growing season in Q. rugosa and was not analyzed for Q. laurina due to the low number of seedlings that survived cotyledon excision. Seed size significantly affected seedling height, diameter, leaf area, and biomass at 6 mo. Seed size and cotyledon retention affected the ability of Q. rugosa to recover from herbivory, as both factors had a significant effect on relative growth rates after aerial biomass removal. The results show that seedlings originating from large seeds can better endure loss of cotyledons and aerial biomass and thus are better equipped to confront stress early in their lives.     

Cracking the case: Seed traits and phylogeny predict time to germination in prairie restoration species

Traits are important for understanding how plant communities assemble and function, providing a common currency for studying ecological processes across species, locations, and habitat types. However, the majority of studies relating species traits to community assembly rely upon vegetative traits of mature plants. Seed traits, which are understudied relative to whole‐plant traits, are key to understanding assembly of plant communities. This is particularly true for restored communities, which are typically started de novo from seed, making seed germination a critical first step in community assembly and an early filter for plant establishment. We experimentally tested the effects of seed traits (mass, shape, and embryo to seed size ratio) and phylogeny on germination response in 32 species commonly used in prairie grassland restoration in the Midwestern USA, analyzing data using time‐to‐event (survival) analysis. As germination is also influenced by seed dormancy, and dormancy break treatments are commonly employed in restoration, we also tested the effects of two pretreatments (cold stratification and gibberellic acid application) on time to germination. Seed traits, phylogeny, and seed pretreatments all affected time to germination. Of all traits tested, variables related to seed shape (height and shape variance) best predicted germination response, with high‐variance (i.e., pointier and narrower) seeds germinating faster. Phylogenetic position (the location of species on the phylogenetic tree relative to other tested species) was also an important predictor of germination response, that is, closely related species showed similar patterns in time to germination. This was true despite the fact that all measured seed traits showed phylogenetic signal, therefore phylogeny provided residual information that was not already captured by measured seed traits. Seed traits, phylogenetic position, and germination pretreatments were important predictors of germination response for a suite of species commonly used in grassland restoration. Shape traits were especially important, while mass, often the only seed trait used in studies of community assembly, was not a strong predictor of germination timing. These findings illustrate the ecological importance of seed traits that are rarely incorporated into functional studies of plant communities. This information can also be used to advance restoration practice by guiding restoration planning and seed mix design.     

Seed Architecture Shapes Embryo Metabolism in Oilseed Rape

Constrained to develop within the seed, the plant embryo must adapt its shape and size to fit the space available. Here, we demonstrate how this adjustment shapes metabolism of photosynthetic embryo. Noninvasive NMR-based imaging of the developing oilseed rape (Brassica napus) seed illustrates that, following embryo bending, gradients in lipid concentration became established. These were correlated with the local photosynthetic electron transport rate and the accumulation of storage products. Experimentally induced changes in embryo morphology and/or light supply altered these gradients and were accompanied by alterations in both proteome and metabolome. Tissue-specific metabolic models predicted that the outer cotyledon and hypocotyl/radicle generate the bulk of plastidic reductant/ATP via photosynthesis, while the inner cotyledon, being enclosed by the outer cotyledon, is forced to grow essentially heterotrophically. Under field-relevant high-light conditions, major contribution of the ribulose-1,5-bisphosphate carboxylase/oxygenase–bypass to seed storage metabolism is predicted for the outer cotyledon and the hypocotyl/radicle only. Differences between in vitro– versus in planta–grown embryos suggest that metabolic heterogeneity of embryo is not observable by in vitro approaches. We conclude that in vivo metabolic fluxes are locally regulated and connected to seed architecture, driving the embryo toward an efficient use of available light and space.     

Variation in seed and seedling traits in Pithecellobium pedicellare,a tropical rain forest tree

Summary Pithecellobium pedicellare, a mimosoid legume, is a large canopy tree in the tropical rain forests of Costa Rica. We examined the pattern of variation in seed weight, germination date, hypocotyl length (stem), and rachis length (the first leaf) of the seedlings in this species. Seeds collected from widely dispersed individual trees at the La Selva Biological Station, Costa Rica, were randomly planted in blocks, and grown under controlled, indoor conditions for about 2 weeks. There-fore, we were able to quantify the effects of maternal family on mean seed weight and the effects of maternal family and microenvironment on the remaining traits examined. A significant effect of maternal family was detected for all traits. In particular, the maternal effects on germination date and seedling size traits which were consistently significant even after controlling the initial seed weight may indicate that the maternal effects reflect, at least to some extent, maternal genetic control over these traits. Despite overall strong maternal effects, the performance of maternal siblings, such as the rachis length, differed among blocks. The sensitivity of maternal siblings to the local environments may contribute to the maintenance of genetic variability in this highly outcrossing tropical species.     

Seed reserve translocation and early seedling growth of eight tree species in a tropical deciduous forest in Mexico

Seed reserves play an essential role during germination and seedling establishment and are particularly important for species that grow in seasonal ecosystems with a short growing season. In this study, we examined (a) how and when the seedlings change their dependence from seed resources to external resources, (b) the lipid, nitrogen, and non-structural carbohydrate reserve translocation from seeds to seedlings over time, and (c) whether reserve translocation may be correlated to cotyledon and leaf lifespan of seedlings for eight tree species in a tropical deciduous forest in north-western Mexico. Our results showed that the cotyledon lifespan was not related to the cotyledon type (photosynthetic or reserve) and that the cotyledon biomass did not decrease significantly until germination. In six of the eight studied species, biomass allocation to the leaves was favored; lipids were the first reserve exhausted before the first leaves were totally expanded in seven of the eight study species. Species with the highest N concentration had expanded leaves and lost their cotyledons faster than species with a low N concentration. Our results suggest that tropical deciduous forest species employ different strategies to survive the dry season and re-sprout in the next growing season mediated by seed reserve concentrations, translocation patterns and subsequent biomass allocation.     

Light requirements for regeneration in tropical forest plants: Taxon-level and ecological attribute effects

Abstract Understanding co-adapted traits and strategies in organisms has been increasingly shown to require a broader view of structure, function, taxonomic affiliation (phylogeny) and their possible interactions. In order to understand mechanisms of recruitment dynamics in tropical forest, nine juvenile (fruit, seed and seedling) and seven adult ecological and morphological traits were examined in 89 woody plant species, from 75 genera, 35 families and 21 orders. The species were from tropical rainforest in northern Queensland and varied widely in light requirements and hence regeneration niches. The importance of taxonomic (phylogenetic) constraints was considered using various techniques. Data were collected mostly from herbarium specimens, augmented by observations in the field. The main source of variation in most traits was at the species level, although fruit size and light requirement varied most at the genus level, and flower size at the level of order. Covariation among attributes increased in strength with increasing taxonomic level. Cluster analyses of the species arising either from five or three groups reflected juvenile rather than adult attributes. However, these groups were not morphologically distinct. Sets of juvenile traits poorly predict adult functions (and vice-versa) at species, genus and family levels, but do so more strongly at the order level. Analyses of variance and multivariate analyses, with and without the effects of phylogeny, indicated that fruit size, seed size, hardness of seed coat, seedling cotyledon function, fruit maturation period and, to a lesser extent, seed number per fruit and wood density could predict light requirement, and hence regeneration niche. Flower size showed a strong phylogenetic effect, and thus is conserved along taxonomic lines. It is concluded that as different traits may vary at different taxonomic levels, the influence of phylogeny on interspecific variation needs to be routinely recognized by ecologists involved in comparative analyses of plant life-history functions.     

Evolution and ecology of seed internal morphology in relation to germination characteristics in Amaranthaceae

Background and AimsInternal seed morphological traits such as embryo characteristics and nutritive tissue can vary considerably within a plant lineage. These traits play a prominent role in germination processes and the success of seedling establishment, and are therefore under high selective pressure, especially in environments hostile to seedlings, such as arid, saline or highly dynamic habitats. We investigated the relationships of seed internal morphology and germination characteristics of 84 species of Amaranthaceae s.l., a family with numerous lineages that have adapted to stressful growing conditions.MethodsWe used seed cross-sections to assess embryo type and the ratios of embryo to seed surface and radicle to cotyledon length. Furthermore, seed mass, mean time to germination, habitat preferences and further plant traits such as C₃ or C₄ photosynthesis and life form were compiled for each species. Data were analysed using phylogenetic comparative methods.Key resultsWe found embryo type (λ = 1), log seed mass (λ = 0.86) and the ratio of embryo to seed size (λ = 0.78) to be evolutionarily stable, with an annular embryo as ancestral in the family. Linked to shifts to the three derived embryos types (spiral, horseshoe-shaped and curved) is an increase in the ratio of root to cotyledon length and a reduction of nutritive tissue. We observed stabilizing selection towards seeds with relatively large embryos with longer radicles and less nutritive tissue that are able to germinate faster, especially in lineages with C₄ photosynthesis and/or salt tolerance.ConclusionsWe conclude that the evolutionary shift of nutrient storage from perisperm to embryo provides an ecological advantage in extreme environments, because it enables faster germination and seedling establishment. Furthermore, the evolutionary shift towards a higher ratio of root to cotyledon length especially in small-seeded Amaranthaceae growing in saline habitats can provide an ecological advantage for fast seedling establishment.     

Climate warming delays and decreases seedling emergence in a Mediterranean ecosystem

Temperature and moisture impact strongly on the early stages of a plant's life cycle. Global climate change is altering the environmental cues that seeds receive resulting in compromised seedling emergence and changes to seedling performance. Here, we investigate how temperature and moisture affect these early stages of plant development in four Banksia species collected from a longitudinal climate gradient in southwest Western Australia. A common garden was used to examine the between‐species and among‐population variation in seedling emergence, growth and leaf traits under two soil temperature regimes and three levels of precipitation. We predicted that reduced moisture and increased temperature would delay and reduce total seedling emergence and negatively affect seedling performance. Furthermore, we expected that within species there would be geographically structured variation in response to the treatments. Species differed significantly in all measured traits. Soil warming resulted in strong impacts on regenerative traits, significantly slowing seedling emergence in two species and reducing total seedling emergence in three species. In addition, warming altered seedling performance with significant reductions to the above‐ground leaf biomass ratio of three species. In contrast, response to soil moisture manipulation was minimal across all species but possibly due to issues regarding implementation of an effective moisture treatment. The species that showed the greatest decline in emergence under warmed conditions (B. quercifolia) also showed the smallest vegetative shift; the species with the smallest decline in emergence (B. coccinea) showed a relatively large vegetative shift. Among‐population differences were significant for many traits, however, trait differentiation was inconsistent across species and, contrary to our hypothesis, the variation we observed was not clearly associated with the climate gradient. As these among‐population differences in traits are not easy to predict, we caution the use of simple rules for choosing seed populations for conservation and restoration.     

Utilization of Seed Reserves and Currently Produced Photosynthates by Embryonic Tissues of Pine Seedlings

The importance of seed reserves for growth of Pinus resinosaAit. during and shortly after seed germination was studied undercontrolled conditions. Tissues in the resting embryo were notcompletely differentiated. Many small, presumably reserve particleswere present in the embryo in addition to reserves in the megagametophyte.During seed germination, procambia in the embryo first differentiatedprotophloem 2 days after seeds were sown. The radicle beganto emerge from the seed coat at 5 days, at which time initialxylem formation was observed. Also, at approximately the sametime, primordia of primary needles were forming in the peripheralzone of the apex. Elements of the photosynthetic apparatus,including stomata and mesophyll with chloroplasts, were differentiatedfirst in the hypocotyl and then in cotyledons between 5 and8 days after seeds were sown. Photosynthetic rates of youngseedlings were correlated with rates of cotyledon expansion.During early developmental stages, reserve particles in megagametophytecells and embryo cells gradually disappeared. Surgical removalof megagametophytes at various stages of seed germination resultedin subsequent growth inhibition of the hypocotyl-radicle axis,with early removal of cotyledons suppressing most growth. Growthof primary needles appeared to be influenced indirectly by megagametophytereserves, probably by changes in amount of photosynthetic tissue.The embryo alone possessed capacity to differentiate such tissuesas primary needle primordia, stomata, and primary and secondaryvascular systems. Megagametophyte reserves appeared to contributeto growth of embryonic tissues only after the embryo itselfinitiated growth. Both current photosynthesis of seedlings andseed reserves contributed importantly to seedling development.     

Scorzonera ahmet‐duranii sp. nov. (Asteraceae) from southwest Anatolia,and its phylogenetic position

Scorzonera ahmet‐duranii S. Makbul & Coskuncelebi sp. nov. (Asteraceae) is described and illustrated as a new species endemic to Turkey. It is morphologically similar to S. semicana DC., but differs by its rootstock, deeply undulating basal leaves and glabrous achenes. Additionally, the size and micro‐morphological properties of achenes and some anatomical traits of the leaf and stem are helpful in distinguishing these closely related taxa. A phylogenetic analysis based on nrDNA ITS sequence data showed that S. semicana is the sister species of the new taxon presented in this study.     

Coordination between leaf and root traits in Mediterranean coastal dune plants

• Plant trait-based functional spectra are crucial to assess ecosystem functions and services. Whilst most research has focused on aboveground vegetative traits (leaf economic spectrum, LES), contrasting evidence on any coordination between the LES and root economic spectrum (RES) has been reported. Studying spectra variation along environmental gradients and accounting for species' phylogenetic relatedness may help to elucidate the strength of coordination between above- and belowground trait variation.
• We focused on leaf and root traits of 39 species sampled in three distinct habitats (front, back and slack) along a shoreline–inland gradient on coastal dunes. We tested, within a phylogenetic comparative framework, for the presence of the LES and RES, for any coordination between these spectra, and explored their relation to variation in ecological strategies along this gradient.
• In each habitat, three-quarters of trait variation is captured in two-dimensional spectra, with species' phylogenetic relatedness moderately influencing coordination and trade-off between traits. Along the shoreline–inland gradient, aboveground traits support the LES in all habitats. Belowground traits are consistent with the RES in the back-habitat only, where the environmental constraints are weaker, and a coordination between leaf and root traits was also found, supporting the whole-plant spectrum (PES).
• This study confirms the complexity when seeking any correlation between the LES and RES in ecosystems characterized by multiple environmental pressures, such as those investigated here. Changes in traits adopted to resist environmental constraints are similar among species, independent of their evolutionary relatedness, thus explaining the low phylogenetic contribution in support of our results.

     

Seedling diversity in Hydatellaceae: implications for the evolution of angiosperm cotyledons

BACKGROUND AND AIMS: Cotyledon number has long been a primary morphological feature distinguishing monocots from other angiosperms. Recent placement of Hydatellaceae near the early-divergent angiosperm order Nymphaeales, rather than in the monocot order Poales, has prompted reassessment of seedling morphology in this poorly known family. METHODS: Seedlings of six species representing all eco-geographical groups of Hydatellaceae are described using light and scanning electron microscopy. KEY RESULTS: Two seedling types were discovered. Material examined of Trithuria submersa, T. bibracteata, T. austinensis and T. filamentosa possess a transparent bilobed sheathing structure that surrounds the main axis below the first foliage leaf. The seed coat is attached to the sheathing structure. Seedlings of Trithuria lanterna and T. konkanensis lack a sheathing structure, and the seed coat is attached to a short, narrow lateral outgrowth on the main axis of the seedling. CONCLUSIONS: The sheathing structure that is present in seedlings of some Hydatellaceae could be homologized with the two united cotyledons of water lilies. It also resembles the single cotyledon of some monocots, and hence demonstrates a possible pathway of the origin of a monocot-like embryo, though no homology is implied. The sheathing structure is reduced in Trithuria lanterna and T. konkanensis, and the short, narrow outgrowth of its seedling could represent a single cotyledon. This synapomorphy suggests that the only Indian species of Hydatellaceae, T. konkanensis, is closer to the northern Australian T. lanterna than to the south-western Australian T. bibracteata.     

Restionaceae seedlings: Morphology,anatomy and systematic implications

Restionaceae differ from most monocot families in having both epigeal and hypogeal germination. The green cotyledons associated with epigeal germination have a central vascular strand as found in most epigeal monocotyledons. In some genera the cotyledon may have a hairpin‐like structure, also described for Anthericaceae. The cotyledon of the hypogeal seedlings is short, without green pigment and largely remains embedded in the seed coat. Hypogeal germination is correlated with large, woody, indehiscent, frequently myrmecochorous nuts, while epigeal germination is found in species with smaller indehiscent nutlets or seeds, dispersed in a variety of ways. The primitive condition is most likely epigeal germination. In hypogeal seedlings of some African and Australian taxa an epicotyledonary rhizome is found between the primary root and the first leaves. Seedlings of African Restionaceae frequently have elongated culm internodes, whereas in the Australian species studied, internodes are very short, resulting in a cluster of seedling leaves. The leaf blades, which in most species are only found on the seedlings, are very simple anatomically. However, they appear to be unifacial, similar to the leaf blades of Anarthria (Anarthriaceae). The anatomical specialisations in the blades mirror those recorded for the culm anatomy. These observations are consistent with the hypothesis that Centrolepidaceae may be neotonous Restionaceae. They also corroborate the morphology of the African Restionaceae, and the presently accepted phylogeny of the African genera of Restionaceae.     

Photosynthesizing Tissue Development in C4 Cotyledons of Two Salsola Species (Chenopodiaceae)

The quantitative anatomy of developing cotyledons of NAD-malic enzyme species Salsola incanescens and NADP-malic enzyme species S. paulsenii (Chenopodiaceae) was studied. S. incanescens belongs to the group of species with foliar type of seedling development characterized by slowly growing cotyledons and a rosette form at juvenility. The rosette is the consequence of fast leaf formation, which was correlated with a low rate of leaf growth. S. paulsenii belongs to the group with the cotyledonous type of seedling development. A high growth rate of cotyledons, slow leaf formation, and absence of the rosette characterize this type. Slow leaf formation was correlated with a high rate of leaf growth. The Kranz–anatomy in cotyledons of S. incanescens (atriplicoid type) and S. paulsenii (salsoloid type) determines the duration of cotyledon development proceeding for 15 days after seed germination. The rate of growth changes during the developmental period was correlated with the type of seedling development. Cotyledons of a foliar species S. incanescens exhibit 2 to 5 times slower growth changes in cotyledon area, width, thickness, volume of mesophyll and bundle sheath cells, and number of chloroplasts per bundle sheath cell than the cotyledons of a cotyledonous species S. paulsenii. During cotyledon development in both species, the number of chloroplasts per mesophyll cell remained unchanged, and developmental changes in the bundle sheath occurred at higher rate than in mesophyll cells. Thus, these two indices seem to be independent of the type of Kranz–anatomy. The presence of atriplicoid type cotyledons in the species with salsoloid structure of true leaves might indicate a close genetic relationship between these two patterns of Kranz-anatomy.     

温度对干旱、盐胁迫下两种黄芪属种子萌发和幼苗生长的影响

为探讨温度对干旱、盐胁迫下黄芪属种子萌发和幼苗生长特性的影响,以黄芪属蒙古黄芪和扁茎黄芪2种种子为研究对象,纯净水处理为对照组,NaCl、PEG处理为实验组,设置4个渗透势水平(0、-0.1、-0.3、-0.5 MPa),置于5种不同的温度(10、15、20、25、30 ℃)下,每日观察并记录两种种子萌发和幼苗生长情况。结果表明：旱盐胁迫下蒙古黄芪和扁茎黄芪种子萌发最适宜的温度分别为25和20 ℃左右;蒙古黄芪耐高温不耐低温,而扁茎黄芪恰恰相反;但25和20 ℃均适宜两种幼苗生长,包括胚根、胚轴和子叶的生长。蒙古黄芪各处理组(除未发芽的种子)的平均发芽时间都比扁茎黄芪长;NaCl胁迫程度的增加使得两种种子的最终发芽率降低,但蒙古黄芪的耐盐性高于扁茎黄芪;随着PEG胁迫程度的增加,二者的发芽均受到抑制,甚至会出现完全不萌发,但扁茎黄芪的耐旱性高于蒙古黄芪;在相同的渗透势时,尤其是-0.5 MPa,PEG比NaCl对两种种子的影响大;交互胁迫作用下,随着渗透势的增加两种幼苗的鲜重、干重以及胚根、胚轴、子叶的长和宽变化较大;利用Design Expert软件预测发现：温度25 ℃、NaCl渗透势为-0.1 MPa,温度24 ℃、PEG渗透势为-0.04 MPa的处理是蒙古黄芪种子萌发和幼苗生长达到最优化的组合;而扁茎黄芪最优化的组合则为23 ℃下NaCl渗透势为-0.07 MPa的处理,20 ℃下PEG渗透势为-0.13 MPa的处理。