Population differentiation for germination and early seedling root growth traits under saline conditions in the annual legume Medicago truncatula (Fabaceae)

Maternal Effects of Habitats Induce Stronger Salt Tolerance in Early-Stage Offspring of Glycyrrhiza uralensis from Salinized Habitats Compared with Those from Non-Salinized Habitats

(1) Wild Glycyrrhiza uralensis Fisch (licorice) seeds from different habitats are often mixed for cultivation. However, differences in the responses of seeds from different habitats to salt at the early-stage offspring stage are unclear. (2) Our objective was to evaluate the salt tolerance of G. uralensis germplasms by comparing differences in seed germination and seedling vigor in salinized (abandoned farmland and meadow) and non-salinized (corn farmland edge) soil habitats under different sodium chloride (NaCl) concentrations. (3) The germination rates and germination indexes of seeds from the two salinized habitats with 0-320 mmol·L-1 NaCl were higher and their germination initiation times were earlier. Only seeds from salinized habitats were able to elongate their germs at 240 mmol·L-1 NaCl. Seedlings from salinized habitats had higher fresh weights and relative water contents, while they exhibited lower accumulation of malondialdehyde and less cell electrolyte leakages. Under NaCl treatment, seedlings from the salinized habitats displayed higher superoxide dismutase, catalase, and peroxidase (SOD, CAT, and POD) activities and lower superoxide anion and hydrogen peroxide (O2- and H2O2) contents. Their comprehensive scores showed that the vigor of licorice seeds from salinized habitats was higher. (4) The salt tolerances of different wild G. uralensis seeds were different, and the offspring of licorice from salinized habitats had stronger early-stage salt tolerances.

At the Crossroads of Salinity and Rhizobium-Legume Symbiosis

Legume roots interact with soil bacteria rhizobia to develop nodules, de novo symbiotic root organs that host these rhizobia and are mini factories of atmospheric nitrogen fixation. Nodulation is a sophisticated developmental process and is sensitive to several abiotic factors, salinity being one of them. While salinity influences both the free-living partners, symbiosis is more vulnerable than other aspects of plant and microbe physiology, and the symbiotic interaction is strongly impaired even under moderate salinity. In this review, we tease apart the various known components of rhizobium-legume symbiosis and how they interact with salt stress. We focus primarily on the initial stages of symbiosis since we have a greater mechanistic understanding of the interaction at these stages.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Salinity, not genetic incompatibilities, limits the establishment of the invasive hybrid cattail Typha × glauca in coastal wetlands

Hybrids of a single pair of parent species can be much more common in some geographical regions than in others. The reasons for this are not well understood, but could help explain processes such as species diversification or the range expansion of invasive hybrids. The widespread cattails Typha latifolia and T. angustifolia seldom hybridize in some parts of their range, but in other areas produce the dominant hybrid T. × glauca. We used a combination of field and greenhouse experiments to investigate why T. × glauca has invaded wetlands in the Laurentian Great Lakes region of southern Ontario, Canada, but is much less common in the coastal wetlands of Nova Scotia (NS) in eastern Canada. One potentially important environmental difference between these two regions is salinity. We therefore tested three hypotheses: (1) T. latifolia and T. angustifolia in NS are genetically incompatible; (2) the germination or growth of T. × glauca is reduced by salinity; and (3) T. latifolia, a main competitor of T. × glauca, is locally adapted to saline conditions in NS. Our experiments showed that NS T. latifolia and T. angustifolia are genetically compatible, and that saline conditions do not impede growth of hybrid plants. However, we also found that under conditions of high salinity, germination rates of hybrid seeds were substantially lower than those of NS T. latifolia. In addition, germination rates of NS T. latifolia were higher than those of Ontario T. latifolia, suggesting local adaptation to salinity in coastal wetlands. This study adds to the growing body of literature which identifies the important roles that local habitat and adaptation can play in the distributions and characteristics of hybrid zones.

Ontogenetic variation in salinity tolerance and ecophysiology of coastal dune plants

BACKGROUND AND AIMS

Global climate change includes shifts in temperature and precipitation, increases in the frequency and intensity of extreme weather events and sea level rise, which will drastically impact coastal ecosystems. The aim of this study is to quantify salinity tolerance and to identify physiological mechanisms underlying tolerance across wholeplant ontogeny in two widespread native coastal plant species in Hawai'i, Jacquemontia sandwicensis (Convolvulaceae) and Sida fallax (Malvaceae).

METHODS

At the seed, seedling, juvenile and mature ontogenetic stages, plants were exposed to high salinity watering treatments. Tolerance was assayed as the performance of stressed compared with control plants using multiple fitness metrics, including germination, survival, growth and reproduction. Potential physiological mechanisms underlying salinity tolerance were measured at each ontogenetic stage, including: photosynthesis and stomatal conductance rates, leaf thickness, leaf mass per area and biomass allocation.

KEY RESULTS

Salinity tolerance varied between species and across ontogeny but, overall, salinity tolerance increased across ontogeny. For both species, salinity exposure delayed flowering. Physiological and morphological leaf traits shifted across plant ontogeny and were highly plastic in response to salinity. Traits enhancing performance under high salinity varied across ontogeny and between species. For J. sandwicensis, water use efficiency enhanced growth for juvenile plants exposed to high salinity, while chlorophyll content positively influenced plant growth under salinity in the mature stage. For S. fallax, transpiration enhanced plant growth only under low salinity early in ontogeny; high transpiration constrained growth under high salinity across all ontogenetic stages.

CONCLUSIONS

That salinity effects vary across ontogenetic stages indicates that demographic consequences of sea level rise and coastal flooding will influence population dynamics in complex ways. Furthermore, even coastal dune plants presumably adapted to tolerate salinity demonstrate reduced ecophysiological performance, growth and reproduction under increased salinity, highlighting the conservation importance of experimental work to better project climate change effects on plants.

Salinity Adaptation and the Contribution of Parental Environmental Effects in Medicago truncatula

High soil salinity negatively influences plant growth and yield. Some taxa have evolved mechanisms for avoiding or tolerating elevated soil salinity, which can be modulated by the environment experienced by parents or offspring. We tested the contribution of the parental and offspring environments on salinity adaptation and their potential underlying mechanisms. In a two-generation greenhouse experiment, we factorially manipulated salinity concentrations for genotypes of Medicago truncatula that were originally collected from natural populations that differed in soil salinity. To compare population level adaptation to soil salinity and to test the potential mechanisms involved we measured two aspects of plant performance, reproduction and vegetative biomass, and phenological and physiological traits associated with salinity avoidance and tolerance. Saline-origin populations had greater biomass and reproduction under saline conditions than non-saline populations, consistent with local adaptation to saline soils. Additionally, parental environmental exposure to salt increased this difference in performance. In terms of environmental effects on mechanisms of salinity adaptation, parental exposure to salt spurred phenological differences that facilitated salt avoidance, while offspring exposure to salt resulted in traits associated with greater salt tolerance. Non-saline origin populations expressed traits associated with greater growth in the absence of salt while, for saline adapted populations, the ability to maintain greater performance in saline environments was also associated with lower growth potential in the absence of salt. Plastic responses induced by parental and offspring environments in phenology, leaf traits, and gas exchange contribute to salinity adaptation in M. truncatula. The ability of plants to tolerate environmental stress, such as high soil salinity, is likely modulated by a combination of parental effects and within-generation phenotypic plasticity, which are likely to vary in populations from contrasting environments.

Genetic variation of transgenerational plasticity of offspring germination in response to salinity stress and the seed transcriptome of Medicago truncatula

BACKGROUND

Transgenerational plasticity provides phenotypic variation that contributes to adaptation. For plants, the timing of seed germination is critical for offspring survival in stressful environments, as germination timing can alter the environmental conditions a seedling experiences. Stored seed transcripts are important determinants of seed germination, but have not previously been linked with transgenerational plasticity of germination behavior. In this study we used RNAseq and growth chamber experiments of the model legume M. trucantula to test whether parental exposure to salinity stress influences the expression of stored seed transcripts and early offspring traits and test for genetic variation.

RESULTS

We detected genotype-dependent parental environmental effects (transgenerational plasticity) on the expression levels of stored seed transcripts, seed size, and germination behavior of four M. truncatula genotypes. More than 50% of the transcripts detected in the mature, ungerminated seed transcriptome were annotated as regulating seed germination, some of which are involved in abiotic stress response and post-embryonic development. Some genotypes showed increased seed size in response to parental exposure to salinity stress, but no parental environmental influence on germination timing. In contrast, other genotypes showed no seed size differences across contrasting parental conditions but displayed transgenerational plasticity for germimation timing, with significantly delayed germination in saline conditions when parental plants were exposed to salinity. In genotypes that show significant transgenerational plastic germination response, we found significant coexpression networks derived from salt responsive transcripts involved in post-transcriptional regulation of the germination pathway. Consistent with the delayed germination response to saline conditions in these genotypes, we found genes associated with dormancy and up-regulation of abscisic acid (ABA).

CONCLUSIONS

Our results demonstrate genetic variation in transgenerational plasticity within M. truncatula and show that parental exposure to salinity stress influences the expression of stored seed transcripts, seed weight, and germination behavior. Furthermore, we show that the parental environment influences gene expression to modulate biological pathways that are likely responsible for offspring germination responses to salinity stress.

Plastic responses of native plant root systems to the presence of an invasive annual grass

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PREMISE OF THE STUDY

The ability to respond to environmental change via phenotypic plasticity may be important for plants experiencing disturbances such as climate change and plant invasion. Responding to belowground competition through root plasticity may allow native plants to persist in highly invaded systems such as the cold deserts of the Intermountain West, USA.•

METHODS

We investigated whether Poa secunda, a native bunchgrass, could alter root morphology in response to nutrient availability and the presence of a competitive annual grass. Seeds from 20 families were grown with high and low nutrients and harvested after 50 d, and seeds from 48 families, grown with and without Bromus tectorum, were harvested after ∼2 or 6 mo. We measured total biomass, root mass fraction, specific root length (SRL), root tips, allocation to roots of varying diameter, and plasticity in allocation.•

KEY RESULTS

Plants had many parallel responses to low nutrients and competition, including increased root tip production, a trait associated with tolerance to reduced resources, though families differed in almost every trait and correlations among trait changes varied among experiments, indicating flexibility in plant responses. Seedlings actively increased SRL and fine root allocation under competition, while older seedlings also increased coarse root allocation, a trait associated with increased tolerance, and increased root mass fraction.•

CONCLUSIONS

The high degree of genetic variation for root plasticity within natural populations could aid in the long-term persistence of P. secunda because phenotypic plasticity may allow native species to persist in invaded and fluctuating resource environments.

The ecological genomic basis of salinity adaptation in Tunisian Medicago truncatula

Background

As our world becomes warmer, agriculture is increasingly impacted by rising soil salinity and understanding plant adaptation to salt stress can help enable effective crop breeding. Salt tolerance is a complex plant phenotype and we know little about the pathways utilized by naturally tolerant plants. Legumes are important species in agricultural and natural ecosystems, since they engage in symbiotic nitrogen-fixation, but are especially vulnerable to salinity stress.

Results

Our studies of the model legume Medicago truncatula in field and greenhouse settings demonstrate that Tunisian populations are locally adapted to saline soils at the metapopulation level and that saline origin genotypes are less impacted by salt than non-saline origin genotypes; these populations thus likely contain adaptively diverged alleles. Whole genome resequencing of 39 wild accessions reveals ongoing migration and candidate genomic regions that assort non-randomly with soil salinity. Consistent with natural selection acting at these sites, saline alleles are typically rare in the range-wide species' gene pool and are also typically derived relative to the sister species M. littoralis. Candidate regions for adaptation contain genes that regulate physiological acclimation to salt stress, such as abscisic acid and jasmonic acid signaling, including a novel salt-tolerance candidate orthologous to the uncharacterized gene AtCIPK21. Unexpectedly, these regions also contain biotic stress genes and flowering time pathway genes. We show that flowering time is differentiated between saline and non-saline populations and may allow salt stress escape.

Conclusions

This work nominates multiple potential pathways of adaptation to naturally stressful environments in a model legume. These candidates point to the importance of both tolerance and avoidance in natural legume populations. We have uncovered several promising targets that could be used to breed for enhanced salt tolerance in crop legumes to enhance food security in an era of increasing soil salinization.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1160) contains supplementary material, which is available to authorized users.