Next Article in Journal
Mycorrhization of Quercus dentata Seedlings with Laccaria bicolor Enhances Salt Tolerance of Plants Only Under Relatively Moderate Soil Salinity Level
Next Article in Special Issue
Integrated Multi-Omics Analysis Reveals Photosynthetic Acclimation and Metabolic Reprogramming in Populus ussuriensis kom. Under Cold Stress
Previous Article in Journal
Surface Crack Occurrence and Resistance During Moisture Content Changes in MF-Resin-Impregnated Paper-Decorated Blockboard
Previous Article in Special Issue
Integration of Illumina and PacBio HiFi Sequencing Reveals a Three-Linear-Molecule Mitogenome with RNA-Editing Sites and Phylogeny in Arrow Bamboo (Fargesia qinlingensis)
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Forests
Volume 16
Issue 3
10.3390/f16030412
forests-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Polyploid Advantage? Comparing Salt Stress Responses of Di- and Tetraploid Acacia senegal (L.) Willd. Seedlings

by
Adja Madjiguene Diallo
1,*,
Erik Dahl Kjær
2,
Lene Rostgaard Nielsen
2 and
Anders Ræbild
2
1
Centre National de Recherches Forestières/Institut Sénégalais de Recherches Agricoles (ISRA/CNRF), Route des Pères Maristes, Dakar BP 2312, Senegal
2
Department of Geosciences and Natural Resource Management, University of Copenhagen, Rolighedsvej 23, 1958 Frederiksberg C, Denmark
*
Author to whom correspondence should be addressed.
Forests 2025, 16(3), 412; https://doi.org/10.3390/f16030412
Submission received: 10 February 2025 / Revised: 21 February 2025 / Accepted: 23 February 2025 / Published: 25 February 2025
(This article belongs to the Special Issue Genomic Analysis of Growth and Stress Adaptation in Forest Trees)
Browse Figures
Review Reports Versions Notes

Abstract

:
Polyploidy is often associated with the ability to grow under harsh conditions. The objective of this study was to test whether genome doubling in Acacia senegal confers superiority for growth under saline conditions. For this purpose, we assessed the cytotype distribution across ten natural stands in Senegal, representing different soil salinities. We further compared the growth of diploid and tetraploid A. senegal seedlings in a shared-pot greenhouse experiment, in which seedling pairs (diploids and polyploids) were irrigated with and without added NaCl. We found polyploids in six stands, and the proportion of polyploids in these stands was significantly and positively correlated with their level of soil salinity. Under experimental conditions, we found that the growth rate of diploid and tetraploid seedlings was equally depressed by salt stress, but the mortality rate for tetraploids was lower than that for diploids (34% versus 54%). In addition, the root-top ratio was higher in tetraploids compared to diploids, which may influence fitness under harsh conditions. Overall, this study provides support for polyploid superiority in A. senegal growing in saline soils. The findings of this study may have practical implications for the reforestation of saline soils with polyploid A. senegal, and we recommend further studies to elucidate their potential.

1. Introduction

Polyploid plants often display novel traits (e.g., increased cell size, changes in physiology, and ecological tolerance to a range of stresses such as cold, drought, and salinity) relative to their parental ancestors, which may enable them to occupy new niches in which their diploid progenitors cannot survive [1,2,3,4]. In relation to salt tolerance, it is debated whether polyploidy, in general, is associated with a higher stress tolerance per se, or whether reported cases of polyploids tolerant to salinity represent examples in which poly-ploids have acquired new traits that increase their performance in some specific environments but not in others [5].
Polyploids could be good candidates for the re-vegetation of salt-affected soils as studies on neo-polyploids have shown higher biomass accumulation and less necrosis in polyploids compared to their parental diploids under salinity stress [6,7,8,9]. A study by [10] demonstrated increased salt tolerance in naturally occurring tetraploid Arabidopsis (Arabidopsis thaliana) compared to diploids, and tetraploid rootstock-grafted watermelon (Citrullus lanatus) plants were found to be more tolerant to salt stress than their diploid progenitors [11].
The improved performance of polyploids may be due to their better ability to maintain a favorable K+/Na+ balance, as observed in Arabidopsis [10], or better functioning photosynthetic protective systems, as found in tetraploid Brassica compared to its diploid progenitor [7]. Likewise, polyploid Citrus cultivars were more tolerant to low salinity levels than diploids [12]; however, the opposite conclusion was reached when the same cultivars were exposed to higher levels of salinity [13], indicating that polyploidy does not always confer better salt tolerance. The question of whether polyploids are generally favored under saline conditions is thus still unresolved, and studies based on trees are scarce.
Recently, the role of polyploidy in adaptation to saline conditions has attracted interest in relation to the socio-economically important African dry zone tree species Acacia senegal (L.) Willd. (Fabaceae) (syn. Senegalia senegal (L.) Britton). A. senegal is reported to naturally grow in salt-affected lands in Senegal, estimated at about 1.7 million hectares [14]. Several studies have highlighted the ability of A. senegal to tolerate a high level of salinity [15,16,17,18] without considering the potential effect of ploidy level within the species. Thus, understanding and clarifying the basis of observed tolerance in A. senegal with respect to genome size is of prime importance, especially in the context of selecting appropriate genotypes for the reforestation of saline zones.
Diploids and polyploids of this species are known to co-occur in Senegal and elsewhere in Africa [19,20,21], with a high frequency of polyploid cytotypes reported from a saline site in Senegal [22]. This has led us to the hypothesize that polyploid plants of A. senegal are more tolerant to salinity stress than diploid cytotypes. Here, we test this hypothesis based on the assessment of (i) the distribution of polyploids in relation to soil characteristics (pH and electric conductivity) in natural stands and (ii) the performance of seedlings grown under controlled saline conditions.

2. Materials and Methods

2.1. Description of Stands with Respect to Salinity and pH

The presence of diploid and polyploid A. senegal at 10 sites in Senegal was estimated by [22] based on 30 random trees per site. As we used the site as the experimental unit, soil samples from 0–20 cm depth were collected using a hand auger at 10 randomly selected locations at each site and mixed to constitute one composite soil sample per site. Soil samples were then transported to the ISRA soil lab for analysis. For each composite sample, the electric conductivity (as a proxy for salinity) and pH (assessed in water and KCl solutions) were measured and compared to the estimated frequency of polyploids.

2.2. Plant Material for Controlled Salinity Study and Experimental Design

Seeds were collected from one of the natural stands in Diery, in the dry zone of Dahra in Senegal (15°20′ N and 15°28′ W; annual rainfall < 408 mm). This site has a relatively low level of salinity (Table 1). Seeds from four randomly chosen diploid trees (families: DB17, DB23, DB25, and DB26) and four randomly chosen tetraploid trees (families: DB9, DB10, DB13, and DB14) as assessed in [22] were used for a salt stress experiment.
Seeds were germinated in a climate chamber under a 16 h photoperiod. The temperature in the chamber varied between 28 and 33 °C, while the humidity ranged between 47 and 71%. The ploidy levels of the seedlings were determined by flow cytometric analysis following the method described in [20,21]. At age 2 months, 128 seedlings (64 diploids and 64 tetraploids) were transplanted into pots (13 cm) filled with peat soil (Plugg och Såjord) from Weibulls Horto AB, Sweden. Two seedlings were placed in each pot, one diploid and one tetraploid, in a design in which all diploid families were tested against all tetraploid families. The pairing of plants ensured that diploid and tetraploid seedling pairs were experiencing exactly the same conditions in their common pot, irrespective of size and water consumption [23]. This makes the two plants in a pot compete for the same resources, thus providing a better impression of their relative performance.
Two treatments (control and salt) were applied to the 64 pots, corresponding to 32 pots for the control and 32 pots for the salt treatment (Figure 1).
Pots were randomized and kept in a greenhouse under tropical conditions (minimum temperature of 20 °C and minimum 16 h of daylight for 3 months under well-watered conditions). The experiment began when the seedlings were three months old. The control pots were irrigated with tap water and added standard fertilizer. For the salt stress experiment, the pots were watered with the same fertilizer solution but with increasing concentrations of NaCl (0.05, 0.10, 0.15, and 0.20 mM) to slowly increase the stress level without osmotic shock [23]. Each concentration of salt was applied for 9 days by watering every 3rd day except for the last level, where pots were watered for one month with 0.20 mM of salt, corresponding to a highly saline soil. The pots were irrigated with a large volume (400 mL) of water or salt solution, which leaked from the bottom of all pots. This was done to avoid the buildup of high salt concentrations during salt treatment. During the experiment, the greenhouse temperature on one occasion reached 40 °C, which appeared lethal for some plants and introduced unintended heat stress into the trial.

2.3. Measurement of Morphological and Physiological Changes in Response to Salt Stress

Height and diameter were recorded for all individuals at (i) the start of the experiment, (ii) before changing to a higher salt concentration, and (iii) at the end of the experiment. At the end of the experiment, the number of leaves and survival rate were determined, and the plants were harvested and separated into stems and roots. Survival of plants was evaluated based on leaf loss and the presence/absence of green tissues under the bark (dryness). Tissues were briefly rinsed in water, weighed for fresh weight determination after surplus water was wiped off, and oven-dried at 80 °C for 48 h for assessment of dry weight. Growth and biomass were assessed in surviving plants, considering the values for dead seedlings as missing.
Stem tissues from five control pots and 10 salt-treated pots were used to compare Na+ and Cl− accumulation between diploids and tetraploids. The dried stems were homogenized into a fine powder using a mortar in liquid nitrogen. A 40 mg sample was suspended in 40 mL of water, and the solution was shaken on a horizontal shaking machine at 220 rpm for 30 min to ensure complete dissolution. After this step, all suspensions were filtered through Whatman filter paper, and the concentrations of Na+ and Cl− were measured using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES Perkin Elmer Optima 3000 XL, PerkinElmer Inc., 940 Winter Street, Waltham, MA, USA) and Ion chromatography (Shimadzu Corporation, Kyoto, Japan), respectively.

2.4. Data Analysis

Statistical analyses were performed using R version 3.4.3 (R Core Team 2017).
-
Cytotype frequency in relation to site characteristics
We tested for differences in cytotype frequency among the ten sampled natural stands by conducting a chi-square test of homogeneity. Simple regression analyses were performed to examine the links between cytotype frequency (expressed as a percentage) and the following explanatory variables: longitude and latitude (converted to decimal degrees), electric conductivity, rainfall, and pH in water and KCl. Because electric conductivity (EC) (salinity) showed a stochastic rather than a continuous distribution, the data were log-transformed. Additionally, the analysis was supplemented with a one-way ANOVA where the Arcsine transformed frequency of polyploids was modeled as a function of sites with high (EC above 800 µS/cm) or low (EC below 50 µS/cm) salinity.
-
Salt stress tolerance evaluation between ploidy levels
Mortality at the end of the experiment was analyzed using a chi-square significance test for the odds ratio (OR) to calculate the odds of a death outcome given exposure versus non-exposure to salt (the estimated likelihood that the diploid group experiences the event (death) compared to the tetraploid group).
Growth and salt accumulation were compared in pots in which both diploid and tetraploid plants survived, corresponding to 30 pots. This was based on a linear model implemented in the lm function in R:
Yij = Fd +Ft + Treatmenti + errorij, (i = salt, control; j = (1…32))
where Yij represents the average or the difference in growth or salinity between the two plants in the same pot (see below), and Fd and Ft are the effects of the family of the diploid individual and tetraploid individual in the pot, respectively. First, letting Yij represent the average (growth or salt accumulation) of the two plants in a pot, we tested the overall effect of treatment using an F-test. Secondly, to test the effects of ploidy, we let Yij represent the difference (Dij) between the tetraploid and the diploid plants in each pot, i.e., we used pairwise observations. The hypothesis of no differences between tetraploid and diploid plants in the model corresponds to D = 0, which was tested using the intercept of the model. Finally, again, letting Yij represent the difference (Dij) between the tetraploid and diploid plants in each pot, we tested the possible interaction between ploidy level and the treatment. The hypothesis of a similar response of tetraploid and diploid plants to salt treatment was tested using an F-test of the effect of treatment in the model. This approach allowed us to assume that the residuals were independent since each observation was based on a randomized pot. The assumptions of normality and homogeneity of the variance of residuals were checked graphically, and where necessary, a logarithmic transformation was applied to achieve normality. In the case of height, one outlier was deleted due to a typing error.
Bonferroni corrections for multiple tests were not applied to any of the statistical tests. We find this justified since we only performed tests of meaningful biological hypotheses closely linked to the research questions behind the study. However, this means that significant results based on test statistics close to the 5% significance level should be interpreted with caution.

3. Results

3.1. Cytotype Occurrence in Relation to Site Characteristics

The variation in ploidy level among sites was statistically correlated with salinity (p = 0.02; Table 1 and Table 2). The significant relationship between polyploidy and soil salinity was driven by the high frequencies of polyploid trees at the two highly saline sites, Ngane and Velor. This was confirmed by one-way ANOVA comparing the polyploid frequency at these two sites to the other sites (p = 0.02). It is important to note that the lower-salinity site Bakel also had a high frequency of polyploidy (see Table 1), and the statistical relationship must, therefore, be interpreted with care.
No significant relationship was observed between rainfall and cytotype occurrence (p = 0.15). The pH (water) was borderline significant (p = 0.06); however, the variations in pH were small among sites, and the values were all in the neutral range.

3.2. Performance of Diploid and Tetraploid Seedlings Under Salt Stress

3.2.1. Survival

At the end of the trial, the survival of the control plants was 80%, which differed significantly from the 56% survival of the salt-stressed plants (χ2 (1) = 8.7; p = 0.005). Diploid plants had significantly (χ2 (1) = 12.0; p < 0.001) larger mortality under salt stress compared to the control treatment (17/32 = 53% versus 4/32 = 13%), while mortality in tetraploid plants was almost unaffected by the salt treatment (11/32 = 34% for salt-stressed plants versus 9/32 = 28% for control) (Figure 2).
When assessing the interaction between cytotypes and treatment, a significant difference was observed (p = 0.03), with diploids recording a higher mortality rate under salt stress compared to tetraploids (17/32 = 53% versus 11/32 = 34%). The analysis of the odds ratio (OR) revealed that diploid seedlings had a 2.74 higher risk of death when grown under saline conditions compared to tetraploid ones (Figure 2).

3.2.2. Growth

Initially, height and diameter growth were unaffected by salt stress, but at day 124, after exposure to 0.15 mM NaCl, height was significantly lower in salt-stressed plants than in control plants (p = 0.0008, Figure 3). At the final assessment, after exposure to 0.20 mM NaCl for one month, both height and diameter were smaller in the salt-stressed plants than in the control plants (p <0.0001 for both). The polyploid seedlings revealed a tendency to grow slightly faster than diploids, but the differences were not significant, and there were no significant interactions between ploidy and treatment, the latter suggesting that the diploid and tetraploid plants reacted in a similar manner to the salt stress for growth traits (Figure 3).

3.2.3. Root-Shoot Biomass

At the time of assessment, several plants had shed their leaves, indicating that comparisons of leaf biomass were not meaningful. However, analyses of stem and root biomass confirmed that seedlings from the unstressed control group were larger than the salt-treated plants, both for fresh and dry weights (Figure 4, p < 0.01 for all).
No interactions were observed between ploidy levels and treatments; however, the fresh and dry weights of the roots were greater in tetraploids than in diploids (p = 0.008 and p = 0.004, respectively, Figure 4). In addition, the ratio between the fresh weight and dry weight of the roots was significantly higher in diploids than in tetraploids (p = 0.03) and was increased in the salt treatments (p = 0.01). The ratios between stem and root biomass were not significantly affected by the treatments, but (when calculated on the basis of dry weight) there was a highly significant difference between diploids and tetraploids (p < 0.0001), with tetraploids having a larger proportion of the biomass invested in roots compared to diploids (Figure 4). Because such changes could be caused by changed allometry in the slightly larger tetraploid plants, we plotted the stem/root ratio against the total dry weight of the plants (Figure 5). This shows a decreasing stem/root ratio as plants grow larger, but also a generally higher level of the stem/root ratio in diploids, irrespective of size.

3.2.4. Na+ and Cl− Uptake Under Salt Stress

Salt stress treatment resulted in a significant accumulation of salt in the stems of both diploid and tetraploid seedlings (p = 0.003 for Na+; p = 0.002 for Cl−). The concentration of Na+ increased from 5.1 ± 7.8 mg g−1 to 39.5 ± 5.3 mg g−1, and the concentration of Cl− increased from 9.3 ± 10.0 mg g−1 to 58.0 ± 7.1 mg g−1. However, there were no significant differences between the two levels of ploidy in their accumulation of salt.

4. Discussion

Acacia senegal is occasionally found in saline soils in Asia and Africa [21,24] and possesses traits that allows it to tolerate mild salt stress. Plants in our experimental trial, growing under gradually increasing concentrations of salt, accumulated Na+ and Cl− in stems up to levels comparable to levels observed in, e.g., salt-stressed Citrus and Lonicera cultivars [8,25]. The responses to salt stress observed in the present study were highly significant and typical for A. senegal, and included slower growth rates and changed ratios between fresh and dry weights [17,18,24]. From these results, we conclude that our experiment was successful in creating conditions of salt stress.
The experimental design with a diploid and a tetraploid plant growing in the same plot was designed to expose the two plants to the same level of stress, irrespective of the size of the plants and the different transpiration rates that they may have [23]. This design should lead to a strong comparison between plants of the two ploidy levels competing for the same resources. We observed that salt treatment significantly increased mortality in diploids but not in tetraploids, and the odds ratio of 2.7 suggested that diploids had a considerably higher risk of death under salt stress compared to tetraploids. Although care should be taken when extrapolating the survival of seedlings in a greenhouse to field conditions, this supports the hypothesis of better salt adaptation of polyploids and may explain the high frequency of polyploids observed in the Ngane and Velor stands growing on saline soils [22]. Although the effects of salinity may become more severe over time as Na+ and Cl− accumulate in the plant, studies comparing the responses of seedlings with those of mature trees are rare. However, Ref. [26] found that the growth rates of Populus tremuloides decreased over time in high-salinity soils compared to sites with low salinity, suggesting that some species may react progressively to salinity. The growth rates of Picea glauca under the same conditions were not affected by salinity. Likewise, a screening of Eucalyptus for salinity tolerance in Australia under field conditions showed consistent results from age 1 to 4 years, indicating that early results are valid for this genus [27]. In the case of A. senegal, it was previously found that different cytotypes are almost reproductively isolated [21,22]. Thus, given that salt tolerance is stable across the lifetime of A. senegal, one may speculate that polyploidization facilitates niche differentiation in this species. In the long term, the higher mortality of diploids in saline soils may lead to the dominance of polyploids in such soils and facilitate the divergent evolution of the two cytotypes. Additional studies are needed to understand and compare the response norms between early life stages and mature trees grown in common gardens.
The changed allometric relationships in tetraploids compared to diploid A. senegal that we observed (Figure 4) are likely to influence performance. Previously, we found that tetraploid seedlings grew faster than diploid seedlings under water-stressed conditions in a greenhouse, and in a long-term common garden trial in Senegal, we found superior growth of the tetraploid cytotype [21], supporting the notion of differentiation between diploids and tetraploids in terms of growth. In addition, our results suggest that tetraploids invest more resources in root growth compared to diploids, which could be considered an adaptive mechanism to enhance their survival under stressful conditions.
It has often been reported that drought-tolerant species allocate more resources to root growth than shoot growth for their survival in dry environments [28,29], and it is therefore interesting that we found a relatively larger root growth and better survival in tetraploids compared to diploids (Figure 4). As salt stress is caused by both osmotic stress and the toxicity of Na+ and Cl−, plant responses include the accumulation of osmolytes and maintenance of ionic homeostasis [30,31]. Our analysis of Na+ and Cl− indicated no differences in ion homeostasis between ploidies, but we cannot exclude the possibility that larger root systems in polyploids would increase the uptake of compatible ions, such as K+. Responses to salt stress are controlled by complex interactions among several hormones [30]; however, how this is affected by polyploidy in A. senegal is currently unknown.
Polyploids are often associated with increased fitness, usually attributed to the existence of heterosis, allowing polyploids to cope with a broader array of conditions [32]. Polyploids have long been reported to be more frequent in harsh conditions (subarctic regions, high elevations, and xeric environments) and more successful than related diploids in colonizing relatively disturbed areas [1,2,3,4]. Polyploidization often leads to the acquisition of novel traits (e.g., increased cell size), genomic restructuring, and changes in gene expression, leading to changes in physiology and ecological tolerance [32,33,34,35] that, together with reproductive isolation caused by chromosome doubling, may support adaptation to distinct environmental niches. However, polyploidization often comes at a cost in terms of reduced reproductive success and high levels of apomixis [36], which also seems to be the case for A. senegal [20,22], potentially reducing the long-term adaptive potential of this cytotype.
Genetic analysis by [22] revealed a clear separation between diploid and polyploid individuals, but sub-groupings were also found between polyploid genotypes occurring naturally in the saline areas (Ngane and Velor sites) and those used in this experiment (Diery site). Further comparative studies involving polyploid genotypes occurring in saline and non-saline areas are needed to elucidate whether different genetic groups produce different adaptive strategies in response to salt stress.
It would be especially valuable to have studies based on larger plants (e.g., trees that have developed more mature root architecture) growing under conditions close to in situ conditions. However, selection is likely to be especially strong during the very early establishment phase, and studies of seedlings remain highly relevant from an evolutionary perspective.

5. Conclusions

Our results revealed that tetraploid A. senegal exhibited higher survival rate and root biomass allocation under salinity stress, supporting the hypothesis of better salt tolerance and adaptation in tetraploids. In addition, the observed differences in shoot/root ratios suggest that diploids and tetraploids may have different adaptive strategies to cope with salt exposure. Thus, stands with a higher frequency of polyploid trees could be considered suitable seed sources for future reforestation actions on salt-affected lands. Our results also document the early stage increased survival of tetraploid A. senegal under controlled conditions, which is crucial for population establishment and dynamics. However, it remains crucial to verify whether the superiority of tetraploids under salt stress is expressed only at early stages or applies more generally to mature trees. Thus, further studies focusing on comparisons of mature A. senegal cytotypes in different habitats or field trials are needed to clarify the genetic basis of salt tolerance mechanisms and confirm long-term adaptive benefits.

Author Contributions

Conceptualization, A.M.D., E.D.K., L.R.N. and A.R.; methodology, A.M.D., E.D.K., L.R.N. and A.R.; software, A.M.D., E.D.K. and A.R.; validation, A.M.D., E.D.K. and A.R.; formal analysis, A.M.D., E.D.K. and A.R.; writing—original draft preparation, A.M.D., E.D.K., L.R.N. and A.R.; writing—review and editing, A.M.D., E.D.K., L.R.N. and A.R. Supervision, A.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Islamic Development Bank, under the PhD Merit Scholarship Program, grant number (Student Grant Number 600014414), “ISRA” and “University of Copenhagen”.

Data Availability Statement

The data will be made available in the University of Copenhagen-Electronic Research Data Archive, ERDA.

Acknowledgments

We wish to thank Momar Wade for assistance with fieldwork, Karin Henriksen for assisting with the flow cytometric analysis, Kurt Dahl and Theodor Emil Bølsterli for assistance in the greenhouse, and Antoine Sambou for assistance with measurements and watering. Financial support was provided by the Islamic Development Bank (IDB) under the PhD Merit Scholarship Program and by the University of Copenhagen, Denmark.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Te Beest, M.; Le Roux, J.J.; Richardson, D.M.; Brysting, A.K.; Suda, J.; Kubesová, M.; Pysek, P. The more the better? The role of polyploidy in facilitating plant invasions. Ann. Bot. 2012, 109, 19–45. [Google Scholar] [CrossRef]
  2. Gunn, B.F.; Murphy, D.J.; Walsh, N.G.; Conran, J.G.; Pires, J.C.; Macfarlane, T.D.; Birch, J.L. Evolution of Lomandroideae: Multiple origins of polyploidy and biome occupancy in Australia. Mol. Phylogenet. Evol. 2020, 149, 106836. [Google Scholar] [CrossRef]
  3. Van de Peer, Y.; Ashman, T.L.; Soltis, P.S.; Soltis, D.E. Polyploidy: An evolutionary and ecological force in stressful times. Plant Cell 2021, 33, 11–26. [Google Scholar] [CrossRef] [PubMed]
  4. Ræbild, A.; Anamthawat-Jonsson, K.; Egertsdotter, U.; Immanen, J.; Jensen, A.M.; Koutouleas, A.; Martens, H.J.; Nieminen, K.; Olofsson, J.K.; Röper, A.C.; et al. Polyploidy—A tool in adapting trees to future climate changes? A review of polyploidy in trees. For. Ecol. Manag. 2024, 560, 121767. [Google Scholar] [CrossRef]
  5. Buggs, R.J.; Pannell, J.R. Ecological differentiation and diploid superiority across a moving ploidy contact zone. Evolution 2007, 61, 125–140. [Google Scholar] [CrossRef] [PubMed]
  6. Liu, S.; Sumei, C.; Yu, C.; Zhiyong, G.; Dongmei, Y.; Fadi, C. In vitro induced tetraploid of Dendranthemanankingense (Nakai) Tzvel.shows an improved level of abiotic stress tolerance. Sci. Hortic. 2011, 127, 411–419. [Google Scholar] [CrossRef]
  7. Meng, H.; Jiang, S.; Hua, S.; Li, Y.; Guo, W.; Jiiang, L. Comparison Between a Tetraploid Turnip and Its Diploid Progenitor (Brassica rapa L.). Agric. Sci. China 2011, 10, 1671–2927. [Google Scholar] [CrossRef]
  8. Yan, K.; Wu, C.; Zhang, L.; Chen, X. Contrasting photosynthesis and photoinhibition in tetraploid and its autodiploid honeysuckle (Lonicera japonica Thunb.) under salt stress. Front. Plant Sci. 2015, 6, 227. [Google Scholar] [CrossRef]
  9. Wang, Z.; Wang, M.; Liu, L.; Meng, F. Physiological and Proteomic Responses of Diploid and Tetraploid Black Locust (Robinia pseudoacacia L.) subjected to Salt Stress. Int. J. Mol. Sci. 2013, 14, 20299–20325. [Google Scholar] [CrossRef]
  10. Chao, D.-Y.; Dilkes, B.; Luo, H.; Douglas, A.; Yakubova, E.; Lahner, B.; Salt, D.E. Polyploids exhibit higher potassium uptake and salinity tolerance in Arabidopsis. Science 2013, 341, 658–659. [Google Scholar] [CrossRef] [PubMed]
  11. Zhu, H.; Zhao, S.; Lu, X.; He, N.; Gao, L.; Dou, J.; Bie, Z.; Liu, W. Genome duplication improves the resistance of watermelon root to salt stress. Plant Physiol. Biochem. 2018, 133, 11–21. [Google Scholar] [CrossRef] [PubMed]
  12. Saleh, B.; Allario, T.; Dambier, D.; Ollitrault, P.; Morillon, R. Tetraploid citrus rootstocks are more tolerant to salt stress than diploid. Comptes Rendus Biol. 2008, 331, 703–710. [Google Scholar] [CrossRef]
  13. Mouhaya, W.; Allario, T.; Brumos, J.; Andrés, F.; Froelicher, Y.; Luro, F.; Talon, M.; Ollitrault, P.; Morillon, R. Sensitivity to high salinity in tetraploid citrus seedlings increases with water availability and correlates with expression of candidate genes. Funct. Plant Biol. 2010, 37, 674–685. [Google Scholar] [CrossRef]
  14. Sonneveld, B.G.J.S.; Keyzer, M.A.; Zikhali, P.; Merbis, M.D. National Land Degradation Assessment Senegal and Review of Global Socio-Economic Parameters in the LADA Data Base; Land Degradation Assessment Project, LADA Project Paper (Centre for World Food Projects (SOW-VU) Project Papers); Centre for World Food Studies: Amsterdam, The Netherlands, 2010. [Google Scholar]
  15. Pandey, S.; Zhang, W.; Assmann, S.M. Roles of ion channels and transporters in guard cell signal transduction. FEBS Lett. 2007, 581, 2325–2336. [Google Scholar] [CrossRef]
  16. Sambou, A.; Ndour, B.; Cheng, S.; Senghor, E. Ligneous species tolerance in acid sulphated and saline soils of sine saloum: Case of rural community of Djilass and Loul Secene. J. Sustain. Dev. 2010, 3, 174. [Google Scholar] [CrossRef]
  17. Fall, D.; Bakhoum, N.; Fall, F.; Diouf, F.; Ly, M.O.; Diouf, M.; Gully, D.; Hocher, V.; Diouf, D. Germination, growth and physiological responses of Senegalia senegal (L.) Britton, Vachellia seyal (Delile) P. Hurter and Prosopis juliflora (Swartz) DC to salinity stress in greenhouse conditions. Afr. J. Biot. 2016, 15, 37. [Google Scholar]
  18. Sarr, M.S.; Seiler, J.R.; Sullivan, J. Growth and physiology of Senegalia senegal (L.) Britton seedlings as influenced by seed origin and salinity and fertility treatments. Forests 2017, 8, 388. [Google Scholar] [CrossRef]
  19. Odee, D.W.; Wilson, J.; Omondi, S.; Perry, A.; Cavers, S. Rangewide ploidy variation and evolution in Acacia senegal: A north-south divide? AoB Plants 2015, 7, lv011. [Google Scholar] [CrossRef] [PubMed]
  20. Diallo, A.M.; Nielsen, L.R.; Hansen, J.K.; Ræbild, A.; Kjær, E.D. Study of quantitative genetics of gum arabic production complicated by variability in ploidy level of Acacia senegal (L.) Willd. Tree Genet. Genomes 2015, 11, 80–92. [Google Scholar] [CrossRef]
  21. Diallo, A.M.; Nielsen, L.R.; Kjær, E.D.; Petersen, K.K.; Ræbild, A. Polyploid can confer superiority to West African Acacia senegal (L.) Willd. trees. Front. Plant Sci. 2016, 7, 821. [Google Scholar] [CrossRef] [PubMed]
  22. Diallo, A.M.; Kjær, E.D.; Ræbild, A.; Nielsen, L.R. Coexistence of diploid and polyploid Acacia senegal (L.) Willd. and its implication for interploidy pollination. New For. 2022, 54, 67–82. [Google Scholar] [CrossRef]
  23. Verslues, P.E.; Agarwal, M.; Katiyar-Agarwal, S.; Zhu, J.; Zhu, J.K. Methods and concepts in quantifying resistance to drought, salt and freezing, abiotic stresses that affect plant water status. Plant J. 2006, 45, 523–539. [Google Scholar] [CrossRef] [PubMed]
  24. Hardikar, S.A.; Pandey, A.N. Growth, water status and nutrient accumulation of seedlings of Acacia senegal in response to soil salinity. Ann. Biol. 2008, 30, 17–28. [Google Scholar]
  25. Ruiz, M.; Pina, J.A.; Alcayde, E.; Morillon, R.; Navarro, L.; Millo, E.P. Behavior of diploid and tetraploid genotypes of ‘carrizo’ citrange under abiotic stress. Int. Soc. Hort. Sci. 2016, 1065, 1283–1292. [Google Scholar] [CrossRef]
  26. Lilles, E.B.; Purdy, B.G.; Macdonald, S.E.; Chang, S.X. Growth of aspen and white spruce on naturally saline sites in northern Alberta: Implications for development of boreal forest vegetation on reclaimed saline soils. Can. J. Soil Sci. 2012, 92, 213–227. [Google Scholar] [CrossRef]
  27. Zohar, Y.; Di Stefano, J.; Bartle, J. Strategy for screening eucalypts for saline lands. Agroforest. Syst. 2010, 78, 127–137. [Google Scholar] [CrossRef]
  28. Aroca, R. Plant Response to Drought Stress: From Morphological to Molecular Features; Springer: Berlin/Heidelberg, Germany, 2012; Volume 1, pp. 1–33. [Google Scholar]
  29. Gning, F.; Jourdan, C.; Marone, D.; Ngom, D.; Ræbild, A. Root growth and biomass partitioning of nine juvenile Sahelian agroforestry tree species under drought and irrigation treatments. Plant Soil 2025. [Google Scholar] [CrossRef]
  30. Zhao, C.; Zhang, H.; Song, C.; Zhu, J.-K.; Shabala, S. Mechanisms of plants responses and adaptation to soil salinity. Innovation 2020, 24, 100017. [Google Scholar] [CrossRef] [PubMed]
  31. Läuchli, A.; Epstein, E. Plant responses to saline and sodic conditions. In Agricultural Salinity Assessment and Management; Tanji, K.K., Ed.; ASCE Manuals and Reports on Engineering Practice; ASCE: New York, NY, USA, 2010; pp. 113–137. [Google Scholar]
  32. Levin, D.A. The Role of Chromosomal Change in Plant Evolution; Oxford University Press: New York, NY, USA, 2002. [Google Scholar]
  33. Ramsey, J.; Schemske, D.W. Neopolyploidy in flowering plants. Annu. Rev. Ecol. Syst. 2002, 33, 589–639. [Google Scholar] [CrossRef]
  34. Paterson, A.H.; Chapman, B.A.; Kissinger, J.C.; Bowers, J.E.; Feltus, F.A.; Estill, J.C. Many gene and domain families have convergent fates following independent whole-genome duplication events in Arabidopsis, Oryza, Saccharomyces and Tetraodon. Trends. Genet. 2006, 22, 597–602. [Google Scholar] [CrossRef] [PubMed]
  35. Alix, K.; Gérard, P.R.; Schwarzacher, T.; Heslop-Harrison, J.S. Polyploidy and interspecific hybridization: Partners for adaptation, speciation and evolution in plants. Ann. Bot. 2017, 120, 183–194. [Google Scholar] [CrossRef] [PubMed]
  36. Hojsgaard, D.; Hörandl, E. The rise of apomixis in natural plant populations. Front. Plant Sci. 2019, 10, 358. [Google Scholar] [CrossRef] [PubMed]
Forests 16 00412 g001
Figure 1. (A) whole experiment: pots with blue labels represent controls; pots with red labels represent plants exposed to salinity. (B) Tetraploid (left) and diploid (right) Acacia senegal plants subjected to salt stress.
Figure 1. (A) whole experiment: pots with blue labels represent controls; pots with red labels represent plants exposed to salinity. (B) Tetraploid (left) and diploid (right) Acacia senegal plants subjected to salt stress.
Forests 16 00412 g001
Forests 16 00412 g002
Figure 2. Variation in survival between diploid and tetraploid Acacia senegal seedlings in a salt stress experiment.
Figure 2. Variation in survival between diploid and tetraploid Acacia senegal seedlings in a salt stress experiment.
Forests 16 00412 g002
Forests 16 00412 g003
Figure 3. Variation in growth in (a) height and (b) diameter between diploid and tetraploid seedlings of Acacia senegal under salt stress conditions. The line in the lower part of (b) shows the concentration of NaCl in the irrigation water in the salt stress treatment.
Figure 3. Variation in growth in (a) height and (b) diameter between diploid and tetraploid seedlings of Acacia senegal under salt stress conditions. The line in the lower part of (b) shows the concentration of NaCl in the irrigation water in the salt stress treatment.
Forests 16 00412 g003
Forests 16 00412 g004
Figure 4. Dry and fresh weights of stems (upper) and roots (lower) of diploid and tetraploid Acacia senegal in the salt stress experiment. Values represent means ± sd (n = 15–28).
Figure 4. Dry and fresh weights of stems (upper) and roots (lower) of diploid and tetraploid Acacia senegal in the salt stress experiment. Values represent means ± sd (n = 15–28).
Forests 16 00412 g004
Forests 16 00412 g005
Figure 5. Differences in stem/root ratios for dry weight between diploid and tetraploid Acacia senegal seedlings under salt stress conditions.
Figure 5. Differences in stem/root ratios for dry weight between diploid and tetraploid Acacia senegal seedlings under salt stress conditions.
Forests 16 00412 g005
Table 1. Site characteristics.
Table 1. Site characteristics.
SitesNFreq. Diploid
(%)		Freq. Polyploid (%)LatitudeLongitudeAnnual Rainfall (mm)Electric Conductivity (µS/cm)pH WaterpH
KCl
Kamb30673315°31′32″ N15°26′06″ W40036.676.45.7
Diery30772315°23′47″ N15°22′54″ W40814.756.14.9
Gniby28100014°26′11″ N15°38′07″ W55525.656.95.8
Velor30435714°03′26″ N16°15′25″ W6368026.35.9
Ngane25307014°12′06″ N16°12′09″ W60819096.25.8
Pete30100016°03′02″ N14°01′04″ W29824.36.65.6
Ourouss30100015°34′56″ N13°21′54″ W40019.756.75.8
Semme3093715°11′00″ N12°56′50″ W48620.996.45.3
Bakel30336714°52′16″ N12°29′20″ W53519.966.04.9
Seoudji30100014°19′46″ N12°26′43″ W65527.696.25.2
Table 2. Results of simple regressions analyzing the relationship between geographical and edaphic parameters and the frequency of polyploids in % across 10 populations of Acacia senegal in Senegal.
Table 2. Results of simple regressions analyzing the relationship between geographical and edaphic parameters and the frequency of polyploids in % across 10 populations of Acacia senegal in Senegal.
TraitsSlopeSEt-ValuePr > t
Longitude0.620.660.950.37
Latitude0.190.90.210.84
pH water−7132−2.20.06
pH KCl−330−0.10.93
log(EC)321030.02
Rainfall0.130.081.60.15
SE: Standard error; Significant value (p ≤ 0.05) in bold.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Diallo, A.M.; Kjær, E.D.; Nielsen, L.R.; Ræbild, A. Polyploid Advantage? Comparing Salt Stress Responses of Di- and Tetraploid Acacia senegal (L.) Willd. Seedlings. Forests 2025, 16, 412. https://doi.org/10.3390/f16030412

AMA Style

Diallo AM, Kjær ED, Nielsen LR, Ræbild A. Polyploid Advantage? Comparing Salt Stress Responses of Di- and Tetraploid Acacia senegal (L.) Willd. Seedlings. Forests. 2025; 16(3):412. https://doi.org/10.3390/f16030412

Chicago/Turabian Style

Diallo, Adja Madjiguene, Erik Dahl Kjær, Lene Rostgaard Nielsen, and Anders Ræbild. 2025. "Polyploid Advantage? Comparing Salt Stress Responses of Di- and Tetraploid Acacia senegal (L.) Willd. Seedlings" Forests 16, no. 3: 412. https://doi.org/10.3390/f16030412

APA Style

Diallo, A. M., Kjær, E. D., Nielsen, L. R., & Ræbild, A. (2025). Polyploid Advantage? Comparing Salt Stress Responses of Di- and Tetraploid Acacia senegal (L.) Willd. Seedlings. Forests, 16(3), 412. https://doi.org/10.3390/f16030412

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop