Growth, leaf gas exchange and physiological parameters of two Glycyrrhiza glabra L. populations subjected to salt stress condition
Introduction
Salt stress is the most critical and harmful factor that affects reducing plant growth, development, and yield (Hadi and Karimi, 2012; Saidimoradi et al., 2019). Soil salinity is caused by excessive use of fertilizers, irrigation of plants with low-quality water, high evaporation of soil, as well as applied soils with little drainage (Hadi and Karimi, 2012).
Three major effects of salinity stress are ion toxicity, osmotic, and oxidative stress (Hniličková et al., 2017). Salt stress reduces plant growth and development, which leads to altering in water and mineral uptake, reduction of net photosynthesis and membrane stability, cell division inhibition, damage on photosynthetic pigments, as well as an increase in respiration rate (Saidimoradi et al., 2019).
The short or long-term impacts of salt stress on the photosynthesis process are complex. Plant biomass is an indication of net photosynthesis (Tavakkoli et al., 2011). Prior researches demonstrated the impacts of salt stress on photosynthetic pigments, photosystems, CO2 assimilation, stomatal conductance, electron transport system, and water use efficiency that finally lead to a reduction of the photosynthetic process (Mahouachi, 2018). Many studies reported that the chlorophyll content and the efficiency of photosynthesis are reduced in Miscanthus giganteus (Płażek et al., 2014) and Pistacia vera (Hajiboland et al., 2014) under the high NaCl content in the rhizosphere.
The osmotic stress caused by salinity leads to reduce osmotic potential, turgor damage, and prevention of water absorption by plants (Mahouachi, 2018). Relative water content (RWC) is a determining factor of the physiological process and survival of plants (Sarabi et al., 2017). Accumulation of compatible solutes is the usual response of plant adaptation to changes in the external osmotic potential and protects the membrane against various stress (Hajiboland et al., 2014; Saidimoradi et al., 2019).
The major ionic stress is related to high salinity and Na+ toxicity. Some plant species are also vulnerable to Cl−, a key anion in saline soils (Hadi and Karimi, 2012). The high concentration of Na+ and Cl− in saline soils leads to competition between sodium and other inorganic nutrients, ion imbalances, and nutrient deficiencies, such as K+, Ca2+, and Mn2+ (Hadi and Karimi, 2012; Hajiboland et al., 2014). Plants can withstand salinity by restricting the absorption of toxic ions and compartmentation of the ions in cell vacuoles (Płażek et al., 2014). Under the high salt levels in the rhizosphere, further selective uptake of K+ rather than Na+ by plant cells, Na+ compartmentation, and distribution in shoots represent to be the important mechanisms for keeping sufficient K+ levels (Mahouachi, 2018).
Cell membrane stability has been widely considered as an index of cellular damages under the high salt concentration because the salinity leads to produce reactive oxygen species (ROS) in plants (Sarabi et al., 2017; Saidimoradi et al., 2019). Both non-enzymatic and enzymatic antioxidant mechanisms have a considerable function in the detoxifying ROS generated from the electron transport chains of mitochondria and chloroplasts (Behdad et al., 2020a).
Phenolic compounds and flavonoids are secondary metabolites that have antioxidant activities due to the presence of free OH groups in their structure (Behdad et al., 2020b). Glabridin, liquiritin, liquiritigenin contents, and antioxidant capacity were different in the licorice rhizomes of different populations from Iran (Esmaeili et al., 2019). Plant responses to soil salinity depend on plant growth stage, plant populations, and the duration and severity of salinity to which the plants are exposed (Behdad et al., 2020a). The production of the plant secondary metabolites is strongly related to environmental factors (Esmaeili et al., 2019; Behdad et al., 2020b).
Glycyrrhiza glabra L. (Licorice) is the oldest and famous medicinal plant belonging to the Fabaceae family (Shirazi et al., 2019). The rhizomes of Glycyrrhiza species are one of the valuable and most important sources of biologically active compounds, including glycyrrhizin, phenolic compounds, flavonoids, different sugars, saponins, sterols, starches, amino acids, tannins, and essential oils (Behdad et al., 2020b). G. glabra grows as a wild plant from North to South of Iran. The major producer and exporter of licorice rhizomes on a global scale are Iran, especially Shiraz, the region located in the southwest of Iran (Esmaeili et al., 2019). Because of the high economic and medical importance of licorice, the demand and export of licorice rhizomes have increased, although the availability of wild licorice has declined (Esmaeili et al., 2019; Behdad et al., 2020b). On the other hand, there are 6.8 million hectares of salt-affected agricultural lands in Iran (Moameni, 2011). Thus, it's necessary to study the cultivation of licorice rhizomes in saline soils.
To the best of our knowledge, limited information is available on the impacts of salt stress on licorice cultivated from seeds (Amanifar et al., 2019; Shirazi et al., 2019). According to the wide distribution of G. glabra in Iran and its tolerance to environmental stresses, evaluation of the response of licorice populations to salinity stress for the cultivation extension of this important medicinal plant in regions with saline soil of Iran is essential. Moreover, the major proliferation of licorice is through its rhizomes (Behdad et al., 2020a). The objective of this research was to survey the impacts of different treatments of salt stress (0, 100, 200, 400, 600, and 800 mM NaCl) on growth parameters, leaf relative water content (LRWC), chlorophyll index (SPAD), gas exchange parameters, membrane stability index (MSI), antioxidant activity, phenolic compounds, flavonoid, and soluble carbohydrate contents, as well as, element contents of Fars and Khorasan rhizomes grown with two different diameters.
Section snippets
Plants
Licorice rhizomes were harvested from Khorasan and Fars provinces (exact locations have been provided elsewhere). Collectively, these locations had a rainfall range of 260–350 mm with moderate weather during the year (Behdad et al., 2020b). The plants were collected in October 2016 and identified by experts of the Shiraz University Herbarium by matching with voucher specimens. After dividing rhizomes into two groups with diameters of less than 1 cm and 1–2 cm, 15–20 cm segments containing 2 or
Growth parameters and leaf relative water content (LRWC)
Salt stress negatively affected the length and dry weight of shoots and rhizomes, and also leaf RWC, significantly (P < 0.001). Compared to the control, the lowest length and dry weight were observed in rhizomes and shoot length in plants below 800 and 600 mM NaCl, respectively. The aerial part of licorice, unlike rhizomes, could survive up to 600 mM NaCl. The shoot length and dry weight in both populations were reduced (16–51% and 15–63%, respectively), while a reduction in rhizome dry weight
Discussion
Based on the results, salinity reduced biomass production and water uptake of licorice shoots and rhizomes. The intense salt stress (800 mM NaCl) severely affected the biomass and vegetative growth of licorice without killing the rhizomes. This result is in line with the studies on Glycyrrhiza uralensis (Egamberdieva and Mamedov, 2015) and Miscanthus giganteus (Płażek et al., 2014). Generally, the main effect of salinity stress is osmotic and ionic disorders that lead to a decreased growth rate
Conclusion
The results of the study revealed that the growth parameters of licorice were significantly affected by salinity stress. G. glabra could tolerate salinity levels up to 600 mM NaCl. The thicker rhizomes are faster growing than thinner ones in saline soil. The hypertonic stress caused by the excessive accumulation of Na+ and Cl− ions leads to a reduction of photosynthetic parameters, membrane stability, and relative water content. Licorice can resist salt stress through elevation of the soluble
Authors’ contributions
Assieh Behdad, performed the experiments, did sampling and data analysis, wrote and revised the manuscript. Sasan Mohsenzadeh, supervised the whole research work and revised the manuscript. Majid Azizi, assisted in providing some facilities and revised the manuscript.
Declaration of competing interest
The authors declare no conflicts of interest.
Acknowledgements
This research was supported by a grant from Shiraz University (grant number 1952), Shiraz, Iran.
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2022, Industrial Crops and ProductsCitation Excerpt :Also, remarkable low values were found for shoot length and FW and root DW in ‘SE’, and for shoot length in ‘FA’. Overall, the decreases found in growth parameters are consistent with previous studies using licorice seedlings grown under salinity (Amanifar et al., 2019) and two G. glabra populations grown in greenhouse conditions with 100–800 mM NaCl (Behdad et al., 2021). Salinity usually causes decreases in root hydraulic conductivity and RWC (Zahedi et al., 2019), which can result in closure of stomata and reduction of plant water flow (Prisco, 1980).