Ullah et al. BMC Plant Biology (2022) 22:453 https://doi.org/10.1186/s12870-022-03832-1 RESEARCH Open Access Alhagi sparsifolia acclimatizes to saline stress by regulating its osmotic, antioxidant, and nitrogen assimilation potential Abd Ullah1,2,3,4, Akash Tariq1,2,3,4*, Jordi Sardans5,6, Josep Peñuelas5,6, Fanjiang Zeng1,2,3,4*, Corina Graciano7, Muhammad Ahsan Asghar8, Ali Raza9, You‑Cai Xiong10, Xutian Chai1,2,3,4 and Zhihao Zhang1,2,3,4 Abstract Background: Alhagi sparsifolia (Camelthorn) is a leguminous shrub species that dominates the Taklimakan desert’s salty, hyperarid, and infertile landscapes in northwest China. Although this plant can colonize and spread in very saline soils, how it adapts to saline stress in the seedling stage remains unclear so a pot-based experiment was carried out to evaluate the effects of four different saline stress levels (0, 50, 150, and 300 mM) on the morphological and physio-biochemical responses in A. sparsifolia seedlings. Results: Our results revealed that N-fixing A. sparsifolia has a variety of physio-biochemical anti-saline stress acclima‑ tions, including osmotic adjustments, enzymatic mechanisms, and the allocation of metabolic resources. Shoot–root growth and chlorophyll pigments significantly decreased under intermediate and high saline stress. Additionally, increasing levels of saline stress significantly increased ­Na+ but decreased ­K+ concentrations in roots and leaves, resulting in a decreased ­K+/Na+ ratio and leaves accumulated more Na + and K + ions than roots, highlighting their ability to increase cellular osmolarity, favouring water fluxes from soil to leaves. Salt-induced higher lipid peroxida‑ tion significantly triggered antioxidant enzymes, both for mass-scavenging (catalase) and cytosolic fine-regulation (superoxide dismutase and peroxidase) of ­H2O2. Nitrate reductase and glutamine synthetase/glutamate synthase also increased at low and intermediate saline stress levels but decreased under higher stress levels. Soluble proteins and proline rose at all salt levels, whereas soluble sugars increased only at low and medium stress. The results show that when under low-to-intermediate saline stress, seedlings invest more energy in osmotic adjustments but shift their investment towards antioxidant defense mechanisms under high levels of saline stress. Conclusions: Overall, our results suggest that A. sparsifolia seedlings tolerate low, intermediate, and high salt stress by promoting high antioxidant mechanisms, osmolytes accumulations, and the maintenance of mineral N assimila‑ tion. However, a gradual decline in growth with increasing salt levels could be attributed to the diversion of energy from growth to maintain salinity homeostasis and anti-stress oxidative mechanisms. Keywords: Hyperarid desert, Ions homeostasis, Physiological indices, Saline stress, Xerophytes Background Of the drylands that cover 41% of the Earth’s surface, *Correspondence: akash.malik786@mails.ucas.ac.cn; zengfj@ms.xjb.ac.cn 15% are salt-affected [1, 2] and as a consequence, the 1 productivity of many dryland regions, including those Xinjiang Key Laboratory of Desert Plant Roots Ecology and Vegetation Restoration, Xinjiang Institute of Ecology and Geography, Chinese Academy with saline soils, are limited by nutrient deficiency [3, of Sciences, Urumqi, China 4]. Nitrogen-fixing leguminous trees and shrubs play an Full list of author information is available at the end of the article essential role in improving dryland soil structure and © The Author(s) 2022. 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The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​ mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Ullah et al. BMC Plant Biology (2022) 22:453 Page 2 of 17 productivity as they can thrive in nitrogen-depleted soils N demand in terms of soil N availability [29]. Soil salin- [5] and have an important bioremediating capacity in ity can affect both symbiotic N ­ 2-fixation and mineral N areas subject to salinity [6, 7]. Therefore, planting plants assimilation. The extent to which these mechanisms dif- capable of adaptation to survival in these conditions (i.e. fer between different plant species and environmental N-deficient and salinity) is worthwhile but, nonetheless, conditions remains unclear but research does report that extremely challenging [8]. ­ O3− reduction and ­NH4+ cell concentra- salt ions limit N It still remains unclear how young leguminous seed- tion by affecting the activities of NR, GS and GOGAT lings adjust their metabolism to salinity to ensure growth enzymes [30–32]. and survival in the hyperarid saline desert of Taklimakan The regulation of N metabolism profoundly influences (NW China). As a consequence of salinity, toxic accumu- the ability of plants to tolerate salinity stress. However, lations of N ­ a+ and ­Cl− occurring in the soil can enter into the relationship between N metabolism and salinity is plants and inhibit metabolism and growth [9]. When salt complex as it depends on the level and duration of salt concentrations increase, ionic imbalance and osmotic stress, the plant species, and the quantity, type and form stress develop in plants, which can negatively affect of N available in the soil [33–35]. Interestingly, most their morphology, biomass and biochemical processes studies examining the response of N metabolism to salin- [10, 11]. To overcome this, plants have developed a vari- ity have been conducted on cultivated plants [32, 36], ety of strategies, including (a) the elimination of excess leaving uncertainty as to whether leguminous plants will Na + and Cl- ions to the vacuole or older parts to mini- have similar responses, particularly in drylands [37]. mize the damage associated with excess salt ions, (b) bio- Alhagi sparsifolia Shap. is a perennial phreatophyte synthesis of osmolytes (soluble sugar, amino acids, and native to the saline, hyperarid desert regions of northwest proline) which protect plants salinity-induced osmotic China and adjacent countries in Central Asia. It serves stress and (c) activation of both enzymatic and non- various social and ecological services, such as prevent- enzymatic and antioxidant defence systems to remove ing desertification and dunes, reducing salinization, and the excess Reactive Oxidative Species (ROS) and protect improving livelihoods. However, anthropogenic activi- plants cells from oxidative damage [12–14]. ties such as population growth, urbanization, industri- The enzymatic antioxidant mechanisms include alization, overgrazing, over-harvesting, and agricultural changes in the activities of antioxidant enzymes [(super- expansion threaten its abundance and habitats [38]. Evi- oxide dismutase (SOD), catalase (CAT) and peroxi- dence has underlined the urgent need for the revegeta- dase (POD)] [15, 16]. For instance, the SOD dismutases tion and restoration of Alhagi vegetation [39]. Mature A. ­O2- into ­H2O2, while POD and CAT are responsible for sparsifolia benefits from its deep and extensive root scavenging ­H2O2. These antioxidant enzymes have been system to exploit and use the groundwater resources. reported to positively correlate with a plant’s ability However, extreme environmental conditions persist in to resist salt stress [17]. Plants often undergo a reduc- the hyperarid desert and can severely affect its growth tion in biomass due to salinity stress, which is linked to and metabolism, particularly at the initial growth stages, decreased carbon assimilation [18, 19]. Plants exposed to causing a severe threat to its establishment and sur- these conditions devote more carbon to energy produc- vival since its roots have not yet reached groundwater tion and to maintaining salinity homeostasis and stress- [38]. This scenario makes planting young seedlings for coping mechanisms than to plant organ development [20, vegetation restoration challenging in a hyperarid and 21]; a good example of this is the increased biosynthesis saline desert environment [11]. Therefore, investigating of stress-relieving biomolecules such as sugar and proline the saline stress adaptation strategies in young A. spar- [22–24]. The accumulation and remobilization of photo- sifolia seedlings could provide a theoretical framework synthetic products also play a key role in alleviating salt- for restoring Alhagi communities and protecting the associated damage in plants and examples include the fragile ecosystem of the Taklimakan desert. Previously, accumulation of soluble sugar [25], starch [26] and non- mature Alhagi stands in the natural desert have been structural carbohydrates [27]. Moreover, these products studied previously for absorption of toxic salt ions [40] also play critical roles in signalling, osmotic adjustment, and N acquisition strategies [41], in response to soil fac- ROS scavenging [22] and the regulation of water trans- tors. Research by Zeng et al. [42] also examined salt ions port mechanisms [28], as well as photosynthesis through distribution and photosynthesis in one-year-old A. spar- feedback inhibition [22]. sifolia under different NaCl stress levels but the response Leguminous plants meet nitrogen (N) requirements of young A. sparsifolia seedlings to varying levels of either by symbiotic N ­ 2 fixation or by taking up mineral N saline stress still remains largely unknown. and they also use a facilitative strategy whereby symbiotic The aim of this research was (1) to investigate the mor- ­N2 fixation can be increased or decreased by reducing the phological and physio-biochemical responses of young A. Ullah et al. BMC Plant Biology (2022) 22:453 Page 3 of 17 sparsifolia seedlings to different levels of saline stress; at low salinity levels, although, by contrast, it fell at high and (2) to ascertain its level of saline stress tolerance– and intermediate levels (but only significantly at high based on the interplay between nitrogen assimilation, saline stress) (Fig. 2e). antioxidant defence mechanisms, and osmolytes accu- mulation that is used to mitigate the negative impacts Influence of saline stress on chlorophyll concentrations associated with an excess of salt ions. Parameters selected We observed a slight increase in the concentrations of for measurement to meet the objectives of the research chlorophyll a and chlorophyll b and in the chlorophyll a/b were shoot and root growth, fresh and dry biomass, chlo- ratio at low saline stress compared to the control treat- rophyll pigment concentrations, nitrogen metabolism, ment (Fig. 3a-c). Intermediate and high saline stress sig- osmolytes accumulation, reactive oxygen species produc- nificantly decreased both chlorophyll a and chlorophyll b tion rate, antioxidant enzymatic activities, and root and concentrations, although the chlorophyll a/b ratio did not leaf Na + and K + concentrations. change significantly, relative to the unstressed control. Results Effect of salt stress on MDA and H ­ 2O2 Salt‑stress‑dependent changes in growth attributes Saline stress gave rise to significantly higher concen- Salinity stress significantly decreased the growth attrib- trations of MDA and ­H2O2 compared to the controlled utes of A. sparsifolia plants compared to the controlled conditions (Fig. 4a and b). Interestingly, the maximum conditions (Figs. 1a-d and 2a-e). The fresh root weight, concentrations of MDA occurred after the addition of dry weight, length and moisture content were sig- 150 mM and not after 300 mM (Fig. 4a). Moreover, the nificantly twofold inhibited as the saline stress rose to additions of salt stress significantly increased ­H2O2 levels 300 mM (Fig. 1a-d). Similarly, saline stress also signifi- in leaves, relative to the unstressed control, which indi- cantly reduced shoot-related attributes, the maximum cates the persistence of oxidative stress in the studied inhibition occurring in the highest salt-stress treatment plants (Fig. 4b). (300 mM saline stress) (Fig. 2a-e). The fresh shoot weight, dry weight, length, and shoot water content decreased Changes in the activities of antioxidant enzymes 2-, 3-, 1- and onefold, relative to the unstressed control, When under stress the scavenging of reactive oxygen spe- respectively. In addition, the root/shoot ratio increased cies is mainly associated with the production of various Fig. 1 Effects of salinity on (a) primary root length, (b) root fresh weight, (c) root dry weight, and (d) root moisture content of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant differences among the treatments at P < 0.05 Ullah et al. BMC Plant Biology (2022) 22:453 Page 4 of 17 Fig. 2 Effects of salinity on (a) shoot length, (b) shoot fresh weight, (c) shoot dry weight, (d) shoot moisture content, and (e) root/shoot ratio of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant differences among the treatments at P < 0.05 antioxidant enzymes that protect plants from severe oxi- all modified in a similar way after the addition of saline dative damage. Moreover, SOD, POD and catalase activi- stress (Fig. 6a, b, and d). Their values initially increased ties were gradually enhanced as the saline stress rose, but then were gradually inhibited as the salt stress relative to the unstressed control (Fig. 5a-c). For example, intensified relative to the unstressed control. The starch SOD, POD and catalase activities increased 3-, 3-, and and non-structural carbohydrate concentrations in the sevenfold, respectively, when the plants were analysed 150 mM saline treatment decreased twofold compared after the 300 mM saline stress application. to the 300 mM saline treatment (Fig. 6b and d). How- ever, the soluble sugars/starch ratio acted inversely as Salt‑stress‑dependent changes in carbohydrates, soluble the saline condition initially inhibited and then gradu- protein and proline concentrations ally enhanced ratio (Fig. 6c), and a twofold increase in The concentrations of carbohydrates and proline were saline stress was detected relative to the control. In the also strongly affected by the exposure of A. sparsi- case of soluble protein concentrations, salt stress greatly folia plants to saline stress relative to the unstressed enhanced its production in A. sparsifolia and a tenfold control (Fig. 6a-f ). Of the carbohydrates, the soluble difference was recorded between the control and highest sugars, starch and non-structural carbohydrates were saline treatment (Fig. 6e). Ullah et al. BMC Plant Biology (2022) 22:453 Page 5 of 17 difference compared to plants with no salt stress in the latter two saline treatments. Finally, compared to the 50 mM saline treatment, a twofold reduction occurred in the 150 mM and 300 mM saline treatments. Changes in ­Na+ and ­K+ in leaves and roots The imposition of saline stresses significantly unbalanced ­Na+ and ­K+ ions in the leaves and roots of A. sparsifo- lia compared to the controlled conditions (Fig. 7a-f ). The increasing concentrations of saline stress significantly enhanced leaf Na + levels, while the K + ion uptake was decreased (Fig. 7a and b). More specifically, when com- pared to the control, plants showed a twofold increment ­ a+ ion levels when exposed to the high saline in leaf N stress (Fig. 7a). Compared to the control plants, the plants treated with 300 mM saline had a threefold inhibi- tion in the ­K+/Na+ ratio (Fig. 7c). The root ­K+ ion and ­Na+ ion levels fell or were enhanced, respectively, com- pared to the controlled conditions. However, differences were much more significant for ­K+ ions (Fig. 7d, e). The same increments in ­Na+ ion levels occurred in roots as in leaves (Fig. 7e). The levels of ­K+ ions were upregulated fourfold in the high saline treatment compared to the control (Fig. 7d) and as a result their ratio had a seven- fold inhibition when plants were exposed to the 300 mM saline addition (Fig. 7f ). Changes in ­NO3− reduction and N ­ H4+ assimilation The ­NO3− and ­ NH4+ concentrations in A. sparsifolia plants were notable when exposed to saline stress con- ditions, relative to the unstressed control (Fig. 8a and b). Specifically, a significant increment was observed in ­NH4+ ion levels as the salt stress increased. The high- saline-treated plants had onefold greater N ­ H4+ ion lev- − els than the untreated plants. The N ­ O3 ion levels fell significantly in the 50 mM and 300 mM saline treat- ments compared to the controlled environment, with the 300 mM saline application exerting the most powerful effect. Interestingly, the addition of 150 mM saline did not provoke any such change. The NR, GS, and GOGAT Fig. 3 Effects of salinity on (a) Chlorophyll a, (b) Chlorophyll b, and all reacted remarkably as their activities were initially (c) Chlorophyll a/Chlorophyll b ratio of Alhagi sparsifolia at days 90th enhanced but then decreased in the high treatment of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). (Fig. 8c-e). Surprisingly, their (NR, GS, and GOGAT) Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant activities fell significantly after the 300 mM saline appli- differences among the treatments at P < 0.05 cation relative to the150mM saline treatment. Principal component analysis (PCA) The PCA showed along the first PC axis (explaining the Significantly, proline accumulation initially increased 69.1% of total variables variance) that the sets of samples vigorously but then declined after the latter two saline of plants submitted to different levels of salinity had dis- additions compared to controlled conditions (Fig. 6f ). tinct coefficient scores positions in the same order than A fourfold difference existed between the control and salinity intensity (Fig. 9). This axis was mainly loaded by 50 mM saline treatment. In contrast, it detected a twofold plant ­Na+ and ­K+ concentrations, chlorophyll contents, Ullah et al. BMC Plant Biology (2022) 22:453 Page 6 of 17 Fig. 4 Effects of salinity on the concentration of (a) malondialdehyde (MDA), and (b) hydrogen peroxide (­ H2O2) of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant differences among the treatments at P < 0.05 ­H2O2 concentrations and enzymes related to ROS elimi- high root-shoot ratio is regarded as one of the key adap- nation. Along PC 2 axis (explaining 15.2% of total vari- tative responses to standing salt stress, which involves ables variance) it was observed that the sample sets of directing photosynthetic products to the most limiting plant growing at intermediate levels of soil salinity were organ of the plant [47–49]. The root-shoot ratio then separated by their higher concentrations of proline, also decreased with salinity levels relative to unstressed enzymes related to N metabolism and sugars contents control and it has been previously reported that high (Fig. 9). salt stress reduces the distribution of photoassimilates to the root system [50], leading to a low root-shoot ratio. Discussion Therefore, we can suggest that increasing salinity stress Changes in growth and biomass accumulation reduced the root growth by decreasing the allocation The assessment of biomass accumulation in plants of photoassimilates to roots to establish a possible joint exposed to salinity can be used as a cohesive attribute for plant mechanism to improve water fluxes from soil to predicting the responses of plants to salinity stress [43]. leaves by creating a favorable osmotic pathway. According to our study, increasing saline stress decreased the biomass, length, and water content of both shoots Photosynthetic pigments and roots of A. sparsifolia. A salt-induced reduction in Variations in chlorophyll concentrations have an impact shoot and root growth and biomass attributes has also on plant metabolism [51]. Both chlorophyll a chlorophyll previously been reported in other plant species [10, 18, b fell significantly under intermediate and high saline 19, 44, 45], supporting our findings. Salt-induced reduc- stress similar to other research in salt-stressed plants tion in plant biomass is a crucial survival strategy asso- [52–55]. As a response to salt stress, chlorophyllase activ- ciated with reduced carbon (C) assimilation [18, 19] as ity increases, which leads to a decrease in chlorophyll under these conditions, plants allocate more C to energy concentrations as salt-stress levels increases with the and maintaining salinity homeostasis (anti-stress mecha- extent of the decline in salt stress varying between plant nisms) than to development and growth [20, 21, 46]. For species [56]. instance, the biosynthesis and accumulation of stress- The salt-induced response of chlorophyll pigments is relieving biomolecules such as sugar and proline [22–24] recognized as one of several biochemical indicators of is a trade-off with growth, i.e., the resources needed to salt tolerance in plants [57]. In comparison, increases in sustain growth is reduced. Therefore, we can potentially the chlorophyll a and chlorophyll a/b ratios in our study attribute the decrease in growth in A. sparsifolia to the were observed at low saline stress which reflects other allocation of resources by young seedlings to anti-oxidant research that found that a salt-induced increase in chlo- and osmotic adjustment mechanisms provoked by soil rophyll concentrations in plants could be attributed to salinity rather than growth. Additionally, the root/shoot the rise in chloroplast numbers [58, 59]. The results of ratio also increased (non-significantly) at low salinity lev- this research also confirm that salt stress is more detri- els and belowground biomass dispatch for maintaining a mental to chlorophyll b than chlorophyll a [60] and this Ullah et al. BMC Plant Biology (2022) 22:453 Page 7 of 17 an essential role in salt tolerance [58] so it could also be debated that PSII is a crucial element in the salt tolerance of A. sparsifolia, although further research on this subject is still needed. Ion distribution Plants under salt stress take up and distribute salt ions via a number of mechanisms [62, 63]. In our study, in agree- ment with other studies, the accumulation of N ­ a+ in root and leaf tissues caused a nutrient imbalance, as shown by the lower K ­ +/Na+ ratio as salinity stress levels rose that resulted in plant tissues accumulating less dry matter and growing less [64–66]. The concentration of ­K+ may have also fallen antagonistically during the absorption of nutri- ents due to competition with N ­ a+ or to the similarity of its charge. In our study, the saline conditions appears to have impaired high potassium transporters (HKT), which are ­Na+- ­K+ symporters in plants and play an important role in salt tolerance by maintaining K ­ + uptake through + + ­K - ­Na cotransport [67]. It has been widely speculated that plants under salt stress regulate N ­ a+ uptake and transport by maintaining high tissue K ­ /Na+ ratios and, + + + therefore, high cytosolic K ­ /Na ratios, an idea that has become central to salt-tolerance research. ­K+ is crucially important in various physiological processes in plants and in situations of salt stress, high levels of surrounding ­Na+ compete with ­K+ uptake and cause severe ­K+ defi- ciency and growth impairment [68]. ­Na+ ion-induced outflow of K ­ + from roots and leaves are a significant effect of salt stress on ­K+ regulation [17, 69]. This efflux could potentially be attributed to the excess ­Na+ in the cytoplasm, resulting in lower membrane potential and, consequently, the activation of ­K+ outward rectifier chan- nels, which is thought to be the mechanism by which K ­+ + is extruded from cells. Decreasing ­K levels in A. sparsi- folia with increasing saline stress could be the result of a salt-induced inhibition of the ability of cells to maintain a more negative inside potential and so improve intracel- lular retention of K ­ + (or inhibition of K ­ + efflux) [70]. The Fig. 5 Effects of salinity on the enzymatic activities of (a) superoxide + ability to retain intracellular ­K has also been proposed dismutase (SOD), (b) peroxidase (POD), and (c) catalase (CAT) of as crucial for salt stress resistance [71]. In our study, Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the the salt-induced retention of cellular ­K+ decreased with means (n = 3). According to Duncan’s Multiple Range Test, different increasing saline stress levels with A. sparsifolia retain- letters indicate significant differences among the treatments at ing cellular ­K+ at low salinity levels but losing this ability P < 0.05 as the salt concentrations rise to 150 mM and 300 mM demonstrating that its ability to maintain K ­ + retention is dependent on salt concentrations. In addition, ­ Na+ ions enter roots passively through then creates a high chlorophyll a/b ratio since the very voltage-independent or faintly voltage-dependent non- first step of chlorophyll b breakdown is its transformation selective cation channels so an increase in external ­Na+ into chlorophyll a [61]. Similar research has suggested will result in a moderate rise in N ­ a+ uptake and accumu- that the salt-stress resistance of photosystem II (PSII) and lation, with a consequent reduction in ­K+ uptake [64, 65]. the increased chlorophyll concentrations in plants play In this study, the concentrations of these ions were higher Ullah et al. BMC Plant Biology (2022) 22:453 Page 8 of 17 Fig. 6 Effects of salinity on the concentration of (a) soluble sugar, (b) starch, (c) soluble sugar/starch ratio, (d) nonstructural carbohydrates (NSC), (e) soluble protein, and (f) proline of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant differences among the treatments at P < 0.05 in leaves than in roots, which has also been reported in transported from roots to shoots when the transpira- other research [59, 72, 73]. Mature A. sparsifolia plants tion stream in the xylem moves [75] it could also be pro- in natural deserts have been reported to exhibit a high posed that the increase in leaf ­Na+ and ­K+ ions could be degree of ion selectivity as a result of arresting excess an important survival strategy for juvenile A. sparsifolia ­Na+, which keeps salt levels in roots high compared to seedlings where they may use excess ions as osmolytes in leaves [72]. Similarly, other research has also reported to decrease the leaf water potential and increase water that ­Na+ accumulation in tissues of natural mature A. absorption, and so normalize their photosynthetic sparsifolia plants followed the order root > stem > leaf capacity. [74]. Mature A. sparsifolia vegetation in natural deserts appears to be most effective at restricting N ­ a+ in root Lipid peroxidation, ROS production and antioxidant tissues whilst in comparison, field-grown A. sparsifo- system lia plants form interconnected clones with extensive Given its ability to act as indicator of oxidative dam- root systems that probably enable them to dilute and age induced by salt stress, lipid peroxidation may be an limit excess salt in their roots, which was not possible adequate physiological indicator for evaluating plant in our pot experiment with young seedlings. If ­Na+ is stress resulting from both biotic and abiotic factors. Ullah et al. BMC Plant Biology (2022) 22:453 Page 9 of 17 Fig. 7 Effects of salinity on the concentration of (a) leaf ­Na+, (b) leaf K­ +, (c) leaf K­ +/Na+ (d), root N ­ a+, (e) root ­K+, and (f) root ­K+/Na+ of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant differences among the treatments at P < 0.05 This research recorded significantly higher accumula- [34]. In this study, antioxidant enzymes (SOD, POD and tions of MDA and ­H2O2 at all levels of saline stress. An CAT) were significantly more abundant in saline-treated increase in leaf ­H2O2 could have led to membrane dam- A. sparsifolia seedlings than in the control. For instance, age in young A. sparsifolia due to lipid peroxidation, compared to the control, SOD, POD and CAT increased and to the production of MDA [22, 55, 65]. In addition, 3-, 3- and sevenfold, respectively, under 300 mM saline ROS not only serve as stress-signalling molecules [76] stress indicating that it is a solid antioxidant mechanism but also plays an essential role in regulating growth [77] for detoxifying ROS [34, 79, 80]. SOD is the first line of and development [78]. For example, a high ­H2O2content defence in the antioxidant defence mechanisms, as it should not be viewed simply as a harmful phenomenon converts the superoxides into ­ H2O2 and subsequently to be avoided or alleviated but, instead, also as a necessity conversion of H ­ 2O2 into ­H2O and oxygen is performed for plants needing to respond and adapt effectively and by CAT. Under stress conditions, low levels of ­H2O2 may initiate better acclimatization mechanisms [76]. play a role in signalling [81]. ­H2O2-detoxifying enzymes Plants have a highly specialized antioxidant enzymatic restrict the amount of ­H2O2 that cells accumulate rather defence system responsible for scavenging reactive oxy- than eliminate it completely and in addition, POD also gen species (ROS) at cellular level when under salt stress scavenges ­H2O2 efficiently from the chloroplast [80, Ullah et al. BMC Plant Biology (2022) 22:453 Page 10 of 17 Fig. 8 Effects of salinity on the concentration of (a) ­NO3− and (b) ­NH4+ and enzymatic activities of (c) nitrate reductase (NR), (d) glutamine synthetase (GS), and (e) glutamate synthase (GOGAT) of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Bars represent standard errors of the means (n = 3). According to Duncan’s Multiple Range Test, different letters indicate significant differences among the treatments at P < 0.05 82]. Several studies have reported more SOD, CAT and activity could be linked to the mass scavenging of ­H2O2 POD activity in plants subjected to salt stress [45, 65, [76]. A recent study of Echinochloa crusgalli mutants 80]. However, the relative significance of each antioxi- has also demonstrated that POD, APX and GR are dant enzymatic activity (SOD, POD and CAT) needed involved in fine-tuning ROS production, and that their for scavenging ROS varies from one plant to another loss can lead to high levels of ROS, which in turn affects in terms of the rates of ROS production and the major CAT development. CAT is however, unable to reduce sources of ROS, as well as the respective antioxidative ­H2O2 to physiological concentrations due to its low activities. affinity so plants suffer from oxidative stress even in the In our study, CAT activity was (sevenfold) greater presence of high CAT activity [83]. This study demon- than POD (threefold) at 300 mM saline stress than in strates that A. sparsifolia contains reliable antioxidant the control, which reflects the greater accumulation of mechanisms, both for cytosolic fine-regulation (SOD ­H2O2 at high salt stress. Generally, the affinity of CAT and POD) and mass-scavenging H ­ 2O2 [60], which could for ­H2O2 is lower than that of POD, although a bulk help reduce the detrimental effects of oxidative stress accumulation of ROS clearly induced CAT activity. induced by high lipid peroxidation levels. However, a With increasing saline stress, A. sparsifolia as an adap- gradual response of these enzymes to gradual increases tion mechanism may have increased POD to ensure the in saline stress suggests that this plant species has an cytosolic regulation of H ­ 2O2, whereas the higher CAT excellent capacity to adapt to saline stress, including Ullah et al. BMC Plant Biology (2022) 22:453 Page 11 of 17 Fig. 9 Principal component analysis (PCA) between various growth and physio-biochemical attributes of Alhagi sparsifolia at days 90th of exposure to a different gradient of salinity (0, 50, 150, and 300 mM). Acronyms of variables SL = Shoot length, SFW = Shoot fresh weight, SDW = Shoot dry weight, SMC = Shoot moisture content, PRL = Primary root length, RFW = Root fresh weight, RDW = Root dry weight, RMC = Root moisture content, RSR = Root shoot ratio, Chla = Chlorophyll a, Chlb = Chlorophyll b, SP = Soluble protein, MDA = Malondialdehyde, ­H2O2 = Hydrogen peroxide, SOD = Superoxide dismutase, POD = Peroxidase activity, CAT = Catalase, NR = Nitrate reductase, GS = glutamine synthetase, GOGAT, P = Proline, SS = Soluble sugar, ST = Starch, NSC = Non-structural carbohydrates, L-K+ = Leaf ­K+, L-Na+ = Leaf ­Na+, R-K+ = Root ­K+, R-Na+ = Root ­Na+ mechanisms especially designed to increase activity controlling transcription of certain genes [22]. Increased when salinity conditions are high. salt levels significantly decreased starch accumulation and significantly increasing soluble sugar at 150 mM Biochemical changes and their role in role in salt saline stress (Fig. 9). This might be due to greater activ- mitigation ity by the starch-degrading enzymes that mobilize sugars This study recorded a significant accumulation of pro- via an intricate network of reactions, as demonstrated in line at all saline stress levels, which may contribute to the plant A. thaliana, where multiple enzymes work syn- the protection of the photosynthetic apparatus, the ergistically [87]. The accumulation of starch and soluble elimination of ROS, and the stabilization of membranes, sugars and their interrelationships demonstrated in this enzymes, and proteins in salt-stressed young A. sparsifo- result that they play a significant role in the salt tolerance lia [84–86]. Additionally, there was a significant increase of young A. sparsifolia at low and intermediate saline in soluble sugar at low and intermediate levels, although, stress levels (Fig. 9) [25–27]. compared to the controls, starch content only increased High soluble sugar/starch ratio recorded in this study at low levels (Fig. 9). In plants, soluble sugars play sev- indicate that in the hyperarid saline desert, this could be eral vital roles, including limiting water loss and chloro- viewed as an adaptive strategy of young A. sparsifolia for phyll degradation, regulating cell division, eliminating synthesizing the enzymes of soluble sugars and avoiding excess ROS, stabilizing proteins and membrane struc- the synthesis of starch enzymes in order to accumulate ture, maintaining osmotic and ionic homeostasis, and soluble sugar and adjust the osmotic pressure to maintain Ullah et al. BMC Plant Biology (2022) 22:453 Page 12 of 17 water uptake. Proteins also have the potential to act as for predicting the responses of plants to salinity stress osmotins and play a part in the development of toler- [43]. In this experiment, the imposition of saline stress ance to salt stress as identified in other research [11, 88, significantly influenced the biomass and growth attrib- 89]. In this research, protein concentrations significantly utes of A. sparsifolia plants and shoot and root length, increased in A. sparsifolia at all levels of saline stress (low shoot and root biomass, and shoot and root water salt < intermediate salt < high salt). Under saline stress, content were significantly inhibited as saline stress the accumulation of soluble protein in young A. sparsifo- increased (Fig. 1). A salt-induced reduction in shoot lia may contribute to the osmotic adjustment and to the and root growth and biomass attributes has been previ- supply of nitrogen that can be utilized once the salt stress ously reported in other plant species [10, 18, 19, 44, 45]. is abated [85, 86]. The decrease in growth in A. sparsifolia appears to be associated with the allocation of resources by seedlings Nitrogen assimilation to anti-oxidant and osmotic adjustment mechanisms To ensure salt tolerance, the regulation of nitrogen (N) provoked by soil salinity rather than to growth. metabolism is of vital importance, and a complex inter- play occurs between salinity and N nutrition [90]. In this study, although, N ­ O3− levels fell significantly at 50 mM Conclusion and 300 mM saline stress, at 150 mM no significant The saline stress treatments in our experiment elicited changes relative to the control occurred (Fig. 8b). Lower different responses in plant growth and physiological levels of N ­ O3− impede N assimilation and the synthesis traits. Young A. sparsifolia seedlings demonstrated the of amino acids and proteins, which can result in a fall in use of a wide range of salt-tolerant strategies to tolerate plant dry weight [91]. Salt ions also limit ­NO3− reduc- low-to-high saline stress, including (i) increased enzy- tion by affecting the activity of NR [31, 32, 92]. In con- matic anti-oxidant defense mechanism to reduce oxi- trast to other research this study found that NR activity dative stress through the inhibition of ROS and MDA showed no significant changes at low or high saline stress accumulations (ii) enhanced osmolytes synthesis (iii) levels (Fig. 9), and even increased at intermediate saline maintenance of mineral N metabolism (iv) increased stress [31, 32]. This could be explained as young plants chlorophyll a/b ratio and (v), accumulating higher lev- that have not initiated nodulations have been reported to els of Na + and K + ions in leaves compared to roots have less restricted mineral N metabolism due to salinity that could act as osmolytes to decrease the leaf water and they can then germinate and grow in places that have potential and increase water absorption for the nor- been flooded where soil salt concentrations are lower malization of metabolism, in hyperarid desert condi- [93]. tion. The results strongly suggest a high capacity by A. It has long been understood that the GS/GOGAT cycle sparsifolia seedlings to manage with low and interme- links N and C metabolism in plants by binding inor- diate-to-high levels of soil salinity; but at very high lev- ganic ­NH4+ with C skeleton synthesis, a critical step in els of salinity, the excess of ROS production cannot be the metabolism and growth of plants [94]. In this study, fully (or with great difficulty) counteracted and plants GS and GOGAT activities were initially enhanced and can still survive, albeit with reduced growth. Consist- then decreased under high saline stress (Fig. 5d, e, and ent with this observation, were the recorded shifts f ), indicating that A. sparsifolia under low and interme- from more osmolytes adjustment mechanisms to anti- diate saline stress could incorporate N ­ H4+ effectively to oxidative stress mechanisms, such as the synthesis of fill its glutamate pool. Even though high salt stress signifi- anti-oxidative stress enzymes when salinity rose from cantly decreased the GS/GOGAT cycle, higher level of low-intermediate to high intensity. The results of this soluble proteins and antioxidant enzymes observed in A. research provide a baseline study to improve knowledge sparsifolia could be attributed to its N-fixing ability. For of the salt-induced changes in the growth and physi- instance, the nodulation and biological N ­ 2 fixation of A. ological mechanisms of young A. sparsifolia plants sparsifolia has been reported to exhibit high salt toler- in hyperarid saline deserts and potentially assist in ance [41, 72]. Under high salinity stress with a retarded future planting of A. sparsifolia seeds to improve veg- GS/GOGAT cycle, A. sparsifolia could have the capacity etation restoration in the Taklimakan desert. Further to allocate sufficient energy (sugars) to sustain the bacte- research is required however to understand the under- rial symbionts that ensure a certain level of organic nitro- lying physio-biochemical and molecular mechanisms gen for the synthesis of anti-oxidative enzymes. operating under saline stress conditions to increase The assessing of biomass accumulation in plants knowledge of the salt-tolerance capacity of young A. exposed to salinity can be used as a cohesive attribute sparsifolia plants. Ullah et al. BMC Plant Biology (2022) 22:453 Page 13 of 17 Materials and methods 665 and 649 nm following the method described by [95]. A randomized block design (RBD) using pots protected We calculated the chlorophyll concentrations using the from the rain to control the desired concentration of the following equations (mg ­g−1 FW): applied salt solution was set up as an outdoor experiment Chl a = 13.98 A665 - 6.88 A649 (1) in the vicinity of Qira oasis on the southern fringe of the Taklimakan desert (37°00′N, 80°43′E). The annual aver- age temperature in the area is 11.9 °C, with extremes of Chl b = 24.96 A649 - 7.32 A665 (2) 41.9 °C and -23.9 °C. The vegetation around the oasis is sparse, with cover of 5–20%, and is composed primarily Chl a/b = Chl a / Chl b (3) of shrubs and sub-shrubs such as A. sparsifolia and Tam- arix ramosissima. Oxidative stress indicators We collected A. sparsifolia seeds from the desert and Hydrogen peroxide ­(H2O2) concentrations were meas- planted them in plastic pots (30-cm diameter at the top ured using a standardized method [96]. Fresh leaves and 25-cm at the bottom, 25-cm high) filled with 12 kg (0.2 g) were homogenized in 5 ml of trichloroacetic acid of soil, and with a hole in the bottom. During the first (0.1%) in an ice bath, transferred to test tubes, and finally 50 days, water was supplied to each pot (n = 1 seed- centrifuged at 5000 × g for 10 min (4 °C). The superna- ling) every three days to field capacity (18% w/w) using tant containing 0.1 mL of titanium reagent (50 µL of a weight method. The pots were watered and weighed 20% titanium tetrachloride) and 0.2 mL of ammonia was to replace the evaporated and transpired water. We cal- centrifuged at 10,000 × g for 10 min. After washing five culated the soil relative water content (SRWC) using the times with acetone, the precipitate was centrifuged at following formula: 10,000 × g for 10 min and then 3 mL of 1 M ­H2SO4 was SRWC = ([(Wsoil − Wpot − DWsoil)∕ added. The absorbance was read at 410 nm. ((WFC − Wpot − DWsoil)] ∗ 100) Malondialdehyde (MDA) was assessed based on the thiobarbituric acid (TBA) test [97]. Fresh leaves (0.5 g) In this equation, Wsoil represents the current soil were homogenized in 1 ml of 5% trichloroacetic acid weight (soil + pot + water), Wpot represents the weight (TCA) and centrifuged for 10 min at 5000 g (4 °C). In of the empty pot, DWsoil the dry soil weight, and WFC a separate test tube, 4 ml of the supernatant was added the soil weight at field capacity (soil + pot + water). We to 2 ml of 20% TCA and the mixture was then heated at selected 48 pots with uniform seedlings and divided them 100 °C for 15 min and centrifuged at 5000 g (10 min). A into four groups for the application of the stress treat- spectrophotometer was used to measure absorbance at ments: three sets of 12 pots for saline stress (NaCl and 450, 532 and 600 nm; the concentrations of MDA were ­Na2SO4, each at a 1:1 molar ratio) and one set of 12 pots calculated using the following equation: for the positive control (0 mM). To avoid osmotic shock, we gradually introduced salt stress by adding 50 mM ­L−1 MDA (mol g−1 FW) = = 6.45 (A532- A600) - 0.56A450. of saline solution to the stress treatment groups for the first week. Afterwards, saline stress concentrations of 50, 150, and 300 mM were applied. The salt chemicals were Antioxidant enzyme activity mixed in water (500 ml/pot) and applied after every four We homogenized the ground leaves in a chilled mortar days. The doses selected were based on real conditions with 0.1 M phosphate buffer (pH 7.3) with 0.5 mM eth- occurring in the field to stimulate saline osmosis stress. ylenediaminetetraacetic acid (EDTA). Afterwards, the Finally, after 90 days of growth, we harvested the leaves of homogenate was centrifuged for 10 min at 8000 × g and the seedlings and immediately stored them at -80 °C until 4 °C. The activity of SOD was assayed by measuring the further analysis (see below). reduction rate of nitroblue tetrazolium (NBT) at 560 nm [98]. One unit of SOD activity was defined as the amount Determination of growth parameters of enzyme required for 50% inhibition of NBT reduction We harvested three randomly selected A. sparsifolia at 560 nm. seedlings and measured their shoot height, root length, The POD activity was determined according to stand- shoot and root fresh weights, shoot and root dry weights, ard methods [99, 100], with minor modifications. A and water content. reaction mixture was prepared by mixing 2 ml of buffer substrate (8 mM guaiacol and 100 mM ­Na3PO4 pH 6.4), Measurement of photosynthetic pigments 24 mM ­H2O2 in 0.5 ml of enzyme extract). At 460 nm, Chlorophyll (0.1–0.3 g fresh leaves) was extracted from absorbance values were measured twice at 1-min inter- the leaves using ethanol (95%, vol/vol) and measured at vals. We calculated enzyme activity by increasing the Ullah et al. BMC Plant Biology (2022) 22:453 Page 14 of 17 absorbance of the reaction system by 0.01 up to a maxi- 2 mL of 10% HCl. A quantitative colorimetric method mum of 1U per min, which was then converted into [109], was used to analyze the supernatants. U/g·min − 1. CAT activity was determined by monitor- ing the disappearance of H ­ 2O2 [101]. Initially, 50 mL of Determination of Na+ and K+ enzyme extract was poured into 1.5 mL of reaction mix- Each dry root and leaf sample (0.05 g) was digested with ture containing 50 mM K-phosphate buffer (pH 7.0) and concentrated ­HNO3 (3 mL). Then the extracts were 15 mM ­H2O2. One unit of CAT corresponds to one mole brought up and adjusted to 15 mL with deionized water. of ­H2O2 degradation per minute measured at 240 nm for The concentrations of N­ a+ and ­K+ in leaf and root sam- 1 min. The absorbance was recorded at 240 nm for 1 min. ples were determined using inductively coupled plasma- One unit of CAT corresponds to one mole of ­H2O2 deg- optical emission spectrometry (ICP-OES), according to a radation per min. standard method [110]. Determination of nitrate assimilation enzymes Statistical analysis Nitrate reductase [102] activity was determined by We repeated all measurements three times and then homogenizing fresh leaves (0.2 g) in 2 mL of 25 mM organized the data with a Microsoft Excel 2019 spread- phosphate buffer saline (PBS, pH 8.7) containing 10 mM sheet in terms of the mean values ± SE. The assessment cysteine and 1 mM EDTA, which was then centrifuged of normality and homogeneity was performed using the for 20 min at 30,000 g. The resulting supernatant was Shapiro–Wilk normality test. A one-way analysis of vari- tested for NR activity using a diazocoupling method with ance was performed with SPSS software (version 13.0; Griess reagent [103]. The GS activity of frozen leaves was IBM, Armonk, NY, USA). To make pairwise comparisons determined by homogenizing them in 2 mL of 50 mM of the mean values for a given response variable, Dun- Tris–HCl buffer (pH 7.8; containing 15% glycerol, 0.1% can’s multiple range test was used with an alpha level of TritonX-100, 1 mM of EDTA and 14 mM of 2-mercap- 0.05 for significance. The graphics in the figures were cre- toethanol) and centrifuging them twice at 4 °C for 10 min. ated using Origin Pro 2019 software (Origin Lab Corpo- After complexing with acidified ferric chloride, the ration Northampton, MA, USA). To aid interpretation, supernatant was used to determine GS (EC 6.3.1.2) with Pearson correlation analyses (PCA) of the leaf chloro- a 540 nm fluorescence measurement [104]. To determine phyll pigment concentrations, N metabolism, osmolytes GOGAT activity, the reaction mixture was composed of accumulation, reactive oxygen species production rate, 20 mM L-glutamine, 100 mM α-ketoglutaric acid, 10 mM and antioxidant enzymatic activities, as well as root and KCl, and 3 mM NADH in 25 mM Tris–HCl (pH 7.6), to leaf ­Na+ and K ­ + concentrations, were performed using which the plant extract was added to initiate the reaction. Origin Pro 2019 software (Origin Lab Corporation The absorbance at 340 nm was continuously recorded to Northampton, MA, USA). monitor the NADH oxidation [104]. To determine the overall relationships of studied plant variables among the samples of plants submit- Determination of biochemical parameters ted to distinct intensities of salinity, we used principal A ball mill was used to grind the dried leaves samples. component analyses (PCAs) to determine the overall The colorimetric determination of sugar concentrations differences of the the studies variables among different was performed by extracting soluble sugar with ethanol salinity levels. We first analysed the data quality by the according to a standardized method [105]. Starch was Kaiser–Meyer–Olkin measure and also eliminated vari- measured after perchloric acid extraction (35%; v/v) and ables with excessive multicollinearity. We conducted analyzed colorimetrically at 620 nm using a slightly mod- one-way ANOVAs with Bonferroni post hoc tests of ified anthrone method [106]. NSC was obtained by sum- the scores of the first PC axes to determine differences ming the soluble sugar and starch concentrations. among the treatments by using Statistica 8.0 (StatSoft, The concentration of Proline (0.2 g fresh levees) was Inc. Tule, Oklahoma, USA). determined using ninhydrin following a standard pro- cedure (105) Toluene was used as a blank for measuring Acknowledgements We thank all the departmental colleagues for their help during data collection the absorption at 520 nm [107]. Approximately 0.3 g of and laboratory analysis and would like to thank the anonymous reviewers for fresh leaves were used to determine the concentrations of their constructive comments and suggestions. soluble proteins [108], with bovine serum albumin used Authors’ contributions as the standard. We homogenized 0.2 g of frozen leaves FZ and AT designed this research project, AU, XC, ZZ, conducted and per‑ in 5 mL of deionized water to determine ­NO3−; for ­NH4+ formed the experiments, AU, AT, JS, CG, MAA, and XY analysed the data, AU, AT, determination, we homogenized 0.2 g of frozen leaves in JS, JP, and FZ wrote the manuscript, AU, AT, JS, JP, AR, CG, and FZ revised the manuscript. All authors have read and approved the final manuscript. Ullah et al. BMC Plant Biology (2022) 22:453 Page 15 of 17 Funding salinity and waterlogging in dryland cropping systems. Aust J Agric Res. This work was supported by the National Natural Science Foundation of China 2001;52:137–51. (No. 41977050); the Key Program of Joint Funds of the National Natural Sci‑ 7. Abdalla MA, AwadElkarim AH, Taniguchi T, Endo T, Yamanaka N. Phy‑ ence Foundation of China and the Government of Xinjiang Uygur Autono‑ toremediation of calcareous saline-sodic soils with mesquite (Prosopis mous Region of China (Nos. U1903102). This research was further supported glandulosa). Acta Agric Scand B Soil Plant Sci. 2017;67:352–61. by the Ministry of Science and Technology, China (QN2022045005); the 8. Bhattachan A, D’Odorico P, Dintwe K, Okin GS, Collins SL. Resilience and President’s International Fellowship Initiative (PIFI), and the Chinese Academy recovery potential of duneland vegetation in the southern Kalahari. of Sciences (2022VBA0024, 2021VBA0001). JP and JS acknowledge the finan‑ Ecosphere. 2014;5:1–14. cial support from the Catalan Government grant SGR 2017–1005, the Spanish 9. Teakle NL, Tyerman SD. Mechanisms of Cl-transport contributing to salt Government grants PID2019-110521 GB-I00, and the Fundación Ramón tolerance. Plant Cell Environ. 2010;33:566–89. Areces grant CIVP20A6621. 10 Rahneshan Z, Nasibi F, Moghadam AA. Effects of salinity stress on some growth, physiological, biochemical parameters and nutrients in two Availability of data and materials pistachio (Pistacia vera L.) rootstocks. J Plant inteRact. 2018;13:73–82. All the data generated or analysed during this study are included in this 11. Zhang M, Fang Y, Ji Y, Jiang Z, Wang L. Effects of salt stress on ion published article. content, antioxidant enzymes and protein profile in different tissues of Broussonetia papyrifera. S Afr J Bot. 2013;85:1–9. 12. Rahman M, Mostofa MG, Islam M, Keya SS, Das AK, Miah M, et al. Acetic Declarations acid: A cost-effective agent for mitigation of seawater-induced salt toxicity in mung bean. Sci Rep. 2019;9:1–15. Ethics approval and consent to participate 13. Patel MK, Kumar M, Li W, Luo Y, Burritt DJ, Alkan N, et al. Enhancing salt The specimen was identified by Prof. Dr. Fanjiang Zeng and preserved in the tolerance of plants: From metabolic reprogramming to exogenous herbarium of Cele National Station of Observation and Research for Desert- chemical treatments and molecular approaches. Cells. 2020;9:2492. Grassland Ecosystem, Xinjiang Institute of Ecology and Geography, Chinese 14. Mostofa MG, Rahman MM, Ansary MMU, Keya SS, Abdelrahman M, Academy of Sciences under the accession number (CNRS1985). Permission Miah MG, et al. Silicon in mitigation of abiotic stress-induced oxidative and license were obtained to collect specimens and all the methods were damage in plants. Crit Rev Biotechnol. 2021;41:918–34. carried out in accordance with relevant guidelines and regulations. 15 Sarker U, Oba S. The response of salinity stress-induced A. tricolor to growth, anatomy, physiology, non-enzymatic and enzymatic antioxi‑ Consent for publication dants. Front Plant Sci. 2020;11:559876. Not applicable. 16. 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Pompeiano A, Landi M, Meloni G, Vita F, Guglielminetti L, Guidi L. Alloca‑ Urumqi, China. 3 Cele National Station of Observation and Research for Desert- tion pattern, ion partitioning, and chlorophyll a fluorescence in Arundo Grassland Ecosystems, Cele 848300, China. 4 University of Chinese Academy donax L. in responses to salinity stress. Plant Biosyst Int J Dealing of Sciences, Beijing, China. 5 CSIC, Global Ecology Unit, CREAF-CSIC-UAB, Bel‑ Aspects Plant Biol. 2017;151:613–22. laterra, 08193 Barcelona, Catalonia, Spain. 6 CREAF, 08193 Cerdanyola del Vallès, 20 Asrar H, Hussain T, Hadi SMS, Gul B, Nielsen BL, Khan MA. Salin‑ Catalonia, Spain. 7 Instituto de Fisiología Vegetal, Consejo Nacional de Investi‑ ity induced changes in light harvesting and carbon assimilating gaciones Científicas Y Técnicas, Universidad Nacional de La Plata, Buenos Aires, complexes of Desmostachya bipinnata (L.) Staph. Environ Exp Bot. 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Estimation of hydrogen peroxide in plant extracts using titanium (IV). Anal Biochem. 1984;139:487–92. • gold Open Access which fosters wider collaboration and increased citations 97. Heath RL, Packer L. Effect of light on lipid peroxidation in chloroplasts. • maximum visibility for your research: over 100M website views per year Biochem Biophys Res Commun. 1965;19:716–20. 98. Giannopolitis CN, Ries SK. Superoxide dismutases: I. Occurrence in At BMC, research is always in progress. higher plants. Plant Physiol. 1977;59:309–14. Learn more biomedcentral.com/submissions