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Article

Salinity Threshold of Tall Wheatgrass for Cultivation in Coastal Saline and Alkaline Land

by
Hongwei Li
1,*,
Wei Li
1,2,
Qi Zheng
1,
Maolin Zhao
1,3,4,
Jianlin Wang
1,3,4,
Bin Li
1 and
Zhensheng Li
1
1
State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
2
College of Agriculture, Yangtze University, Jingzhou 434023, China
3
Zhongke-Dongying Research Center of Molecular Designed Breeding, Dongying 257509, China
4
Agricultural Experiment Station for Saline-Alkaline Land in Yellow River Delta Region, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Dongying 257509, China
*
Author to whom correspondence should be addressed.
Agriculture 2023, 13(2), 337; https://doi.org/10.3390/agriculture13020337
Submission received: 14 December 2022 / Revised: 14 January 2023 / Accepted: 27 January 2023 / Published: 30 January 2023
(This article belongs to the Section Crop Production)
Browse Figures
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Abstract

:
Tall wheatgrass (Elytrigia elongata) has the potential to be utilized on marginal land, such as coastal saline-alkaline soils, to meet rising ruminant feed demand. However, the salinity threshold for cultivation of tall wheatgrass remains unclear, which restricts its extensive application. Here, a tall wheatgrass line, Zhongyan 1, was grown in saline-alkaline soils in the Yellow River Delta region to determine its salinity threshold. The results showed that the soil salinity of AM = 1.23, measured with a PNT3000 activity meter, led to only 5% dead plants of tall wheatgrass. Four grades of seedling plants were classified according to the morphological response of Zhongyan 1 to saline soils. The soil salinity declined while the survival rate and forage yield increased from grade 1 to grade 4 plants. Plant height and dry matter yield were negatively related to soil salinity. When the salinity in the soil depth of 0–10 cm was over 1%, the survival rate of tall wheatgrass declined dramatically with the increase in soil salinity. Under saline-alkaline stress, the plant height during 12–31 May was positively related to forage yield, which can be used as an indicator of productivity. The tall type (70–120 cm) produced 5627.2 kg ha−1 of dry matter, which was 3.32 times that of the dwarf type (20–69 cm). The forage yield of tall wheatgrass in saline-alkaline land was largely affected by the proportion of highly saline soil. Collectively, the soil salinity of 1% at a depth of 0–10 cm and the AM values of 1.23 measured with a PNT3000 activity meter can be used as the salinity threshold for cultivation of tall wheatgrass in coastal saline-alkaline land.

1. Introduction

Tall wheatgrass (Elytrigia elongata = Thinopyrum ponticum, 2n = 10X = 70) is a perennial cool-season bunchgrass. It originated in southern Europe, Asia Minor, and southern Russia [1]. For the purposes of saline rangelands, soil reclamation, and as an energy plant, tall wheatgrass has been widely cultivated in the United States of America, Canada, Austria, Argentina, and some European countries [2,3,4]. For example, there are currently 1 × 106 ha of tall wheatgrass planted for cattle grazing in the Salado River basin, Argentina [5]. Since the first released variety, Largo, in 1937, more than ten varieties have been released to date [6,7]. In the early 1950s, tall wheatgrass was introduced to Northwest China for conservation of water and soil. Since 1956, the research group led by Li Zhensheng has used it as a wild relative parent for distant hybridization with bread wheat (Triticum aestivum). Consequently, a series of Xiaoyan wheat varieties, for instance Xiaoyan 6, were developed through distant hybridization, which contributed significantly to the food security of China. Nowadays, tall wheatgrass is still an important gene resource for wheat genetic improvement worldwide. During the 1980–1990s, some tall wheatgrass varieties like Jose, Largo, and Akar were introduced to Northwest China as forage grass and as a stabilizing plant for sand [8]. Long-term studies on tall wheatgrass salt tolerance [9,10,11,12], photosynthesis [13], inflorescence differentiation [14], leaf morphology [15], and regeneration culture [16,17] have been conducted in China. However, it has not been extensively cultivated in China for the purpose of forage production since its introduction.
To meet the increasing demand for ruminants’ feed resulting from the rapid expansion in dairy and beef cattle operations, marginal lands, such as saline-alkaline land, have the potential for forage production, which can avoid competition with cereal crops for arable land and water [18,19,20]. More than 8 × 108 ha of land are salt affected worldwide [21]. There are in total 7.8 × 107 ha of marginal land in China, of which 1.2 × 106 ha are coastal saline-alkaline land in the Circum-Bohai Sea region [18]. Tall wheatgrass exhibits significant tolerance to water logging [22,23] and saline-alkaline stress and is considered one of the most salt-alkali-tolerant plants [24,25,26,27,28,29,30]. Additionally, it was considered one of the most productive grasses under saline-alkaline stress [31]. Recently, Li Zhensheng proposed to construct a Coastal Grass Belt (CGB) in the Circum-Bohai Sea region by cultivating salt-alkali-tolerant forage grasses like tall wheatgrass on coastal saline-alkaline soils [6,32,33,34]. The proposal for CGB raises a new opportunity for the industrialization of tall wheatgrass in China.
The surface soil salinity in the CGB targeted region ranges from 0.2 to 1.0% (w/w), with the maximum reaching 3.0%. Hence, it is critical to know the salinity threshold of tall wheatgrass before cultivating in coastal saline-alkaline land. Soil salinity generally slows crop growth rate and reduces leaf size, plant architecture, and ultimately economic yield [35]. The soil salinity is usually described as the electric conductivity of “saturation paste extract” (ECe), soil:water = 1:5 (EC1:5), or ECa computed from electromagnetic induction [36]. Tall wheatgrass can grow in 7.5 dS m−1 ECe saline soil without any forage yield penalty [37]. Most of the research on salt tolerance on tall wheatgrass was performed by irrigation using NaCl solution. For instance, when several lines of tall wheatgrass were cultivated in approximately 300 mM NaCl for two months, three tall wheatgrass accessions produced the highest biomass yield relative to the other 22 Agropyrum species [24]. According to recovery from stepwise increases in salinity up to 765 mEq L−1, 32 tall wheatgrass accessions were classified into five groups, of which the most tolerant group showed a 95–100% recovery rate [38]. Further, Mcguire and Dvôrák [39] found that two of the nine accessions had a 87–93% survival rate at 750 mM of NaCl, which is one or one and a half times the NaCl concentration of seawater. Tall wheatgrass can survive when osmotic potentials decrease to −35 bar but grows very little below −10 bar, under saline stress [40]. Tall wheatgrass, grown on 19 dS m−1 ECe saline soil, produced 5.9–8.3 t ha−1 dry matter [41]. Further, a greenhouse evaluation indicated that it produced 85% forage yield under high salinity [42]. A recent study demonstrated that irrigation with 300 mM NaCl (ECw = 20.9 dS m−1) for 90 days reduced plant height by half and biomass by approximately one-third [5]. Riedell [43] observed that the salinity threshold of tall wheatgrass cv. Akar was 10 dS m−1 without biomass reduction and 30.2 dS m−1 for 50% growth reduction, according to a greenhouse pot experiment with NaCl and Na2SO4 solution. The salinity threshold of tall wheatgrass in real saline and alkaline soils in the field is currently unknown.
Seven tall wheatgrass lines were evaluated in coastal saline land with salinities of 0.3% and 0.5% since 2012, resulting in the productive and salt-alkali-tolerant line C2 (now named Zhongyan 1) [6,44]. It is unclear whether Zhongyan 1 can be planted in saline-alkaline land with a salinity over 0.5% or to what extent the maximal soil salinity is. The objective of this study is to explore the salinity threshold of tall wheatgrass like Zhongyan 1 for cultivation in a coastal saline-alkaline land.

2. Material and Methods

2.1. Plant Material

The tall wheatgrass line Zhongyan 1, previously described as C2 [44], was used in this study. Both vegetative and seed propagation were conducted at the Agricultural Experiment Station for Saline-Alkaline Land in the Yellow River Delta region (118°84′03″ E, 37°68′74″ N), Institute of Genetics and Developmental Biology, Chinese Academy of Sciences. Three types of saline soils were selected: types A, B, and C, with salinities of 0.2–2.2%, 0.2–1.5%, and 0.2–1.0%, respectively. The proportion of high soil salinity declined from type A to type C. Type A was used to explore the survival rate when tall wheatgrass was subjected to high salinity. Types B and C were used to explore the salinity threshold for forage productivity. The soil consisted of heavy clay with poor drainage. The mean content of P2O5, K2O, and N in the 0–30 cm soil layer from all the types of soils was 30.3, 331.7, and 55.6 mg kg−1, respectively. The organic matter content in the 0–30 cm soil layer ranged from 1.5 to 2.0%. No fertilizer was applied during the growing season. Transplanting of cloned seedlings and plants derived from seeds was performed for types A and C soil experiments, while seed sowing was carried out for the type B soil experiment.
For the type A soil experiment, cloned seedlings with 5–10 tillers, manually split from one-year-old plants, were transplanted into the field on October 10, 2020, with a four-row transplanter (2ZBX-4, Weifang Chengfan Agricultural Equipment Co., Ltd., Weifang, China). The rows were spaced 0.3 m apart, with an interval of 0.3 m between the plants. The plot area of the type A soil experiment was approximately 0.67 ha. During the end of February and the start of March 2021, the survival rate of tall wheatgrass as well as soil salinity were surveyed. At least 100 continuous plants were assessed for the number of surviving plants with green leaves, and the percentage of surviving plants was expressed as the survival rate.
For the type B soil experiment, seeds were manually sown on 1 September 2021, to determine the response of seedling establishment of tall wheatgrass to saline and alkaline soil. The plot had 4 rows spaced 0.3 m apart, and the sowing rate was 20–24 kg ha−1. The plot area of the type B soil experiment was approximately 100 m2.
Additionally, plants derived from seeds were transplanted in the spring for the type C soil experiment. Seeds were germinated at 26 °C in the dark for five days on 10 January 2021. The germinated seeds were then sown in 98-cell seedling trays (540 × 280 mm) filled with a mixed medium of peat moss substrate (LV252 0–10 mm, Pindstrup) and field soil (1:1, v/v). The salt content in the mixed media varied from 0.2 to 0.3%. Next, the seedling trays were cultivated in the greenhouse and irrigated with tap water every three days. The temperature was kept between 5 and 15 °C with a 12–14 h photoperiod. The relative humidity ranged from 50 to 70%. From the two-leaf stage, the seedlings were irrigated with 1 g L−1 greenhouse-grade soluble NPK fertilizers (Poly-Feed GG, Haifa). On 5 March, the seedlings were transferred outside of the greenhouse until they were transplanted in the field on 5 April 2021, with a transplanter (2ZBX-4). The rows were spaced 0.3 m apart, with an interval of 0.3 m between the plants. The plot area of the type C soil experiment was nearly 0.33 ha.

2.2. In Situ Measurement of Rhizosphere Soil Salinity in the Field

To explore the relationship between the soil salinity and the survival rate of the tall wheatgrass, the rhizosphere salinity of both surviving and dead plants was measured in situ by using an activity meter (PNT3000, STEP systems, Nürnberg, Germany), which considers soil moisture, temperature, and soil compaction. The PNT3000 activity meter (AM) has a measuring range of 0–10 activity and a resolution of 0.01 activity in g L−1. The assayed location was 2–3 cm apart from the root and 5–8 cm in depth. A total of 53 rows were surveyed for survival rates by counting the number of alive or dead plants for each row consisting of 100 continuous plants. This work was performed on type A soil.

2.3. Determination of Soil Salinity on Soluble Ion Content

After being air-dried at room temperature for 5 days, the soil samples were ground to pass through a 2.5 mm screen. Then, 5 g of soil powder was dissolved in 25 mL of deionized water. Five minutes later, EC1:5 was measured with a DDS-12DW (Shanghai Liguang, Shanghai, China), and pH was measured with a pH838 m (Smart Sensor, Dongguan, China) according to the manufacturer’s instructions. Finally, the contents of HCO3−, Cl−, SO42−, Ca2+, Mg2+, and K+ + Na+ were determined according to Bao [45]. The soil salt content was computed as follows: total salt content (%, w/w) = (HCO3−% + Cl−% + SO42−% + Ca2+% + Mg2+% + K+% + Na+%). The standard linear curves for EC1:5 and total salt content were fitted based on soil samples from all the types of soil experiments. Then, the EC1:5 for type B and C soil experiments was expressed as the salt content based on the standard linear curve (Figure S2).

2.4. Field Evaluation of Tall Wheatgrass Seedling Plants

According to architecture and tillers, seedling plants were classified into 1–4 grades for the type B soil experiment. Grade 1 means a poor survival rate; grade 2 means a good survival rate, a very small shoot size, and leaf necrosis; grade 3 means a near-normal shoot size but with curled and slim leaves; and grade 4 means a normal shoot size with fully expanded dark green leaves.
Plant height was measured on 12 May, 31 May, 22 June, and 3 July, which were 131, 150, 172, and 183 days from 1 January, respectively. Plant height measurements from the soil surface to the plant tip were conducted for 10–15 plants. On 5 July, whole plants, including both the shoot and root, were harvested and oven-dried at 65 °C for 48 h, followed by measuring the shoot and root dry weight.

2.5. Forage Yield Evaluation of Tall Wheatgrass Grown in Coastal Saline-Alkaline Soils

As the soil salinity in saline land is actually often uneven, the tall wheatgrass plants grown in type C soil were grouped together as tall (70–120 cm) and dwarf (20–69 cm) types on 21 May 2022. Three 8 m2 plots, 2 m × 4 m, were surveyed for forage dry matter yield for both tall and dwarf types. On 6 June, the entire forage plot was cut to a 10–15 cm stubble height. Fresh weight was measured immediately. About 0.8–1.0 kg of fresh sample was oven-dried and weighted, resulting in the ratio of dry to fresh weight. Finally, dry matter yield was computed by multiplying the ratio of dry to fresh weight by the fresh forage yield.

2.6. Statistical Analysis

The statistical analysis, including percentiles, one-way analysis of variance (ANOVA), multiple comparison, least significant difference (LSD) test, and an independent t test, was performed using SPSS software (version 19.0, IBM, Armonk, NY, USA). Linear regression equations (y = ax + b) and the determination coefficient (R2) were conducted using Excel (Microsoft Office 2016, IBM). Data were represented as mean ± standard deviation (SD). Figure plotting was carried out with SigmaPlot software (version 10.0, San Jose, CA, USA) and Excel (Microsoft Office 2016, IBM, Armonk, NY, USA).

3. Results

3.1. The Salinity Threshold of Surviving Tall Wheatgrass

The survival rate of transplanted tall wheatgrass on high-salinity soil in the coastal Yellow River Delta region was assessed. The salt content in the soils, sampled on 28 February 2021, ranged 0.23–2.16%, 0.16–1.37%, 0.15–1.29%, 0.15–1.45%, and 0.17–1.19% at the soil depths of 0–10, 10–20, 20–30, 30–40, and 40–50 cm, respectively (Figure S1). The survival rate of tall wheatgrass ranged between 0 and 98%, with an average of 41.2%. The seedlings’ survival rates at percentiles 5%, 10%, 25%, and 50% were 0%, 2.6%, 16.0%, and 40.5% (Table 1), accordingly. The low survival rate of tall wheatgrass seedlings was mostly ascribed to the high salinity they encountered. The rhizosphere salinity of 167 surviving and 173 dead plants randomly selected was tested in situ by using a PNT3000 activity meter. For the plants that survived, the AM values varied from 0.26 to 1.88, with a mean value of 1.11. The AM values at percentiles 5%, 10%, 25%, and 50% were 0.48, 0.59, 0.87, and 1.14, respectively. While for the dead plants, the AM values ranged 0.75–2.08 with a mean value of 1.69, which was higher than for the surviving plants. The AM values at the 5%, 10%, 25%, and 50% percentiles were 1.23, 1.32, 1.51, and 1.74, respectively. Therefore, it appeared that AM = 1.23 may be the salinity threshold for tall wheatgrass, which may result in only 5% dead plants.

3.2. Seedling Response of Tall Wheatgrass to Soil Salinity

According to their morphological responses to saline soil, tall wheatgrass seedling plants were grouped into four grades. Most of the grade 1 plants died in the spring, although their seeding emergence was good in the autumn. More surviving seedling plants occurred for the grade 2 plants, however, for which severe salt levels induced a symptom of leaf tip necrosis and yellowing of old leaves as expected. For the grade 3 plants, more tillers were found, but their leaves were curly and very slim, while the grade 4 plants looked normal (Figure 1A). The survival rates of grades 1 and 2 plants were below 20% and 80%, respectively, while for grade 3 plants the survival rate was approximately 100%, and for grade 4 plants it was 100% (Figure 1B). From grade 1 to grade 4 seedlings, the salinity decreased significantly (Figure 2A,B), while the pH values increased (Figure 2C,D) in the rhizosphere soils. For grade 1 and 2 plants, the low survival rates were mostly due to high soil salinity. For instance, the salinity at the soil depth of 0–10 cm was over 1% for grades 1 and 2 seedlings, whereas it was below 1% for grades 3 and 4 plants. The highest pH value (around 9) was observed for grade 4 seedling plants, which exhibited normal growth performance. Therefore, the effect of pH range in this study on tall wheatgrass seemed to be negligible.

3.3. The Response of Plant Height and Forage Yield to Soil Salinity

The plant height and its increasing rate differed significantly among the four grades of seedling plants during the booting and heading stages. The grade 1 plants were the lowest, while the grade 4 plants were the highest. The plant height of the grade 3 plants increased faster than that of the grade 2 plants, but they reached their maximum height 10 days later than the grade 4 plants (Figure 3). Therefore, soil salinity affected plant height to a large extent. Consequently, the shoot and root dry weight per plant increased drastically from grade 1 to grade 4 plants, accordingly (Figure 4). Although the survival rate of grade 3 plants was approximately equal to that of grade 4 plants, their biomass reduced considerably. The soil salinity at a depth of 0–10 cm, sampled on 7 April and 26 June, was negatively related to the shoot dry weight per plant (Figure 5A). Additionally, a strong negative relationship was also observed for the soil salinity at a depth of 0–10 cm and the plant height measured on 12 May (131 days from 1 January, Figure 5B) and 31 May (150 days from 1 January, Figure S3). Additionally, the plant heights measured on 12 May and 31 May were positively related to the shoot dry weight per plant (Figure 5C). Therefore, it seemed that the plant height during the period 12–31 May could be used as an indication of soil salinity and forage productivity.

3.4. The Forage Yield of Two Types of Tall Wheatgrass Grown in Saline Soil

According to the plant height on 21 May 2022, two types of tall wheatgrass, tall (70–120 cm) and dwarf (20–69 cm), from the same plot were compared for soil salinity and forage yield. Consistent with the above result, in comparison with the tall type, the variation ranges of salinity at soil depths of 0–10, 10–20, and 20–30 cm were all higher in the dwarf type (Table 2). In addition to the plant height, the length and width of the leaves from the dwarf type were also significantly reduced compared with the tall type (Figure S4). Consequently, the tall type produced 5627.2 kg ha−1 dry matter, which was 3.32 times that of the dwarf type (Table 2). Therefore, the forage productivity of tall wheatgrass was largely affected by the proportion of highly salinized soil.

4. Discussion

The competition for arable land and water between forage and cereal crops is a growing challenge for food security to meet the demand of an increasing population. Cultivation of tall wheatgrass in saline-alkaline land, for instance, in the coastal Circum-Bohai Sea region, provides an opportunity to balance food for humans and ruminants [6,33]. Additionally, tall wheatgrass performed better than rye for lower energy input, enhancement of profit margins, and more neutralization of CO2 in a marginal agricultural region [19]. However, tall wheatgrass has been neglected for a long time [46]. Especially in China, no varieties have been certified and released up until now, and only a few large areas of cultivation of tall wheatgrass have been reported [6,7]. Recently, based on eight years of screening in Beijing, Caofeidian, Nanpi, Haixing, and Dongying, China, the research group led by Li Zhensheng obtained a tall wheatgrass line (C2) with enhanced salt tolerance and forage productivity [6,44], which was named Zhongyan 1. The salinity threshold of tall wheatgrass like Zhongyan 1 is critical before it can be used for forage production in a coastal saline-alkaline region.
According to seed germination rates, Bazzigalupi et al. [47] recommended that a salinity of 18 dS m−1 (220 mM of NaCl solution) be used to screen salt-tolerant genotypes of tall wheatgrass. Several lines of evidence demonstrate that tall wheatgrass is one of the most salt-tolerant plants [24,25,26,27,28,29,30]. Interestingly, some tall wheatgrass accessions can even maintain high survival rates at 750 mM of NaCl [38,40]. The situation is more complex in the field; for instance, the soil salinity, water and nutrient availability, extreme temperatures, and waterlogging are often dynamic. Such exciting results, usually obtained under laboratory conditions [5], were not always consistent with field conditions. Therefore, field evaluation for a salinity threshold for tall wheatgrass is essential.
An easy and convenient technique should be direct and favor quick decisions if the targeted saline-alkaline land is suitable for tall wheatgrass. In this study, we found that soil salinity with a maximal AM of 1.23, measured with a PNT3000 activity meter, can be used as a salinity threshold, which can result in only 5% dead plants. Further, this study demonstrated that the soil salinity at a depth of 0–10 cm seemed to play a pivotal role in the zonation of tall wheatgrass in a saline-alkaline land. For instance, when the salt content in soil at a depth of 0–10 cm was over 1%, the survival rate of tall wheatgrass seedlings declined to 20–80% (grades 1 and 2 seedlings) depending on soil salinity, which resulted in unsuccessful establishment. On the contrary, in saline soils where the salinity at a soil depth of 0–10 cm is below 1%, tall wheatgrass can establish successfully (grades 3 and 4 plants). Collectively, the soil salinity of 1% at a depth of 0–10 cm appeared to be the salinity threshold for tall wheatgrass zonation. According to the linearly fitted regression curves of soil salt content and EC1:5, a soil salinity of 1% corresponds to an EC1:5 = 3.08 dS m−1, which is approximately equal to an ECe = 24.64 dS m−1 according to the ratio of EC1:5/ECe ≈ 8 (for clays, saturation percentage ≈ 45%) [48]. Therefore, ECe = 24.64 may be the salinity threshold of tall wheatgrass for cultivation in a coastal saline-alkaline land.
Plant height and dry matter yield were negatively related to soil salinity. High salinity considerably reduced plant height and dry matter (Figure 5A,B), which was consistent with work by Shannon and Noble [35]. Under saline stress, plant height was positively correlated with dry matter yield (Figure 5C). It seemed that the plant height of tall wheatgrass during the period 12–31 May could be used as an indirect indicator of soil salinity and forage productivity. The tall type of tall wheatgrass plants produced 3.32 times the dry matter yield compared to the dwarf type. It can be deduced that the forage yield was largely affected by the proportion of high-salinity soils. Salinity and waterlogging are constraints for a coastal region [36]. Even tall wheatgrass exhibited good flood resistance [20], as it was ranked as moderately tolerant to salinity and waterlogging [36]. Hence, tall wheatgrasses may not be the answer for all coastal saline sites [49], especially for soils with a salinity over 1%.

5. Conclusions

This study suggested that a salt content of 1% at a soil depth of 0–10 cm can be a salinity threshold for the cultivation of tall wheatgrass in coastal saline-alkaline lands. Plant height during the period 12–31 May can be used to predict soil salinity and forage yield of tall wheatgrass under saline stress. Forage yield was largely affected by the proportion of high-salinity soils.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agriculture13020337/s1, Figure S1. The soil salt content of tall wheatgrass grown in highly saline soils. Figure S2. The linear correlation curve between the soil salinity (%, w/w) and EC1:5 (N = 198). Figure S3. The relationship between soil content sampled on 7 April and 26 June and plant height measured on 31 May. The circle indicates the soil salt content sampled on 7 April, while the triangle indicates the soil salt content sampled on 26 June. Linear regression equations (y = ax + b) and the determination coefficient (R2) are shown with the fitted trend lines. Figure S4. Leaf length and width of tall and dwarf types of tall wheatgrass grown in saline and alkaline soil. **, denotes the significant difference at p < 0.01.

Author Contributions

Conceptualization, Funding acquisition, Investigation, Writing—original draft, H.L.; Data curation, Formal analysis, Investigation, W.L.; Investigation, Validation, Writing— review and editing, Q.Z.; Investigation, Writing—review and editing, Q.Z., M.Z. and J.W.; Data curation, Resources, B.L.; Supervision, Funding acquisition, Writing—review and editing, Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA26040105).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

Authors declare that there are no conflict of interest.

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Figure 1. Photograph and survival rate of tall wheatgrass seedlings grown in saline-alkaline soils with different salinities. (A–D) Photographs of seedlings in grades 1–4; and (E) the survival rate of four seedling grades. Photographed on 11 April 2022, in Dongying, China. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
Figure 1. Photograph and survival rate of tall wheatgrass seedlings grown in saline-alkaline soils with different salinities. (A–D) Photographs of seedlings in grades 1–4; and (E) the survival rate of four seedling grades. Photographed on 11 April 2022, in Dongying, China. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
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Figure 2. The salt content and pH in the soils from the four grades of tall wheatgrass seedlings grown in different saline-alkaline soils. (A,B) Sampled on 7 April 2022, and (C,D) sampled on 26 June 2022. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
Figure 2. The salt content and pH in the soils from the four grades of tall wheatgrass seedlings grown in different saline-alkaline soils. (A,B) Sampled on 7 April 2022, and (C,D) sampled on 26 June 2022. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
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Figure 3. Plant heights of the four grades of tall wheatgrass seedlings grown in different saline-alkaline soils. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
Figure 3. Plant heights of the four grades of tall wheatgrass seedlings grown in different saline-alkaline soils. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
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Figure 4. Shoot and root dry matter per plant in the four grades of tall wheatgrass seedlings grown in different saline-alkaline soils. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
Figure 4. Shoot and root dry matter per plant in the four grades of tall wheatgrass seedlings grown in different saline-alkaline soils. Data were represented as mean ± SD. Different letters indicate a significant difference at p < 0.05.
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Figure 5. The relationships between soil salinity and shoot dry weight (A) and plant height (B), as well as between shoot dry weight and plant height (C). (A,B) A circle indicates the soil salt content sampled on 7 April, while a triangle indicates the soil salt content sampled on 26 June. (C) A circle indicates the plant height measured on 12 May, while a triangle indicates the plant height measured on 31 May. Data were represented as mean ± SD. Linear regression equations (y = ax + b) and the determination coefficient (R2) are shown with the fitted trend lines.
Figure 5. The relationships between soil salinity and shoot dry weight (A) and plant height (B), as well as between shoot dry weight and plant height (C). (A,B) A circle indicates the soil salt content sampled on 7 April, while a triangle indicates the soil salt content sampled on 26 June. (C) A circle indicates the plant height measured on 12 May, while a triangle indicates the plant height measured on 31 May. Data were represented as mean ± SD. Linear regression equations (y = ax + b) and the determination coefficient (R2) are shown with the fitted trend lines.
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Table
Table 1. The rhizosphere salinity of surviving or dead tall wheatgrass plants grown in saline-alkaline soils as measured with an activity meter (AM) PNT3000. The AM mean activity values are in g L−1.
Table 1. The rhizosphere salinity of surviving or dead tall wheatgrass plants grown in saline-alkaline soils as measured with an activity meter (AM) PNT3000. The AM mean activity values are in g L−1.
NMin.Max.MeanPercentiles
5%10%25%50%
Survived1670.261.881.110.480.590.871.14
Dead1730.752.081.691.231.321.511.74
Overall3400.262.081.410.590.811.141.46
Survival rate530.0%98.0%41.2%0.0%2.6%16.0%40.5%
Notes: N, the number of seedling plants; Min., minimum; Max., maximum.
Table
Table 2. Comparison of soil salt content and dry matter yield between dwarf and tall types of tall wheatgrass grown under saline stress.
Table 2. Comparison of soil salt content and dry matter yield between dwarf and tall types of tall wheatgrass grown under saline stress.
TypesPlant Height (cm)Range of Soil Salt Content (%)Dry Matter Yield † (kg ha−1)
0–10 cm10–20 cm20–30 cm
Dwarf20–690.58–0.930.37–0.580.33–0.551696.5 ± 294.8
Tall70–1200.15–0.260.19–0.220.16–0.225627.2 ± 242.0 **
Note: † Data were represented as mean ± SD. **, denotes a significant difference at p < 0.01.
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MDPI and ACS Style

Li, H.; Li, W.; Zheng, Q.; Zhao, M.; Wang, J.; Li, B.; Li, Z. Salinity Threshold of Tall Wheatgrass for Cultivation in Coastal Saline and Alkaline Land. Agriculture 2023, 13, 337. https://doi.org/10.3390/agriculture13020337

AMA Style

Li H, Li W, Zheng Q, Zhao M, Wang J, Li B, Li Z. Salinity Threshold of Tall Wheatgrass for Cultivation in Coastal Saline and Alkaline Land. Agriculture. 2023; 13(2):337. https://doi.org/10.3390/agriculture13020337

Chicago/Turabian Style

Li, Hongwei, Wei Li, Qi Zheng, Maolin Zhao, Jianlin Wang, Bin Li, and Zhensheng Li. 2023. "Salinity Threshold of Tall Wheatgrass for Cultivation in Coastal Saline and Alkaline Land" Agriculture 13, no. 2: 337. https://doi.org/10.3390/agriculture13020337

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