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Introduction
In 2018, 182.3 million t of fresh tomatoes were produced on 4.7 million ha worldwide (Organización de las Naciones Unidas para la Alimentación y la Agricultura [FAO], 2020). In the same year, Mexico produced 3.7 million t on 44,183 ha; of this production, Sinaloa contributed 29.7 % on 13,657 ha, under protected and open-field conditions (Servicio de Información Agroalimentaria y Pesquera [SIAP, 2020]).
A limitation of tomato production in open-field conditions in the Culiacán Valley, Sinaloa, is the presence of pests, such as nematodes and some species of Fusarium oxysporum; this is due, among other factors, to the lack of crop rotation. For this reason, growers in this area plant in soils near the coast, where temperatures are more favorable for crop development, since the sea is a climate regulator. However, sea breezes and rainfall deposit significant amounts of chlorine in the soil (Xu, Magen, Tarchitzky, & Kafkafi, 2000), and irrigation water may contain Cl and Na ions that affect tomato, a plant classified as salt-sensitive (glycophyte) (White & Broadley, 2001).
The Cl- anion is the main form of chlorine in soils and irrigation water. Cl- is a cofactor in oxygen formation in chloroplasts (Kawakami, Umena, Kamiya, & Shen, 2009), and is the most abundant anion in plant cells, as it is involved in the electrical charge balance of cations in cell membranes and in pH regulation (Marschner, 2012). Some researchers consider Cl beneficial when it accumulates at a macronutrient level in plant tissues, as it promotes water balance, photosynthesis, water-use efficiency, cellular osmoregulation, leaf turgor and elongation, and reduced stomatal conductance (Franco-Navarro et al., 2016; Wege, Gilliham, & Henderson, 2017; Colmenero-Flores, Franco-Navarro, Cubero-Font, Peinado-Torrubia, & Rosales, 2019; Maron, 2019). Franco-Navarro et al. (2019) point out that Cl- increases water-use efficiency in tobacco (Nicotiana tabacum L.) plants.
Excessive Cl- accumulation in crops sensitive to this element under salt stress conditions is detrimental (Geilfus, 2018 ). Dang, Dalal, Routley, Schwenke, and Daniells (2006) indicate that Cl concentrations in soil reduce growth and yield of wheat and chickpea, compared to the Na+ predominant in saline soils and an important component in poor quality irrigation water, which affects vegetables by causing toxicity or nutrient imbalances (Grattan & Grieve, 1998; Rodríguez-Navarro, 2000; Parida & Das, 2005). On the other hand, Idowu and Aduayi (2006) report that the application of 5 mg Na and 40 mg of K in 1 kg of soil increased tomato yield. The effect of NaCl on crops is well documented (Turhan & Eris, 2005; Khayyat et al., 2009; Tavakkoli, Rengasamy, & McDonald, 2010; Tavakkoli, Fatehi, Coventry, Rengasamy, & McDonald, 2011; Plaza, Jiménez, & Lao, 2012; Shiyab et al., 2013; Flowers, Munns, & Colmer, 2015), although there are few studies that separate the effects of Cl and Na on crops (Tavakkoli et al., 2011; Flowers et al., 2015).
In most saline soils, NaCl contributes between 50 and 80 % of total soluble salts (Rengasami, 2010a), which cause three effects on plant growth: 1) they reduce the hydric potential of water by decreasing the osmotic potential (Ψs) of the solution, 2) they cause ion imbalances in the cells and 3) they cause Cl- and Na+ toxicity. Tavakkoli et al. (2010) note that in salt stress studies it is important that treatments have similar Ψs so as not to affect plant growth differentially. Therefore, the objective of the present work was to evaluate three percentage ratios of Cl-/anions [25/100, 50/100 and 75/100, Cl-/anions (NO3 -, H2PO4 -, SO4 2- and Cl-)] and three percentage ratios of Na+/cations [25/100, 50/100 and 75/100, Na+/cations (Ca2+, K+, Mg2+ and Na+)] in Steiner’s (1984) nutrient solution adjusted to a Ψs of -0.072 MPa, to compare the separate effects of Cl- and Na+ on mineral composition, dry matter production and yield in hydroponically-grown tomato.
Materials and methods
The research was conducted from November 2019 to March 2020 in a multi-tunnel greenhouse, with fixed zenithal ventilation and anti-aphid mesh on the side walls, belonging to the Faculty of Agronomy at the Universidad Autónoma de Sinaloa, Culiacán, Sinaloa, Mexico (24° 37’ 29” NL and 107° 24’ 30” WL, at 38 m a. s. l.). The average minimum and maximum temperatures inside the greenhouse were 16 and 36 °C, respectively.
Saladette-type tomato cv La Roca plants of indeterminate growth obtained from Nirit Seeds Ltd. were transplanted in a closed hydroponic system. The system consisted of 72 plastic containers, painted black, with a capacity of 20 L each, of which 36 contained 15 L of brown Sphagnum peat moss (Kekkila Professional) as substrate, and the other 36 contained 10 L of nutrient solution (NS) of the corresponding treatments. The containers with the substrate were provided with a 1.27 cm diameter drainage hole 2 cm from the base and were fitted with a rubber band, an irrigation starter, a 30 cm long rubber hose and a stopcock to drain the excess SN after watering and to recover the drained solution. The substrate containers were placed on benches 50 cm high and 5 m long. The separation between benches was 1.2 m, and the distance between plants on the benches was 0.4 m.
The factors and levels evaluated were the percentage ratio of Cl-/anions (25/100, 50/100 and 75/100) and Na+/cations (25/100, 50/100 and 75/100), the combination of which generated nine treatments (Table 1), all adjusted to a Ψs of -0.072 MPa. Steiner's (1984) universal solution was used as a reference. The NSs were prepared with irrigation water with an electrical conductivity of 0.3 dS·m-1 and pH of 7, classified as C1S1 (low risk of salinization and sodification). The nutrients present in the water were considered in the formulation of the NSs. Commercial fertilizers (monopotassium phosphate, magnesium sulfate, potassium sulfate, calcium nitrate, potassium nitrate and magnesium nitrate) were used as a source of macronutrients. The source of Na and Cl was reagent-grade NaCl, and the micronutrients were supplied with Hidromix Proan, whose chemical composition is (%, w/w): 4.9 Fe, 2.7 Mn, 0.4 Zn, 0.2 Cu, 0.3 B and 0.1 Mo.
Table 1 Chemical composition of the nutrient solutions used in the experiment.
| Treatment | Cl-/Na+ ratio (%) | NO3 - | H2PO4 - | SO4 2- | Cl- | K+ | Ca2+ | Mg2+ | Na+ |
|---|---|---|---|---|---|---|---|---|---|
| (molc·m-3) | |||||||||
| 1 | 25/25 | 8.31 | 0.69 | 4.84 | 4.61 | 4.84 | 6.23 | 2.77 | 4.61 |
| 2 | 50/25 | 5.39 | 0.45 | 3.15 | 9.00 | 4.72 | 6.07 | 2.70 | 4.50 |
| 3 | 75/25 | 2.63 | 0.22 | 1.53 | 13.14 | 4.60 | 5.91 | 2.63 | 4.38 |
| 4 | 25/50 | 7.91 | 0.66 | 4.61 | 4.39 | 3.08 | 3.96 | 1.76 | 8.79 |
| 5 | 50/50 | 5.14 | 0.43 | 3.00 | 8.57 | 3.00 | 3.86 | 1.71 | 8.57 |
| 6 | 75/50 | 2.51 | 0.21 | 1.46 | 12.54 | 2.93 | 3.76 | 1.67 | 8.36 |
| 7 | 25/75 | 7.55 | 0.63 | 4.40 | 4.19 | 1.47 | 1.89 | 0.84 | 12.58 |
| 8 | 50/75 | 4.91 | 0.41 | 2.87 | 8.19 | 1.43 | 1.84 | 0.82 | 12.28 |
| 9 | 75/75 | 2.40 | 0.20 | 1.40 | 12.00 | 1.40 | 1.80 | 0.80 | 12.00 |
The experimental design was completely randomized with a 32 factorial arrangement and four replications, giving a total of 36 experimental units. Each experimental unit consisted of one tomato plant per container with substrate. Daily irrigation was applied to the substrate and the evapotranspiration water was replaced with irrigation water, without adjusting the pH of the NSs. The solutions were renewed every 15 days during the first 30 days after transplanting (dat), and thereafter were renewed every 10 days until the end of the experiment. At the end of the harvest (108 dat), the plants of each experimental unit (four plants per treatment) were cut, sectioned into their different organs, dried at 70 °C until constant weight, ground and passed through a 0.5 mm diameter sieve. To quantify the nutrient concentration in leaves, stems and fruits, the plant organs were subjected to dry digestion at 500 °C for 3 h. Sodium, potassium, calcium and magnesium were analyzed by atomic absorption, and chlorides were determined by titration (Motsara & Roy, 2008). A total of six fruit cuts were made, and in each cut the number and weight of the fruits were recorded.
The data obtained were subjected to an analysis of variance and Tukey's multiple comparison test (P ≤ 0.05) for the main factors and their interaction. For the analysis, the SAS ver. 9.4 statistical package (SAS Institute Inc., 2013) was used.
Results and discussion
Nutrient concentrations in tomato leaves, stems and fruits
The Cl-/anions ratio in the NS caused significant differences in Na and Cl concentrations in leaves, stems and fruits, and of Ca in leaves (Tables 2, 3 and 4). Na concentrations in the plant organs had an inverse relationship to the Cl-/anions ratio, since increasing the ratio from 25/100 to 75/100 decreased the Na concentration (P ≤ 0.05). Xu, Magen, Tarchitzky and Kafkafi (2000) obtained a critical toxicity range (CTR) of 4 to 7 mg Cl·g-1 dry matter in Cl-sensitive plant species, and from 15 to 35 mg Cl·g-1 dry matter in tolerant plants. In the present work, 26, 24 and 29 mg Cl·g-1 of leaf dry matter were obtained at the 25, 50 and 75 Cl-/anions ratio, values that are in the CTR. Excessive Cl uptake at the 75/100 Cl-/anions ratio caused lower Na uptake (Table 2) due to unbalanced ratios of Na+ to Ca2+ and K+ in the NS (Fageria, 2001).
Table 2 Effects of Cl-/anions and Na+/cations ratios in the nutrient solution and K, Ca, Mg, Na and Cl concentrations on tomato leaves.
| Factor | K | Ca | Mg | Na | Cl |
|---|---|---|---|---|---|
| (%) | |||||
| Percentage ratio of Cl-/anions | |||||
| 25/100 | 1.08 az | 0.85 a | 0.15 a | 0.40 a | 2.6 b |
| 50/100 | 1.08 a | 0.60 b | 0.19 a | 0.36 a | 2.4 c |
| 75/100 | 1.03 a | 0.66 b | 0.18 a | 0.31 b | 2.9 a |
| Percentage ratio of Na+/cations | |||||
| 25/100 | 1.17 a | 0.69 a | 0.18 a | 0.30 b | 2.5 a |
| 50/100 | 1.08 a | 0.74 a | 0.18 a | 0.38 a | 2.7 a |
| 75/100 | 0.93 b | 0.69 a | 0.17 a | 0.40 a | 2.7 a |
| CV (%) | 10.6 | 22.9 | 32.7 | 16.6 | 7.7 |
| LSD | 0.09 | 0.13 | 0.04 | 0.04 | 0.20 |
| Cl-/anions x Na+/cations | ns | ns | ns | ns | ns |
CV = coefficient of variation; LSD = least significant difference. zMeans with the same letters within each column and each factor do not differ statistically (Tukey, P ≤ 0.05). ns = not significant.
Table 3 Effects of Cl-/anion and Na+/cation ratios in the nutrient solution and concentrations of K, Ca, Mg, Na and Cl on tomato stems.
| Factor | K | Ca | Mg | Na | Cl |
|---|---|---|---|---|---|
| (%) | |||||
| Percentage ratio of Cl-/anions | |||||
| 25/100 | 1.14 az | 0.19 a | 0.08 a | 0.49 a | 2.37 b |
| 50/100 | 1.14 a | 0.18 a | 0.08 a | 0.43 b | 2.57 a |
| 75/100 | 1.12 a | 0.19 a | 0.09 a | 0.42 b | 2.59 a |
| Percentage ratio of Na+/cations | |||||
| 25/100 | 1.19 a | 0.21 a | 0.09 a | 0.38 b | 2.4 b |
| 50/100 | 1.16 a | 0.21 a | 0.08 a | 0.47 a | 2.5 ab |
| 75/100 | 1.05 b | 0.16 a | 0.07 a | 0.49 a | 2.6 a |
| CV (%) | 5.0 | 32.9 | 36.3 | 15.6 | 6.2 |
| LSD | 0.04 | 0.05 | 0.02 | 0.05 | 0.15 |
| Cl-/anions x Na+/cations | ns | ns | ns | ns | ns |
CV = coefficient of variation; LSD = least significant difference. zMeans with the same letters within each column and each factor do not differ statistically (Tukey, P ≤ 0.05). ns = not significant.
Table 4 Effects of Cl-/anion and Na+/cation ratios in the nutrient solution and concentrations of K, Ca, Mg, Na and Cl on tomato fruit.
| Factor | K | Ca | Mg | Na | Cl |
|---|---|---|---|---|---|
| (%) | |||||
| Percentage ratio of Cl-/anions | |||||
| 25/100 | 1.29 az | 0.11 a | 0.05 a | 0.25 a | 2.0 b |
| 50/100 | 1.31 a | 0.10 a | 0.05 a | 0.22 ab | 2.2 ab |
| 75/100 | 1.28 a | 0.11 a | 0.04 a | 0.21 b | 2.3 a |
| Percentage ratio of Na+/cations | |||||
| 25/100 | 1.30 a | 0.11 a | 0.05 a | 0.20 b | 2.2 a |
| 50/100 | 1.29 a | 0.10 a | 0.04 a | 0.21 b | 2.2 a |
| 75/100 | 1.29 a | 0.10 a | 0.05 a | 0.26 a | 2.1 a |
| CV (%) | 2.5 | 18.7 | 13.4 | 15.4 | 11.9 |
| LSD | 0.02 | 0.01 | 0.013 | 0.03 | 0.26 |
| Cl-/anions x Na+/cations | ns | ns | ns | ns | ns |
CV = coefficient of variation; LSD = least significant difference. zMeans with the same letters within each column and each factor do not differ statistically (Tukey, P ≤ 0.05). ns = not significant.
There was a positive relationship between the Cl concentration in the NS and in the leaves, stems, and fruits; thus, the highest Cl values in these organs were obtained with 75/100 Cl-/anions, and the lowest were observed with 25/100 Cl-/anions, except in leaves (Tables 2, 3 and 4). Villa-Castorena, Catalán-Valencia, Inzunza-Ibarra, and Ulery (2006), Kowalczyk et al. (2008), Giuffrida, Martorana, and Leonardi (2009), Komosa and Górniak (2015), and Parra-Terraza (2016) obtained the same relationship in leaf Cl contents and Cl- concentrations in NS. Increasing the Cl- concentration in the NS increased the amount of Cl in fruits, which is similar to that reported by Komosa and Górniak (2015). On the other hand, the 50/100 and 75/100 Cl-/anions ratios reduced Ca concentrations in leaves, which is in agreement with what was reported by Parra-Terraza (2016), and Komosa and Górniak (2015).
The 75/100 percentage ratio of Na+/cations in the NS significantly reduced K concentrations in leaves (Table 2) and stems (Table 3), and increased Na concentrations in leaves, stems, and fruits (Tables 2, 3, and 4), relative to the 25/100 Na+/cations ratio. Tavakkoli et al. (2011) reported that Na reduced K concentrations and increased Na amounts in aerial biomass of barley plants. Rengasamy (2010b) notes that Na accumulation can cause toxicity or ion imbalance, which is consistent with the present study with the 75/100 Na+/cations ratio.
The antagonism of Na over K has been reported in several studies (del Amor, Martinez, & Cerdá, 2001; Halperin & Lynch, 2003; Turhan & Eris, 2005; Parida & Das, 2005; Naeini, Khoshgoftarmanesh, & Fallahi, 2006; Lu, Shang, Xu, Korpelainen, & Li, 2009; Vaghela, Patel, Pandey, & Pandey, 2010; Tavakkoli et al., 2011; Ahmad, Kholgh-Sima, & Mirzaei, 2013; Shiyab et al., 2013; Komosa & Górniak, 2015; Parra-Terraza, 2016), where the higher Na+ concentration in the NS reduced root hydraulic conductivity by displacing K+ from the exchange sites, and reducing K uptake and accumulation in leaves. The higher Na concentrations in plant organs obtained with Na increases in the NS coincide with the findings reported by Tavakkoli et al. (2011), Shiyab et al. (2013), Maqsood et al. (2015) and Wang, Fang, and Wang (2015).
Aerial biomass production
The dry weight of leaves, stems and plants decreased (P ≤ 0.05) due to the factors Cl-/anions and Na+/cations in the NS (Table 5). In each factor, the highest organ dry weights were obtained with 25/100 Cl-/anions and 25/100 Na+/cations. In contrast, the lowest dry weights were obtained with 75/100 Cl-/anions and 75/100 Na+/cations, which is attributed to the toxicity caused by excessive Cl- and Na+ uptake, and to the nutrient imbalance generated by affecting K and Ca uptake and accumulation in leaves. Tavakkoli et al. (2010) point out that toxicity and nutrient imbalance reduce stomatal conductance and photosynthesis, which in turn reduces dry matter in broad bean (Vicia fava L.) plants. Shiyab et al. (2013) and Giuffrida et al. (2009) report the reduction of dry biomass in tomato due to the effect of Cl-, Na+ and NaCl. In the present work, high Cl- and Na+ ratios reduced plant dry weight by 48 and 25.8 %, respectively, with the greatest reduction caused by Cl-. Dang et al. (2010) obtained similar results in barley, wheat and triticale. Tavakkoli et al. (2010) state that high Cl- concentrations in soil reduce barley growth more compared to Na+. Tavakkoli et al. (2011) report 10-45 % reductions in plant biomass in barley caused by Cl-, while Na+ reduced biomass accumulation from 20 to 25 %.
Table 5 Effects of Cl-/anion and Na+/cation ratios in the nutrient solution on leaf dry weight (LDW), stem dry weight (SDW) and plant dry weight (PDW).
| Factor | LDW | SDW | PDW |
|---|---|---|---|
| (g) | |||
| Percentage ratio of Cl-/anions | |||
| 25/100 | 110.6 az | 77.4 a | 188.0 a |
| 50/100 | 78.0 b | 65.7 b | 143.7 b |
| 75/100 | 51.8 c | 45.8 c | 97.7 c |
| Percentage ratio of Na+/cations | |||
| 25/100 | 99.2 a | 66.7 a | 165.9 a |
| 50/100 | 77.2 b | 65.8 a | 143.0 b |
| 75/100 | 65.4 b | 57.6 b | 123.0 c |
| CV (%) | 26.2 | 15.9 | 17.4 |
| LSD | 17.2 | 8.2 | 20.4 |
| Cl-/anions x Na+/cations | ns | ns | ns |
CV = coefficient of variation; LSD = least significant difference. zMeans with the same letters within each column and each factor do not differ statistically (Tukey, P ≤ 0.05). ns = not significamt.
Yield and its components
The Cl-/anions and Na+/cations factors of the NS decreased (P ≤ 0.05) fruit number and fruit yield (Table 6). By increasing the Cl-/anions ratio from 25 to 75/100, fruit number and fruit yield decreased by 54.5 and 50.8 %, respectively. This contrasts with the results of Kowalczyk et al. (2008) and Voogt and Sonneveld (2004), who, when applying 14.4 and 17 mg Cl-1·L-1, detected no effect on tomato yield in peat and rockwool substrates, respectively. The differences in yields obtained in the above-mentioned studies and those reported in the present work are associated with the culture media, production systems and genotypes used, the concentrations of Cl-accompanying cations (Caines & Shennan, 1999) and the salinity of the medium (Komosa & Górniak, 2015). Similarly, by increasing the Na+/cations ratio from 25/100 to 75/100, fruit number and yield decreased by 50 and 45.7 %, respectively (Table 6).
Table 6 Effects of Cl-/anions and Na+/cations ratios in the nutrient solution on fruit number (FN), mean fruit weight (MFW) and fruit yield (FY) (average of six cuts).
| Factor | FN | MFW (g) | FY (t·ha-1) |
|---|---|---|---|
| Percentage ratio of Cl-/anions | |||
| 25/100 | 11 az | 123 a | 29.9 a |
| 50/100 | 7 b | 129 a | 20.5 b |
| 75/100 | 5 b | 124 a | 14.7 c |
| Percentage ratio of Na+/cations | |||
| 25/100 | 10 a | 125 a | 26.5 a |
| 50/100 | 9 a | 129 a | 24.1 a |
| 75/100 | 5 b | 122 a | 14.4 b |
| CV (%) | 37.3 | 20.8 | 25.1 |
| LSD | 3 | 23.3 | 5.5 |
| Cl-/aniones x Na+/cationes | ns | ns | ns |
CV = coefficient of variation; LSD = least significant difference. zMeans with the same letters within each column and each factor do not differ statistically Tukey, P ≤ 0.05). ns = not significant
Conclusions
The 75/100 percentage ratio of Cl-/anions in the nutrient solution increased Cl concentrations in leaves, stems and fruits by 11.5, 9.3 and 15 %, respectively, compared to 25/100 Cl-/anions. On the other hand, the 75/100 Na2+/cations ratio increased Na concentrations in leaves and stems by 33.3 and 28.9 %, respectively, compared to 25/100 Na2+/cations.
Dry matter production and yield of tomato were reduced due to excessive Cl and Na accumulation and nutrient imbalance in the plants. The reduction in yield, caused by the higher Cl-/anions and Na2+/cations ratios, indicate that both ions were toxic to tomato and their main effects were individual.
