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Article

Alginate Oligosaccharide Promoted the Nutrient Uptake and Growth of Cucumber Seedlings Under Suboptimal Temperature Conditions

by
Xu Guo
1,†,
Yun Li
1,†,
Kai Fan
1,
Lingru Guo
1,
Yongzhao Yang
1,
Chunming Cheng
2,
Leiping Hou
1,
Yanxiu Miao
1,
Meihua Sun
1,
Yaling Li
1,* and
Longqiang Bai
1,*
1
College of Horticulture, Shanxi Agricultural University, Jinzhong 030801, China
2
College of Animal Science, Shanxi Agricultural University, Jinzhong 030801, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Horticulturae 2025, 11(5), 501; https://doi.org/10.3390/horticulturae11050501
Submission received: 8 April 2025 / Revised: 3 May 2025 / Accepted: 6 May 2025 / Published: 7 May 2025
(This article belongs to the Section Biotic and Abiotic Stress)
Browse Figures
Versions Notes

Abstract

:
Due to its sensitivity to cold temperatures, cucumber growth is substantially constrained by suboptimal temperature stress in northern China’s off-season production systems. Suboptimal temperatures severely repress the nutrient absorption, growth, and yield formation of vegetables in solar greenhouses during winter and early spring in China. Alginate oligosaccharides (AOSs) are anionic acidic polysaccharides derived from brown algae, known for promoting plant growth and alleviating abiotic stress. In this study, we aimed to investigate the effects of different nutrient solution concentrations combined with AOS on the growth and nutrient uptake of cucumber seedlings under suboptimal temperatures (15/8 °C, day/night). Potted ‘Jinchun 4’ cucumber seedlings grown in coconut coir were treated with 0.5×, 1.0×, or 1.5× strength of Hoagland solution alone (N0.5, N1, N1.5), or with 30 mg·L−1 AOS (A0.5, A1, A1.5). The results showed that the growth attributes and nitrogen (N) accumulation of cucumber plants of N1 and N1.5 were significantly higher than those of N0.5. Additionally, plants of A0.5 exhibited significantly higher plant height, chlorophyll a content, root surface area, root volume, root vitality, N metabolism enzyme (NR, GDH, GS) activities, and N accumulation, than those under N0.5, N1, or N1.5. Moreover, compared to A0.5, the net photosynthetic rate, total root length, root surface area, root N content, leaf nitrate reductase activity, root glutamate dehydrogenase activity, and N accumulation of A1 and A1.5 were significantly higher than those of A0.5. Correlation analysis revealed strong linkages between root morphology traits and tissue N content. In summary, under suboptimal temperature conditions, the application of AOS improved cucumber seedlings’ nutrient absorption and growth more efficiently than merely raising nutrient levels, as it enhanced root surface area, root vitality, and N metabolic enzyme activities.

1. Introduction

Cucumber (Cucumis sativus L.) is a widely cultivated horticultural crop that thrives at a temperature range of 22–32 °C/15–18 °C (day/night) [1,2]. While winter- and early spring-grown cucumbers command higher market prices due to off-season supply, their cultivation in northern China’s solar greenhouses is severely limited by suboptimal temperature stress, a key limiting factor that impairs plant nutrient uptake [3]. Suboptimal temperatures inhibit the expression of AKT1 (which encodes a K+ channel), reducing whole-plant K+ content and net K+ uptake in tomato [4]. In cucumbers, suboptimal temperatures lead to decreased root growth, reduced root vitality, lower N metabolism enzyme activities, and downregulated expression of nitrate transporter genes, resulting in diminished NO3−-N uptake [2,3,5]. An enhanced nutrient supply substantially promotes plant growth [6,7,8]. Thus, farmers often overuse chemical fertilizers to increase out-of-season vegetable yields, a practice that is both costly and damaging to the environment [9].
China is currently driving green agricultural development by implementing eco-friendly farming practices and advocating for a reduction in chemical fertilizer use. Biostimulants are natural or synthetic substances which can improve plant growth, stress tolerance, or nutrient use efficiency [10,11,12]. The supplementation of biostimulants in fertilization programs can enhance plant growth and crop yields while reducing fertilizer inputs [12]. Alginate oligosaccharides (AOSs), a type of biostimulant, are produced through enzymatic or acid hydrolysis of alginate—a natural polysaccharide extracted from brown algae that consists of mannuronic acid and guluronic acid residues [13]. AOSs are biodegradable and have the advantages of being environmentally friendly [14]. Accumulating evidence has demonstrated the multifaceted physiological roles of AOSs, including the regulation of root and shoot morphogenesis [15,16,17,18], photosynthetic efficiency [19,20], and enhanced abiotic stress (drought, salinity, acid rain, and high temperature) tolerance [21,22,23]. Application of AOSs under normal temperatures significantly increased tissue N, P, and K concentrations in multiple crop species [24,25,26]. Therefore, it is interesting to investigate whether AOS can promote growth and nutrient acquisition in horticultural crops at suboptimal temperatures, as this could potentially reduce dependence on chemical fertilizers.
In this study, we employed seedling experiments to explore the combined effects of different concentrations of Hoagland nutrient solution and AOS on the growth and nutrient uptake of cucumber seedlings under suboptimal temperature stress. Results showed that AOS application enhanced root growth, root activities, N metabolism enzyme activities, and nutrient accumulation of cucumber seedlings in each concentration of nutrient solution under 15/8 °C temperatures (day/night). These findings provide theoretical support for improving nutrient absorption efficiency and mitigating the adverse effects of suboptimal temperatures on greenhouse vegetable production.

2. Materials and Methods

2.1. Experimental Materials

AOSs were purchased from HEHAI Biotech (Qingdao, China). The cucumber seeds of Cv. Jinchun 4 were used in this study. Seeds were soaked in water at 55 °C for 15 min. When the water cooled to room temperature, seeds were transferred into a constant-temperature incubator and germinated at a temperature of 28 °C for 24 h. Germinated seeds were sowed into 72 holes seedling-raising plates filled with a mixture of coir-coconut, vermiculite, and perlite (2:1:1, v:v:v). Seedlings were watered with 0.5 strength of Hoagland solution [27] and raised under natural temperature and light conditions in a solar greenhouse. Seedlings were then transplanted into pots containing coir-coconut when the first true leaves started to develop. After a 5-day rejuvenation period, the seedlings were transferred and acclimated in the climate chambers for 3 days under conditions of 25 ± 1 °C/18 ± 1 °C (day/night) with a 12 h photoperiod (500 ± 20 μmol·m−2·s−1).

2.2. Experimental Design

Suboptimal temperatures were set at 15 ± 1 °C during the day and 8 ± 1 °C at night, with a 12 h photoperiod (400 ± 20 μmol·m−2·s−1). Cucumber seedlings were treated with 0.5×, 1.0×, and 1.5× strength of Hoagland solution without AOS (N0.5, N1, and N1.5), or with 30 mg·L−1 AOS (A0.5, A1, and A1.5). Seedlings were irrigated every 3 days (100 mL per plant) and 5 times during the experiment. Sampling and measurements were conducted on day 18 after treatment. Each treatment consisted of 25 cucumber seedlings with three replicates.

2.3. Measurement of Growth Parameters

Plant height, stem thickness, leaf area, as well as fresh and dry weights of root, stem, and leaf were measured in this study. Plant height was defined as the height from the cotyledon node to the apex of the stem and determined with a ruler. Stem diameter was measured at the midpoint between the cotyledon and the first true leaf using a digital Vernier caliper. Leaves were photographed, and leaf area was calculated using LA-S plant leaf image analyzer software (Smart Lite Version, WSeen, Hangzhou, China). Seedling plants were separated into roots, stems, and leaves. The fresh mass of organs was weighed after being rinsed three times with distilled water and blotted dry with filter paper. Then, samples were first heated at 105 °C for 15 min, followed by drying at 80 °C until constant mass for dry weight measurement.

2.4. Measurement of Photosynthetic Characteristics

The net photosynthetic rate (Pn) of the second fully expanded leaf from top was measured with Li-6800XT photosynthesis system (LI-COR Biosciences, Lincoln, NE, USA) under a photosynthetic photon flux density (PPFD) of 400 μmol·m−2·s−1.

Measurement of Root Morphology

Roots were carefully washed, scanned using an Epson Expression V850 Pro scanner (Epson, Suwa, Nagano, Japan), and analyzed with WinRHIZO root analysis software version 2.0.3 (Regent Instruments, Québec, QC, Canada) to quantify root tip number, root average diameter, total root length, root fork count, root surface area, and root volume.

2.5. Macronutrient Content and Accumulation Analysis

The oven-dried roots, stems, and leaves were ground to pass through a 100-mesh sieve, then digested with H2SO4-H2O2 and analyzed for total nitrogen (N), phosphorus (P), and potassium (K) content following the method of Thomas et al. [28]. N content was determined using an automated Kjeldahl analyzer (KN520, Alva Instrument, Jinan, China). P content was quantified by molybdenum blue colorimetry. K content was measured by flame atomic absorption spectrometry (NovAA 800D, Analytik Jena AG, Jena, Germany).
Nutrient accumulation = nutrient content × dry biomass weight;
Nutrient distribution rate (%) = nutrient accumulation per organ/total plant nutrient accumulation × 100%.

2.6. Biochemical Analysis Assays

Leaf samples were collected from the second fully expanded, healthy leaf without pest or disease damage. Root samples were collected from the primary root zone near the root tip. Chloroplast pigment was extracted with 95% ethanol and quantified spectrophotometrically (UV-2600, Shimadzu, Kyoto, Japan), following the method described by Sumanta et al. [29]. Root activity was assayed using the triphenyltetrazolium chloride (TTC) method as previously described [30]. Briefly, root samples were vacuum-infiltrated and incubated in a TTC reaction mixture, then extracted in 95% ethanol, and finally quantified spectrophotometrically. Root activity was represented by dehydrogenase activity. Samples for enzyme activity analyzing were rapidly frozen in liquid nitrogen and then stored at −80 °C. The activities of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) were determined using commercial assay kits (NR: BC0080; GS: BC0915; GOGAT: BC0070; GDH: BC0915; Solarbio, Beijing, China) following the manufacturers’ protocols and established methods in previous study [31]. The key steps involve: (1) enzyme extraction in extraction buffer, (2) centrifugation, (3) supernatant collection, and (4) absorbance measurement after reaction mixture addition.

2.7. Data Analysis

Experimental data were processed using Microsoft Excel 2021 MSO (Microsoft Corporation, Redmond, WA, USA) and visualized with GraphPad Prism 8.0 (GraphPad Software Inc., San Diego, CA, USA). Correlation analysis was performed, and results were visualized as a heat map generated with ChiPlot (https://www.chiplot.online/, accessed on 7 April 2025). Statistical analysis was performed with the Data Processing System (DPS) version 17.0 (Refine, Hangzhou, China). Comparison between groups was made by two-way ANOVA, followed by Duncan’s new multiple range test for multiple comparisons (p < 0.05). Data were presented as mean ± SD (n = 3).

3. Results

3.1. Effects of Different Nutrient Solution Concentrations with AOS on the Growth of Cucumber Seedlings Under Suboptimal Temperatures

Growth parameters were quantified to evaluate the growth response of cucumber seedlings to elevated nutrient supply with or without AOS under suboptimal temperature conditions. Compared to N0.5, only a limited number of measured parameters showed significant increases in N1.0 and N1.5 (Figure 1). When maintaining equivalent nutrient supply levels, AOS application improved all examined parameters to varying degrees compared to those that were non-AOS treated. Two-way ANOVA revealed that nutrient level (NL) alone significantly influenced only plant height, stem thickness, leaf area, and stem fresh weight (Figure 1). Moreover, AOS and the interaction between NL and AOS (NL × AOS) significantly affected all nine plant growth parameters measured.
As shown in Figure 2, elevated nutrient supply increased the measured root architecture parameters, consistent with its effects on plant growth traits. Moreover, AOS application significantly improved these parameters under suboptimal temperature conditions compared to non-AOS treatments. Two-way ANOVA revealed that both the AOS and the NL × AOS interaction significantly influenced all six root traits, while NL alone significantly affected root tip numbers, total root length, root forks, and root surface area (Figure 2).

3.2. Effects of AOS and Different Nutrient Solution Levels on the Chlorophyll Content and Pn of Cucumber Seedlings Under Suboptimal Temperatures

The contents of chlorophyll a (Chl. a), chlorophyll b (Chl. b), and Pn all showed increasing trends with elevated nutrient levels, particularly under AOS treatments, where the enhancement was more pronounced (Figure 3). Two-way ANOVA demonstrated that both AOS and the NL × AOS interaction had significant effects on the contents of Chl. a, Chl. b, and Pn, while NL significantly affected Chl. a content and Pn.

3.3. Effects of AOS and Different Nutrient Solution Levels on the Root Activity of Cucumber Seedlings Under Suboptimal Temperatures

Plants in A0.5 exhibited significantly higher root activity compared to those in N0.5, N1, and N1.5, while A1.5 provided an additional 19.97% enhancement compared to A0.5 (Figure 4). Statistical analysis revealed that root activity was significantly influenced by NL, AOS, and NL × AOS.

3.4. Effects of AOS and Different Nutrient Solution Levels on the N Metabolism Enzymes Activities in Cucumber Seedlings Under Suboptimal Temperatures

The results in Figure 5 showed that while elevated nutrient supply alone exerts only marginal effects on N metabolism enzyme activities, AOS treatment significantly enhances these enzymatic activities in cucumber seedlings. Statistical analysis revealed significant effects of AOS and the NL × AOS interaction on all four N metabolism enzymes in both leaves and roots. However, NL significantly affected the activities of GDH in leaf, as well as GOGAT, GDH, and GS in root.

3.5. Effects of AOS and Different Nutrient Solution Levels on N Content, Accumulation, and Distribution in Different Cucumber Organs Under Suboptimal Temperatures

As shown in Figure 6a,b, the N1.5 treatment significantly increased N content and accumulation in all examined tissues (root, stem, leaf) compared to N0.5, i.e., increasing nutrient supply had a positive effect on N content and accumulation in the roots, stems, and leaves of cucumber seedlings under suboptimal temperature conditions. Furthermore, AOS treatments amplified this effect, since the AOS treatments consistently resulted in higher N content and accumulation compared to non-AOS treatments. Two-way ANOVA analysis showed that NL, AOS, and NL × AOS all significantly affected tissue N content and plant N accumulation.
Neither NL and AOS, nor NL × AOS significantly affected distribution of N in cucumber seedlings (Figure 6c). The N distribution ratio in cucumber roots decreased slightly with increasing nutrient solution concentration, while leaf N distribution increased slightly without significance. However, AOS significantly enhanced N allocation to leaves, indicating that AOS application promoted N transport from roots to shoots, enhancing overall plant growth.

3.6. Correlation Analysis Between Different Traits

As shown in the correlation heat map (Figure 7), N content in root, stem, and leaf tissues exhibited significant positive correlations with root morphology indices, root activity, and N metabolism enzyme activities.

4. Discussion

Uptake rates of most essential mineral ions are regulated by specific demand-driven mechanisms that dynamically adjust nutrient acquisition to meet physiological requirements across growth rate [32]. Under suboptimal temperature conditions, plant growth is inhibited and the NO3− influx rate decreases, while exogenous application of 24-epibrassinolide and gibberellin (GA) promotes plant growth and enhances both NO3− influx rate and N accumulation [2,5]. In our study, elevated nutrient solution concentrations have positive effects on N, P, and K content and accumulation in all examined tissues (roots, stems, and leaves) of cucumber seedlings, meanwhile, the co-application of AOS further enhanced these nutrient parameters compared to nutrient elevation alone (Figure 6, Figures S1 and S2). This may be attributed to the suppressed growth and consequently lower nutrient demand of cucumber seedlings under suboptimal temperature stress, where increased nutrient supply shows limited efficacy in enhancing uptake. In contrast, AOS application can stimulate plant growth (Figure 1) and enhance nutrient demand in cucumber seedlings, which may improve nutrients acquisition through coordinated modulation of uptake systems and root growth [33,34].
Root architecture is of great importance for the ability of crops to absorb mineral nutrients [35]. Additionally, the modification of root architecture represents an effective strategy to enhance nutrient use efficiency and crop yield [36]. Suboptimal temperatures inhibited root growth in cucumbers by downregulating GA 20-oxidase and GA 3-oxidase genes (involved in active GA biosynthesis) while upregulating GA 2-oxidase genes (responsible for GA deactivation), ultimately decreasing bioactive GA4 levels [2]. Previous studies indicated that AOS could elevate the levels of auxins and gibberellins in roots, stimulate cell division, and promote root elongation, thereby expanding the root absorption area and enhancing N uptake [17,37,38]. In this study, the combined application of varying nutrient solution concentrations and AOS enhanced cucumber root architecture, significantly increasing root tip number, average root diameter, total root length, root volume, and root surface area. Additionally, these root morphological characteristics exhibited strong positive correlations with organ-level N content (Figure 7), which align with established theories connecting root system architecture to nutrient uptake capacity [36,39]. Root activity is closely correlated with mineral nutrient uptake [3,40]. Previous studies have reported that AOS increased not only the root absorption area but also root activity in Chinese cabbage [18]. Our results also demonstrate that AOS, nutrient solution, and their synergistic interaction significantly enhanced root activity in cucumber seedlings (Figure 4). These findings suggest that AOS improves root vitality and architecture to facilitate more efficient nutrient uptake, thereby promoting plant growth under suboptimal temperature conditions.
Crop N use efficiency (NUE) is governed by four key physiological processes: uptake, transport, assimilation, and remobilization. The assimilation phase involves several critical enzymes, including NR, GS, GOGAT, and GDH [41]. Among these, NR initiates inorganic N utilization, while the GS/GOGAT cycle drives the conversion of inorganic N to organic forms, ultimately determining NUE. Genetic evidence underscores the functional importance of these enzymes in NUE [41]. In Arabidopsis, the nia1 nia2 double mutant retains merely 0.5% of WT NR activity and exhibits severe growth defects under nitrate supply [42]. Similarly, the knockdown of OsNR2 in rice significantly reduces grain yield [43]. GS and GOGAT encoding genes in roots are transcriptionally activated by NO3− supply [44,45,46]. The Arabidopsis gdh1 mutant shows impaired growth when supplemented with inorganic N [47]. Increased N metabolism enzyme activities facilitate rapid N assimilation, promoting growth and development [48]. The application of chitosan and chitosan oligosaccharides significantly enhanced activities of NR, GS, and GOGAT, which enables plants to efficiently convert nitrite into amino acids, facilitating N uptake [49]. Moreover, Kchikich et al. showed that seaweed extract significantly increased the GS and GDH activities in leaves, and promoted the effective absorption and assimilation of N in sorghum plants under cadmium stress [50]. Low-molecular-weight sodium alginate fragments produced by radiation degradation were also reported to enhance N metabolic enzyme activities in various crop species [16,19,51]. Studies by Zhang et al. confirmed that AOS stimulates NR enzymatic activity via coordinated gene expression induction and post-transcriptional control mechanisms in wheat roots [18]. They also reported that the Ca2+ metabolism inhibitors attenuated the promoting effects of AOS on NR and GS activities, as well as total N concentration in flowering Chinese cabbage, which suggested Ca2+ signaling participates in mediating AOS-triggered N metabolic regulation [24]. In this study, AOS combined with nutrient solutions significantly enhanced NR, GOGAT, GDH, and GS activities in plants, and showing a positive correlation with stem N content.

5. Conclusions

Under suboptimal temperature conditions, increasing nutrient input promoted cucumber seedling growth. However, supplementing with AOS further enhanced root architecture, root activity, and N metabolism enzyme activities, resulting in superior growth promotion and nutrient uptake compared to raising nutrient input alone.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11050501/s1, Figure S1: Effects of AOS and different nutrient solution levels on P content, accumulation, and distribution in different cucumber organs under suboptimal temperature; Figure S2: Effects of AOS and different nutrient solution levels on K content, accumulation, and distribution in different cucumber organs under suboptimal temperature.

Author Contributions

Conceptualization, L.B. and Y.L. (Yaling Li); methodology, Y.L. (Yun Li), M.S. and Y.M.; investigation, X.G., K.F. and L.G.; data curation, X.G., Y.L. (Yun Li) and L.B.; writing—original draft preparation, X.G. and Y.Y.; writing—review and editing, L.B., Y.L. (Yun Li) and Y.L. (Yaling Li); funding acquisition, L.H. and C.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Shanxi Province Key R&D Plan (202102140601013, 202302010101003).

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
AOSAlginate oligosaccharide
NNitrogen
PPhosphorus
KPotassium
NRNitrate reductase
GOGATGlutamate synthase
GSGlutamine synthetase
GDHGlutamate dehydrogenase
NLNutrient level
NCL-RN content in root
NCL-SN content in stem
NCL-LN content in leaf
Chl. aChlorophyll a content
Chl. bChlorophyll b content
PnNet photosynthetic rate
RTNRoot tip number
RADRoot average diameter
RLTotal root length
RFRoot forks
RSARoot surface area
RVRoot volume
RARoot activity
NR-RNitrate reductase activity in root
GOGAT-RGlutamate synthase activity in root
GDH-RGlutamate dehydrogenase activity in root
GS-RGlutamine synthetase in root.
NR-LNitrate reductase activity in leaf
GOGAT-LGlutamate synthase activity in leaf
GDH-LGlutamate dehydrogenase activity in leaf
GS-LGlutamine synthetase in leaf
NUEN use efficiency
GAGibberellin

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Figure 1. Effects of AOS and different nutrient solution levels on the growth of cucumber seedlings under suboptimal temperature. Bar = 5 cm. (a) The appearance of cucumber seedlings; (b) plant height; (c) stem thickness; (d) leaf area; (e) fresh weight of root; (f) fresh weight of stem; (g) fresh weight of leaf; (h) dry weight of root; (i) dry weight of stem; (j) dry weight of leaf. Different lowercase letters indicate significant differences at 0.05 level. The same is shown below. NS: not significant. * indicate the statistical significance at 0.05.
Figure 1. Effects of AOS and different nutrient solution levels on the growth of cucumber seedlings under suboptimal temperature. Bar = 5 cm. (a) The appearance of cucumber seedlings; (b) plant height; (c) stem thickness; (d) leaf area; (e) fresh weight of root; (f) fresh weight of stem; (g) fresh weight of leaf; (h) dry weight of root; (i) dry weight of stem; (j) dry weight of leaf. Different lowercase letters indicate significant differences at 0.05 level. The same is shown below. NS: not significant. * indicate the statistical significance at 0.05.
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Figure 2. Effects of AOS and different nutrient solution levels on the root morphology of cucumber seedlings under suboptimal temperature. (a) Root tip number; (b) root average diameter; (c) total root length; (d) root fork count; (e) root surface area; (f) root volume. Different lowercase letters indicate significant differences at 0.05 level. NS: not significant. * indicate the statistical significance at 0.05.
Figure 2. Effects of AOS and different nutrient solution levels on the root morphology of cucumber seedlings under suboptimal temperature. (a) Root tip number; (b) root average diameter; (c) total root length; (d) root fork count; (e) root surface area; (f) root volume. Different lowercase letters indicate significant differences at 0.05 level. NS: not significant. * indicate the statistical significance at 0.05.
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Figure 3. Effects of AOS and different nutrient solution levels on chlorophyll content and net photosynthetic rate of cucumber seedlings under suboptimal temperature. (a) Chlorophyll a content; (b) chlorophyll b content; (c) net photosynthetic rate. Different lowercase letters indicate significant differences at 0.05 level. NS: not significant. * indicate the statistical significance at 0.05.
Figure 3. Effects of AOS and different nutrient solution levels on chlorophyll content and net photosynthetic rate of cucumber seedlings under suboptimal temperature. (a) Chlorophyll a content; (b) chlorophyll b content; (c) net photosynthetic rate. Different lowercase letters indicate significant differences at 0.05 level. NS: not significant. * indicate the statistical significance at 0.05.
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Figure 4. Effects of AOS and different nutrient solution levels on root activity of cucumber seedlings under suboptimal temperatures. Different lowercase letters indicate significant differences at 0.05 level. * indicate the statistical significance at 0.05.
Figure 4. Effects of AOS and different nutrient solution levels on root activity of cucumber seedlings under suboptimal temperatures. Different lowercase letters indicate significant differences at 0.05 level. * indicate the statistical significance at 0.05.
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Figure 5. Effects of AOS and different nutrient solution levels on the N metabolism enzymes activities in cucumber seedlings’ leaves and roots under suboptimal temperatures. (a) NR activity in leaf; (b) NR activity in root; (c) GS activity in leaf; (d) GS activity in root. (e)GOGAT activity in leaf; (f) GOGAT activity in root; (g) GDH activity in leaf; (h) GDH activity in root. Different lowercase letters indicate significant differences at 0.05 level. NS: not significant. * indicate the statistical significance at 0.05.
Figure 5. Effects of AOS and different nutrient solution levels on the N metabolism enzymes activities in cucumber seedlings’ leaves and roots under suboptimal temperatures. (a) NR activity in leaf; (b) NR activity in root; (c) GS activity in leaf; (d) GS activity in root. (e)GOGAT activity in leaf; (f) GOGAT activity in root; (g) GDH activity in leaf; (h) GDH activity in root. Different lowercase letters indicate significant differences at 0.05 level. NS: not significant. * indicate the statistical significance at 0.05.
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Figure 6. Effects of AOS and different nutrient solution levels on N content, accumulation, and distribution in different cucumber organs under suboptimal temperatures. (a) N content; (b) N accumulation; (c) N matter ratio. Different lowercase letters indicate significant differences at 0.05 level. * indicate the statistical significance at 0.05.
Figure 6. Effects of AOS and different nutrient solution levels on N content, accumulation, and distribution in different cucumber organs under suboptimal temperatures. (a) N content; (b) N accumulation; (c) N matter ratio. Different lowercase letters indicate significant differences at 0.05 level. * indicate the statistical significance at 0.05.
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Figure 7. Correlation analysis between physiological and biochemical parameters of cucumber seedlings (n = 18). NCL-R, N content in root. NCL-S, N content in stem. NCL-L, N content in leaf. Chl. a, chlorophyll a content. Chl. b, chlorophyll b content. Pn, net photosynthetic rate. RTN, root tip number. RAD, root average diameter. RL, total root length. RF, root forks. RSA, root surface area. RV, root volume. RA, root activity. NR-R, nitrate reductase activity in root. GOGAT-R, glutamate synthase activity in root. GDH-R, glutamate dehydrogenase activity in root. GS-R, glutamine synthetase in root. NR-L, nitrate reductase activity in leaf. GOGAT-L, glutamate synthase activity in leaf. GDH-L, glutamate dehydrogenase activity in leaf. GS-L, glutamine synthetase in leaf. *, ** and *** indicate the statistical significance at 0.05, 0.01 and 0.001 levels, respectively.
Figure 7. Correlation analysis between physiological and biochemical parameters of cucumber seedlings (n = 18). NCL-R, N content in root. NCL-S, N content in stem. NCL-L, N content in leaf. Chl. a, chlorophyll a content. Chl. b, chlorophyll b content. Pn, net photosynthetic rate. RTN, root tip number. RAD, root average diameter. RL, total root length. RF, root forks. RSA, root surface area. RV, root volume. RA, root activity. NR-R, nitrate reductase activity in root. GOGAT-R, glutamate synthase activity in root. GDH-R, glutamate dehydrogenase activity in root. GS-R, glutamine synthetase in root. NR-L, nitrate reductase activity in leaf. GOGAT-L, glutamate synthase activity in leaf. GDH-L, glutamate dehydrogenase activity in leaf. GS-L, glutamine synthetase in leaf. *, ** and *** indicate the statistical significance at 0.05, 0.01 and 0.001 levels, respectively.
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MDPI and ACS Style

Guo, X.; Li, Y.; Fan, K.; Guo, L.; Yang, Y.; Cheng, C.; Hou, L.; Miao, Y.; Sun, M.; Li, Y.; et al. Alginate Oligosaccharide Promoted the Nutrient Uptake and Growth of Cucumber Seedlings Under Suboptimal Temperature Conditions. Horticulturae 2025, 11, 501. https://doi.org/10.3390/horticulturae11050501

AMA Style

Guo X, Li Y, Fan K, Guo L, Yang Y, Cheng C, Hou L, Miao Y, Sun M, Li Y, et al. Alginate Oligosaccharide Promoted the Nutrient Uptake and Growth of Cucumber Seedlings Under Suboptimal Temperature Conditions. Horticulturae. 2025; 11(5):501. https://doi.org/10.3390/horticulturae11050501

Chicago/Turabian Style

Guo, Xu, Yun Li, Kai Fan, Lingru Guo, Yongzhao Yang, Chunming Cheng, Leiping Hou, Yanxiu Miao, Meihua Sun, Yaling Li, and et al. 2025. "Alginate Oligosaccharide Promoted the Nutrient Uptake and Growth of Cucumber Seedlings Under Suboptimal Temperature Conditions" Horticulturae 11, no. 5: 501. https://doi.org/10.3390/horticulturae11050501

APA Style

Guo, X., Li, Y., Fan, K., Guo, L., Yang, Y., Cheng, C., Hou, L., Miao, Y., Sun, M., Li, Y., & Bai, L. (2025). Alginate Oligosaccharide Promoted the Nutrient Uptake and Growth of Cucumber Seedlings Under Suboptimal Temperature Conditions. Horticulturae, 11(5), 501. https://doi.org/10.3390/horticulturae11050501

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