Biochemical responses and air pollution tolerance of philodendron scandens to Nano urea under different potting media

Introduction

Rapid urbanization and industrial growth have resulted in elevated levels of air pollutants such as sulfur dioxide (SO₂), nitrogen oxides (NOₓ) and particulate matter, which adversely affect plant health and urban environmental quality (Prajapati and Tripathi, 2008; Rai et al., 2013) [19,20] . In this context, ornamental foliage plants play a dual role by enhancing aesthetic value and mitigating air pollution through absorption, adsorption and accumulation of pollutants on leaf surfaces (Escobedo et al., 2011) [8] . The ability of plants to tolerate polluted environments is commonly assessed using the Air Pollution Tolerance Index (APTI), which integrates key biochemical and physiological parameters such as relative water content, leaf pH, total chlorophyll and ascorbic acid content (Singh and Rao, 1983; Ogunkunle et al., 2015) [25,16] . Plants with higher APTI values are considered more suitable for urban and vertical landscaping. Nitrogen nutrition is a major determinant of plant growth, chlorophyll synthesis, water relations and stress tolerance. Conventional nitrogen fertilizers often exhibit low nitrogen use efficiency, leading to nutrient losses and environmental contamination (Peng et al., 2007) [18] . Recently, nano urea has gained attention as an efficient nitrogen source due to its controlled release, higher absorption efficiency and reduced losses, resulting in improved chlorophyll content and physiological performance (Bondada et al., 2003; Abdel-Salam, 2018) [4,1] . However, studies evaluating the role of nano urea on biochemical traits linked to pollution tolerance in ornamental foliage plants are limited. Potting media composition also significantly influences plant performance by affecting moisture retention, aeration and nutrient availability. Organic amendments such as cocopeat and farmyard manure (FYM) are known to improve substrate properties and support better biochemical and physiological responses in container-grown ornamentals (Rameshkumar et al., 2018; Swami et al., 2018) [22,26] . Despite increasing interest in pollution-tolerant ornamental plants for urban and vertical landscapes, limited information is available on the combined influence of nano urea nutrition and potting media composition on biochemical attributes and air pollution tolerance of foliage plants. Philodendron scandens, a widely used ornamental species, has received little scientific attention with respect to its response to nano urea application and its potential for pollution mitigation based on APTI parameters. In view of the above, the present study was undertaken to standardize nano urea levels and potting media composition and to evaluate their effects on biochemical parameters and Air Pollution Tolerance Index of Philodendron scandens, with the objective of identifying suitable nutrient and media combinations for enhancing its performance and suitability for urban and vertical landscaping.

Materials and methods

The experiment was conducted in a shade net at the Floriculture block of College of Horticulture, Mojerla, Wanaparthy, situated at an altitude of 347.3 m above mean sea level on 78 ̊ 29 ̊ East longitude and 17 ̊ 19 ̊ North latitude. The experiment was conducted in Factorial Randomized Block Design with three replications and two factors with Factor 1 consisting of six levels of Nano urea (N 0 -Without spray of Nano Urea, N 1 -Conventional urea (2 g L -1 ), N 2 -0.5 ml L -1 , N 3 -1.0 ml L -1 , N 4 -1.5 ml L -1 , N 5 -2.0 ml L -1 ) and Factor 2 comprising of four levels of potting media (M 1 -Red earth, M 2 -Redearth +Cocopeat (1:1), M 3 -Red earth + Cocopeat + FYM (1:1:1), M 4 -Redearth + Cocopeat + FYM (2:1:1)). First spraying was done at 35 days after planting. Other sprays were applied at every 15-day interval for three months. A total of 6 sprays were carried out. Biochemical parameters, namely relative water content (RWC), total chlorophyll content, ascorbic acid content and leaf pH, were estimated using fully expanded leaves collected from the second or third node from the top of the shoot of all plants at 125 days after planting. Quality parameters, including leaf colour and Air Pollution Tolerance Index (APTI), were also assessed at 125 days after planting.

Relative water content (RWC)

Leaf samples were immediately weighed to record fresh weight (W 1 ) and immersed in distilled water for 2 hrs, blotted with filter paper (Whatman No. 1, Sigma Aldrich), and weighed again to measure turgid weight (W 2 ). Afterwards, leaves were placed in the oven at 70 °C for 48 hrs and reweighed to record the dry weight (W 3 ). RWCs were calculated using the following formula (Wveatherle 1950) [29] .

Where, W 1 = fresh weight of the leaf, W 2 = turgid weight of the leaf, W 3 = dry weight of the leaf

Chlorophyll content

Estimation of chlorophyll content in leaves was carried out by the acetone extraction method (Arnon 1949). Each collected leaf sample was chopped finely and 100mg was collected separately from each chopped leaf sample. These samples were submerged in volumetric flasks with 25 ml of 80% acetone solution in a refrigerator for 2 days. After 2 days, the total leaf extracts were absorbed into the acetone by leaving the pale coloured tissues of the chopped samples. Then, these pale coloured tissues were removed and the remaining solutions were collected separately from each volumetric flask. By using these collected samples, absorbance was taken at 663.2 nm and 646.8 nm using a spectrophotometer. Calculations were done using the formula.

Chlorophyll 'a' (mg/g Fresh Wt.) (12.7 Ascorbic acid Estimation of ascorbic acid has done by the titration method, i.e., by using the '2, 6 Dichlorophenol indophenol Titration method' (Sadasivam et al., 1992; AOAC, 1990) [23,2] .

Leaf pH

The pH of leaf samples was measured at 20 °C using a pH meter (pH Tutor, EUTECH Instruments) with a combined glass electrode fitted. Before the experiment, the pH meter was standardized using standard buffers of pH 4.0 and 9.0 at 20 °C. Here, 2.5 g of fresh leaf sample was weighed with the help of an electronic weighing balance, and the sample was finely ground by using a mortar and pestle. 10 ml of distilled water was added to this ground sample, left for 15min and filtered to measure pH with an electric probe.  Quality parameters: Quality parameters like Leaf colour and Air Pollution Tolerance Index (APTI) were measured at 125 days after planting.

Leaf colour

A Hunter CIELAB colorimeter measured leaf colour (Hunter et al., 1987) [11] . CIELAB, developed by the International Commission on Illumination (CIE) or Hunter Lab, coordinates L*, a*, and b*, which have been successfully used for the description of plant colours (Jia et al. (2008) [12] ; Osmani et al. (2009)) [17] . There are three parameters or axes measured with this colorimeter: Colour brightness (L*) and Colour coordinates (a* and b*). The L* axis represents "Lightness" and ranges from "0" to "100" and "0" means no lightness and indicates absolute black; otherwise, "100" indicates white colour. The colour coordinates "a*" and "b*" do not have a certain range of measurement but can be positive or negative. "a*" value represents the red-green axis, positive values are reddish, negative values are green, while 0 is neutral. 2nd colour coordinate "b*" represents the yellow-blue axis, positive values indicate yellow colour and negative values indicate blue colour (Devici et al., 2018) [6] .

Air Pollution Tolerance Index (APTI)

Estimation of different biochemical parameters, such as ascorbic acid, total chlorophyll content, relative water content, and leaf pH, was carried out according to standard procedures. APTI of samples was calculated by the following formula proposed by Singh and Rao (1983) [25] and expressed in numbers.

Where: A= Ascorbic acid contents in mg/g of leaves, T = Total chlorophyll in mg/g fresh weight, P = pH of leaf extract, R = Relative Water Content (%)

Results and Discussion

RWC (Relative Water Content, %) The mean data pertaining to RWC (Relative Water Content, %) in leaves as influenced by nano urea levels and media composition at 125 days after planting is presented in Table1 and depicted in Fig 1a,b. Among the different levels of nano urea, maximum Relative Water Content (92.17 %) of a leaf was recorded with nano urea spray N 5 (2 ml L -1 ), which is followed by N 4 (nano urea 1.5 ml L -1 ) (84.57 %), while minimum (72.05 %) Relative Water Content of a leaf was noticed in N 0 (No spray). Among different composition of potting media, maximum Relative Water Content of a leaf (80.37 %) was recorded in M 3 (Red Earth + Coco peat + FYM (1:1:1)) followed by M 4 (Red Earth +Coco peat + FYM (2:1:1)) (79.87 %) and M 2 (Red Earth + Coco peat (1:1)) (79.71 %) which were on par with each other whereas minimum (78.9 %) Relative Water Content of a leaf was recorded in M 1 (Red Earth). The interaction effect on the Relative Water Content of a leaf was found to be insignificant. The variation in relative water content (RWC) of leaves observed in the present study indicates a pronounced influence of nano urea application and potting media composition on plant water status. Higher RWC values recorded with increasing levels of nano urea suggest improved cellular hydration and water retention capacity in Philodendron scandens. The maximum RWC observed under nano urea spray at 2 ml L⁻¹ may be attributed to the role of nitrogen in enhancing leaf succulency and osmotic adjustment. Nitrogen is known to increase the accumulation of soluble proteins and osmolytes, which improve cell turgidity and water-holding capacity of leaf tissues. Similar findings were reported by Umnajkitikorn et al. (2021) [27] , who demonstrated that increased nitrogen availability significantly enhances leaf succulence and relative water content, thereby improving plant tolerance to environmental stress. The comparatively higher RWC recorded in organically enriched potting media containing coco peat and FYM could be due to improved moisture retention, porosity and nutrient availability. Coco peat enhances water-holding capacity, while FYM improves soil structure and microbial activity, collectively facilitating better root water uptake and sustained leaf hydration. Comparable observations were reported by Swami et al. (2018) [26] and Rameshkumar et al. (2019) [22] in foliage plants grown in organic substrate combinations. The absence of a significant interaction between nano urea levels and media composition suggests that each factor independently contributed to the enhancement of RWC. Overall, increased RWC under higher nano urea levels and improved media composition reflects better plant water relations, which is a key physiological attribute associated with enhanced stress tolerance and growth performance in ornamental foliage plants.

Total Chlorophyll content (mg g -1 ) Total Chlorophyll content (mg g -1 ) of leaves as influenced by nano urea levels and media composition at 125 days after planting is presented in Table 2 and depicted in Fig 2a,b. Among the different levels of nano urea, maximum Total Chlorophyll content (2.491 mg g -1 ) of a leaf was recorded with nano urea spray N 5 (2 ml L -1 ), followed by N 4 (Nano urea 1.5 ml L -1 ) (2.144 mg g -1 ) while minimum (0.998 mg g - 1 ) Total Chlorophyll content of a leaf was noticed in N 0 (No spray). Among different composition of potting media, maximum Total Chlorophyll content (mg g -1 ) was recorded in M 4 (Red Earth +Coco peat + FYM (2:1:1) (1.751 mg g -1 ) followed by M 3 (Red Earth + Coco peat + FYM (1:1:1) (1.716 mg g -1 ) and M 2 (Red Earth + Coco peat (1:1)) (1.688 mg g -1 ) which were on par with each other while minimum (1.593 mg g -1 ) Total Chlorophyll content was recorded in M 1 (Red Earth). Total chlorophyll content of leaves varied significantly in response to nano urea levels and potting media composition at 125 days after planting. Increasing levels of nano urea resulted in a progressive increase in chlorophyll content, indicating enhanced photosynthetic potential in Philodendron scandens. The highest total chlorophyll content was recorded with nano urea spray at 2 ml L⁻¹ (N 5 ), followed by 1.5 ml L⁻¹ (N 4 ), while the lowest chlorophyll content was observed in the control treatment without nano urea application. The increase in chlorophyll content under higher nano urea levels may be attributed to improved nitrogen use efficiency associated with nano-formulated fertilizers, which enhances nitrogen availability and uptake. Since nitrogen is a fundamental constituent of the chlorophyll molecule, adequate nitrogen supply directly influences chlorophyll biosynthesis and chloroplast development (Peng et al., 2007; Bondada et al., 2003; Hudson et al., 2007) [18,4,10] . With respect to potting media composition, media enriched with coco peat and FYM recorded higher chlorophyll content compared to red earth alone. Improved physical and chemical properties of these media, such as enhanced moisture retention, aeration, and nutrient availability, might have facilitated better nitrogen uptake and assimilation, thereby supporting chlorophyll synthesis. Similar observations have been reported by Abdel-Salam (2018) [1] in lettuce and El-Shawa et al. (2022) [7] in Philodendron, who documented significant increases in leaf chlorophyll content with improved nitrogen nutrition and growing media conditions. The non-significant interaction between nano urea levels and media composition indicates that both factors independently influenced chlorophyll accumulation. Overall, the enhanced chlorophyll content observed under higher nano urea application reflects improved photosynthetic efficiency and physiological vigor, contributing positively to growth performance and stress tolerance of Philodendron scandens.

Ascorbic acid content (mg g -1 ) of a leaf as influenced by nano urea levels and media composition at 125 days after planting is presented in Table 3 and depicted in Fig 3a,b. Among the different levels of nano urea, maximum (3.892 mg g -1 ) Ascorbic acid content of leaves was recorded with nano urea spray N 5 (2 ml L -1 ), followed by N 4 (Nano urea 1.5 ml L -1 ) (2.865 mg g -1 ), while minimum (0.811 mg g -1 ) Ascorbic acid content was noticed in N 0 (No spray). The composition of potting media and the interaction effect of nano urea levels with media composition on Ascorbic acid in the leaf was found to be insignificant. High and inadequate supply of nitrogen can decrease the Ascorbic acid content (Feyman et al., 1991; Lee et al., 2000) [9,14] . Chiesa et al. (2009) [5] reported that high N (150 kg ha -1 ) increased ascorbic acid content in lettuce. Variation in the accumulation of ascorbic acid content at different rates of N applications, altered with the findings of Mahlangu et al.

(2016) [15] . In this experiment application of nano urea increased the ascorbic acid, which might be due to the timely release and high nitrogen use efficiency of nano urea.

Leaf pH

Leaf pH as influenced by nano urea levels and media composition at 125 days after planting is presented in Table 4 and depicted in Fig 4a,b. Among the different levels of nano urea, maximum (5.43) Leaf pH was recorded with nano urea spray N 5 (2 ml L -1 ), followed by N 4 (Nano urea 1.5 ml L -1 ) (5.13) while minimum (4. The interaction effect for Leaf pH was found to be insignificant. Leaf pH is an important physiological parameter influencing the plant's tolerance to air pollutants, as it affects enzymatic activity, stomatal function, and pollutant neutralization capacity. In the present study, leaf pH increased progressively with increasing levels of nano urea, indicating improved physiological stability in Philodendron scandens.

The highest leaf pH recorded under nano urea spray at 2 ml L⁻¹ may be attributed to enhanced nitrogen availability, which promotes metabolic balance and reduces cellular acidity. Nitrogen nutrition is known to regulate organic acid metabolism and maintain ionic balance in leaf tissues, thereby resulting in comparatively higher leaf pH. Similar trends were reported by Prajapati and Tripathi (2008) [19] , who observed that plants receiving adequate nitrogen exhibited higher leaf pH and improved tolerance to atmospheric pollutants. With respect to potting media composition, media enriched with coco peat and FYM recorded higher leaf pH values compared to red earth alone.

The presence of organic components may have improved nutrient buffering capacity and reduced acidity in the rhizosphere, which in turn reflected in higher leaf pH.

Comparable observations were documented by Swami et al.

(2018) [26] , who reported improved physiological parameters, including leaf pH, in ornamental plants grown in organically amended substrates. The non-significant interaction between nano urea levels and media composition suggests that both factors independently influenced leaf pH. An increase in leaf pH is considered advantageous, as plants with relatively higher leaf pH possess greater neutralizing capacity against acidic air pollutants such as SO₂ and NO 2 . Therefore, the enhanced leaf pH observed under higher nano urea levels and improved media composition contributes positively to the overall air pollution tolerance of Philodendron scandens.

Leaf colour

The mean data pertaining to Leaf colour as influenced by nano urea levels and media composition at 125 days after planting is presented in Table 5. Among the different levels of nano urea application, highest values in terms of dark greenness (L*: 40. [28] and Umnajkitikorn et al. (2021) [27] , who demonstrated a strong positive relationship between nitrogen nutrition and leaf greenness indices in ornamental foliage plants.

In contrast, the lighter green colour observed in the control treatment reflects reduced chlorophyll concentration due to limited nitrogen availability, as indicated by higher L* values and positive a* values. Such changes in leaf colour are commonly associated with nitrogen deficiency and reduced photosynthetic efficiency. Potting media composition did not exert a significant influence on leaf colour parameters. However, media combinations containing coco peat and FYM (M 3 and M 4 ) exhibited relatively more negative a* values, suggesting improved greenness intensity, possibly due to better nutrient availability and moisture retention. These results indicate that while nano urea application played a dominant role in determining leaf colour, organically enriched media provided supportive conditions for chlorophyll development. Overall, the increase in leaf greenness under higher nano urea levels reflects enhanced chlorophyll content and improved physiological performance, which may contribute to greater photosynthetic capacity and stress tolerance in Philodendron scandens.

APTI (Air Pollution Tolerance Index)

The mean data pertaining to APTI (Air Pollution Tolerance Index) as influenced by nano urea levels and media composition at 125 days after planting is presented in Table 5 and depicted in Fig 5a,b. Among the different levels of nano urea, maximum (12.30) Air Pollution Tolerance Index was recorded with nano urea spray N 5 (2 ml L -1 ) followed by N 4 (Nano urea 1.5 ml L -1 ) (10.54) , N 3 (Nano urea 1 ml L - 1 ) (9.69) while minimum (7.63) Air Pollution Tolerance Index was noticed in N 0 (No spray). Among different composition of potting media, maximum Air Pollution Tolerance Index (9.74) was recorded in M 3 (Red Earth + Coco peat + FYM (1:1:1) and is on par with M 4 (Red Earth +Coco peat + FYM (2:1:1)) (9.67) which is followed by M 2 (Red Earth + Coco peat (1:1)) (9.56) while minimum (9.4) Air Pollution Tolerance Index was recorded in M 1 (Red Earth). The interaction effect of nano urea levels and media composition on APTI (Air Pollution Tolerance Index) was found to be insignificant. The variation in Air Pollution Tolerance Index (APTI) observed in the present study can be attributed to changes in key physiological and biochemical parameters such as leaf pH, relative water content (RWC), total chlorophyll and ascorbic acid content. Higher APTI values recorded with increased nano urea levels indicate improved physiological efficiency and stress tolerance in Philodendron scandens. The maximum APTI under nano urea spray at 2 ml L⁻¹ may be due to enhanced nitrogen availability, which plays a crucial role in chlorophyll biosynthesis and maintenance of photosynthetic activity. Increased chlorophyll content has been widely associated with improved tolerance to air pollutants, as it reflects the plant's ability to sustain photosynthesis under stress conditions. Similar observations were reported by Prajapati and Tripathi (2008) [19] , who noted that plants with higher chlorophyll concentration and balanced leaf pH exhibited greater air pollution tolerance. Relative water content is another important determinant of APTI, as higher RWC enables plants to maintain cellular turgidity and dilute absorbed pollutants, thereby minimizing their toxic effects. The improved APTI values under nano urea treatments suggest better water relations and membrane stability, which corroborates the findings of Rai et al. (2013) [21] and Kaur and Nagpal (2017) [13] in ornamental foliage plants exposed to polluted environments. Ascorbic acid acts as a major non-enzymatic antioxidant involved in scavenging reactive oxygen species generated due to air pollutants. The enhanced APTI in nano urea-treated plants may therefore be linked to increased ascorbic acid synthesis, strengthening the antioxidative defense mechanism. Comparable results were documented by Seyyednejad et al. (2011) [24] and Begum and Harikrishna (2010) [3] , who reported a strong positive relationship between ascorbic acid content and APTI. Potting media composition also influenced APTI, with organically enriched media containing coco peat and FYM recording higher values. Improved physical properties such as moisture retention, aeration and nutrient availability in these media might have favored better physiological performance, resulting in enhanced APTI. Similar responses have been reported in ornamental and landscape plants grown in organic or mixed substrates by Swami et al. (2018) [26] and Rameshkumar et al. (2019) [22] . The non-significant interaction between nano urea levels and media composition indicates that both factors independently contributed to the improvement of APTI without exhibiting interactive effects. Overall, the results confirm that enhancement of leaf pH, relative water content, total chlorophyll and ascorbic acid content leads to increased air pollution tolerance, supporting the suitability of Philodendron scandens as a pollution-tolerant ornamental species for urban landscapes.

Conclusion

The study revealed that nano urea application significantly enhanced physiological and biochemical parameters associated with air pollution tolerance in Philodendron scandens. Foliar application of nano urea at 2 ml L⁻¹ consistently resulted in higher relative water content, leaf pH, chlorophyll content and leaf greenness, leading to a marked improvement in Air Pollution Tolerance Index (APTI). These responses indicate improved nitrogen use efficiency, photosynthetic capacity and physiological stability.

Potting media containing coco peat and FYM performed better than red earth alone by supporting improved water retention and nutrient availability, though their effects were largely independent of nano urea levels. Overall, the results confirm that Philodendron scandens exhibits enhanced pollution tolerance under optimal nano urea nutrition, highlighting its suitability for urban and vertical landscaping applications.

References

1. Abdel-Salam MA. Effect of nitrogen fertilization on growth and chlorophyll content of lettuce (Lactuca sativa L.). Sci Hortic. 2018;235:239-246.
2. AOAC. Official methods of analysis of the Association of Official Analytical Chemists. 15th ed. Washington (DC): AOAC; 1990. p. 1058-1059.
3. Begum A, Harikrishna S. Evaluation of some tree species to absorb air pollutants in three industrial locations of South Bengaluru, India. E-J Chem. 2010;7(1):151-156.
4. Bondada BR, Oosterhuis DM, Norman RJ, Baker WH. Canopy photosynthesis, nitrogen use efficiency, and leaf senescence in cotton. Crop Sci. 2003;43:155-162.
5. Chiesa A, Mayorga I, Leon A. Quality of fresh cut lettuce (Lactuca sativa L.) as affected by lettuce genotype, nitrogen fertilization and crop season. Adv Hortic Sci. 2009;23:143-149.
6. Devici M, Ucar Y, Ozturk B. Determination of colour characteristics of plant leaves using CIELAB colour space. J Agric Sci. 2018;24(3):287-295.
7. El-Shawa GM, Alharbi K, AlKahtani M, AlHusnain L, Attia KA, Abdelaal K. Improving the quality and production of Philodendron plants using nanoparticles and humic acid. Horticulturae. 2022;8(8):678-686.
8. Escobedo FJ, Kroeger T, Wagner JE. Urban forests and pollution mitigation: Analyzing ecosystem services and disservices. Environ Pollut. 2011;159:2078-2087.
9. Feyman S, Toivonen PM, Perrin PW, Lin WC, Hall JW. Effect of nitrogen fertilization on yield, storage losses and chemical composition of winter cabbage. Can J Plant Sci. 1991;71:943-946.
10. Hudson D, Guevara DR, Hand AJ, Xu Z, Hao L, Chen X, et al. Rice cytokinin GATA transcription factor regulates chlorophyll biosynthesis and nitrogen metabolism. Plant Physiol. 2007;143:132-141.
11. Hunter RS, Harold RW. The measurement of appearance. New York: John Wiley & Sons; 1987.
12. Jia N, Shu QY, Wang LS, Du H, Xu YJ, Liu ZA. Analysis of petal anthocyanins to investigate coloration mechanism in herbaceous peony cultivars. Sci Hortic. 2008;117(2):167-173.
13. Kaur M, Nagpal AK. Evaluation of air pollution tolerance index and anticipated performance index of plants and trees in urban areas. Environ Sci Pollut Res. 2017;24:18879-18889.
14. Lee SK, Kader AA. Preharvest and postharvest factors influencing vitamin C content of horticultural crops. Postharvest Biol Technol. 2000;20:207-220.
15. Mahlangu RIS, Maboko MM, Sivakumar D, Soundy P, Jifon J. Lettuce (Lactuca sativa L.) growth, yield and quality response to nitrogen fertilization in a noncirculating hydroponic system. J Plant Nutr. 2016;39:1766-1775.
16. Ogunkunle CO, Suleiman LB, Oyedeji S, Awotoye OO, Fatoba PO. Assessing the air pollution tolerance index and anticipated performance index of some tree species for biomonitoring environmental health. Environ Sci Pollut Res. 2015;22:5549-5558.
17. Osmani SA, Halkjaer Hansen E, Malien-Aubert C, Olsen CE, Bak S, Lindberg Møller B. Effect of glucuronosylation on anthocyanin color stability. J Agric Food Chem. 2009;57(8):3149-3155.
18. Peng S, Buresh RJ, Huang J, Yang J, Zou Y, Zhong X, et al. Strategies for overcoming low agronomic nitrogen use efficiency in irrigated rice systems. Agron J. 2007;99:117-125.
19. Prajapati SK, Tripathi BD. Anticipated performance index of some tree species considered for green belt development in and around an industrial area. Ecol Eng. 2008;35:130-134.
20. Rai PK. Impacts of particulate matter pollution on plants: Implications for environmental biomonitoring. Ecotoxicol Environ Saf. 2016;129:120-136.
21. Rai PK, Panda LLS, Chutia BM, Singh MM. Comparative assessment of air pollution tolerance index (APTI) in the industrial area. Environ Monit Assess. 2013;185:4767-4781.
22. Rameshkumar S, Satheeshkumar P, Ramya S. Vertical garden systems: Role of ornamental plants in urban environmental improvement. J Environ Biol. 2018;39:1056-1062.
23. Sadasivam S, Manickam A. Biochemical methods for agricultural sciences. New Delhi: New Age International; 1992. p. 195-210.
24. Seyyednejad SM, Majdian K, Koochak H. Air pollution tolerance indices of some plants around industrial zones in Iran. Asian J Biol Sci. 2011;4(3):300-305.
25. Singh SK, Rao DN. Evaluation of plants for their tolerance to air pollution. In: Proceedings of the symposium on air pollution control. New Delhi: Indian Association for Air Pollution Control; 1983. p. 218224.
26. Swami A, Bhatt R, Joshi N. Effect of growing media on growth and quality of ornamental foliage plants. Int J Chem Stud. 2018;6(5):2451-2455.
27. Umnajkitikorn K, Seripong S, Rerkasem B. Nitrogen nutrition influences leaf succulence and water relations in ornamental plants. J Plant Nutr. 2021;44:1563-1574.
28. Wang Y, Chen Y, Li J. Relationship between leaf greenness, chlorophyll content and nitrogen status in ornamental plants. Photosynthetica. 2019;57:10461054.
29. Weatherley P. Studies in the water relations of the cotton plant. I. The field measurement of water deficits in leaves. New Phytol. 1950;49:81-97.