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Influence of different chromium applications on vegetative growth and chemical constituents of Tilia cordata seedlings

The experimental trials were carried out during two successive seasons, 2018 and 2019 at green house of the National Research Centre, Cairo, Egypt. The purpose of this study is to investigate the influence of different chromium concentrations (0, 20, 40, 60 and 80 ppm) on vegetative growth and chemical constituents of Tilia cordata seedlings. Chromium (Cr) at low concentration (20) significantly increased all growth parameters (plant height, fresh and dry weight of leaves, stems and roots) as well as chlorophyll a, b, carotenoids, carbohydrates and nutrient elements in leaves, stems and roots. But chromium at high concentrations (40, 60 and 80 ppm) significantly decreased all growth characters. Additionally, the same results were obtained on carbohydrates, nitrogen, potassium percentage in leaves, stems and roots and pigment content in leaves. On the contrary, chromium contents in all plant organs increased by increasing (Cr) concentrations. It could be recommended to use chromium concentration at 20 ppm to induce the growth parameters and some chemical compositions of Tilia cordata.


Introduction
Tilia cordata originates in North America and belongs to the family Tiliacae Family. Its commonly known name is little leaf linden and it can grow up to 80 feet tall and spread to 50 feet wide. Compared to other linden trees, this tree grows at a slower rate, but it is of a great dense of oval to pyramidial crown that cast deep shade. As a prolific bloomer, Tilia cordata gives small flowers of fragrant smell that show in late June and into July, the flowers; fragrance attracts a lot of bees and the dried flowers remain for a long time on the tree. The tree can grow in the sun or in partial shade, it can grow in moisty alkaline soil, but it is not tolerant to drought. The fast rate growth and deep dense shade of this tree made it is favorite among communities, but it is road-salt intolerant. Linden possesses a clear white wood that is soft and can be used in making inexpensive drawer sides.
In agricultural economic crops, the toxicity of heavy metals on plants poses a challenge to scientists concerned with the quality and yield of crop production (Bishehkolaei et al., 2011). Heavy metals harm the efficiency of farming and endangers animals and plants' health (Mudgal et al., 2010). Chromium (Cr) is detected in all living forms and is mostly known as an essential element for humans and animals (Panda and Choudhury, 2005;Bulk et al., 2007). However, sufficient evidence of its essentiality for the growth of plants is lacking (Zayed and Terry, 2003). Chromium contamination of the environment, nowadays, is a he concern; its valence state affects its toxicity to plants since Cr (VI) is highly toxic and more mobile than Cr (III) (Gupta, et al., 2009).Consumption is how Cr enters the food chain of plant material. It was found that a high dosage of Cr can be harmful to vegetation (Faisal and Hasanin, 2005;Gbaruko and Friday, 2007).Biological parameters of plants are found to be adversely affected by the increase in Cr concentration and it can lead to vegetation loss and even barren lands (Dube et al., 2003). Cr is just one of many harmful heavy metals that can cause serious environmental contamination in soil, ground water and sediments. At rates of 0.5 to 5.0 mgL -1 in nutrient solution, Cr is toxic, but it stimulates growth at lower rates (Kumarrai and Kumar, 2010). Cr phytotoxicity symptoms include seed germination and/or early germination seedling development inhibition, root growth reduction, leaf cholorosis and biomass depression (Sharma et al., 1995). Chromium is reported to have an effect on growth of plants, content of pigments, water balance, and Middle East J. Appl. Sci., 10(4): 780-784, 2020EISSN: 2706-7947 ISSN: 2077-4613 DOI: 10.36632/mejas/2020 initial lipid peroxidation which causes inoxidative damage to the plants (Bonet et al., 1991). Chromium was shown to have a noticeable effect on plants metabolism such as that of Hordeum vulgarae (Ali et al,2004), Citrullus (Dube et al., 2003), Cauliflower (Chattajee and Chatterjee, 2001) and Brassica Juncea (Jan et al. 2010).With these aspects in view, this investigation is carried out aiming to study the effect of various concentrations of chromium on the growth and chemical constituents of Tilia corodata.

Materials and Methods
The experiment was carried out at the greenhouse of the National Research Centre during two successive seasons of 2018 and 2019 to investigate the response of Tilia cordata seedlings grown under polluted condition with Chromium (Cr) metal. The soil of the experimental site was sand of the following characteristics 75.93% sand, 4.35%silt, 19.72% clay, PH 7.71, EC 0.71 dSm -1 , CaCO2 2.3%, OM 1.58%, Ca 2.8% Mg 0.1%, Na 2.2%, K 1.56%, Cl 2.5%, So4 2.8 meqL -1 .
Plant materials and procedure: One year seedlings of Talia cordata were obtained from nursery of forestry Department Horticulture Research Institute, Agriculture Research Centre, the seedlings were planted on the third week of March during the two seasons, as one seedling/pot 30 Cm in diameter filed with ten Kg soil, the average height of the seedling was (20-25cm). The experiments were set in completely randomized design with 5 replicates the treatments used as follows: five chromium levels (0, 20, 40, 60 and 80 ppm). Chromium as potassium chromate K2CrO4 were used after dissolving in distilled water and added as surface irrigation depending on the field capacity. Irrigation regime began after 30 days from transplanting and repeated twice every week till the end of the season (25 th November). The available commercially fertilizer used through this experimental NPK was kristalon (N: P: K) produced phayzon company, Holand. The used rate of fertilizer was 5.0 gm per pot in four doses. The plants were fertilized after 4,8,16 and 20 week. The following data were recorded plant height (cm ),fresh and dry weigh of leaves , stems and roots (g) .The following chemical analysis was determined , chlorophyll a ,b and carotenoids content were determined according to Saric et al ., (1976) . Total carbohydrates percentage was determined according to the method by Herbert et al.,(1971 ).Nitrogen and potassium were determined according to the method described by Cottenie et al .,(1982). Chromium was determined by Atomic Absorption Spectrophotometer Perkin-Elmer Model2380 following the method described by Chapman and Pratt (1961).The physical and chemical properties of the soil were determined according to Black et al. (1982). Obtained results were subjected to statistical analysis of variance according to the method described by Snedecor and Cochran (1982) and the combined analysis of the two seasons was calculated according to the method of Steel and Torrie (1982).
Results and Discussion 1. Vegetative growth: The growth parameters of Tilia cordata as affected by chromium treatments are demonstrated in Table (1): Generally, all growth parameters significantly increased by treating plants with (Cr) at 20 ppm compared with the control. The increments were (6.50%, 33.88%, 15.30% and 10.12 % for plant height, fresh weight of leaves, stems and roots , respectively. and (35.80 % ,16.95%, and 14.78% )for leaves, stems and root dry weight, respectively, in comparison with the control. The lowest values of plant height, fresh weight of leaves, stems and roots and dry weight of leaves, stems and roots were obtained from the plants treated with the maximum concentration of chromium (80 ppm). Numerically, the previous characters decreased by (13.15, 31.38, 55.70, 36.58, 34.03, 58.13and 41.08 %, respectively,) as a result of treatment with chromium at 80 ppm compared with the control. Unfavorable effects of Cr on the height of plant and the growth of shoot were shown by Rout et al., (1997). The transport of Cr to the aerial part of the plant could be directly affecting the shoots ' metabolism which in turn affects the plant height of causes its reduction. Phototoxic symptoms in plant cells can occur because of exposure at micro molar orange of Cr which can cause prevention of germination of seed, degradation of pigments status, balance of nutrients and antioxidant enzymes (Panda and Khan, 2003). Our results were corroborated with the finding of some researches, Rehana et al., (2012) and Nagarajan and Sankar (2014).
Pigments content (mg/g F.W.): The data obtained in Table (2) reported that in leaves chlorophyll (a), (b) and carotenoids increased by Cr at 20 ppm as compared to the control plants. The increments were (1.53%) chlorophyll (a), (9.34%) chlorophyll (b) and (4.27%) carotenoids compared with the control plants. On the other hand ,chlorophyll (a),(b) and carotenoids decreased by increasing other Cr concentrations .Chlorophyll content's decrement could be a result of interaction of enzymes that take part in the chlorophyll biosynthetic pathway which could also be a part of the general decrement in the content of chlorophyll in most plants under chromium stress (Shanker et al ., 2005).  Table (3) indicated That Chromium at 20 ppm increased all macro elements in all plants organs ( leaves, stems and roots ) of Tilia cordata plants .On the contrary, plants treated with chromium at 40,60 and 80 ppm decreased nitrogen percentage in leaves, stem and roots compared with the control . The reductions were (5.48, 30.14 and 45.21 % ,respectively,) in leaves, (13.11, 31.97 and 50.82%,respectively,) in stems and (11.48, 25.00 and 45.69%,respectively,) in roots in comparison with the control .The reduction in nitrogen content under chromium concentrations may be due to heavy metals disturbing the process of nitrogen metabolism (Dube et al., 2003).
In addition, It is obvious from the data that potassium percentage was markedly decreased in leaves, stems and roots when the plants were treated with the following concentrations of chromium 40 ppm giving (25.49, 1.18 and 6.45%, respectively, ) 60 ppm giving (29.41, 8.24 and 6.45% ,respectively, ) and 80 ppm giving (45.10, 41.18 and 13.98 % ,respectively, ) compared with control plants. Chromium at 20 ppm treatment gave the highest percentage of potassium (66.67%) in leaves, (2.35. %) in stems and (16.13 %) in roots compared with the control plants and other Cr treatments.

Conclusion
It could be recommended that using Tilia cordata as phytoremedation plants is suitable in soil polluted with chromium especially the concentration of 20 ppm. .