Effect of Silicon Amendment on Growth and Nitrogen Status of Common Landscaping Plants

B&#225; rbara Nogueira Souza Costa; Milagros Ninoska Munoz Salas; Kylie Gil; Amir Ali Khoddamzadeh

doi:10.4236/ajps.2024.158041

American Journal of Plant Sciences > Vol.15 No.8, August 2024

Effect of Silicon Amendment on Growth and Nitrogen Status of Common Landscaping Plants

Bárbara Nogueira Souza Costa, Milagros Ninoska Munoz Salas, Kylie Gil, Amir Ali Khoddamzadeh^*
Department of Earth and Environment, Institute of Environment, Florida International University, Miami, FL, USA.
DOI: 10.4236/ajps.2024.158041 PDF HTML XML 104 Downloads 476 Views

Abstract

Agriculture and natural vegetations in South Florida face with significant environmental threats such as heat and saltwater intrusion. This study aimed to investigate how silicon application could improve growth parameters and plant health of landscaping plants under extreme temperatures, influenced by global climate changes. Cocoplum (Chrysobalanus icaco), cabbage palm (Sabal palmetto), satinleaf (Chrysophyllum oliviforme), and wild coffee (Psychotria nervosa) plants received an initial slow-release fertilizer of 15 g/pot with an 8N-3P-9K composition. Silicon was applied as a 1% silicic acid solution, with concentrations ranging from 0 g/pot to 6 g/pot of 7.5 L. Evaluations were carried out every 30 days, continuing until 180 days after the treatment was completed. Phenotypic traits, including leaf count and plant height, were assessed alongside measurements from handheld optical non-destructive sensors. These measurements included the normalized difference vegetation index (NDVI), SPAD-502, and atLEAF chlorophyll meters. Application of 4 g/pot and 6 g/pot of silicon significantly improved NDVI values (0.78). Conversely, cocoplum plants exhibited greater plant height (79.6) at 0 g/pot silicon compared to other treatments. In wild coffee samplings, the control group showed the highest plant height and SPAD readings (93.49) compared to other treatments. Interestingly, the control treatment also demonstrated a superior atLEAF value as compared to other treatments, while the tallest samplings were observed with 6 g/pot of silicon (62.82) in cabbage palm plants. The findings indicate that silicon application positively influenced plant growth, particularly evident in cabbage palms. However, cocoplum and wild coffee exhibited a negative correlation between plant height and silicon concentrations.

Keywords

Silicon Application, Chlorophyll Content, Cocoplum, Cabbage Palm, Satinleaf, Wild Coffee

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Costa, B. , Salas, M. , Gil, K. and Khoddamzadeh, A. (2024) Effect of Silicon Amendment on Growth and Nitrogen Status of Common Landscaping Plants. American Journal of Plant Sciences, 15, 603-616. doi: 10.4236/ajps.2024.158041.

1. Introduction

Specialty crops play a significant role in American agriculture, covering a wide range of produce, such as culinary herbs, fruits, vegetables, spices, tree nuts, medicinal plants, nursery, floriculture, and horticulture crops. According to the 2023 data from the U.S. Department of Agriculture (USDA), farms specializing in these crops accounted for 10% of all farm operations [1]. In 2022, these operations generated approximately $84 billion in cash receipts, representing 15% of the total U.S. agricultural cash receipts [1].

In August 2023, global temperatures surpassed the 20th-century average by 1.25˚C, with projections indicating a further acceleration [2]. Florida has experienced a temperature increase of approximately 1˚C over the past several decades, with forecasts suggesting temperatures could exceed 83˚C within two decades [3]. A yearly sea level rise of approximately 1/8th of an inch as of 2023 exacerbates risks to local ecosystems and inhabitants [4].

Silicon (Si), though considered “quasi-essential”, is not indispensable for plant growth. Its accumulation in plants varies significantly between species, primarily due to differences in uptake mechanisms [5]. Additionally, silicon is known to enhance plant resistance to biotic and abiotic stresses and plays a crucial role in nutrient absorption. Studies have highlighted its beneficial impacts across various species and environmental conditions [6], leading to its recognition as a valuable element for plant growth and development [7]. Consequently, the exploration of silicon fertilization effects on crops has become a subject of interest for numerous researchers. Silicon exhibits significant potential in mitigating a broad spectrum of abiotic and biotic stresses [8]. Its application can stimulate plant growth and alleviate multiple stressors, including extreme temperatures, nutritional imbalances, and challenges associated with global climate change [9]. Furthermore, Si plays a pivotal role in enhancing plant resistance against insect pests, as well as fungal, bacterial, and viral diseases, which are major limiting factors impacting crop production worldwide [10].

Recent studies have underscored the advantages of Si application for various plant species across different conditions. Under normal circumstances, Si proves beneficial for plants, such as soybean (Glycine max L.) [11], poinsettia (Euphorbia pulcherrima) [12], and sugarcane (Saccharum officinarum) [13]. In conditions of abiotic stress, it benefits plants such as wheat (Triticum aestivum L.) [14], tomato (Solanum lycopersicum L.) [15], sugarcane (Saccharum officinarum L.) [16], and radish (Raphanus sativus L.) [17]. Moreover, in biotic stress conditions, Si aids banana (Musa paradisiaca L.) [18] and faba bean (Vicia faba L.) [19].

The application of Silicon showed the promise to enhance nutrient availability in the rhizosphere and facilitate root uptake through intricate mechanisms that warrant further elucidation [20]. Furthermore, Si application positively impacts various aspects of nitrogen (N) nutrition, encompassing uptake, assimilation, and remobilization [21]. Additionally, according to reference [22], Si augments nutrient acquisition by roots. Notably, the enhancement of nutrient uptake under suboptimal N supply facilitated by Si has been demonstrated in many plants such as cowpea (Vigna unguiculata) [23], maize (Zea mays) [24], and rice (Oryza sativa) [25].

Other studies indicated that Si significantly contributes to phosphorous (P) nutrition. Two primary mechanisms have been proposed for Si-mediated alleviation of P deficiency: 1) enhanced root uptake and 2) improved utilization of P within the tissues [20]. Increased P uptake following soil Si fertilization has been widely reported [26]-[28]. While the interaction between Si and K in plants has received less attention compared to its interactions with N and P, several studies have demonstrated that Si can influence tissue K concentrations, particularly under stressful conditions like salinity, drought, or excessive nitrogen [26] [29] [30].

The focus of this study revolves around several native Florida plants, namely cocoplum, cabbage palm, satin leaf, and wild coffee, which are extensively cultivated in numerous nurseries and utilized in landscaping across South Florida. However, the production of these species has encountered significant fluctuations attributable to the impacts of climate change. Consequently, it becomes imperative to explore novel approaches to enhance the growth and productivity of these plants. One potential avenue for such enhancement is the application of Si, which merits thorough investigation and consideration within the context of agricultural practices aimed at mitigating the effects of climate change on specialty crop production.

Although numerous studies are available on the benefits of Si application in various plants, limited information is available on the effects of Si on native plants of South Florida, necessitating further investigation. Studying these native plants, particularly those cultivated in nurseries for landscaping purposes, is crucial for developing more resilient plants that are better at nutrient absorption and resistant to pests, diseases, and adverse conditions—a vital consideration given the significant fluctuations in current climatic conditions. This study aimed to investigate how silicon application could improve growth parameters and plant health of landscaping plants under extreme temperatures, influenced by global climate changes.

2. Materials and Methods

The study was performed at the Organic Garden of the Florida International University (FIU), in Miami, Florida, USA. Five native plants were used: cocoplum, cabbage palm, satinleaf, and wild coffee. The plants were cultivated from May until November of 2022 in shade house condition, the plants were irrigated with city water at three times per week. The plants were fertilized with 15 g/pot initial slow-release fertilizer 8N-3P-9K (Harrell’s^®). The treatments were four concentrations (0 g/pot, 2 g/pot, 4 g/pot, and 6 g/pot) of silicon in the form of 1% silicic acid solution (SiO₂·XH₂O) (Pereira et al., 2010). The treatment was applied around the plant strain (drench). Evaluations were conducted at 0 days (one day before treatment) and at 30, 60, 90, 120, 150, and 180 days after treatment (DAT). The analyses performed include:

2.1. Growth Analysis

Every month, five plants per treatment were assessed for leaf count using a counter and for plant height in centimeters using a tape measure. Two branches from each plant, one larger and one smaller, were selected and measured, with the average of these measurements representing the plant’s height. Except for the satin leaf, the plant height of the main branch was measured.

2.2. Plant Health Assessment Using Handheld Optical Non-Destructive Sensor Technology

Chlorophyll content of individual plants was measured from five pots per treatment using a SPAD-502 chlorophyll meter (SPAD-502, Japan) and an atLEAF chlorophyll meter (Wilmington, DE). The GreenSeeker^TM was used to obtain the normalized difference vegetation index (NDVI). For NDVI measurements, the sensor was positioned 45 cm above the plant canopy. SPAD and atLEAF readings were taken from four mature leaves in the middle section of each plant, and the average values were calculated.

2.3. Statistical Analysis

The experiment was designed as a completely randomized trial with four treatments, each replicated five times using single-pot replications (one plant per pot), resulting in a total of 20 plants per species. Data were analyzed using analysis of variance (ANOVA), and the means were compared using Tukey’s test (p ≤ 0.05) with the SISVAR statistical program [31].

3. Results and Discussion

In this study, silicon fertilization rates were applied to enhance plant growth and mitigate multiple stresses, including extreme temperatures, nutritional imbalances, and climate-related challenges. This was assessed by monitoring growth parameters and using optical sensors to measure chlorophyll content.

Chlorophyll content, indicative of leaf greenness, serves as a proxy for plant photosynthetic activity and overall health [32]-[37]. Optical sensors were thus employed to gauge chlorophyll levels and assess plant vigor. The beneficial impact of silicon on photosynthesis may arise from its protective effects on chloroplasts, increased concentrations of photosynthetic pigments responsible for light absorption, or both [38].

The growth characteristics and sensor parameters did not show significant differences (p ≤ 0.05) for the interaction between silicon fertilization rate and evaluation period, represented by days after treatment (DAT), for all samplings. Consequently, these factors were evaluated separately.

3.1. Growth Characteristics, Relative Chlorophyll Content (SPAD and atLEAF), and Normalized Difference Vegetation Index (NDVI) of Satinleaf

Silicon fertilization rates were not significantly different in number of leaves, plant height, atLEAF, and SPAD. However, NDVI values were significantly different (p ≤ 0.05). Using 4 g/pot and 6 g/pot of silicon provided an increase in NDVI (0.78) compared to the control (0.72) in satinleaf plants (Table 1). 

Table 1. Number of leaves (NL), plant height, relative chlorophyll content (SPAD and atLEAF), and normalized difference vegetation index (NDVI) of satinleaf grown in different silicon fertilization rates.

Silicon fertilization rate (g/pot)	NL (unit)	Plant height (cm)	atLEAF	SPAD	NDVI
0	122 a	110.4 a	73.65 a	76.69 a	0.72 b
2	108 a	115.6 a	73.16 a	73.47 a	0.77 ab
4	118 a	112.3 a	73.37 a	74.18 a	0.78 a
6	126 a	113.1 a	73.31 a	75.69 a	0.78 a