INTRODUCTION
According to the genus Alternanthera and species sissoo, Sissoo spinach’s binomial name is Alternanthera sissoo. Other common names are ‘poor man’s spinach,’ Brazilian, Sambu, and Samba lettuce. Despite the growing consumption of vegetables among Malaysians, a recent National Health and Morbidity Survey by Institute for Public Health (2020) revealed that 94.9% of adults fail to consume the recommended five servings of fruits and vegetables daily. The increase in vegetable prices will likely cause them to be unreachable for people with low incomes (Rashid et al., 2020).
Still, Sissoo spinach is getting rapid interest as a homegrown vegetable, especially during the Covid-19 pandemic where everyone is stay-at- home (Ellya et al., 2021). In contrast, spinach is well-known as a food that benefits brain function because of its mineral richness, including folic acid, vitamins A, B6, and C, and antioxidants that can
assist in preventing damage to the brain’s neuronal and cognitive function. Hence, it is believed that the benefits of Brazilian spinach might be utilized to the fullest extent by the community and society.
However, leafy vegetables are sensitive to water scarcity, and water management for spinach is crucial as it could affect its yield (Fazilah et al., 2019). Scheelbeek et al. (2018) have stated that climate change is one of the many environmental changes seen and foreseen to be more serious major problems in the 21st century, resulting in huge threats to food security, agriculture globally, and nutrition. Special emphasis is placed on producing vegetables, which require more irrigation than other crops and whose yield components are strongly influenced by water stress (Pereira et al., 2019). Research by Reyes et al. (2018) reported that ten days of irrigation suspension reduced the moisture content of spinach (Spinacia olerácea L.) plants, while another study shows that water deficit ARTICLE INFO
Keywords:
Alternanthera sissoo Sissoo spinach Water stress Article History:
Received: June 19, 2023 Accepted: October 5, 2023
*) Corresponding author:
E-mail: tnsynajihah@unisza.edu.my
ABSTRACT
The rising popularity of the Sissoo spinach is growing in the vegetable industry along with the increase in its demand. However, water stress conditions may affect the plants’ growth, physiology, and water status. Hence, the research study aims to evaluate Sissoo spinach’s growth, physiological parameters, and water status once subjected to water deficit. Besides, it also focuses on determining the optimum water requirement for Sissoo spinach. There were four different water treatments consisting of 100% (well-watered), 75% (moderate water deficit), 50% (high water deficit), and 25% (severe water deficit) water treatments arranged in Randomized Complete Block Design (RCBD) with five replications in the greenhouse. The research findings show that the results are statistically significant for most parameters: plant height, number of leaves, chlorophyll content, stomatal conductances, plant water status, and chlorophyll fluorescence. Contrarily, the stem diameter, fresh weight, dry weight, and leaf area data do not show any significant differences. As it comes to the point of research findings, the optimum water requirement for Sissoo spinach was 50% water treatment. This is crucial to prevent unnecessary, avoidable water application onto plants.
ISSN: 0126-0537Accredited First Grade by Ministry of Research, Technology and Higher Education of The Republic of Indonesia, Decree No: 30/E/KPT/2018
Cite this as: Mat Hasan, A. N., Najihah, T. S., & Yusoff, N. (2023). Growth, physiology, and water status of Sissoo spinach (Alternanthera sissoo) under different irrigation regimes. AGRIVITA Journal of Agricultural Science, 45(3), 545–553. http://doi.org/10.17503/agrivita.v45i3.4220
Growth, Physiology, and Water Status of Sissoo Spinach (Alternanthera sissoo) Under Different Irrigation Regimes
‘Alyaa’ Najihah Mat Hasan, Tuan Syaripah Najihah*) and Nornasuha Yusoff
School of Agriculture Science and Biotechnology, Faculty of Bioresources and Food Industry, Universiti Sultan Zainal Abidin, Besut Campus, 22200, Terengganu, Malaysia
decreased the chlorophylls and increased the biochemical properties of these plants (Seymen, 2021).
Currently, less research has been done on Sissoo spinach, and the effect of water stress on these plants has never been reported. Thus, this research was conducted to evaluate the growth, physiological parameters, and water status of Sissoo spinach under different water stress conditions and to determine the water requirement for Sissoo spinach. It will offer information on the Sissoo spinach’s ability to face abiotic stress and unpredictable water sources, which implies the adaptation of Sissoo spinach to climate change.
Notably, the research also helps contribute to increasing food security. This experiment is in line with the 13th Sustainable Development Goal (SDG), which is to take urgent action to combat climate change and its impacts; thus, the result from this study is important if growers are to adapt to climate change.
MATERIALS AND METHODS Experimental Design
This project used a Randomized Complete Block Design (RCBD) arrangement for four different water treatments with five replications. The first water treatment was 100% (A) as control, while the rest treatments were 75% (B), 50% (C), and 25%
(D) field capacity (FC) with five replicates each.
This study was conducted in the greenhouse of the University of Sultan Zainal Abidin, Terengganu, Malaysia, from mid-August 2022 to mid-September 2022.
Plant Preparation
The stem of Sissoo spinach around 3-4 nodes (6-8 cm) was cut using a sharp scalpel from the matured plants’ resources. Then, they were transplanted into the prepared topsoil media polybags of size 15 x 16 inches (Alam et al., 2022).
Watering was done once every two days according to each replicate’s water requirement. The plants were fertilized with NPK green fertilizer with a ratio of 15:15:15.
Plant Materials
Source and Numbers of Planting Materials
The plants were taken from the nearby nursery and used in stem-cutting forms. The total of stem cuttings planted were 20 plants.
Water Treatments
The ten soil-filled polybags were weighed first to determine the dry weight, and the average weight would be stated. Then, proceed to be watered until they are moist enough to produce excess water before being re-weighted after all the excess water was drained to get the turgid weight. Then, the soil’s field capacity was calculated and determined as 100% water treatment (well-watered). From the amount obtained, the rest of the 75%, 50%, and 25% of the water treatments were determined by a calculation from the field capacity. These will have five replications each, respectively (Najihah et al., 2020).
Growth Plant Height
The plant height measurement was a modified method of Alam et al. (2022) measured by using a measurement tape starting at the bottom stem right on the soil base until the top highest part of the plant for each replication, taken once per week.
Number of Leaves
Leaves numbers were counted starting upon the stem cutting planting, which leaves already existed on the stem. They were recorded firsthand to know and to identify the leaves’ growth development after planting using different water treatments (Alam et al., 2022).
Physiological Parameters Stomatal Conductance
Using a modified method of Iseki & Olaleye (2020), stomatal conductance was measured using a leaf parameter instrument in the morning between 10.00 a.m. and 1.00 p.m. for each plant every once a week.
Chlorophyll Content
The chlorophyll contents were obtained using the handy and portable SPAD-502 meter. The result would be taken and recorded from 3 leaves of each one of the plants (Sun et al., 2018).
Chlorophyll Fluorescence
The primary idea of the chlorophyll fluorescence measuring technique was based on the distribution of light energy and was used to evaluate the photosynthetic performance of plants.
The most often used fluorimeters were Hansatech’s Pocket PEA and Handy PEA. These systems were used with accessories for dark-adapt samples,
while observations might also be performed in the light (Vlaovic et al., 2020).
Relative Water Content (RWC)
Dry weight was recorded firstly from three discs that were collected using a puncher for each plant, and they were then put into a beaker of water and left for about 24 hours. For the next 24 hours, the disc samples proceeded to be weighed again after drying up carefully using tissue paper to obtain the turgid weight. Straight after turgid weights were obtained, the disc samples were followed up with the drying method procedure using an electronic oven for 24 hours at 75 degrees Celcius and then weighed to get dry weight (Najihah et al., 2020). The formula for RWC is as follows:
...(1) Where: FW = Fresh Weight, DW = Dry Weight, TW
= Turgid Weight
Leaf Moisture Content (LMC)
The puncher took three disc samples for each plant, and the fresh weight was recorded. Then, the samples would be oven-dried at 75 degrees Celsius for 24 hours. After 24-hour periods of drying using
the oven, all the samples would be reweighed to record the dry weight (Najihah et al., 2020). It was calculated using the given formula:
... (2) Where: FW = Fresh Weight, DW = Dry Weight Statistical Analysis
All the data were analyzed based on One- way ANOVA statistical analysis, which was aimed at only one independent variable (water treatments) and run using the Minitab Software version 21.1.
For the post-hoc analysis, the test used in this study was Tukey.
RESULTS AND DISCUSSION Plant Height
The plant height is observed for four weeks (30 days), as shown in Fig. 1. Overall, the measured Sissoo spinach plant’s size was influenced by water availability. Severe water stress (25% ER; Evapotranspiration Replacement) shows the lowest plant height from others, while treatment 75% was the tallest. There is no significant difference between 50% ER and 75% ER.
Remarks: Bars indicate the standard error of the mean (SEM)
Fig. 1. Effects of different water treatments on the plant height of Sissoo spinach week 4
As stated in the past research by Nasarullah et al. (2022), the result of the affected plant height is common for the reduction in water availability. The decrease in turgor pressure causes cell development to be one of the physiological processes most vulnerable to water stress decline, either a decrease in cell expansion or inhibition of cell division that contributes to the plant’s height. This also goes well with what was found in the previous research study, where the reduction in cellular turgidity and CO2 uptake once plants are subjected to a water shortage causes the plant to grow slowly and have a low photosynthetic rate, which in return results in poor plant development and lesser dry mass accumulation (Reyes et al., 2018). According to a previous study by Maseko et al. (2019), a further increase in water application to 100% ETc (water crop requirement based on evapotranspiration) (47 cm) does not significantly enhance plant height during the first season in Amaranthus cruentus plant. However, it did rise significantly (P<.05) from 30% ETc (32 cm) to 60% ETc (47 cm).
Number of Leaves
Fig. 2 shows the result of different water treatments on the number of leaves of Sissoo spinach at week 4. The measured Sissoo spinach plant’s number of leaves is influenced by the availability concentration of water. The number of leaves can be seen generally increase the most for 100% water treatment (control) throughout the weeks, while in the earlier week, there was a significant difference between 100% (control) and the rest of the water treatments; 75%, 50%, and 25%. From the beginning until the last week, the sum of Sissoo spinach leaves applied with 25% water treatment declined compared to the other treatments. However, there is no significant difference between 100% (control) with 70% and 50% water treatment.
This result is consistent with many of the earlier study cases, which state the overall number of leaves per plant declines when the degree level of watering is low (Ghanbari et al., 2013). The current studies show the most reduction in 25% of water treatments, which correlates with Medyouni et al.
(2021), demonstrating that the water deficit treatment reduced the number of leaves. Compared to control leaves, the number of stressed leaves decreased by around 9%. These findings are correlated with the research of Mosenda et al. (2020), who found
that drought stress reduced eggplant vegetative growth. In addition, this current research shows that the lowest water deficit, 25% of water treatments, is significantly lower in the number of leaves than the others. The rate of photosynthesis is influenced by the sum of leaves per plant, size, weight, and rate of leaf development, which are connected to the leaves being produced by each plant.
Chlorophyll Content
Fig. 3 shows the result of different water treatments on the chlorophyll content of Sissoo spinach for four weeks. The chlorophyll contents offer a significant flourishing value for the Sissoo spinach in conjunction with increasing water treatment levels. The decline of water levels from 100% > 75% > 50% > 25% results in a markdown of chlorophyll content. Hence, 100% water treatment (control) is the highest compared with the rest of the water treatments. The 25% water treatment poses the lowest chlorophyll content value, making it statistically significantly different from the control.
In most weeks, between 75% and 50% of water treatments that affect the chlorophyll content, there is no obvious significant difference between both.
As earlier research by Ekinci et al. (2015) report, a healthier plant should be higher in terms of chlorophyll value; hence, they are preferred to be high, and this could relate to where plants under abiotic stresses may have less chlorophyll, or they may have no changes. In Fig. 3, week 3 shows that there are not quite significant differences.
At the same time, another study addresses that despite being exposed to particular levels of water stress, plants do not exhibit changes in chlorophyll synthesis (Reyes et al., 2018). It might be because plants are transplanted into 2 L pots with a mixture of peat and soil (2:1), so they remain moist.
However, past research by Maseko et al. (2019) physiology and yield of ALVs were evaluated under field conditions at the Agricultural Research Council (ARC) proclaimed the decline of chlorophyll levels in other crops under water stress, like sesame, which might be ascribed to increased oxidative stress.
Stomatal Conductance
Fig. 4 shows the result of different water treatments on the stomatal conductance of Sissoo spinach for four weeks. Stomatal conductance can be seen as significantly lower for 25% water treatments. Particularly, there is a significant difference between the rest treatment controls,
100%, 75%, and 50% water treatments with 25%
of water treatments. Nevertheless, there was no significant difference in the stomatal opening of Sissoo spinach subjected to water deficit in between 50% and 75% water treatments.
According to Chaves et al. (2009) and Reyes et al. (2018), the protective effects of stomatal conductance decrease, particularly helping plants conserve water and promoting water use efficiency, is important to highlight. It was found that the stomatal conductance of Sissoo spinach that was exposed to the least 25% water deficit showed a significantly lower outcome. Plants have developed responses
to water deficiency, including morphological, anatomical, and cellular modifications that enable them to survive in conditions of continual water stress. Thus, the stomatal closure process is a physiological resistance mechanism (Reyes et al., 2018). However, the Sissoo spinach was applied once every two weeks with NPK green fertilizer. It might be why the 25% water treatments showed a very low value of stomatal conductance. This leads to the study finding reported by Javed et al.
(2019) that salt stress resulted in a notable drop in net photosynthetic rate and stomatal conductance compared to the control.
Remarks: Bars indicate the standard error of the mean (SEM)
Fig. 2. Effects of different water concentrations on the number of leaves of Sissoo spinach on week 4
Remarks: Bars indicate the standard error of the mean (SEM)
Fig. 3. Effect of different water treatments on the chlorophyll content of Sissoo spinach for four weeks period
Remarks: Bars indicate the standard error of the mean (SEM)
Fig. 4. Effects of different water treatments on the stomatal conductance of Sissoo spinach on week 4
Remarks: Bars indicate the standard error of the mean (SEM)
Fig. 5. Effects of different water treatments on the leaf moisture content of Sissoo spinach on week 4
Remarks: Bars indicate the standard error of the mean (SEM)
Fig. 6. Effects of different water treatments on the relative water contents of Sissoo spinach on week 4
Plant Water Status
Leaf Moisture Content and Relative Water Content
Fig. 5 and Fig. 6 show the results of different water treatments on the leaf moisture content and the relative water content of Sissoo spinach for four weeks, respectively. As seen from Fig. 5, the leaf moisture content is influenced by all these different water treatment levels. The 100% (control) is generally higher than the rest of the treatments. In contrast, there is no significant difference between 100%
(control) and the 50% water treatment. Similarly, as for leaf moisture content, the 100% (control) shows an immense increase in the relative water content, as shown in Fig. 6, compared to 75%, 50%, and 25%
of water treatments. The difference compared with leaf moisture content is that the relative water content increased with the boost of water treatment levels.
However, the 50% and 25% water treatments are not statistically significant. Aside from that, statistically, there is a substantial difference between the three water treatment levels: 100% (control), 75%, and 50% control.
As a result of a previous study, Reyes et al. (2018) note that the production of adenosine triphosphate (ATP), ribulose 1,5-bisphosphate (RuBP), and proteins can be severely inhibited by a total relative water content in cells of less than 75%;
even so, is determined by the water potential in the vascular bundles and restriction to water movement outside the cells. Water constraints cause the cell membrane to alter in terms of permeability and decreased turgidity (Blokhina et al., 2003; Reyes et al., 2018). According to Najihah et al. (2019),
irreparable damage occurred to the photosynthetic machinery when the RWC percentage was reduced by more than 30%.
Chlorophyll Fluorescence (fv/fm)
Fig. 7 shows the result of different water treatments’ effects on the chlorophyll fluorescence of Sissoo spinach for four weeks. The chlorophyll fluorescence (fv/fm), the quantum efficiency of photosynthesis II value, is observed in the last week four and is influenced by the different water concentrations: 100% (control), 75%, 50%, and 25%.
Treatment 25% and 50% display the lowest amount of fv/fm. While 75% shows a higher value of chlorophyll fluorescence, there is no significant difference with 25% of water treatments.
As from this study, the values provided in Fig. 7 of chlorophyll fluorescence are affected by the water deficit. The previous research supported it, which stated thylakoid membranes worsened under water deficit (Najihah et al., 2019). Furthermore, according to Najihah et al. (2019), water stress is discovered to have negatively affected the oxygen-evolving complex as well as the PSII reaction centers. Linked to this study outcome, according to Imadi et al. (2016), studies on cowpeas have found that the initial phases of water stress have no impact on photochemical activity. A decrease in photosystem II activity and a drop in the maximal quantum yield of photosystem II are associated with advanced stress levels. Water stress does not influence photosynthetic efficiency in general. Once plants get subjected to moisture again, approximately three days will be taken for the plant to regain completely.
Remarks: Bars indicate the standard error of the mean (SEM)
Fig 7. Effects of different water treatments on the maximum efficiency of photosynthesis II (fv/fm) of Sissoo spinach on week 4
CONCLUSION AND SUGGESTION
The number of leaves, plant height, chlorophyll content, stomatal conductance, plant water status, and chlorophyll fluorescence show that Sissoo spinach subjected to 50% water treatments is already enough. Fresh weight, dry weight, leaf area, and stem diameter are not discussed, as the outcomes are statistically insignificant. Applying only 50% of water treatments for optimum watering is recommended to achieve optimum water usage without unnecessarily lavishing the water input. It is also recommended that further research be done on the other environmental factors, such as high- temperature stress under water scarcity, as it is one of the climatic factors that influence the growth and development of plants.
ACKNOWLEDGEMENT
The authors would like to express their deepest appreciation for the university’s facilities and staff’s assistance provided throughout the research. The authors also wish to thank the Universiti Sultan Zainal Abidin (UniSZA) for its financial support through GOT (grant numbers UniSZA/2022/GOT.02).
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