Published online August 25, 2023
Journal of Ecology and Environment (2023) 47:10
1Department of Biology, Kyungpook National University, Daegu 41566, Republic of Korea
2Research Institute for Dok-do Ulleung-do Island, Kyungpook National University, Daegu 41566, Republic of Korea
Correspondence to:Yeon-Sik Choo
†These authors contributed equally to this work.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: This study analyzed the physiological adaptations of a woody plant, Vitex rotundifolia, in Goraebul coastal sand dunes from May to September 2022. Environmental factors and physiological of plants growing under field and controlled (pot) conditions were compared.
Results: Photosynthesis in plants growing in the coastal sand dunes and pots was the highest in June 2022 and July 2022, respectively. Chlorophyll fluorescence indicated the presence of stress in the coastal sand dune environment. The net photosynthesis rate (PN) and Y(II) were highest in June in the coastal sand dune environment and July in the pot environment. In August and September, Y(NPQ) increased in the plants in the coastal sand dune environment, showing their photoprotective mechanism. Chlorophyll a and b contents in the pot plant leaves were higher than those in the coastal sand dune plant leaves; however, chlorophyll-a/b ratio was higher in the coastal sand dune plant leaves than in the pot plant leaves, suggesting a relatively high photosynthetic efficiency. Carotenoid content in the coastal sand dune plant leaves was higher in August and September 2022 than that in the pot plant leaves. Leaf water and soluble carbohydrate contents of the coastal sand dune plant leaves decreased in September 2022, leading to rapid leaf abscission. Diurnal variations in photosynthesis and chlorophyll fluorescence in both environments showed peak activity at 12:00 hour; however, the coastal sand dune plants had lower growth rates and Y(II) than the pot plants. Plants in the coastal sand dunes had higher leaf water and ion contents, indicating that they adapted to water stress through osmotic adjustments. However, plants growing in the coastal sand dunes exhibited reduced photosynthetic activity and accelerated decline due to seasonal temperature decreases. These findings demonstrate the adaptation mechanisms of V. rotundifolia to water stress, poor soils, and high temperature conditions in coastal sand dunes.
Conclusions: The observed variations indicate the responses of the V. rotundifolia to environmental stress, and may reveal its survival strategies and adaptation mechanisms to stress. The results provide insights into the ecophysiological characteristics of V. rotundifolia and a basis for the conservation and restoration of damaged coastal sand dunes.
Keywords: chlorophyll, chlorophyll fluorescence, coastal dune plant environmental stress, photosynthesis
Coastal dunes are ecological transformation areas where the characteristics of coastal areas and inland areas are common (Kim and Hong 2009). The ecological and functional characteristics of coastal sand dunes include a buffering role to protect coastal ecosystems from wave action (Arun et al. 1999; Mascarenhas and Jayakumar 2008), underground freshwater storage, storage of sand carried by the wind, and prevention of sand from drifting further inland by sand dune vegetation (Dahm et al. 2005). The metabolism and survival of plant species growing in coastal sand dunes are affected by various environmental stresses, such as drought, salt, flooding, high temperatures, low water acceptability of sand, low nutrient and water availability in coastal dune environments (Hesp 1991; Lawlor and Cornic 2002; Maun 1998). In particular, water scarcity is one of the major stresses in coastal sand dunes, and frequent water scarcity is caused by high evaporation rates that limit plant growth, development, and survival (Bae et al. 2013). Plants respond physiologically and biochemically to varying moisture stress levels by exhibiting reduced moisture content and osmotic potential, reduced relative water content (WC), osmotic regulation, leaf withering, high leaf temperatures, stomatal closure, cell enlargement, and reduced growth (Kumar and Singh 1998; Pasban Eslam et al. 2000; Shao et al. 2007). In addition mosture stress alters various physiological processes such as photosynthesis, respiration, transpiration, ion absorption, carbohydrate metabolism, stomatal conductivity, and electron transport (Acevedo et al. 1971; Angelopoulos et al. 1996; Flexas et al. 1998; Lu and Zhang 1998; Clifton-Brown et al. 2002; Munns 2002; Silva et al. 2007). Coastal sand dune plants are an important factor in the formation of coastal dunes, understanding coastal dunes’ responses to environmental stresses such as dryness, salinity, temperature, and light changes is important for explaining and predicting the distribution of plant colonies in coastal sand dunes, and can also play an important role in protecting natural vegetation through effective management (Hwang and Choo 2017). Plants continuously exposed to environmental stimuli have developed various adaptation strategies to settle and perpetuate within their habitats (Flowers and Colmer 2008), and in general, both stress avoidance and stress tolerance strategies in plants include various plant mechanisms that provide plant viability under environmental stress conditions (Levitt 1980). In this study, research was conducted through various analysis items to identify the physiological characteristics of coastal dune plants. Photosynthesis is the most basic physiological process in which plants obtain energy using light, and is affected by various environments such as atmospheric temperature and rainfall (Kratsch and Wise 2000). Photosynthetic ability is used as an indicator to investigate physiological properties of plants, and chlorophyll fluorescence, which can quantify changes in photosynthetic ability, such as pore opening and water utilization efficiency and photochemical reactions, can provide useful information for investigating plant reactions (Baker 2008; Gunderson 2000; Krause and Weis 1991; Murchie and Lawson 2013).
Coastal sand dune plants are known to be resistant to high-temperature dry environments that can occur for a variety of reasons, including salt, drying, high evaporation, and osmotic bonding of water (Ishikawa et al. 1990; Larcher 2003; Mooney et al. 1983). However, defining factors is a challenge because plant species avoid or adapt to environmental stress through various mechanisms.
Therefore, this study aimed to investigate seasonal variations in physiological characteristics, including photosynthetic raates, chlorophyll fluorescene, and chlorophyll contents, of the perennial sand dune plant species
Furthermore, sand plants are essential for the formation of coastal sand dunes, and
To investigate the monthly photosynthesis pattern of
To investigate the monthly chlorophyll fluorescence pattern, a portable chlorophyll fluorescence measuring device, Portable Chlorophyll Flourometer (PAM-2500; Heinz Walz GmbH, Effeltrich, Germany), was used to measure the follwing chlorophyll fluorescence-related parameters: minimum fluorescene (
The measured leaves were collected, the fresh weight (FW) was measured, dried in a dryer at 70°C for more than 3 days, and the dry weight (DW) was measured. The WC of the leaves was calculating with the formula.
WC (%) = [(FW – DW)/ FW] × 100
The plant sample liquid was ground into a homogeneous powder by grinding dried plant leaves with a pulverizer UDY cyclone sample mill (UDY Corperation, Fort Collins, CO, USA), and then 1 g of the sample was put into a 25 mL measuring flask and then incubated in a water bath at 95°C for 1 hour. After sufficient cooling at room temperature, the final volume was adjusted to 10 mL and extracted by filtering with a GF/C filter (pore size 1.2
A certain area (cm2) of the leaf was collected and chlorophyll was extracted for 48 hours using 5 mL of dimethyl sulfoxide. The extracted chlorophyll was measured using a UV/VIS Spectrophotometer OPTIZEN 2120 (Mecasys, Daejeon, Korea), and the content of chlorophyll
Ca = 12.47 A665.1 – 3.62 A649.1
Cb = 25.06 A649.1 – 6.5 A665.1
Cx+c = (1,000 A480 – 1.29 Ca – 53.78 Cb) / 220
The osmotic concentration was measured with an Osmometer (Micro-Osmometer 3MO; Advanced Instruments, Norwood, MA, USA) using the principle of freezing point enhancement by taking 50
Meteorological data for the study period was obtained from local meteorological stations, and soil moisture content in areas inhabited by
To analyze the diurnal change pattern, three good leaves of plant growing in the coastal sand dunes environment on August 26, 2022 and in the large pot were collected on August 26, 2022 and August 28, 2022, respectively, at 3-hour intervals from 06:00 to 18:00 (i.e., five times a day). After stabilization for approximately 5 minutes,
The diurnal change pattern in the coastal sand dunes on August 26, 2022 and in the large pot on August 28, 2022 was measured at 3 hours intervals (5 times in total) from 06:00 hour to 18:00 hour using a portable chlorophyll fluorescence measuring device, Portable Chlorophyll Flourometer PAM-2500. The foloowing chlorophyll fluorescence-related parameters were measured: (1)
Leaves were collected from plants growing in coastal sand dunes on August 26, 2022 and from plants growing in pots on August 28, 2022. Leaf moisture content, chlorophyll content, osmolarity, total ion content, and soluble carbohydrate content were determined.
The meteorological conditions of the coastal dune area during the study period are shown in Figure 1A, B. The average temperature was the highest in July and August 2022 (24.7°C) and the lowest at 14.4°C in October 2022 (14.4°C). The average maximum temperature was the highest in July 2022 (29.6°C), whereas the average minimum temperature was the lowest in May 2022 (11.8°C). Monthly precipitation was the lowest in May 2022 (5.4 mm) and the highest in September 2022 (141.5 mm). In addition, it was investigated that the soil moisture content in the coastal sand dunes was considerably low (0.1%–0.5%) (Fig. 1A, B).
The weather conditions of Daegu, where the pot experiments were performed, are shown in Figure 1C, D. The average temperature was the highest in July 2022 (27.4°C) and the lowest in May 2022 (20.7°C). The average maximum temperature was the highest in July 2022 (32.4°C), whereas the average minimum temperature was the lowest in May 2022 (14.1°C). Monthly precipitation was the lowest in May 2022 (4.2 mm) and the highest in August 2022 (143.3 mm), (Fig. 1C, D). In the pot experiments, the soil moisture content was maintained at 4.5%–5.5% through regular water supply, and it was higher than that in the coastal sand dune environment (Fig. 2A). Photosynthetically active radiation (PAR) values for the pot plants were higher than those for the coastal sand dune plants, except for July 2022, and PAR values had a similar range at the time of measurement in both environments (Fig. 2B).
Photosynthesis patterns in coastal dunes and large pot environments measured from May to September 2022 are shown in Figure 3. Light is essential for photosynthesis, and plants can convert solar energy into chemical energy through a metabolic process. The net photosynthetic rate is highly dependent on the amount of light absorbed by plants (Ueda et al. 2000). The
The light energy absorbed by chlorophyll is released in the form of heat or fluorescence or used for photosynthesis, and the physiological state of the plant can be determined by calculating the ratio. This ratio is calculated as the values of Y(II), Y(NPQ), and Y(NO), which represent the ratio of energy use in photosystem II, and the value of Y(II) + Y(NPQ) + Y(NO) is 1 (Klughammer and Schreiber 2008). This rate of energy use provides crucial information about plant photosynthesis (Klughammer and Schreiber 2008). Y(II) means the quantum yield of photochemical energy conversion in PSII and has a high correlation with the rate of photosynthesis (Baker 2008). It means the mechanism of photoprotection that protects leaves by releasing excited energy generated under stress environment in the form of heat by active dissipation of regulated non-optical energy (Müller et al. 2001). In this study,
Chlorophyll is an essential pigment for photosynthesis in plants and is a key factor regulating plant physiological processes. Plant leaves consist of chlorophylls
Various in leaf water content (LWC) are not only used to indicate plant health, but also tolerance to dry environmental conditions (Chyliński et al. 2007). The LWC of pot plants was constant during the study period, whereas that of coastal sand dune plants increased in August 2022 and then decreased substantially in September 2022 (Fig. 7A). This observation could be attributed to water stress and high temperature in the coastal sand dunes, and is also believed to influence early leaf detachment.
Variations in osmolality, total ion content, and soluble carbohydrate content in the leaves of
The PAR values for plants growing in coastal sand dunes and pots based on measurement time was the highest at 12:00 hour in August 2022, except for the values observed at 09:00 hour, which were similar (Fig. 8A). The PAR value for the pot plants was lower than that for the coastal sand dune plants at 09:00 hour, and higher in pot plants at 15:00 hour (Fig. 8A). The leaf temperature of
The diurnal variations in photosynthetic parameters of
Chlorophyll fluorescence and related parameters of
Comparison of the chlorophyll contents of
The leaf LWC of
In addition, revealed that osmolality, total ion content, and soluble carbohydrate content of
After transplanting the primary colony of
Seasonal variations in photosynthetic activity indicators, including
Based on the chlorophyll fluorescence results, plants in the coastal sand dune environment were stressed, whereas those grown in pots were not substantially stressed, and the Y(II) ratio exhibited a trend similar to that of
Furthermore, the diurnal variations in photosynthetic parameters of
This study revealed that the photosynthetic rate of
All the authors are deeply grateful to Plant ecophysiology lab in Kyungpook National University, South Korea.
WC: Water content
WUE: Water use efficiency
CE: Carboxylation efficiency
FW: Fresh weight
DW: Dry weight
PAR: Photosynthetically active radiation
LHC: Light harvesting complex
LWC: Leaf water content
Y(II): The quantum yield of photochemical energy conversion in PSII
Y(NPQ): The quantum yield of regulated non-photochemical energy loss in PSII
Y(NO): The quantum yield of non-regulated, non-photochemical energy loss in PSII
BJK did data curation, investigation, and writing-original draft. SH did data curation, funding acquisition, writing-review and editing. YS did data analysis, writing-review and editing. YS did conceptualization, supervision, writing-original draft, and writing-review and editing. All the authors approved the manuscript.
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1A6A1A05011910 & 2016R1D1A1B03934927), and by grants from the National Institute of Ecology (NIE-A-2023-20 & NIE-B-2023-02).
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
The authors declare that they have no competing interests.
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Young-Been Kim1,4†, Sung-Hwan Yim2,3†, Young-Seok Sim2 and Yeon-Sik Choo1,2,3*
Jae-Hoon Park , Jung-Min Lee , Eui-Joo Kim and Young-Han You*