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Article

The Effects of Water Depth on the Growth of Two Emergent Plants in an In-Situ Experiment

by
Xiaowen Lin
,
Xiaodong Wu
*,
Zhenni Gao
,
Xuguang Ge
,
Jiale Xiong
,
Lingxiao Tan
and
Hongxu Wei
College of Urban and Environmental Sciences, Hubei Normal University, Huangshi 435002, China
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(18), 11309; https://doi.org/10.3390/su141811309
Submission received: 5 August 2022 / Revised: 24 August 2022 / Accepted: 6 September 2022 / Published: 9 September 2022
(This article belongs to the Special Issue Wetlands: Conservation, Management, Restoration and Policy)
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Abstract

:
With the degradation of the global lake ecosystem, aquatic plants are more and more widely used in lake ecological restoration. The effects of water depths on the growth and photosynthetic fluorescence characteristics of two emergent plants (Typha orientalis and Zizania caduciflora) were studied in eutrophic Lake Gehu by in-situ experiments. The results showed that water depth had no significant effect on germination of emergent plants. The water depth changed the morphological characteristics of emergent plants. Plant height, tiller number, leaf length, leaf width, the number of leaf, and the root-shoot ratio decreased with increasing water depth, whereas the number of dead leaves increased with increasing water depth. The biomass of emergent plants was highest when water depth was 40 cm. Water depth had a significant effect on the photosynthetic fluorescence of the emergent plant. Fv/Fm tended to decrease first and then increase with increasing water depth. When the water depth was 20 cm, the ETRmax of emergent plants was significantly higher than that of plants at the other water depths. These results show the suitable water depth range for T. orientalis and Z. caduciflora is 20–60 cm. A deeper water depth for a long time is not conducive to the growth of emergent plants.

1. Introduction

Eutrophication, global change, and other factors have caused the rapid degradation of aquatic vegetation in lakes worldwide and have transformed lakes from a clear water state dominated by aquatic plants to a turbid water state dominated by algae, resulting in degradation of the structure and function of lake ecosystems [1,2,3,4]. Emergent plants absorb nitrogen, phosphorus, and other nutrients, as well as adsorb pollutants and heavy metals in the water, which purifies the water [5,6,7,8,9]. Thus, emergent plants are widely used to restore lake ecosystems. However, unsuitable habitats cause emergent plants to wither or die [10,11]. The growth of emergent plants is affected by various environmental factors, such as light, temperature, nutrients, water level, and salinity [12,13,14,15,16,17]. Hydrological dynamic changes will affect the functional and psychological traits of wetland plants, especially emergent plants [18,19,20,21]. Water depth is the most critical environmental factor for emergent plants [22,23]. Emergent plants have higher requirements for water depth, but their adaptability to water depth is lower than that of other aquatic plants. Water depth mainly affects plant growth by limiting carbon dioxide, oxygen, underwater light, and other resources, as well as sediment characteristics [24,25,26,27]. Emergent plants can survive under water depth stress, as they adapt to water depth through a series of morphological and physiological changes [28,29,30,31]. However, water too deep or too shallow can limit growth and can lead to death [32].
Although many studies have investigated the effect of water depth on the growth of emergent plants, most have been simulation experiments. Liu et al. (2015) [12] simulated the wild natural environment in an artificial climate box and explored the effects of light, water depth, and their interaction on the germination of reed seeds. Yuan et al. (2011) [33] set up three water depth treatment groups of 0, 30, and 60 cm under indoor still-water conditions, and determined that a water depth of 60 cm significantly inhibited the growth and reproduction of four emergent plants. Liang et al. (2015) [34] prepared different flooding gradients of 3–12 cm under laboratory conditions. By measuring the growth and physiological indicators of the reeds, they discovered that a 3–6 cm water depth is beneficial to the growth of reed seedlings. However, the conditions of a strictly controlled simulation experiment are quite different from the natural environment, and in-situ experiments are often difficult, so there are few reports of in-situ field experiments.
Lake Gehu (31°3′ N, 119°49′ E) is a typical shallow lake in the middle and lower reaches of the Yangtze River, China. The local government carried out large-scale remediation work in the northern lake area from 2009 to 2010 in response to the degradation of the Lake Gehu ecosystem and water eutrophication. After ecologically reconstructing the northern lake area, the wind and waves decreased and the underwater light field improved significantly, thus providing favorable conditions to restore the aquatic vegetation [35,36]. This study selected two pioneer species of emergent plants in Lake Gehu, such as Typha orientalis and Zizania caduciflora, and conducted in-situ water depth experiments to explore the effects of water depth on the germination and growth of two emergent plant species to provide a scientific basis for reconstructing the emergent vegetation.

2. Materials and Methods

2.1. Study Area

The experimental area was located in the northern area of Lake Gehu (Figure 1). Lake Gehu is a eutrophic lake. In 2008, the construction of a highway divided Lake Gehu into two separate lakes, creating an area of about 14 km2 in the north of Lake Gehu. From 2010 to 2013, in order to reduce the exogenous and endogenous pollution loads, there are many measures that have been taken, such as river diversion, reservoir construction, cyanobacteric algae removal, and dredging. As a result of targeted topographic reconstruction, several shoal areas have been created in the northern area of Lake Gehu, with diverse habitat characteristics and water depths ranging from 0.6 to 2.7 m. Through this series of measures, the transparency of Lake Gehu has reached 42.5 ± 9.8 cm, which is 1.42 times of the previous process. The depth of the eulight layer has also been increased. At the same time, the water quality of Lake Gehu has improved and the related data of water quality and sediment are shown in Table 1.

2.2. Experiment Design

A stainless steel floating body was placed on the edge of a shoal in the northern part of the lake, and plastic buckets were hung on the stainless steel floats using nylon rope. Different water depths were simulated by adjusting the hanging height. Robust rhizomes of T. orientalis and Z. caduciflora were selected and planted in plastic buckets containing about 40 cm of sediment; eight plants were planted in each plastic bucket. The sediment was from the bottom mud in the northern area of Lake Gehu. A total of six water depth treatments were set in the range of 20–120 cm, and the distance between the barrel surface and the water surface was 20, 40, 60, 80, 100, and 120 cm, respectively (Figure 2). Each treatment had six sets of repetitions for a total of 36 buckets.

2.3. Measurement Indicators

2.3.1. Morphological Indicators

The experiment lasted 65 days from 17 March 2015 to 20 May 2015. The germination rates of T. orientalis and Z. caduciflora rhizomes were calculated every 2 days after one week of the experiment. It is considered germinated when leaves grow out of rhizomes, and the germination rate is equal to the number of rhizomes that have germinated, then divided by the total number of rhizomes. The plastic buckets were gently lifted to the water surface every 5 days to determine growth indicators including plant height, number of tillers, number of leaves, length of leaves, width of leaves, and number of dead leaves. Among them, nine plants were randomly selected from each water depth treatment group for measurement, and the average value was used. After the experiment, T. orientalis and Z. caduciflora were removed, washed with water, and weighed to determine the fresh weight after the water was wiped off the plants with absorbent paper.

2.3.2. Chlorophyll Fluorescence Parameters

Five plants were randomly selected from each treatment group, and the 3–4 leaves below the top of plants were collected to measure the chlorophyll fluorescence parameters. The measurements were performed with the DIVING-PAM underwater saturated pulse chlorophyll fluorometer and Wincontrol data acquisition software. The measurement time was 6:00–8:00 a.m. After the leaves were dark-adapted for 10 s, we opened the leaf clip and turned on the detection light (0.15 μmol photons m−2·s−1) to obtain the fixed fluorescence yield (Fo). Then, the maximum fluorescence (Fm) was measured by saturated pulsed light (40,000.15 μmol photons m−2·s−1, 0.8 s). Subsequently, the actinic light was turned on under illumination intensities of 34, 155, 272, 417, 605, 805, 1181, and 1609 μmol photons m−2·s−1. After each intensity of actinic light was irradiated for 10 s, the steady-state fluorescence yield (Ft) and the maximum fluorescence yield (F’m) when the actinic light was turned on were measured by recording the light and the saturated pulsed light. Eight apparent combined electron transfer rate (ETR) values were calculated using the formula: ETR = Yield × PAR × 0.84 × 0.5 [37], and draw the fast light response curve of the average value of the ETR.

2.4. Statistical Analysis

The experimental data were processed with Excel (Microsoft Inc., Redmond, WA, USA), and the one-way analysis of variance procedure in SPSS software (SPSS Inc., Chicago, IL, USA) was used to detect significant differences in the germination rates and growth of T. orientalis and Z. caduciflora at the different water depths. Before ANOVA analysis, data were tested for normality (Shapiro–Wilk) and homogeneity of variance. Data that did not meet normality were log-transformed. p > 0.05, p < 0.05, and p < 0.01 were considered to be insignificant, significant, and extremely significant. Origin 2021 Pro software (Origin Laboratories Inc., San Francisco, CA, USA) was used to draw the line graphs and histograms.

3. Results and Analysis

3.1. The Effect of Water Depth on the Growth of the Emergent Plants

3.1.1. Effects of Different Water Depths on Germination of the Emergent Plants

Both T. orientalis and Z. caduciflora rhizomes germinated at water depths of 20–120 cm, and germination was complete 15 days after the start of the experiment. The germination rates of the two emergent plants were highest at a water depth of 80 cm (Figure 3). The final germination rates of T. orientalis and Z. caduciflora in each group were more than 90% and 85%, respectively.

3.1.2. Effects of Different Water Depths on the Morphological Characteristics of the Emergent Plants

The water depth in the reconstructed area of Lake Gehu had a major effect on the morphological characteristics of the emergent plants. The height of T. orientalis in each treatment group increased rapidly during the experimental period (Figure 4a). At the beginning of the experiment (days 15 and 30), the plant height in each treatment group was insignificantly different (p > 0.05), but the height of T. orientalis at a water depth of 60–80 cm was slightly higher than that in the other treatment groups. As the experiment progressed, the heights of the plants of each treatment groups became significantly different (p < 0.05). The plant height at a water depth of 40–60 cm was higher than that of the other treatment groups. The plant height at a water depth of 40 cm reached 134.6 cm, whereas that of the 120 cm group was 76.3 cm, and the former was 1.76 times that of the latter. The number of T. orientalis tillers decreased extremely significantly with increasing water depth (p < 0.01) (Figure 4b). The number of T. orientalis tillers was the largest when the water depth was 20 cm, whereas in the 20–120 cm water depth group it decreased to 88.89%, 77.78%, 66.67%, 61.11%, and 55.56% of those in the 20 cm water depth group, respectively. The leaf characteristics of T. orientalis were significantly affected by water depth, and the difference in the number of leaves among the treatment groups was little at the beginning. However, as the experiment progressed, the number of leaf pieces at water depths of 20 and 40 cm were both 5.7 pieces/plant, and those in the other treatment groups decreased to 3.0 pieces/plant. Overall, the number of leaves, leaf length, and leaf width of T. orientalis decreased with increasing water depth (Figure 4c,e,f), whereas the number of dead leaves increased (Figure 4d). Water depth had a significant effect on the biomass of T. orientalis (Figure 4h). Biomass increased rapidly at the beginning of the experiment with increasing water depth. The biomass of T. orientalis was the largest when the water depth was 40 cm, reaching 146.2 g FW/plant, which was 1.54, 1.73, 2.36, 3.66, and 5.17 times that of T. orientalis at water depths of 20, 60, 80, 100, and 120 cm, respectively. Biomass decreased with increasing water depth in plants maintained in the water depth range of 40–120 cm.
The different water depths had a significant effect on the height of Z. caduciflora (p < 0.05) (Figure 5a). During the experimental period, the plant heights of Z. caduciflora in all of the treatment groups increased rapidly. At the beginning of the experiment (days 15 and 30), the plant heights were insignificantly different among the treatment groups (p > 0.05), but the heights of plants at water depths of 60–100 cm were slightly higher than those in the other treatment groups. As the experiment progressed, the height of Z. caduciflora at the 60 cm water depth reaches 100.4 cm, which was 130%, 17%, 79%, 174%, and 120% higher than that of plants maintained at the 20, 40, 80, 100, and 120 cm depths on the 40th day, respectively. On the 60th day of the experiment, the height of plants at the 60 cm water depth was 113.7 cm, whereas that of the 120 cm group was only 26.8 cm; the former being 4.24 times higher than the latter. The number of Z. caduciflora tillers showed a decreasing trend with increasing water depth (Figure 5b). When the water depth was 20 cm, the number of Z. caduciflora tillers was the largest. The tiller numbers at water depths of 20–120 cm decreased to 78.95%, 68.42%, 63.16%, 57.89%, and 57.89% of the 20 cm group, respectively. As water depth increased, the number of leaves of Z. caduciflora decreased (Figure 5c). On the 60th day of the experiment, the number of leaves at the 20 cm depth was 5.3 pieces/plant, and the number of leaves in the other treatment groups decreased to 1.3–3.3 pieces/plant. The number of dead leaves increased with increasing water depth (Figure 5d). Leaf length increased first and then decreased with increasing water depth (Figure 5e), whereas leaf width decreased with increasing water depth (Figure 5f). The root-shoot ratio of Z. caduciflora decreased with increasing water depth. The effect of water depth on the biomass of Z. caduciflora was the same as that of T. orientalis; biomass initially increased slowly and then decreased with water depth. The biomass of Z. caduciflora was the largest at a water depth of 40 cm, reaching 104.3 g FW/plant, which was 1.09, 1.17, 2.28, 3.32, and 3.41 times that of plants maintained at the 20, 40, 80, 100, and 120 cm depths, respectively (Figure 5h).

3.2. Effects of Different Water Depths on the Photosynthetic Fluorescence Characteristics of the Emergent Plants

Water depth had an effect on the photosynthetic fluorescence characteristics of the leaves of T. orientalis and Z. caduciflora. The maximum photon yield (Fv/Fm) of T. orientalis decreased with increasing water depths of 20–60 cm, increased at 60–80 cm, and then decreased with further increases in water depth (Figure 6a). The maximum Fv/Fm of Z. caduciflora leaves decreased with increasing water depth of 20–60 cm but increased at the water depths of 60–120 cm (Figure 7a). Overall, the Fv/Fm values of the two emergent plants showed a decreasing trend with increasing water depth. Differences in the maximum electron transfer rate (ETRmax) were observed between the water depth treatment groups of T. orientalis and Z. caduciflora. The ETRmax of the treatment group at the water depth of 20 cm was higher than that of the other groups (Figure 6b and Figure 7b).

4. Discussion

4.1. Effects of Different Water Depths on the Survival of the Emergent Plants

Excessive water depth often results in decreased or failed plant germination [38,39] because of the slower underwater gas exchange with increasing water depth [40,41,42] and the decrease in the redox potential and oxygen concentration [43,44]. Additionally, because the photosynthetic organs are submerged in water, photosynthesis is blocked, and the supply of oxygen to the roots is insufficient [45]. In severe cases, anaerobic respiration is forced to occur in the underground parts, thereby rapidly consuming carbohydrates [46], and inhibiting plant germination and reproduction. It follows from our experimental results that the mortality of the emergent plants increased significantly when the water depth was 100 and 120 cm (Figure 3) because although T. orientalis produces large thick rhizomes when stressed by water depth, the plants can maintain aeration in an oxygen-deficient environment [47]. However, when the water depth increases beyond a certain depth, the leaves cannot reach the water surface, photosynthesis and gas exchange are inhibited, and the plants gradually lose their vitality and die.

4.2. Effects of Different Water Depths on the Morphological Characteristics of the Emergent Plants

Emergent plants produce a series of diverse, plastic morphological responses to changes at different water depths [48]. In the experiment, the response of the morphological characteristics of the emergent plants to water depth was mainly reflected in plant height, the number of tillers, the number of leaves, the leaf length, and the leaf width of T. orientalis and Z. caduciflora, which all decreased with increasing water depth, whereas the number of dead leaves increased with increasing water depth.
During the entire experimental period, the heights of the two emergent plant species increased first and then decreased with increasing water depth, indicating that these two emergent plants can adapt to changes in water depth through morphological changes within the range of 0–60 cm, but that water depths >60 cm inhibit increases in plant height. In addition, the heights of T. orientalis and Z. caduciflora at the 40–60 cm water depth were higher than those of the other water depth treatment groups, indicating that 40–60 cm was the most suitable depth for the growth of T. orientalis and Z. caduciflora. Zhou et al. (2021) [48] have reported that the growth of T. orientalis is best when the water depth is 50 cm. However, some research results reported were not consistent with our experimental results. Tang et al. (2019) [49] set the water depth of 0–60 cm and reported that a water depth lower than 40 cm had little effect on the growth of T. orientalis. T. orientalis died after 84 and 60 days of the experiment when the water depth reached 50 and 60 cm, respectively. In our experiment, the height of T. orientalis at a water depth of 60 cm was the highest among all treatment groups on the 60th day of the experiment. This may have been affected by the experimental conditions. The underwater light environment is an important environmental factor affecting the growth and reproduction of submerged plants. Due to the attenuation of light, the available light of aquatic plants will greatly decrease with the increase in water depth. Yu et al. (2021) [50] found that artificial LED light promoted increased growth of three submersed macrophytes. If the artificial light is added to enhance the light intensity under indoor simulation conditions, the study may be different. Because the former study was a simulation experiment carried out in an indoor sun room, and the light intensity of indoor was not as good as natural wild conditions, so the growth of T. orientalis may have been affected by light stress and the plants died when the water depth reached 60 cm [26,51]. Further, the light quality of indoor can also affect the growth of aquatic plants [52,53]. Additionally, the water level of the indoor simulation experiment was still. Gas diffusion and propagation speed are slow under still-water conditions, so photosynthesis would be limited. The water level of Lake Gehu under natural conditions fluctuated greatly during the experiment (Figure 8), and the water level fluctuations would affect the plants by dissolved oxygen [54,55]. The fluctuating water level promotes the transport of gas and nutrients in the water, thereby enhancing photosynthesis [56]. Furthermore, the height of plants in the 80–120 cm water depth treatment group was not the highest, indicating that neither T. orientalis nor Z. caduciflora exhibited obvious escape strategies.
When resources in a natural environment are limited and drop to a minimum, the individuals with minimum resource requirements will eventually survive [57,58,59]. Faced with resource constraints, plants adapt to changes in water depth by changing their morphological characteristics, which reflects two coping strategies [18,60,61]. One is the quiescent strategy in which plants do not lengthen their stems or leaves to reduce energy and carbohydrate consumption under water depth stress. The other is the escape strategy in which plants add stems and leaves and become exposed to the water surface to obtain sufficient oxygen and light.
Too deep water depth will not only cause tissue hypoxia, but also lead to an accumulation of CO2 and ethylene [62]. Cyril et al. (2017) [63] studied metabolic changes in leaves under low O2 and found that hypoxia negatively affected photosynthesis and showed signs of anoxic response. In the present experiment, the available O2, CO2, light, and other resources were limited with increasing water depth, the photosynthetic rate slowed, and the growth rate of the plants decreased [64], which decreased the leaf length and width. This finding indicates that the two emergent plants passively adopted a quiescent strategy under water depth stress, which is consistent with the study of Wei et al. (2021) [65]. However, some studies have reported that Z. caduciflora adopts an active escape strategy with a change in water level and depth, using more resources for growth of the canopy, and avoiding the stress of deep water by forming floating grass mats [66]. In addition, emergent plants prioritize limited resources for the growth of the main plant and leaves at a shallower water depth, which inhibits the growth of the leaves located deeper. Leaves flooded over the long-term turn yellow, prematurely senesce, and fall off, resulting in a decrease in the number of tillers, the number of leaves, and an increase in the number of dead leaves [67].

4.3. Effects of Different Water Depths on the Biomass of the Emergent Plants

Biomass and the root-shoot ratio are important indicators to measure the effect of stress on the growth of plant [68]. The growth state of a plant can be directly expressed by changes in biomass [69]. Gafny et al. (1999) [70] reported that an “opportunity window” exists for plant growth. The “opportunity window” means that within a range of water depth, plants can profit from the environment in which they grow and have maximum biomass. Because the water-vapor exchange is restricted, the light and oxygen needs of the plants cannot be met, and biomass declines. This has been confirmed previously [64,71,72]. In the present experiment, the biomasses of T. orientalis and Z. caduciflora first increased and then decreased with increasing water depth, reaching the maximum at 40 cm. The biomass decreased with increasing water depth beyond 40 cm, indicating that the window of opportunity for T. orientalis and Z. caduciflora occurred at 40 cm. T. orientalis and Z. caduciflora obtained the best growth environment at a water depth of 40 cm.
Water depth changes the biomass allocation pattern; it changes the ratio of above-ground and below-ground biomass [73,74], and the root-shoot ratio is an important indicator reflecting the trade-off strategy of plant resources in underground and above-ground parts [68]. Most plants allocate biomass to above-ground parts with increasing water depth [75,76]. Han et al. (2019) [77] showed that reeds allocate more biomass to the stems under flooded conditions [78]. Lan et al. (2019) [18] reported that the root-shoot ratio of Carex cinerascen decreases significantly under continuously flooded conditions. In the present experiment, the root-shoot ratios of T. orientalis and Z. caduciflora decreased with increasing water depth, and the root-shoot ratios at water depths of 80–120 cm were lower than those at water depths of 20–60 cm (Figure 4g and Figure 5g). This is because less oxygen is available to the root system in a flooded environment, and the transport of carbohydrates to the roots will decrease, which leads to insufficiencies [78]. In contrast, emergent plants reduce the oxygen consumption of respiration by reducing the weight of the root system.

4.4. Effects of Different Water Depths on Chlorophyll Fluorescence Parameters of the Emergent Plants

The photosynthetic fluorescence parameters are closely related to the photosynthetic rate, and accurately reflect the actual photosynthetic conditions [79]. The maximum photon yield (Fv/Fm) reflects the quantum yield when all PSII reaction centers are in an open state and the potential light energy conversion efficiency of the PSII reaction centers is maximum [80,81]. Fv/Fm changes very little when plants are under favorable conditions. The Fv/Fm of normal growing plants is about 0.8 but decreases significantly in plants under stress [82]. The Fv/Fm of the leaves of T. orientalis and Z. caduciflora tended to decrease with increasing water depth, and both Fv/Fm were less than 0.8, indicating that T. orientalis and Z. caduciflora were under water depth stress, which resulted in different degrees of damage to the PSII reaction centers, and the primary response of photosynthesis was inhibited [83]. The decrease in CO2 concentration with increasing water depth led to an insufficient supply of CO2 during the dark reaction stage of photosynthesis, which reduced the conversion efficiency and activity of the reaction centers. Additionally, light intensity also decreases with increasing water depth, and the intensity cannot satisfy the excitation energy captured by the PSII reaction centers [84].
The rapid light response curve represents the change in the ETR with light intensity, and also reflects the adaptability of the plant to changes in the light environment. The larger the ETRmax, the stronger the adaptability of the leaves [85]). In our experiment, the ETR of each water depth treatment group of T. orientalis and Z. caduciflora first increased rapidly and then decreased slowly when water depth was increased, indicating that the ability of the emergent plants to respond to light was reduced under the deep-water conditions. Under the same water depth, the ETR values of Z. caduciflora were higher than that of T. orientalis, indicating that the adaptability of Z. caduciflora to light was better than that of T. orientalis. The initial slope (α) of the ETR curve reflects photosynthetic capacity under low light and is proportional to the light-harvesting capacity of the leaves [86]. The α of T. orientalis was largest at the 20 cm water depth, whereas Z. caduciflora was largest at the 60 cm water depth. We speculated that the light-harvesting and light-utilizing abilities of the T. orientalis and Z. caduciflora at 20 cm and 60 cm, respectively, were greater than those of the other water depth treatment groups.

5. Conclusions

(1)
The in-situ water depth experiment showed that water depth had no significant effect on the germination of T. orientalis or Z. caduciflora, and the germination rates of the two were 90% and 85%, respectively.
(2)
The water depth changed the morphological characteristics of T. orientalis and Z. caduciflora. Plant height, tiller number, leaf length, leaf width, leaf number, and the root-shoot ratio decreased with increasing water depth, whereas the number of dead leaves increased with increasing water depth.
(3)
The biomass of the emergent plants increased first and then decreased with increasing water depth, and the biomass was largest when the water depth was 40 cm.
(4)
The maximum Fv/Fm of the emergent leaves was higher in the 20–60 cm water depth range. The ETRmax values of the treatment groups were significantly different. The ETRmax of the two emergent plants was highest when water depth was 20 cm.
(5)
Pioneer species of emergent plants have strong morphological plasticity to water depth changes but have a particular tolerance range. The suitable water depth range for T. orientalis and Z. caduciflora seedlings is 20–60 cm, and a higher water depth for a long time is not conducive to growth.

Author Contributions

Conceptualization and methodology, X.L. and Z.G.; experiment, X.W. and X.G.; software and figure image, X.L. and X.W.; data curation, J.X., L.T. and H.W.; writing, X.L.; review and editing, X.W. and X.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science and Technology Research Project of Education Department of Hubei Province (No. Q20182502) and graduate innovative research project construction of Hubei Normal University by Hubei Normal University (No. 20220454).

Data Availability Statement

The datasets generated and/or analyzed during the current study are available from the corresponding author on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The map of study area. The study area is located in the northern part of Lake Gehu. The highway divides the lake into two separate lakes.
Figure 1. The map of study area. The study area is located in the northern part of Lake Gehu. The highway divides the lake into two separate lakes.
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Figure 2. (a) In situ experiment design of emergent plants. T. orientalis being gently lifted to the surface. (b) the design of our experiment. The outermost is a net to keep fish out.
Figure 2. (a) In situ experiment design of emergent plants. T. orientalis being gently lifted to the surface. (b) the design of our experiment. The outermost is a net to keep fish out.
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Figure 3. The germination rates of T. orientalis (a) and Z. caduciflora (b) rhizomes. The error bars represent SE. The lowercase letters indicate that T. orientalis and Z. caduciflora have insignificant differences (p < 0.05) in germination at different water depths.
Figure 3. The germination rates of T. orientalis (a) and Z. caduciflora (b) rhizomes. The error bars represent SE. The lowercase letters indicate that T. orientalis and Z. caduciflora have insignificant differences (p < 0.05) in germination at different water depths.
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Figure 4. The morphological characteristics of T. orientalis at the water depth of 20, 40, 60, 80, 100, 120 cm. Plant height (a), tiller (b), leaf number (c), dead leaf (d), leaf length (e), leaf width (f), root/shoot (g), and biomass (h). The error bars represent SE. Different lowercase letters (a–e) indicate that T. orientalis have significant differences (p < 0.05) in morphological characters at different water depths.
Figure 4. The morphological characteristics of T. orientalis at the water depth of 20, 40, 60, 80, 100, 120 cm. Plant height (a), tiller (b), leaf number (c), dead leaf (d), leaf length (e), leaf width (f), root/shoot (g), and biomass (h). The error bars represent SE. Different lowercase letters (a–e) indicate that T. orientalis have significant differences (p < 0.05) in morphological characters at different water depths.
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Figure 5. The morphological characteristics of Z. caduciflora at the water depth of 20, 40, 60, 80, 100, and 120 cm. Plant height (a), tiller (b), leaf number (c), dead leaf (d), leaf length (e), leaf width (f), root/shoot (g), and biomass (h).The error bars represent SE. Different lowercase letters (a–d) indicate that Z. caduciflor have significant differences (p < 0.05) in morphological characters at different water depths.
Figure 5. The morphological characteristics of Z. caduciflora at the water depth of 20, 40, 60, 80, 100, and 120 cm. Plant height (a), tiller (b), leaf number (c), dead leaf (d), leaf length (e), leaf width (f), root/shoot (g), and biomass (h).The error bars represent SE. Different lowercase letters (a–d) indicate that Z. caduciflor have significant differences (p < 0.05) in morphological characters at different water depths.
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Figure 6. Photosynthetic fluorescence characteristics of T. orientalis at different water depths. The error bars represent SE. The first picture is the maximum photon yield (Fv/Fm) of T. orientalis (a). The second picture is the maximum electron transfer rate (ETR) of T. orientalis (b). ETR values were calculated using the formula: ETR = Yield × PAR × 0.84 × 0.5.
Figure 6. Photosynthetic fluorescence characteristics of T. orientalis at different water depths. The error bars represent SE. The first picture is the maximum photon yield (Fv/Fm) of T. orientalis (a). The second picture is the maximum electron transfer rate (ETR) of T. orientalis (b). ETR values were calculated using the formula: ETR = Yield × PAR × 0.84 × 0.5.
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Figure 7. Photosynthetic fluorescence characteristics of Z. caduciflora at different water depths. The error bars represent SE. The first picture is the maximum photon yield (Fv/Fm) of Z. caduciflora (a). The second picture is the maximum electron transfer rate (ETR) of Z. caduciflora (b). ETR values were calculated using the formula: ETR = Yield × PAR × 0.84 × 0.5.
Figure 7. Photosynthetic fluorescence characteristics of Z. caduciflora at different water depths. The error bars represent SE. The first picture is the maximum photon yield (Fv/Fm) of Z. caduciflora (a). The second picture is the maximum electron transfer rate (ETR) of Z. caduciflora (b). ETR values were calculated using the formula: ETR = Yield × PAR × 0.84 × 0.5.
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Figure 8. The water level of Lake Gehu from 17 March to 20 May.
Figure 8. The water level of Lake Gehu from 17 March to 20 May.
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Table
Table 1. Physical and chemical properties of water and sediment.
Table 1. Physical and chemical properties of water and sediment.
Water (mg/L)Sediment (mg/g)
TPTNNH3-NCODMnChl-aTPTN
0.0892.970.2130.030.542.69
TP: total phosphorus; TN: total nitrogen; NH3-N: ammonia nitrogen; CODMn: permanganate Index; Chl-a: chlorophyll a.
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Lin, X.; Wu, X.; Gao, Z.; Ge, X.; Xiong, J.; Tan, L.; Wei, H. The Effects of Water Depth on the Growth of Two Emergent Plants in an In-Situ Experiment. Sustainability 2022, 14, 11309. https://doi.org/10.3390/su141811309

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Lin X, Wu X, Gao Z, Ge X, Xiong J, Tan L, Wei H. The Effects of Water Depth on the Growth of Two Emergent Plants in an In-Situ Experiment. Sustainability. 2022; 14(18):11309. https://doi.org/10.3390/su141811309

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Lin, Xiaowen, Xiaodong Wu, Zhenni Gao, Xuguang Ge, Jiale Xiong, Lingxiao Tan, and Hongxu Wei. 2022. "The Effects of Water Depth on the Growth of Two Emergent Plants in an In-Situ Experiment" Sustainability 14, no. 18: 11309. https://doi.org/10.3390/su141811309

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