Effects of flooding stress on the growth and photosynthetic characteristics of napier grass (Pennisetum purpureum Schum. Guimu-1)

doi:10.21203/rs.3.rs-4712292/v1

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Effects of flooding stress on the growth and photosynthetic characteristics of napier grass (Pennisetum purpureum Schum. Guimu-1)

https://doi.org/10.21203/rs.3.rs-4712292/v1

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Napier grass (Pennisetum purpureum) holds significant forage value in many tropical and subtropical regions. To investigate the production adaptability of napier grass in flood-prone areas, napier grass seedlings were selected to conduct a flooding stress experiment. By simulating different flooding durations and depths indoors, we studied the changes in the morphology of napier grass leaves, leaf photosynthetic and chlorophyll fluorescence parameters. The results indicated the occurrence of yellow leaves across all three groups. Specifically, under shallow flooding conditions, the tips of the leaves of napier grass turned yellow. In semi-flooding conditions, the leaves of napier grass yellowed, wilted, developed brown spots, and the stem base exhibited reddish-brown swelling. Under fully flooding conditions, the growth of napier grass was significantly impacted, with partial shedding of leaves and stems, and a mortality rate reaching 60% after 12 days. Both shallow and semi-flooding treatments induced the formation of aerial roots at the base of the stem in napier grass. The photosynthetic parameters Pn, Gs, Ci, and Tr of napier grass showed an overall downward trend under flooding stress. After the experiment, the values Fv/Fo, Fv/Fm, NPQ, and Qp of napier grass under flooding conditions were higher than those in the control group at the same time point, while the other two groups were lower than the control. Based on these findings, we conclude that napier grass exhibits good adaptability in shallow flooding environments, and can survive for 12 days under semi-flooding conditions.

Biological sciences/Plant sciences/Plant stress responses/Flooding

Biological sciences/Plant sciences/Photosynthesis/Photosystem ii

Global flooding events are expected to increase in the coming decades¹. This kind of abiotic stress has become one of the main challenges faced by plants². It significantly affects plant growth and development, especially in regions with large populations and limited cultivated land resources such as China³. Therefore, it is crucial to understand the response and adaptation mechanisms of plants to flooding stress. Exploring the interaction between abiotic stress and plant morphology and physiological processes not only helps to deeply understand and evaluate the flood tolerance of plants but also helps to identify opportunities and develop strategies to address these challenges. It provides a scientific basis for fully utilizing floodplain land resources and improving horticultural practices in the future⁴.

Flooding stress causes morphological changes in plants, especially those related to leaf photosynthesis. There is a close correlation between phenotypic plasticity and the adaptability of plants in flooding environments⁵. The roots, stems, and leaves of plants will make corresponding morphological adjustments to cope with the changes in habitat caused by water level fluctuations⁶. These adjustments mainly manifest as increased aboveground biomass, increased root porosity, development of aerial roots, reduced leaf area, regulation of stomata, and development of nutrient-rich lenticels⁷. These adaptive changes help plants maintain their growth and survival under waterlogging conditions. The consequence of waterlogging damage is the reduction of CO₂ influx into the leaves, which also reduces transpiration and leads to leaf wilting. To adapt to waterlogging stress, plants adopt an escape strategy, mainly manifested in the rapid vertical elongation of leaves, internodes, or petioles to restore contact between the leaves and the atmosphere and provide better opportunities for plants to survive under long-term shallow flooding⁸. For example, sesame (Sesamum indicum) exhibits rapid increases in plant height after short-term flooding⁹. Another strategy is the quiescence strategy, which is characterized by maintaining stable energy conservation without elongating buds. For instance, tomatoes exhibit smaller size and leaf area under waterlogging stress, and plant height tends to decrease significantly¹⁰. The impact of waterlogging stress on leaf morphology and biomass depends on the plant's growth stage, duration, and species¹¹. There are complex interactions between the intensity and duration of water stress and environmental factors. As the duration of flooding increases, the survival of plants will also be threatened. The survival rate of B. planiculmis under extended flooding treatment decreased significantly, with 5 out of 35 pots dying before the end of the experiment¹². The formation of adventitious roots is a typical adaptive change in plants under waterlogging stress¹³. For example, cucumber (Cucumis sativus) produces adventitious roots (AR) after 10 days of flooding to promote gas exchange, water and nutrient absorption, and enhance the plant's tolerance to flooding¹⁴. Waterlogging stress can reduce the photosynthetic efficiency of plants due to its effects on stomatal and non-stomatal factors¹⁵. Leaf gas exchange parameters are important indicators reflecting the damage to the photosynthetic system under stress conditions. Studies have shown that with increasing flooding duration, photosynthesis in spring maize (Zea mays) decreases, manifesting as gradual reductions in leaf Pn, Tr, Gs, and Ci¹⁶. The light energy absorbed by chlorophyll in plant leaves mainly flows to photosynthetic electron transport, chlorophyll fluorescence, and heat dissipation, and there is a reciprocal relationship between the three. Changes in photosynthesis and heat dissipation can cause corresponding changes in fluorescence emission. Therefore, changes in chlorophyll fluorescence in plants can be used as a probe to reflect photosynthesis. Chlorophyll fluorescence is an ideal reference for studying the physiological state of plant photosynthesis and its relationship with the environment. Under initial waterlogging stress, the activity of PSII reaction centers in mulberry seedling leaves decreases, manifesting as significant reductions in Fo, Fm, QY, Fv/Fo, Rfd, and QP¹⁷.

Napier grass (Pennisetum purpureum) possesses significant forage value in many tropical and subtropical regions, characterized by high yield, good quality, wide adaptability, few pests and diseases, strong coverage, and high utilization rate^18,19. Current research on napier grass mainly focuses on its yield and value under different factors^20,21,22, heat tolerance genes and molecular mechanisms²³, and phytoremediation²⁴. However, there is still a lack of research on napier grass in the vegetative growth stage under waterlogging stress. The purpose of this study is to investigate the effects of different waterlogging durations and depths on the growth, photosynthetic characteristics, and chlorophyll fluorescence characteristics of napier grass, aiming to provide theoretical support for planting napier grass in flood-prone areas.

Morphological responses to flooding stress

All three treatment groups exhibited yellowing leaves after 3 days of flooding (Table 1), while T1 continuously produced new leaves at the top of the test materials. On the 6th days of flooding, the yellow leaves at the lower part of T2 continued to wilt and exhibited a soft rot-like appearance. Both T1 and T2 developed aerial roots at the flooding line, floating on the water surface. On day 9, yellow leaves and brown spots appeared in the middle leaves of all three treatment groups. On the 12th day of flooding (Fig. 1), T2 showed reddish-brown swelling at the base of the stem, and aerial roots grew at each stem node, with significantly more aerial roots at the flooding line than at other stem nodes. Plant death occurred in T3, with a survival rate of 40%.

Effects of flooding stress on morphological changes

Figure 2 demonstrates that varying flooding durations and depths significantly affect the plant height and leaf number of napier grass (p < 0.05). Additionally, there is an interactive effect between flooding depth and duration on both plant height and leaf number (p < 0.05).

Specifically, the plant height of T1 and T2 increased with longer flooding durations, while T3 exhibited a significant decrease (Fig. 2a). By the 12th day, compared to day 0, the increases were 32.11% and 9.06% respectively, with the difference in T1 being statistically significant (p < 0.05). The plant height of T3 significantly decreased with longer flooding durations, resulting in a 39.34% reduction compared to the start of the experiment by the 12th day, which was also statistically significant (p < 0.05). After 3 days of flooding, the plant heights of T1 and T2 increased by 7.61% and 2.04% respectively, while T3 decreased significantly by 13.36% (p < 0.05). On day 6, T1 and T2 increased by 6.83% and 1.72%, while T3 decreased by 2.67%. After 9 days, T1 and T2 increased by 7.48% and 2.82%, with T3 experiencing a significant 25.98% reduction (p < 0.05). By the 12th day, T1 and T2 increased by 6.83% and 1.72%, while T3 decreased by 2.88%. On the 3rd day of flooding, the plant height of T1 was significantly higher than T2 and T3.

The number of leaves in T1 increased with flooding duration, while T2 and T3 showed a decrease (Fig. 2b). After 3 days of flooding, T1 increased by 6.80%, while T2 and T3 decreased by 6.09% and 20% respectively, with the difference in T3 being statistically significant (p < 0.05). By the 6th day, T1 increased by 2.72%, while T2 and T3 decreased by 9.68% and 20.88%, with the difference in T3 again being statistically significant (p < 0.05). After 9 days, T1 increased by 2.65%, while T3 decreased significantly by 42.18% (p < 0.05). By the 12th day, T1 and T2 increased by 3.45% and 3.54% respectively, while T3 decreased significantly by 45.36% (p < 0.05). During the 6th to 12th day of flooding, T1 was significantly higher than in groups T2 and T3.

Effects of flooding stress on photosynthetic parameters

Figure 3 demonstrates different flooding durations and depths significantly affect the values of Pn, Ci, Tr and Gs (p < 0.05), and there is an interaction between them (p < 0.05). The Pn, Gs, Tr values of T1, T2, and T3 decreased over time. The values Ci of T1 and T2 decreased, while that of T3 increased. Specifically, the Pn values of T1 and T2 increased significantly by 32.19% and 4.92% (p < 0.05) on the 3rd day of flooding, whereas T3 decreased by 68.20% (Fig. 3a). However, as flooding progressed, the Pn of T1 and T2 gradually decreased, notably by 13.35% and 28.57% (p < 0.05) on the 6th day, and 18.70% and 13.51% (p < 0.05) on the 12th day. In contrast, the Pn of T3 rebounded on the 6th day, increasing by 72.39%. Notably, during the 6th to 9th day of flooding, the Pn of T1 was significantly higher than T2 and T3 (p < 0.05). On the 3rd day of flooding, the Gs of T1, T2, and T3 all decreased significantly, with T1 and T2 declining by 33.33% and 18.18% respectively, and T3 experiencing the largest drop of 58.33% (p < 0.05) (Fig. 3d). However, on the 9th day, the Gs of T1 and T2 increased significantly by 66.67% and 12.5% respectively, while T3 continued to decrease by 33.33%. By the 12th day, the Gs of T1 had declined significantly by 40% (p < 0.05). But on the 9th day, the Gs of T1 was significantly higher than T2 and T3 (p < 0.05). The Ci of T1 and T2 increased initially during flooding but then gradually decreased, while T3 exhibited an opposite trend (Fig. 3c). Specifically, on the 3rd day, the Ci of T1 and T2 increased by 9.08% and 3.79% respectively, while T3 decreased by 40.06%. By the 12th day, the Ci of T1 and T2 had declined by 15.87% and 2.34% respectively (Fig. 3b). The Tr of T1, T2, and T3 decreased significantly on the 3rd day of flooding, with T1 and T2 declining by 27.40% and 65.33% respectively, and T3 by 46.17% (p < 0.05). However, in the later stages of flooding, the Tr of T1 and T2 rebounded, especially on the 12th day, where Tr of T1 and T2 increased significantly by 54.44% and 9.57% (p < 0.05), while T3 continued to decrease.

Effects of flooding stress on the kinetic parameters of chlorophyll fluorescence

Figure 4 shows different flooding durations and depths significantly affect the Fv/Fo, Fv/Fm, NPQ, and Qp values of Guimu-1 leaves (p < 0.05), and there is an interactive effect between flooding depth and duration on these parameters (p < 0.05). Specifically, the Fv/Fo values of T1, T2, and T3 decreased over time (Fig. 4b). By the third day of flooding, the Fv/Fo values of T1, T2, and T3 leaves decreased significantly by 23.01%, 31.34%, and 42.72%, respectively (p < 0.05). By the sixth day, these values increased by 1.99%, 21.38%, and 56.36%, respectively. On the ninth day, the Fv/Fo values of T1 and T2 increase by 17.27% and 29.25%, respectively, while T3 decreases by 28.46%. By the 12th day, the Fv/Fo value of T1 increases by 1.66%, while T2 decreases by 10.85%. The Fv/Fm values of T2 and T3 leaves decreased with flooding duration, while T1 also decreased but recovered to pre-experiment values between the 9th and 12th day of flooding (Fig. 4a). By the third day, the Fv/Fm values of T1, T2, and T3 leaves decreased significantly by 4.93%, 7.5%, and 13.75%, respectively (p < 0.05). By the sixth day, these values increased significantly by 14.29%, 4.05%, and 14.49%, respectively (p < 0.05). On the ninth day, the Fv/Fm values of T1 and T2 increased significantly by 3.85% and 3.08%, respectively (p < 0.05), while T3 decreases by 7.59%. By the 12th day, the Fv/Fm value of T2 decreased significantly by 2.47% (p < 0.05). The NPQ values of T1, T2, and T3 leaves decreased with flooding duration (Fig. 4c). By the third day, the NPQ values of T1 and T3 decreased by 10.71% and 36.27%, respectively, while T2 increased significantly by 27.36% (p < 0.05). By the sixth day, the NPQ values of T1 and T2 decreased significantly by 46% and 49.63%, respectively (p < 0.05), while T3 increased by 16.92%. On the ninth day, the NPQ values of T1 and T2 increased significantly by 75.93% and 58.82%, respectively (p < 0.05), while T3 decreased by 9.21%. By the 12th day, the NPQ value of T1 increased significantly by 12.63% (p < 0.05), while T2 decreased significantly by 16.67% (p < 0.05). The Qp value of T1 leaves rise, while the qp values of T2 and T3 leaves decreased over time (Fig. 4d). By the third day, the Qp values of T1 and T2 leaves decreased significantly by 7.5% and 9.88%, respectively (p < 0.05). By the sixth day, the Qp values of T1, T2, and T3 leaves increased significantly by 12.16%, 10.96%, and 3.66%, respectively (p < 0.05). On the ninth day, the Qp values of T1, T2, and T3 leaves decreased by 4.82%, 12.35%, and 11.76%, respectively. By the 12th day, the Qp value of T1 increased significantly by 5.06% (p < 0.05), while T2 decreased significantly by 1.25% (p < 0.05).

Correlations between various indexes of Pennisetum purpureum Schum. Guimu-1 leaves under flooding stress

Table 2 shows a highly significant positive correlation between leaf number and plant height, Pn, Gs, Tr, Fv/Fm, and Fv/Fo. Additionally, there is a significant positive correlation with NPQ. Similarly, plant height exhibits a highly significant positive correlation with Pn, Gs, Fv/Fm, and Fv/Fo, along with a significant positive correlation with transpiration rate Tr. Pn demonstrates a highly significant positive correlation with Gs, Ci, Fv/Fm, and Fv/Fo. It also shows a significant positive correlation with Tr and NPQ. Gs displays a highly significant positive correlation with Tr, Fv/Fm, and Fv/Fo, coupled with a significant positive correlation with NPQ. Ci exhibits a significant negative correlation with Tr. Meanwhile, Tr demonstrates a highly significant positive correlation with Fv/Fm and Fv/Fo. Fv/Fm shows a highly significant positive correlation with Fv/Fo and NPQ, along with a significant positive correlation with NPQ itself. NPQ exhibits a highly significant negative correlation with Qp.

This study investigated the effects of shallow flooding, semi-flooding, and fully flooding environments on the growth, photosynthetic characteristics, and chlorophyll fluorescence parameters of napier grass. We found that the growth of napier grass was affected to varying degrees with the increase in flooding stress time and depth.

Leaves are one of the most sensitive organs of plants to adversity stress²⁵. Plant height, leaf number, and survival rate are indirect indicators reflecting the degree of plant damage. Throughout the flooding process, yellow leaves appeared in all three treatment groups since the 3rd day of the experiment, which directly reflected the inhibition of photosynthesis in napier grass by flooding stress. This may be due to the degradation of napier grass chlorophyll or the obstruction of new chlorophyll synthesis, leading to a reduction in photosynthesis efficiency. T2 and T3 exhibited more severe leaf withering and shedding with the extension of flooding time. This is similar to the response of Artemisia selengensis under flooding, indicating that flooding time and depth severely hinder the gas exchange between plants and the outside world²⁶. The growth rate of plant height and leaf number in T1 were significantly higher than CK, which is consistent with the growth trend of Oryza sativa under flooding stress. This suggests that napier grass has a certain survival ability and adaptability in waterlogged environments, and moderate flooding can promote the growth of elephant grass²⁷. The continuous increase in plant height in T1 and T2 indicates that although the flooding conditions in these two groups have a certain impact on the growth of napier grass, they have not completely inhibited its growth. However, the plant height of T3 continued to decline since the 3rd day of flooding, and the survival rate was only 40% at the end of the experiment, which further proves that napier grass cannot adapt to a fully flooded environment for a long time.

Plants adjust their morphological characteristics under different water environments and evolve a series of mechanisms through long-term adaptation to ensure their normal growth and survival. There is a positive correlation between the formation of adventitious roots (ARs) and aerenchyma and waterlogging tolerance²⁸. Plants develop aerial roots that float on the water surface at the base of their stems, replacing the primary roots that suffocate due to lack of oxygen, thus enhancing their ability to tolerate flooding²⁹. Napier grass adapts to the environment by changing its morphology to ensure its growth and development under flooding stress. We found that under T1 and T2 treatments, white protrusions similar to aerial roots appeared at the base of stems, which is consistent with the phenomenon observed in Polygonum hydropiper under flooding stress. This is a paramount response of plant stems after flooding³⁰. With different flooding depths, there are also differences in the plant positions where aerial roots are generated in napier grass. After 12 days of flooding, all stem nodes of T2 grew aerial roots, and the number of aerial roots at the flooding line was significantly higher than at other stem nodes. With the increase in flooding time, the number of aerial roots increased, which is consistent with the morphological characteristics of Pennisetum × sinese after flooding. These aerial roots can replace some functions of the suffocated roots and have more air chambers to ensure the survival of napier grass ³¹. The formation of external roots (ARs) transfers the root system to a higher position in the plant, promoting oxygen supply and improving the survival of roots and plants²⁴. For example, the long-term hypoxia tolerance mechanism of tomatoes seems to be an escape mechanism that avoids low oxygen concentrations through the formation of aerenchyma and adventitious roots³². However, during the experiment, T3 did not form aerial roots, further indicating that napier grass cannot adapt to a full-submergence environment for a long time.

Leaf gas exchange parameters can reflect the degree of damage to the photosystem under flooding stress. We found that different flooding durations and flooding depths both had significant effects on napier grass (p < 0.05). Overall, during the experimental period, napier grass exhibited an adaptive strategy in response to flooding stress, which manifested as a general downward trend in the four parameters of leaf Pn, Gs, Ci, and Tr. This trend is consistent with the photosynthetic parameters observed in sorghum leaves under water stress³³. In the early stage of the experiment (3d), the Gs of T1 and T2 showed a decreasing trend while Ci increased. This is a protective mechanism for napier grass to maintain its photosynthetic capacity. Guimu-1 closes its stomata to prevent excessive transpiration and maintain leaf water potential, further delaying leaf senescence and chlorosis³⁴. This further demonstrates that napier grass has a certain degree of flood tolerance in environments with less than half-flooding. The Tr of T3 showed a continuous and significant downward trend during flooding, similar to the phenomenon observed in Euterpe oleracea during waterlogging³⁵. This indicates that under full flooding stress, stomatal factors may be the main reason for the decrease in photosynthetic rate of napier grass. Regarding stomatal factors, chemical signals from the roots are transmitted to the leaves, forcing the closure of stomata and reducing photosynthetic rate by decreasing the absorption capacity of photosynthetic substrate CO2³⁶. This suggests that full flooding environments can affect photosynthesis in napier grass leaves, and napier grass cannot adapt to a continuous 16-day full flooding environment.

Chlorophyll fluorescence parameters are often used to observe plants' adaptability and tolerance to changes in growth environments during stress. We found that the Fv/Fm and Fv/Fo of napier grass leaves in T3 were significantly lower than those in CK, consistent with the research results of Catalpa ovata under flooding stress. This further proves that flooding stress can lead to damage to the chloroplast photosynthetic apparatus of napier grass, inhibiting the primary reaction process of photosynthesis and reducing the efficiency of photosynthetic carbon dioxide assimilation³⁷. With the prolongation of flooding duration, the Fv/Fm and Fv/Fo of napier grass in T3 and T2 showed a downward trend at 9d and 12d, respectively, indicating that napier grass has a certain degree of flood tolerance but lacks the ability to adapt to long-term flooding depths above semi-flooding. In this experiment, significant differences in NPQ and Qp of napier grass were observed under different flooding depths and durations. As flooding duration increased, NPQ in T1 and T2 leaves showed a significant increasing trend, similar to the trend observed in lucerne leaves under waterlogging stress³⁸. During the 6-8d flooding period, the NPQ and Qp of leaves in T1 and T2 showed opposite trends, with NPQ significantly increasing and qp significantly decreasing. The decrease in Qp indicates that flooding stress damaged the photosynthetic apparatus of napier grass, interfering with the electron transfer process and reducing the activity of the PSII reaction center¹⁷. Meanwhile, the increase in NPQ suggests that under flooding stress, napier grass activates protective adaptation mechanisms to increase heat dissipation, thereby reducing the inhibition and damage of flooding on the PSII system. However, the negative correlation between NPQ and Qp may indicate that under extreme flooding stress, this protective mechanism may not fully counteract the damage caused by the stress to the photosynthetic apparatus. Future research can further delve into aspects such as evaluating the longer-term flooding tolerance of napier grass over time, investigating the repair mechanisms of the photosynthetic apparatus, and exploring the antioxidant system response, in order to gain a deeper understanding of the flooding tolerance of napier grass.

Based on our experiments, we have concluded that napier grass possess a certain level of flood tolerance, which can be affected by the duration and depth of flooding. Under shallow flooding conditions, napier grass demonstrate robust adaptability, sustaining growth and leaf production while maintaining high Pn and Gs. Additionally, it partially recovers Tr in later stages, supporting growth and development in flooded environments. It also restores or maintains high Fv/Fo, Fv/Fm, and Qp values, effectively dissipating excess light energy to mitigate photoinhibition. Under semi-flooding conditions, napier grass show moderate flood tolerance, coping with stress by increasing aerial root production. However, under fully flooding conditions, it is highly sensitive, displaying poor flood tolerance with significant declines in Pn, Gs, and Tr, and an increase in Ci, indicating severe photosynthetic inhibition. Chlorophyll fluorescence parameters are also significantly impacted, indicating severe stress on photosynthetic machinery. This study provides insights into napier grass's response to flooding stress and scientific basis for its cultivation and management in flood-prone areas.

Plant materials and cultivation

On May 11, 2023, 50 Pennisetum purpureum Schum. Guimu-1 seedlings (average plant height of 20cm) were planted in plastic pots with a top diameter of 21cm and a height of 18cm (one plant per pot) and placed at the horticultural nursery of Hunan Agricultural University (28º 17' 72" N, 113º 08' 24" E). The nursery is located in the southeast of China, which has a subtropical monsoon climate with an annual average temperature of 17.2℃ and a multiyear average precipitation ranging from 1358.6mm to 1552.5 mm. The potting substrate was prepared with river sand soil, loess, nutrient soil, and perlite in a ratio of 4:3:2:1.

Experimental design and treatment

On August 4, 2023, a flooding stress experiment was conducted on well-grown napier grass (average plant height of 160cm). The experiment involved four treatments, with five repetitions for each treatment: a shallow flooding treatment (T1), with a flooding depth exceeding 2cm above the soil surface; a semi-flooding treatment (T2), with a flooding depth of 50cm; a fully flooding treatment (T3), with the plants completely submerged up to the top; CK, maintaining regular and normal watering and maintenance. Before the experiment, all test materials were thoroughly watered, and all were placed in foam boxes of the same specifications filled with tap water. The foam boxes were promptly refilled to the corresponding water level every day. The flooding stress experiment ended on August 16, 2023, lasting for 12 days.

Observation of external morphological changes

Observations and recordings of the external morphological characteristics of the test materials, including plant height, leaf numbers, leaf color, leaf condition, and adventitious root formation, were conducted using a camera and tape measure at 9:00 AM each day of the cycle. These observations were compared with the CK group. On August 7, 2023, when the experiment began, a camera was used to record the initial morphological characteristics of each plant's experimental material. After the experiment, the survival rate was calculated using the formula:

$$\:\left(\right(\text{N}\_\{\backslash\:\text{t}\text{e}\text{x}\text{t}\{\text{t}\text{o}\text{t}\text{a}\text{l}\left\}\right\})\:-\:(\text{N}\_\{\backslash\:\text{t}\text{e}\text{x}\text{t}\{\text{d}\text{e}\text{a}\text{t}\text{h}\left\}\right\}\left)\right)\:/\:(\text{N}\_\{\backslash\:\text{t}\text{e}\text{x}\text{t}\left\{\text{t}\text{o}\text{t}\text{a}\text{l}\right\}\left\}\right)\:\text{*}\:100\text{%}$$

Photosynthetic parameters

The photosynthetic parameters of the second or third leaf of Pennisetum purpureum Schum. Guimu-1 under different flooding gradients were measured using the LI-6400XT portable photosynthetic apparatus (Li-COR, USA). The measurement indicators, including the net photosynthesis rate (Pn), the transpiration rate (Tr), the stomatal conductance (Gs), and the intracellular CO₂ concentration (Ci), were obtained by utilizing the photosynthetic active radiation (PAR) set at 1600µmol m^− 2 from the LED light source, while the CO2 concentration was maintained at 360µmolmol^− 1 through the buffer bottle. Each measurement was repeated three times, and the average value was taken. The measurements were conducted between 09:00 and 11:00 in the morning, once every 3 days.

Determination of the kinetic parameters of chlorophyll fluorescence

Chlorophyll fluorescence parameters were measured, including the potential photochemical efficiency of PSII (Fv/Fo), the maximum photochemical efficiency of PSII (Fv/Fm), the non-photochemical quenching coefficient (NPQ), and the photochemical quenching coefficient (Qp) using a FP 110 handheld chlorophyll fluorescence meter (FluorPen, CZ). Before the measurement, leaves of Pennisetum purpureum Schum. Guimu-1 were selected and dark-adapted for 20 minutes using a sample holder with aluminum foil. Each measurement was repeated three times, and the average value was taken. The measurements were conducted between 14:00 and 16:00 on the 0th, 3rd, 6th, 9th, and 12th day of the experiment.

Statistical analysis

The experimental data obtained was compiled using Microsoft Excel 2017. Two-way ANOVA and correlation analysis were performed on the data using SPSS 22.0 software. Duncan's multiple range test was conducted to estimate significant differences between treatments at a probability level of 0.05 (p < 0.05). The data visualization was created using Origin Pro 2021 software.

Author contributions statement

L.Y.L. contributed to supervising the study. L.Y.L., J.Y., L.C.Z. and W.C.J. conceived and designed the experiment. M.Q. and W.C.J. participated in the experiment. W.C.J. contributed to data analysis and writing the manuscript. L.C.Z. and W.C.J. prepared Figs. 1–3 and tables 1–2. All authors polished and approved the final manuscript.

Author Contribution

L.Y.L. contributed to supervising the study. L.Y.L., J.Y., L.C.Z. and W.C.J. conceived and designed the experiment. M.Q. and W.C.J. participated in the experiment. W.C.J. contributed to data analysis and writing the manuscript. L.C.Z. and W.C.J. prepared figures 1-3 and tables 1-2. All authors polished and approved the final manuscript.

Data Availability

All methods were performed following the relevant guidelines and regulations. All data generated or analyzed during this study are included in this published article.

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Tables 1 and 2 are available in the Supplementary Files section.

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Effects of flooding stress on the growth and photosynthetic characteristics of napier grass (Pennisetum purpureum Schum. Guimu-1)

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Abstract

Figures

Introduction

Results

Morphological responses to flooding stress

Effects of flooding stress on morphological changes

Effects of flooding stress on photosynthetic parameters

Effects of flooding stress on the kinetic parameters of chlorophyll fluorescence

Discussion

Conclusion

Methods

Plant materials and cultivation

Experimental design and treatment

Observation of external morphological changes

Photosynthetic parameters

Determination of the kinetic parameters of chlorophyll fluorescence

Statistical analysis

Declarations

Author contributions statement

Author Contribution

Data Availability

References

Tables

Additional Declarations

Supplementary Files

Status:

Version 1