Positive contribution of shoot apex to the growth and flooding tolerance of Hemarthria altissima upon complete submergence

ABSTRACT

Flooding events tend to destroy the original flood-intolerant vegetation in riparian zones, but the flood-tolerant species can confront the stress, and contribute to the riparian ecosystem. Grass species, Hemarthria altissima, are usually dominant in the riparian zones. This species is considered as good forage which is usually grazed by livestock or mowed by local people. Therefore, the apical tissues of the plants are often removed, and the plants have to grow without stem apexes, during their life cycle. In this study, we aimed to examine the differences in growth performance of intact versus apex-cut individuals of H. altissima upon complete submergence. Two groups of H. altissima plants (with and without shoot apexes) were treated with dark non-submergence and dark complete submergence conditions for 200 days. During the experiment, we measured plant growth, biomass changes in plant organs, and the consumption of non-structural carbohydrates (NSC) by different tissues. During submergence, shoot elongation stopped, and around six lateral buds were developed averagely by each plant without apexes. This growth performance finally caused 60% decline of NSC in underground parts. The relatively intensive consumption of carbohydrates in submerged apex-removed plants induced the 21% stem length decreased under water, which indicated the decreasing submergence tolerance of plants with shoot apex removed. Therefore, we suggest that when using H. altissima for restoring degraded riparian ecosystems, the shoot apexes should be protected from grazing by livestock or harvesting by local people in order to maintain the submergence tolerance of H. altissima.

摘要

完全水淹环境下茎顶端留存有助于牛鞭草维持水下生长和水淹耐受性

洪水(或者洪涝)会摧毁河岸带不具有水淹耐受性的植被，但具有水淹耐受性的植物物种可以克服这种胁迫，并能维持河岸带生态系统的稳定性。草本植物牛鞭草(Hemarthria altissima)是河岸带常见的一种耐淹植物，并且该物种被认为是优质牧草。生长在河岸带的牛鞭草幼嫩部分容易被牲畜啃食或者被当地老百姓刈割作为饲料，进而使得牛鞭草在其生活史内常因上述原因而损失其茎顶端。为了探究完全水淹环境下茎顶端完好和茎顶端缺失的牛鞭草是否会表现出不同的水下生长以及是否具有不同的水淹耐受性，我们对保留茎顶端和去除茎顶端的牛鞭草进行了200天的黑暗完全水淹和黑暗不水淹处理。同时，测量了其在处理期间的生长情况，各组织器官生物量的变化，以及不同组织器官对非结构性碳水化合物的消耗量。结果发现，顶端去除的牛鞭草在水淹处理期间停止了其主茎的伸长生长，但增强了侧芽/侧枝的生长(平均每株主茎新生长出约6个侧芽/侧枝)。完全水淹环境中茎顶端去除的牛鞭草植株的侧芽/侧枝生长增强导致植株地下部分非结构性碳水化合物含量下降了60%，植株主茎存活长度减少了约21%，使茎顶端去除的牛鞭草植株的水淹耐受性显著下降。因此，我们建议当应用牛鞭草对河岸带生态系统进行修复时，应避免牛鞭草茎顶端被牲畜啃食或者被刈割，从而保证其在受淹时具有较高的水淹耐受性。

INTRODUCTION

Plants growing in natural habitats and farmlands are commonly subjected to submergence, for instance in wetlands, riparian zones, sea shores and lowlands. Plant submergence is likely to become more widespread and frequent owing to increased number of flooding events and water level rise caused by global climate change (Hirabayashi et al. 2013; IPCC 2012; Opperman et al. 2009). Moreover, rapid growth of human population and economic development have been increasing the need for the construction of hydropower dams worldwide, e.g,. by 2014, a total of 3700 hydropower dams were planned or under construction (Zarfl et al. 2014). For energy production, the water levels of related rivers are being controlled to a quite high level, usually higher than the natural level. During the water storing period in dams and natural flooding seasons, a certain number of plants species growing on the riparian zones suffer adversely submergences during their life cycle (Yang et al. 2015). However, some plant species have a remarkable capability to endure these submerging conditions, and certain species can even grow vigorously in response to flooding (Bailey-Serres and Voesenek 2008).

Riparian vegetation plays a key role in: regulating microclimates and water quality; preventing riverbank erosion and promoting landform stability; subsidizing aquatic and terrestrial food webs; and providing habitat for a wide range of aquatic, amphibious and terrestrial organisms (Rusnák et al. 2022; Zhang et al. 2019). Grass species are usually dominant in the riparian zones, especially the region adjacent to the water surface. The grass species, Hemarthria altissima, grows in the riparian zones, which is a stoloniferous tropical grass of the family Poaceae. In its original habitat, this species is found along stream banks and in other wet or seasonably wet soils in southern Africa (Sellers et al. 2007). Moreover, in terms of economics, this species is considered as good forage which is usually grazed by livestock or mowing by local people, thereby making a contribution to local forage production (Pitman et al.1994). Therefore, most of the grass species are cut regularly, growing without stem apex during their life cycle. So, we formulate the first question, do the plants with intact or apex-cut stem adapt the environment in the same way? Generally, the solubility and diffusion of O₂ in water is lower than that in the atmosphere (Mcdonald et al. 2002), and complete submergence imposes severe stress for the aerobic metabolism of plants, so submerged plants usually confront an energy crisis. Some species have evolved complementary traits to facilitate escape from submergence stress and thus avoids carbohydrate starvation and oxygen depletion. These traits include upward growth of leaves, petiole/stem elongation, thinner leaves, re-orientation of chloroplasts, leaf gas film, aerenchyma and a barrier for radial oxygen loss (Colmer et al. 2019; Jiménez et al. 2024). The stem elongation facilitates shoots to reach the water surface and contact with atmosphere again to get enough oxygen. However, surprisingly little research attention has been given to the different adaptation of underwater growth performance between the plants with intact shoot and with apex removed stem. Therefore, it is easy to ask the second question, is the stem elongation of plants with intact stem stronger than that of plants with apex-cut stem under submergence condition?

Any production of new tissues needs to consume NSC to provide energy. However, under water, the entry of CO₂ into the plants is impeded and light amount is quite low, which greatly restricted the accumulation of carbohydrates from underwater photosynthesis (Pedersen et al. 2006); therefore, any growth of plant organs underwater needs consume the NSC which are reserved before submergence. Additionally, under hypoxia condition, the anoxic cells alter plant metabolism to increase anaerobic generation of ATP by cytosolic glycolysis (Bailey-Serres and Voesenek 2008; Striker and Colmer 2017). A crisis in ATP availability emerges because glycolysis is inefficient, yielding 2–4 mol of ATP per molecule of hexose, which is significantly lower than 30–36 mol ATP generated by the mitochondrial electron-transport chain (mtETC) (Bailey-Serres and Voesenek 2008). Therefore, more underwater growth happens in submerged plants, the more NSC are consumed. Based on these facts, we hypothesized that utilization of NSC is different between the plants with and without stem apex, if these plants have contrast adaptive traits under submergence.

To test our hypothesis, we compared the growth performance of H. altissima and the utilization of non-structural carbohydrates between the plants with and without stem apex upon complete submergence without any underwater photosynthesis. The verification of our hypothesis will expand and deepen our understanding of how plants respond to and tolerate flooding/submergence under different environmental regimes.

MATERIALS AND METHODS

Plant materials and growth conditions

Hemarthria altissima plants used in the experiments were cultivated from cuttings obtained in early spring from plants naturally growing on the banks of the Jialing River in Beibei, Chongqing, China (29° 50ʹ N, 106° 26ʹ E). Unbranched plants with stem length of approx. 35 cm were selected and cut at the stem base. Each cutting branch was planted individually in a plastic pot (15 cm diameter and 15 cm height) filled with a soil mixture of 40% clay, 40% humus soil, and 20% sand. Two stem nodes of each plant were buried in the soil for rooting. All plants were cultivated in an open field of the experimental garden of the Key Laboratory of the Three Gorges Reservoir Region’s Eco-Environment (Ministry of Education) in Southwest University (located in Chongqing, China) under the following ambient conditions: daytime temperature approx. 15–20 °C, relative humidity 70–85%, maximum daily light 500–900 µmol m⁻² s⁻¹, and they were provided with ample water (approx. 80%–90% of the soil water-holding capacity). The experimental garden was located approximately 2 km away from the banks of Jialing River. After cultivating about one month, the plants with similar stem length (around 50 cm) and number of leaves (about 10 leaves) were selected randomly for the following experimental treatments.

Experimental design

A total of 90 plants were selected to treat in this experiment. First, the total number of 45 plants (subsequently referred to as treated plants) were treated by removing the shoot apexes and one immature internode on the top of the shoots, the total length of which was around 0.5 cm. These shoot apexes and immature internodes were gently removed using a small knife, carefully avoiding hurting neighbouring leaves or tissues; the cuts were then covered with vaseline to prevent bacterial infections. Our pilot experiment had completely convinced us that there were no visible negative effects of the cutting technique conducted in our research. The other 45 plants (subsequently referred to as apex non-removed plants) were not cut their shoot apex. Additionally, all the petioles on the stems of all studied plants were marked by waterproof red maker in order to distinguish the newly produced leaves from the older ones during the experiment. After this, the submergence experiment was conducted as follows: 15 plant with apex and 15 plants without apex were placed in a concrete water tank (length × width × height: 5 m × 5 m × 2.5 m) located in the experimental garden. Then, the water tank was filled with tap water until the water level reached 2 m above the bottom of the tank. The top of the water tank was covered by six layers of black shading net to create completely dark conditions under water. During the submergence experiment, the water in the concrete tank was gently bubbled with air twice a day, and the dissolved oxygen concentration in water column was monitored at each half meter point under water to ensure it was maintained around 6.5–7 mg/L throughout the water column. The dissolved oxygen concentration was monitored by a multi-parameter water quality analyser (HYDRO Lab, Hach, USA). In addition, the water temperature was measured by the multi-parameter water quality analyser, and the temperature was about 19-20 °C throughout the experiment. The rest 15 plants with stem apex and 15 plants without stem apex were placed in a dark room as the non-submergence group. These plants were watered every day, the room temperature was controlled by air conditioner at around 19–20 °C. After 200 days of treatment, all submerged and non-submerged plants were harvested for further measurements.

Plant measurements before the experiment

In order to estimate the initial concentrations of total NSC in all plants before treatments, 15 plants with stem apex and 15 plants without stem apex were harvested before treatment. Each harvested plant was divided into aboveground part and underground part. Additionally, the aboveground stems after harvest divided into three parts equally, the one part nearest to the soil surface was called as the lower part of stem, the one part including the top of stem was called as the upper part of stem. The dry mass of the collected plant parts was determined after drying the stem to a constant weight at 70 °C. The concentrations of total NSC in different parts were determined which was described in below part.

Measurement of plant growth and biomass during the experiment

During the experiment, stem length of all treated plants was measured every 20 days. Because all of plants were under dark conditions, green light was used when the measurements were carried out, and the submerged plants were not taken out of the water during measuring.

After 200 days of treatment, all treated plants were harvested in order to determine their final stem length and total number of lateral buds. In addition, the stems, leaves, lateral buds, adventitious roots and underground plant parts were collected separately, and their biomass was determined after drying the plants to a constant weight at 70 °C.

NSC measurements

The NSC are defined here as free, low molecular weight sugars (glucose, fructose, sucrose, malt sugar and fructosan) plus starch. The plants harvested after submergence or non-submergence treatment were divided into aboveground part and underground part, as in the plants harvested before the experiment. After excising, drying, grinding, and weighing these plant parts, total NSC in different parts were determined as described in Wong (1979) and Hoch et al. (2003). Ground plant material firstly was extracted by 80% alcohol to determine the alcohol soluble sugar, which included glucose, fructose, sucrose and malt sugar. Then the rest ground material was extracted by distilled water to test the content of fructosan, which was called as water soluble sugar. At last, the remaining material was extracted by hydrochloric acid to determine the content of starch, called as insoluble sugar. In our study, the content of total NSC was sum of the content of alcohol soluble sugar, water soluble sugar and insoluble sugar.

Data analysis

Ratio of surviving stem length was calculated as follows: (the length of surviving stem after treatment/the total length of stem before treatment) × 100%.

The percentage of rest NSC content in different tissue was calculated as follows: The content of NSC in tissue after treatment/the content of NSC in tissue before treatment × 100%

Two-way ANOVA was conducted to evaluate the differences in length of newly produced stem, total number of lateral buds, biomass of lateral buds, biomass of newly produced organs, ratio of survived stem length and the percentage of rest NSC content of plants under different treatments. Independent samples t-test were applied to determine the differences between treatments. All statistical analyses were conducted in SPSS 21. Data transformation was performed to equalize variances when necessary.

RESULTS

In our study, the stem with or without apex showed different performance under different treatments (Fig. 1). Under non-submergence condition, the plants with apex increased their stem length during 200 days treatment. Under submergence condition, the shoots of the plants with apex grew very little after 90 days complete submergence, which increased 1.21 cm; after 120 days of submergence, the increase in shoot length reached 1.35 cm. After this, no increase in shoot length was observed until the end of the experiment. In contrast, the plants without apex completely stopped their shoot growth during the whole experimental period, whether submerged or not.

Besides stem growth performance, we investigated the different production of lateral buds on treated plants (Fig. 2). The production of lateral buds was significantly affected by stem apex removing (Supplementary Table S1). No matter under completely submerged or non-submerged conditions, the H. altissima plants with removed apexes produced more lateral buds on stem. Under submergence treatment, the plants without apex produced around 5.6 lateral buds on average which were in 0.0207 g total biomass, which was significantly higher than that in plants with apex. The plants with apex only produced 1.1 lateral buds in 0.0008 g total biomass (Fig. 2a and b). Moreover, the plants under non-submergence conditions produced more lateral buds compared to completely submerged plants.

Additionally, we found that the investigated plants produced some new organs during the experiment, including lateral buds, leaves, adventitious roots and stem segments. For a certain organ that was produced under non-submergence conditions, their biomass was higher than that which was produced under submergence conditions. Under submergence, the plants with removed apexes only produced some new lateral buds and adventitious roots, whereas the plants with apexes produced new leaves, lateral buds, stem segments and adventitious roots. At the end of the experiment, the biomass of these newly produced organs produced was determined. The total biomass of the newly formed organs was significantly higher in plants with removed apexes than that in plants with apexes (Table 1).

At end of the experiment, all treated plants were harvested and checked the status of stem. It was showed that submergence and apex-removing treatments significantly affected the ratio of survived stem length (Supplementary Table S1). It was found some part of stem become grey and crispy, easy to destroy by soft touching after 200 days treatment. Then the ratio of surviving of stem length was determined, it was found the plants with apex lost larger ratio of stem length compared to plants without apex under non-submergence condition. However, there was an opposite situation under submergence condition, the plants without apex lost larger ratio of stem length compared to plants with apex (Fig. 3 and Supplementary Fig. S2).

As a consequence of the dark treatment of all investigated plants, we observed that the content of NSC in stem and underground tissues decreased during the experiment compared to that before the experiment (Table 2). After 200 days treatment, comparing the consumption of NSC in underground tissues, it showed that the consumption of apex removed plants was significantly higher than that of apex non-removed plants no matter the plants were treated under non-submerged conditions or plants under submerged condition. However, when comparing the NSC consumption of stem, there were no significant differences between the plants under different treatments (Fig. 4). Additionally, it was analysed that the relationships between the percentage of rest NSC and total number of newly produced lateral buds; and the relationship between the percentage of rest non-structural carbohydrates and ratio of survived stem length (Supplementary Fig. S1).

DISCUSSION

The presence of shoot apex is beneficial to the flooding tolerance of H. altissima under dark submerged conditions

In general, naturally formed vegetation systems in riparian zones show certain original ecosystem functions, which is very important for biodiversity and biogeochemical cycle (Opperman et al. 2009). Owing to the increase in human activities, the original riparian vegetation is frequently disturbed; moreover, global climate change and construction of dams throughout the world increase the chances for the occurrence of flooding events, especially in riparian zones, which always negatively influences riparian vegetation and causes the loss of their original ecosystem functions (Hirabayashi et al. 2013; Wu et al. 2003; Zarfl et al. 2014). Consequently, vegetation restoration is highly recommended by ecologists for maintaining the ecosystem functions of riparian zones (Dufour et al. 2013; Kauffman et al. 1997; Lennox et al. 2011; Wu et al. 2003). The perennial tropical grass H. altissima is considered as a candidate species for vegetation restoration in the Three Gorges Reservoir region because of its high flooding tolerance and its suitability as food for most livestock (Luo et al. 2011; Pitman et al. 1994).

In the present study, we hypothesized that if shoot apexes and immature internodes at the top of H. altissima shoots were removed, the total amount of submerged tissues decreases, which causes the consumption of stored carbohydrates by underwater respiration would slow down and the survival of H. altissima under water would be prolonged, as a result this species shows a high submergence tolerance. Previous research has indicated that flood-tolerant plants are characterized by a continuum of survival strategies, among which the low-O₂ escape syndrome and low-O₂ quiescence syndrome are two extremes (Voesenek and Bailey-Serres 2015). In low-O₂ escape syndrome, escape phenotype changes include upward bending of leaves, enhanced shoot elongation, formation of interconnected air-filled voids, induction of barriers to radial O₂ loss in roots, development of adventitious roots, formation of gas films on leaf surfaces, modifications of leaf anatomy, and pressurised gas flow through porous tissues (Manzur et al. 2009). In contrast to this energy-consuming syndrome, low-O₂ quiescence syndrome manages plant metabolism and constrains plant growth. The results of the present study showed that the intact shoots of H. altissima did not show enhanced elongation under complete submergence (Fig. 1), which was similar to the results on the submergence of many plant species reported in previous studies (Du et al. 2016; Luo et al. 2011). Based on the survival strategies described above, we concluded that the studied species showed low-O₂ quiescence syndrome during submergence.

However, under water, stem elongation of H. altissima plants with removed shoot apexes stopped (Fig. 1). The main reason for this may be because a number of active meristems are present in the shoot apex, and they contribute to the production of new cells and induce stem elongation; therefore, stem elongation stopped because the active meristems were removed from the top of H. altissima shoots. Moreover, we found that the plants with removed shoot apexes produced a number of lateral buds under complete submergence in the dark, and the total number and total biomass of these lateral buds were significantly higher than those of lateral buds produced by plants with intact shoot apexes (Figs. 2 and 3).

It should be noticed that under submerged conditions, the production of lateral buds increases the level of stress in plants. All types of plant growth require energy which is mainly produced by carbohydrate hydrolysis (Heldt and Piechulla 2011; Taiz and Zeiger 2010). Complete submergence imposes severe stress on plants because gas exchange rates between the plant tissues and the environment are severely reduced compared to those under non-submerged conditions. Usually, the diffusion rates of gases are 10⁴ times lower in water than those in air (Armstrong 1980). As a consequence, oxygen deficiency is considered to be a major factor negatively affecting the survival and growth of submerged plants (Mommer et al. 2004). In order to adapt to the submerging conditions, plants tissues undergo a shift from aerobic respiration to anaerobic metabolism to be able to produce sufficient ATP and maintain their viability (Bailey-Serres et al. 2018). It is well known that the utilization efficiency of carbohydrates in anaerobic metabolism is lower than that in aerobic metabolism; to produce the same amount of energy, more reserved carbohydrates are consumed in anaerobic metabolism than in aerobic metabolism. Moreover, underwater photosynthesis is limited by low CO₂ availability owing to slow CO₂ diffusion and light limitation in water (Li et al. 2007). For these reasons, it is difficult to accumulate carbohydrates by underwater photosynthesis under completely submerged conditions, meaning that any growth occurring underwater consumes a large amount of carbohydrates that have been stored before submergence. When the reserved carbohydrates are used up, the plants will not be able to survive and will die out soon.

The present study, clearly showed that during submergence, the ratio of survived stem length was lower in plants that produced more lateral buds than that in plants produced fewer lateral buds (Fig. 3). However, under non-submergence, the ratio of survived stem length of plants with intact apex was significantly lower than that of plant with removed apex. Moreover, under non-submergence conditions, the ratio of survived stem length of plants with or without intact apex was lower than that of plants under submergence conditions (Fig. 3). Moreover, the plants under non-submergence conditions produced more lateral buds and new stem compared to plants under submergence condition (Table 1). In our study, all of the treated plants were under dark conditions, there was no light for photosynthesis to accumulate carbohydrates. All the growth performance of plants during treatments consumed the resources (carbohydrates) that were accumulated before treatments, so more growth of treated plants consumed more resources, and induced less survival of stem length. We also found the consumption of carbohydrates in the underground parts of plants having more underwater growth were faster than that of plants having less underwater growth (Table 2; Fig. 4). These results indicated that the submergence tolerance of plants that produced more lateral buds was critically decreased.

In summary, stem elongation of H. altissima stopped under water when the shoot apex was removed; however, we found that in these plants, the production of lateral buds increased underwater. The growth of lateral buds was accompanied by the consumption of stored carbohydrates; with more lateral buds produced, more carbohydrates were consumed. As a consequence, these plants showed lower submergence tolerance than that of the intact plants. From these results, we concluded that the presence of the shoot apex on H. altissima had a positive effect on the plant’s submergence tolerance.

The growth of lateral buds is not only affected by the presence of shoot apex but also by submergence

Apical dominance is a phenomenon seen in plants in which the central stem becomes dominant, growing faster than the other stems, and hormones inhibit stem growth below the terminal bud at the end of the apical stem. When the apical dominance is inhibited, the lateral buds are released from apical dominance controlling (Li and Bangerth 2003; Phillips 1975; Sachs and Thimann 1964). In the present study, we found that H. altissima exhibited apical dominance, which was similar to lots of other plant species. When the apical dominance was inhibited in plants by removed apexes, a number of lateral buds were released on the stems. Our results showed that the apex removed plants produced significantly more lateral buds than the apex non-removed plants during the experiment (Fig. 2; Table 1). Further, it was found that the apex removed plants produced more lateral buds under non-submerged conditions than the apex removed plants under completely submerged conditions. The reason for these differences was presumably oxygen deficiency, which was the most severe stress for completely submerged plants. Any growth of tissues and organs under submergence requires more energy (Striker et al. 2011). The plant tissues shifted their aerobic respiration to anaerobic metabolism in submerged conditions, so the plants under submergence produced fewer lateral buds than plants under non-submergence, which is why the growth of lateral buds was restrained under submergence.

The variations in consumption of NSC between above ground parts and underground parts of plants

In the present study, it was found the NSC in underground parts were consumed greatly when plants confronted stress. Commonly, the underground parts of plants experience the most severe stress under submerged conditions. Submergence leads to soil anoxia because the slow diffusion of O₂ in water is unable to balance the quick O₂ consumption by soil microorganisms and plant roots (Winkel et al. 2017). In submerged soil, gases produced by plants, such as CO₂ and ethylene, rapidly accumulate. The contents of compounds such as Mn²⁺, Fe²⁺, S²⁻ and carboxylic acids can also increase toxic levels in hypoxic soils. Additionally, secondary metabolites (including phenolics, volatiles, ethanol, and acetaldehyde) can have phytotoxic effects on plant root systems (Broughton et al. 2015). Under toxic conditions, the root systems were too weak to protect the plants from microorganism attacks. Therefore, the fast consumption of carbohydrates in the underground parts of submerged plants was presumably caused by (1) anaerobic respiration of underground parts of plant under hypoxic conditions and (2) the utilization of soil microorganisms. Additionally, there are some possibilities that plants economically transport the stored carbohydrates in underground parts to the aboveground parts in order to support the new tissue production or reduce the death of shoots and leaves under stress conditions, but this point should be investigated further.

CONCLUSIONS

In the present study, we observed the divergent growth performance of the intact versus apex-cut plant of H. altissima upon different conditions. In particular, it was found the positive contribution of shoot apex to the tolerance of H. altissima to dark and complete submergence. During submergence a number of lateral buds were developed by plants without apexes. This growth performance finally caused a strong decline in NSC in underground parts. The relatively intensive consumption of carbohydrates induced the decline in stem survival under water, which indicated the decreasing submergence tolerance of plants without apex. Therefore, we suggest that when using H. altissima for restoring degraded riparian ecosystems, the shoot apexes should be protected from grazing by livestock or harvesting by local people in order to maintain the submergence tolerance of H. altissima.

Supplementary Material

Supplementary material is available at Journal of Plant Ecology online.

Table S1: The results of two-way ANOVA on length of the newly produced stem, total number of newly produced lateral buds, total biomass of newly produced lateral buds, ratio of survived stem length, percentage of rest NSC content in underground part and percentage of rest NSC content in stem with submergence treatment and stem apex-removing as main effects.

Figure S1: The relationships between the percentage of rest NSC and total number of newly produced lateral buds; the relationship between the percentage of rest NSC and ratio of survived stem length. The values indicate the correlation coefficient between two indexes. ‘ns’ indicates no significance at the 0.05 level.

Figure S2: The length of died stem of plants by stem apex non-removed and removed Hemarthria altissima plants (mean ± S.E., n = 15) under different treatments for 200 days.

Funding

This work was financially supported by National Natural Science Foundation of China (grant numbers U22A20448, 31800331, 31400480, 31770465), National Key R&D Program of China (grant number 2023YFF1305204), Chongqing Talents Program (grant number cstc2021ycjh-bgzxm0316), the Fundamental Research Funds for the Central Universities (grant number SWU-KT23001); and Science Foundation of School of Life Sciences SWU (grant numbers 20212017050401, 20212005393901).

Authors’ Contributions

Hangang Niu conducted the experiments and wrote the article; Bo Zeng conceived the original research plans and supervised the experiments; Jiaojiao Xie, Feng Lin, Yujie Zhao, Xian Luo and Xiangzheng Liu conducted some experiments, Qiaoli Ayi, Ting Wang and Bo Zeng designed the experiments and analysed the data; Qiaoli Ayi and Bo Zengs provides assistance in article writing.

Conflict of interest statement. The authors declare that they have no conflict of interest.

REFERENCES

Author notes