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Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration
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Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration Huan Meng a,b , Xuehong Wang a , Shouzheng Tong a,∗∗ , Xianguo Lu a,∗ , Mingxu Hao a,b , Yu An a , Zhongsheng Zhang a a Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agricultural Ecology, Chinese Academy of Sciences, Changchun 130102, PR China b University of Chinese Academy of Sciences, Beijing 100049, PR China
a r t i c l e
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Article history: Received 21 April 2015 Received in revised form 29 February 2016 Accepted 4 March 2016 Available online xxx Keywords: Germination Typha latifolia Phragmites australis Wetland plant restoration
a b s t r a c t Seeds are materials of redevelopment of plant communities, and can be valuable in the wetland conservation and restoration if the seeds germinate and survive. Sexual reproduction of those species is considered the simple and low-cost way to restore wetland. However, seeds usually have the characteristics of deep dormancy and low germination rate, so how to break these bottle-necks is critical to reestablish plant populations. We investigated seed germination environments of Typha latifolia and Phragmites australis, which were the dominant species of the riparian wetland along the downstream of Songhua River, Northeast China, and used to occupy riparian areas. This study involved pretreatment and controlled experiments. Treatments of soaking seed (untreated, distilled water soaked, H2 O2 soaked, H2 O2 soaked and then distilled water cleaned, KNO3 soaked, KNO3 soaked and then distilled water cleaned, KMnO4 soaked and KMnO4 soaked and then distilled water cleaned) and trails on the effect of water depth (0, 2, 4, 6, 8, 10 and 15 cm) on germination were conducted to explore the most effective pretreatment method and optimum water depth of seed germination of T. latifolia and P. australis. Results showed seed-soaking and water depth both had significant influence on seed germination of T. latifolia and P. australis. Based on the result, we found that success in establishing T. latifolia and P. australis in wetland restoration project can be greatly enhanced by treating seeds before sowing. T. latifolia seeds are more adaptive to aquatic condition, and P. australis seeds are more favorable of wet or moist conditions. A main strategy provided from our experiment to accelerate wetland plants restoration is as followed: T. latifolia and P. australis seeds would be soaked in an aqueous solution of 0.1% KMnO4 and a solution of 0.1% KNO3 for 8 h, and then rinsed with distilled water before sowing. T. latifolia seeds are sowed at aquatic condition (about 8 cm) and P. australis seeds are sowed at shallow water (<2 cm). The strategy provide future insight into how to use seed germination successfully in wetland plant restoration. © 2016 Published by Elsevier B.V.
1. Introduction Planting vegetation is one method of passive restorations during the process of wetland restoration. The replanting of wetland dominant of plants can accelerate the recovery of riverine wetland (Qingqing et al., 2016). Wetland plants have the ability to adsorb, take up and concentrate or metabolize pollutant, as well as
∗ Corresponding author. ∗∗ Corresponding author. E-mail addresses: [email protected] (H. Meng), [email protected] (X. Wang), [email protected] (S. Tong), [email protected] (X. Lu), [email protected] (M. Hao), [email protected] (Y. An), [email protected] (Z. Zhang).
to release root exudates that enhance compound biotransformation and microbial degradation (Haberl et al., 2003; Amaya-Chávez et al., 2006; Imfeld et al., 2009). Most wetland plants are flowering and still retain sexual reproduction strategies of terrestrial plants (Gregory, 2013). However, it seems that asexual reproduction tends to dominate in natural wetland ecosystems, such as cattails or common reed. Planting in large area from seeds is much rarer than vegetative colonization in wetland restoration (Nikolajevskij, 1971; Haslam, 1973; Mauchamp and Mésleard, 2001; Karen and Kevin, 2008). Germination stage is a highly vulnerable period, and its optimum habitat conditions in the process differ from what is the typical environment for the adult plants. Previous studies have demonstrated that various factors (Engloner, 2009), such as temperature (Morinaga, 1926; Sifton, 1959; Chauhan and Johnson,
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Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003
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2008), light exposure (Rivard and Woodard, 1989), water regime (Norsworthy and Oliveira, 2006), O2 concentrate (Bonnewell et al., 1983), and salt stress (Junbao et al., 2012; Junhong et al., 2014) could influence seed germination and seedling growth. Besides, findings also indicated that KMnO4 , H2 O2 and KNO3 could break dormancy, facilitate seed germination and improve germination percentage (Juxiang et al., 2003; Chuanjie et al., 2009). Songhua River is the main water supply source of people’s production and living in Northeast China. However, with the development of agriculture and industry, the riparian wetland along the downstream of Songhua River has degraded seriously and the Songhua River is severely polluted (Jiaren et al., 2009). The contamination is mainly N, P inorganic substance, organic substance and heavy metals (Jiaren et al., 2007). Water pollution has threatened ecological security and public health seriously. The phenomena has drawn a high level of attention to wetland restoration. Due to high adaptation capacity of local plant species (Ziqiang et al., 2009), successful vegetation restoration not only provide habitats for other lives, but also depurate water contaminated components (Park et al., 2009; Dordio et al., 2010; Hijosa-Valsero et al., 2010). As domain species in Northeast China, T. latifolia and P. australis were considered as key species in wetland vegetation restoration. In natural conditions, these plants both produce large quantities of small seeds which are pollinated by wind, but very few seedlings survive hampered by dormancy and low survival percentage, especially the environmental requirements for germination (Bischoff, 2002; Katja and Axel, 2010). Hypothesizing that dormancy and water depth are the important factors on seed germination of T. latifolia and P. australis in wetland plants restoration in the region, and optimal condition could promote germination, so germination experiments of these plants were conducted in laboratory by simulating field conditions similar with the riparian wetland along the downstream of Songhua River. Different responses of seeds to the detailed treatments are examined to guide further measures in wetland plants restoration and construction. Our objectives were to find favorable seed germination conditions for the plants, and to accelerate the process of wetland vegetation restoration, so as to strengthen the water quality purification.
The trial water (average pH 6.65, measured by PHS-3C) and the seeds were kept in ice-boxes with dark and dry conditions at 4 ◦ C and 0 ◦ C, respectively. Seed soaking treatments were conducted to explore optimal seed-soaking method of promoting seeds germination. Four seed soaking treatments were trailed—distilled water and 0.1% concentrations of H2 O2 , KNO3 , and KMnO4. Each treatment ran for 8 h and then was divided into two parts, seeds being clean with distilled water and unclean. To make seeds nondormant before they could eventually germinate (Baskin and Baskin, 2014), the choice of the chemicals, concentrations and time was based on previous published results (Chuanjie et al., 2009). The germination experiment was then conducted for ten days. Water depth experiment was conducted with water collected from the Songhua River with water depth at 0 cm, 2 cm, 4 cm, 6 cm, 8 cm, 10 cm and 15 cm. The experiment lasted 20 days. People considered that coleoptile rupture pericarp as seed germination (Rivard and Woodard, 1989). Shoot length (SL) and root length (RL) of seeds germinated were measured by digital vernier caliper until the experiment ended. For each treatment, four replicates of 100 seeds were placed on two layers of Whatman No.1 filter paper (pH 7). What different between seed soaking treatments and water depth experiment is that they happened in petri plates and beakers, respectively. All the petri plates and beakers were sealed with Parafilm® M Laboratory Film to prevent water evaporation and placed in an incubator (LRH-250-GS II, China) with the conditions of an alternating diurnal regime of daylight at 25 ◦ C and darkness at 15 ◦ C. Temperature regime of the incubator set represented approximately field conditions in late spring (temperature ranges from 7.9 ◦ C to 19.7 ◦ C in May) and early summer (temperature ranges from 14.3 ◦ C to 24.9 ◦ C in May). The climate data mentioned above comes from statistical data of Fujin city weather station from 1981 to 2013. Germination percentage (GP) was recorded for each day. 2.3. Statistical analyses SPSS software version 17 (SPSS Inc., Chicago, IL, USA. Feature 1200-SPSS Statistics Base 17.0) was used to the statistical analysis in this study. Germination speed (GS) was represented by a speed of germination index (Chiapusio et al., 1997).
2. Materials and methods
S = [N1 +(N2 − N1 )/2 + (N3 − N2 )/3 + . . .. . . + (Nn-Nn-1 )/N] × 100
2.1. Study area
where S is germination speed, N is the proportion of germinated seeds obtained at nth days. GP and GS of each species subjected to different treatments were examined by one-way analysis of variance (ANOVA) at the level of p = 0.05, for independent variables of seed-soaking reagents and water depth, respectively. Only when the result of ANOVA was significant (p < 0.05), Tukey’s HSD significant difference test was employed to separate factors with in these effects and different letters a, b, and c were used to express the differences at the p = 0.05 level. OriginPro8.0 was used to map.
The Songhua River Basin is located in the north of Northeast China, between 41◦ 42 –51◦ 38 N and 119◦ 52 –132◦ 31 E. Basin covers 55.68 km2 and traverses Inner Mongolia Municipality, Jilin Province, and Heilongjiang Province. The Songhua River originates from the Changbai Mountain, and converges Heilong River at the town of Tongjiang with a length of 1927 km. The average annual temperature is 3.4 ◦ C and annual precipitation is 518 mm in this area. T. latifolia, P. australis, Calamagrostis angustifolia and Carex are the most important plants in this region, where fresh water marshes are concentrated in China. Average pH of wetlands measured by PHS-3C is 6.62. However, overranging dredging damaged the emergent plants and changed the riparian wetland to road. Bans on dredging and returning farmlands to wetland have been implemented since 2012. We hoped the reaches could be rewet and the plants returned to the previous or close to the previous state through restoration projects. 2.2. Experimental design Trial water and seeds of T. latifolia and P. australis were collected in autumn from the riparian wetland along the downstream of Songhua River, Northeast China (47◦ 16 39.4. N, 132◦ 02 44.2 E).
3. Results 3.1. Effect of seed-soaking treatment on germination To accelerate T. latifolia and P. australis seed germination, seedsoaking experiment were conducted for 10 days to explore the optimal seed-soaking reagents. Results showed as Fig. 1. Seeds began to germinate by the third day of the experiment. Seed-soaking reagents significantly influenced the germination of T. latifolia (GP, F = 31.70, p = 0.00 < 0.05; GS, F = 32.362, p = 0.000 < 0.05), and also for P. australis (GP, F = 34.28, p = 0.00 < 0.05; GS, F = 44.084, p = 0.000 < 0.05). Both GP and GS of seeds under the treatment of soaking with reagents were significantly greater than those without soaking, with an exception of
Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003
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b b
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40 a a
20 c 15
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germintion speed (%)
germination percentage (%)
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A BCDE FG H
A BCDE FG H
T. latifolia
P. australis
0
bd d
b
a b
a
bc
a a
A B CDE FG H
A BCDE FG H
T. latifolia
P. australis
Fig. 1. Effect on germination of seed-soaking reagents. A—nontreated, B—distilled water soaked, C—H2 O2 soaked, D—H2 O2 soaked and then distilled water cleaned, E—KNO3 soaked, F—KNO3 soaked and then distilled water cleaned, G—KMnO4 soaked and H—KMnO4 soaked and then distilled water cleaned. Letters on the bars indicated differences subjected to seed-soaking reagents.
samples treated with C. GP and GS of T. latifolia treated with H were significantly higher than others. The average GP and GS, up to 74 ± 3.83 and 16.17 ± 0.80, were about 3 times and 4 times as A, respectively. Seeds of P. australis germinated best treated with F, and its average GP and GS were up to 97% and 28.43 ± 0.71. Multiple comparison results of GP and GS of both species showed differences between the pretreatments of B and D to H were not significant, but those treated with A and C were significantly lower than other rest treatments.
emergence under different water depths. Related data to T. latifolia and P. australis were presented by Table 1. For T. latifolia, SL and RL firstly increased and then declined with water depth increasing. The maximum of SL was 5.94 ± 0.62 mm which appeared at 2 cm water depth treatment, while the maximum of RL, 4.00 ± 0.26 mm, appeared at 8 cm water depth. For P. australis, SL and RL varied with increased water depth. The maximum of SL, 9.33 ± 1.63 mm, and RL, 12.25 ± 9.29 mm, appeared at 0 cm and 2 cm, respectively. The maximum RR of T. latifolia and P. australis appeared at 8 cm and 2 cm, respectively.
3.2. Seed germination under different water depths 4. Discussion 3.2.1. GP under different water depths Results showed water depth had significant effects on GP of T. latifolia (F = 4.503, p = 0.004 < 0.05) and P. australis (F = 30.403, p = 0.000 < 0.05) as Fig. 2. The GP curve of T. latifolia raised quickly and then remained stable with increased water depth. In this experiment of the effect of water depth on germination, the maximum of GP was found at 4 cm (52% ± 1.633, Mean ± SE). GP of P. australis seeds decreased in response with increasing water depth. The maximum of GP was at 0 cm water depth treatment (84% ±2.828), and it failed to germinate at 15 cm. 3.2.2. GS under different water depths Results showed as Fig. 3. Differences analysis results showed water depths had significant effects on GS of P. australis (F = 4.069, p = 0.007 < 0.05), but not on that of T. latifolia (F = 2.067, p = 0.101 > 0.05). GS of T. latifolia varied in an irregular way as water depth increased. The maximum of GS (6.776 ± 0.440) was found at 8 cm water depth. The effects of water depth on GS of P. australis seeds were notable (p < 0.05), and the curve of GS showed a similar trend with that of GP (Figs. 2 and 3). The maximum of GS was at 0 cm water depth treatment. When the water depth increased to 15 cm, P. australis seeds failed to germinate. 3.3. SL and RL under different water depths To some extent, SL, RL and root ratios (RR, the ratio of root to whole plant length) could be as indications to explain seedling
Sexual reproduction of plants is considered the simple and lowcost way to wetland vegetation restoration. Seeds are materials of redevelopment of plant communities and seed germination is the critical phases of sexual reproduction, which is considered the valuable technology in wetland restoration. Each plant species has specific environmental requirements and favorable conditions for germination (Baskin and Baskin, 1989). As so many T. latifolia and P. australis seeds are produced, it would allow ample opportunity for colonization by sexual propagation. However, germination of T. latifolia and P. australis recorded in earlier studies varied greatly, their germination percentages fluctuate from 0% to 100% (Bonnewell et al., 1983; Rivard and Woodard, 1989; Ekstam et al., 1999) due to their local characteristics. In our study, results of experiments showed seed pretreatment and water depth were key influence factors for germination of T. latifolia and P. australis seeds. 4.1. Seed-soaking reagent In the field, seeds can germinate only if they become nodormant (Baskin and Baskin 2014). It is long and difficult to for seeds breaking dormancy, germinating and eventually growing in the nature. It is well known that appropriate environmental conditions, nitrate, or hormonal treatments may favor seeds germination of many species. Potassium permanganate, hydrogen peroxide, potassium nitrate significantly improved the germination rate (Chuanjie et al., 2009). Several studies have showed that species seeds that
Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003
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Fig. 2. GP of T. latifolia and P. australis under different water depths.
Fig. 3. GS of T. latifolia and P. australis under different water depths.
Table 1 SL, RL and RR of T. latifolia and P. australis under different treatments. Treatments
Water depth (cm)
SL (mm)
0 2 4 6 8 10 15
RL (mm)
RR
T.latifolia
P.australis
T.latifolia
P.australis
T.latifolia
P.australis
4.08 ± 0.79 5.94 ± 0.62 5.67 ± 0.86 5.57 ± 0.70 5.50 ± 0.85 4.75 ± 0.74 4.57 ± 0.89
9.33 ± 1.63 6.88 ± 2.30 7.83 ± 1.72 4.40 ± 3.29 2.86 ± 1.68 5.00 ± 2.83 0.00
0.001 1.5 ± 0.27 3.17 ± 0.47 3.29 ± 0.47 4.00 ± 0.26 3.33 ± 0.62 2.14 ± 0.26
3.83 ± 1.17 12.25 ± 9.29 8.17 ± 3.06 4.00 ± 2.35 4.57 ± 3.46 5.50 ± 2.12 0.00
0.00 0.20 0.36 0.37 0.42 0.41 0.32
0.29 0.64 0.51 0.48 0.62 0.52 0.00
“0.001” stands for the smallest value of shoot and root. Bold lettering represents the maximum of statistical indicators.
respond positively to NO3 (Bungard et al., 1997; Cruz et al., 2003; Oliva et al., 2009), similar effects in our study were observed for germination of T. latifolia and P. australis, especial for P. australis. KMnO4 played a vital role in promoting germination of T. latifolia, which is because potassium permanganate can promote seed cap-
sule oxidation, and make starch and protein in seeds absorb fully moisture. Consequently, seeds quickly meet the necessary requirements of germination, and increased germination rate (Chuanjie et al., 2009). From the pretreatment results, we found that T. latifolia pretreated with KMnO4 soaking and rinsing with distilled water
Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003
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and P. australis soaking KNO3 and rinsing germinate best. Reagent seed soaking is a simple and reliable effective method of breaking dormancy and promoting germination Therefore, success in establishing T. latifolia and P. australis in wetland restoration project can be greatly enhanced by treating seeds before sowing.
4.2. Water depth Results from the effect of water depth on seed germination, we founded that GP of T. latifolia seeds raised quickly and then remained stable and GS of T. latifolia seeds fluctuated in response with increased water depth. While GP and GS of P. australis seeds both decreased as water depth increased. Several studies suggested water depth was one of the most important factors affecting seed germination in wetlands (McKee and Richards, 1996; Wijte and Gallagher, 1996; Gorai et al., 2010). Water depth may decrease the levels of available oxygen and exposure to light (red light or far-red light), leading to lower levels of dormancy loss compared with those under non-logging conditions (Bonnewell et al., 1983; Weisner and Strand, 1996; Xiuli et al., 2012). It is reported that except 0 cm water depth, lower water depth (4 or 5 cm) was the optimum water level allowing reed germination (Haslam, 1973; Junbao et al., 2012), 2.5% and O2 concentration were sufficient for reed germination (Wijte and Gallagher, 1996). Junbao et al. (2012) also pointed out germination percentage of reed seeds decreased to 2%, it could still germinate at 15 cm water depth. The water depth conditions for germination of T. latifolia is that shallow water warms more quickly than deep water, with conditions of reduced O2 concentrations (Bonnewell et al., 1983). In this paper, GP of T. latifolia increased as increasing water depth, and showed similar trend with previous studies. However, result of that reed seeds failed to germinate at 15 cm water depth, was not coincident with earlier studies (Junbao et al., 2012). Except for function of adaptive physiological characteristics of P. australis seeds, this result may be affected by water quality. In experiment, water used for germination was collected from Songhua River, while in other experiments that was distilled water. The ratio of root to whole plant length is generally used to indicate the morphology of roots relative to the growth of the entire plant (Rivard and Woodard, 1989). In the result, the maximum of SL, RL and RR of T. latifolia and P. australis appeared at different water depths. This suggests seeding establishment would be more successful under the treatments where the maximum appeared, if seed germination activities were the same. We also found that seed germination of P. australis is more seriously restricted by hydrological condition in wetland and T. latifolia seeds have an excellent adaption to germinate under water.
5. Conclusion From the research, we found that success in establishing T. latifolia and P. australis in wetland restoration project can be greatly enhanced by treating seeds before sowing. T. latifolia seeds are more adaptive to aquatic condition, and P. australis seeds are more favorable of wet or moist conditions in wetland plant restoration and establishment. Based on the results, T. latifolia and P. australis seeds would be soaked in an aqueous solution of 0.1% KMnO4 and a solution of 0.1% KNO3 for 8 h, and then rinsed with distilled water before sowing. P. australis seeds are sowed at shallow water (<2 cm). The condition of saturated water is relatively favor of seedling survival of P. australis. T. latifolia seeds are sowed at aquatic condition (about 8 cm). In addition, the sowing time in temperate regions is considered in spring but not autumn, because the climatic features of short fall and long winter are not suitable for plant growth and development.
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Acknowledgments This research was supported by Major Science and Technology Program for Water Pollution Control and Treatment (2012ZX07201004), the National Key Technology R & D Program (2012BAC19B05) and the Natural Science Foundation of China (41401102). We are grateful to Professor Douglas George Watkins from WWF and also to the reviewers for their comments.
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Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration Huan Meng a,b , Xuehong Wang a , Shouzheng Tong a,∗∗ , Xianguo Lu a,∗ , Mingxu Hao a,b , Yu An a , Zhongsheng Zhang a a Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agricultural Ecology, Chinese Academy of Sciences, Changchun 130102, PR China b University of Chinese Academy of Sciences, Beijing 100049, PR China
a r t i c l e
i n f o
Article history: Received 21 April 2015 Received in revised form 29 February 2016 Accepted 4 March 2016 Available online xxx Keywords: Germination Typha latifolia Phragmites australis Wetland plant restoration
a b s t r a c t Seeds are materials of redevelopment of plant communities, and can be valuable in the wetland conservation and restoration if the seeds germinate and survive. Sexual reproduction of those species is considered the simple and low-cost way to restore wetland. However, seeds usually have the characteristics of deep dormancy and low germination rate, so how to break these bottle-necks is critical to reestablish plant populations. We investigated seed germination environments of Typha latifolia and Phragmites australis, which were the dominant species of the riparian wetland along the downstream of Songhua River, Northeast China, and used to occupy riparian areas. This study involved pretreatment and controlled experiments. Treatments of soaking seed (untreated, distilled water soaked, H2 O2 soaked, H2 O2 soaked and then distilled water cleaned, KNO3 soaked, KNO3 soaked and then distilled water cleaned, KMnO4 soaked and KMnO4 soaked and then distilled water cleaned) and trails on the effect of water depth (0, 2, 4, 6, 8, 10 and 15 cm) on germination were conducted to explore the most effective pretreatment method and optimum water depth of seed germination of T. latifolia and P. australis. Results showed seed-soaking and water depth both had significant influence on seed germination of T. latifolia and P. australis. Based on the result, we found that success in establishing T. latifolia and P. australis in wetland restoration project can be greatly enhanced by treating seeds before sowing. T. latifolia seeds are more adaptive to aquatic condition, and P. australis seeds are more favorable of wet or moist conditions. A main strategy provided from our experiment to accelerate wetland plants restoration is as followed: T. latifolia and P. australis seeds would be soaked in an aqueous solution of 0.1% KMnO4 and a solution of 0.1% KNO3 for 8 h, and then rinsed with distilled water before sowing. T. latifolia seeds are sowed at aquatic condition (about 8 cm) and P. australis seeds are sowed at shallow water (<2 cm). The strategy provide future insight into how to use seed germination successfully in wetland plant restoration. © 2016 Published by Elsevier B.V.
1. Introduction Planting vegetation is one method of passive restorations during the process of wetland restoration. The replanting of wetland dominant of plants can accelerate the recovery of riverine wetland (Qingqing et al., 2016). Wetland plants have the ability to adsorb, take up and concentrate or metabolize pollutant, as well as
∗ Corresponding author. ∗∗ Corresponding author. E-mail addresses: [email protected] (H. Meng), [email protected] (X. Wang), [email protected] (S. Tong), [email protected] (X. Lu), [email protected] (M. Hao), [email protected] (Y. An), [email protected] (Z. Zhang).
to release root exudates that enhance compound biotransformation and microbial degradation (Haberl et al., 2003; Amaya-Chávez et al., 2006; Imfeld et al., 2009). Most wetland plants are flowering and still retain sexual reproduction strategies of terrestrial plants (Gregory, 2013). However, it seems that asexual reproduction tends to dominate in natural wetland ecosystems, such as cattails or common reed. Planting in large area from seeds is much rarer than vegetative colonization in wetland restoration (Nikolajevskij, 1971; Haslam, 1973; Mauchamp and Mésleard, 2001; Karen and Kevin, 2008). Germination stage is a highly vulnerable period, and its optimum habitat conditions in the process differ from what is the typical environment for the adult plants. Previous studies have demonstrated that various factors (Engloner, 2009), such as temperature (Morinaga, 1926; Sifton, 1959; Chauhan and Johnson,
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2008), light exposure (Rivard and Woodard, 1989), water regime (Norsworthy and Oliveira, 2006), O2 concentrate (Bonnewell et al., 1983), and salt stress (Junbao et al., 2012; Junhong et al., 2014) could influence seed germination and seedling growth. Besides, findings also indicated that KMnO4 , H2 O2 and KNO3 could break dormancy, facilitate seed germination and improve germination percentage (Juxiang et al., 2003; Chuanjie et al., 2009). Songhua River is the main water supply source of people’s production and living in Northeast China. However, with the development of agriculture and industry, the riparian wetland along the downstream of Songhua River has degraded seriously and the Songhua River is severely polluted (Jiaren et al., 2009). The contamination is mainly N, P inorganic substance, organic substance and heavy metals (Jiaren et al., 2007). Water pollution has threatened ecological security and public health seriously. The phenomena has drawn a high level of attention to wetland restoration. Due to high adaptation capacity of local plant species (Ziqiang et al., 2009), successful vegetation restoration not only provide habitats for other lives, but also depurate water contaminated components (Park et al., 2009; Dordio et al., 2010; Hijosa-Valsero et al., 2010). As domain species in Northeast China, T. latifolia and P. australis were considered as key species in wetland vegetation restoration. In natural conditions, these plants both produce large quantities of small seeds which are pollinated by wind, but very few seedlings survive hampered by dormancy and low survival percentage, especially the environmental requirements for germination (Bischoff, 2002; Katja and Axel, 2010). Hypothesizing that dormancy and water depth are the important factors on seed germination of T. latifolia and P. australis in wetland plants restoration in the region, and optimal condition could promote germination, so germination experiments of these plants were conducted in laboratory by simulating field conditions similar with the riparian wetland along the downstream of Songhua River. Different responses of seeds to the detailed treatments are examined to guide further measures in wetland plants restoration and construction. Our objectives were to find favorable seed germination conditions for the plants, and to accelerate the process of wetland vegetation restoration, so as to strengthen the water quality purification.
The trial water (average pH 6.65, measured by PHS-3C) and the seeds were kept in ice-boxes with dark and dry conditions at 4 ◦ C and 0 ◦ C, respectively. Seed soaking treatments were conducted to explore optimal seed-soaking method of promoting seeds germination. Four seed soaking treatments were trailed—distilled water and 0.1% concentrations of H2 O2 , KNO3 , and KMnO4. Each treatment ran for 8 h and then was divided into two parts, seeds being clean with distilled water and unclean. To make seeds nondormant before they could eventually germinate (Baskin and Baskin, 2014), the choice of the chemicals, concentrations and time was based on previous published results (Chuanjie et al., 2009). The germination experiment was then conducted for ten days. Water depth experiment was conducted with water collected from the Songhua River with water depth at 0 cm, 2 cm, 4 cm, 6 cm, 8 cm, 10 cm and 15 cm. The experiment lasted 20 days. People considered that coleoptile rupture pericarp as seed germination (Rivard and Woodard, 1989). Shoot length (SL) and root length (RL) of seeds germinated were measured by digital vernier caliper until the experiment ended. For each treatment, four replicates of 100 seeds were placed on two layers of Whatman No.1 filter paper (pH 7). What different between seed soaking treatments and water depth experiment is that they happened in petri plates and beakers, respectively. All the petri plates and beakers were sealed with Parafilm® M Laboratory Film to prevent water evaporation and placed in an incubator (LRH-250-GS II, China) with the conditions of an alternating diurnal regime of daylight at 25 ◦ C and darkness at 15 ◦ C. Temperature regime of the incubator set represented approximately field conditions in late spring (temperature ranges from 7.9 ◦ C to 19.7 ◦ C in May) and early summer (temperature ranges from 14.3 ◦ C to 24.9 ◦ C in May). The climate data mentioned above comes from statistical data of Fujin city weather station from 1981 to 2013. Germination percentage (GP) was recorded for each day. 2.3. Statistical analyses SPSS software version 17 (SPSS Inc., Chicago, IL, USA. Feature 1200-SPSS Statistics Base 17.0) was used to the statistical analysis in this study. Germination speed (GS) was represented by a speed of germination index (Chiapusio et al., 1997).
2. Materials and methods
S = [N1 +(N2 − N1 )/2 + (N3 − N2 )/3 + . . .. . . + (Nn-Nn-1 )/N] × 100
2.1. Study area
where S is germination speed, N is the proportion of germinated seeds obtained at nth days. GP and GS of each species subjected to different treatments were examined by one-way analysis of variance (ANOVA) at the level of p = 0.05, for independent variables of seed-soaking reagents and water depth, respectively. Only when the result of ANOVA was significant (p < 0.05), Tukey’s HSD significant difference test was employed to separate factors with in these effects and different letters a, b, and c were used to express the differences at the p = 0.05 level. OriginPro8.0 was used to map.
The Songhua River Basin is located in the north of Northeast China, between 41◦ 42 –51◦ 38 N and 119◦ 52 –132◦ 31 E. Basin covers 55.68 km2 and traverses Inner Mongolia Municipality, Jilin Province, and Heilongjiang Province. The Songhua River originates from the Changbai Mountain, and converges Heilong River at the town of Tongjiang with a length of 1927 km. The average annual temperature is 3.4 ◦ C and annual precipitation is 518 mm in this area. T. latifolia, P. australis, Calamagrostis angustifolia and Carex are the most important plants in this region, where fresh water marshes are concentrated in China. Average pH of wetlands measured by PHS-3C is 6.62. However, overranging dredging damaged the emergent plants and changed the riparian wetland to road. Bans on dredging and returning farmlands to wetland have been implemented since 2012. We hoped the reaches could be rewet and the plants returned to the previous or close to the previous state through restoration projects. 2.2. Experimental design Trial water and seeds of T. latifolia and P. australis were collected in autumn from the riparian wetland along the downstream of Songhua River, Northeast China (47◦ 16 39.4. N, 132◦ 02 44.2 E).
3. Results 3.1. Effect of seed-soaking treatment on germination To accelerate T. latifolia and P. australis seed germination, seedsoaking experiment were conducted for 10 days to explore the optimal seed-soaking reagents. Results showed as Fig. 1. Seeds began to germinate by the third day of the experiment. Seed-soaking reagents significantly influenced the germination of T. latifolia (GP, F = 31.70, p = 0.00 < 0.05; GS, F = 32.362, p = 0.000 < 0.05), and also for P. australis (GP, F = 34.28, p = 0.00 < 0.05; GS, F = 44.084, p = 0.000 < 0.05). Both GP and GS of seeds under the treatment of soaking with reagents were significantly greater than those without soaking, with an exception of
Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003
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b b
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b
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bb
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40 a a
20 c 15
10
20 5
0
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a
germintion speed (%)
germination percentage (%)
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A BCDE FG H
A BCDE FG H
T. latifolia
P. australis
0
bd d
b
a b
a
bc
a a
A B CDE FG H
A BCDE FG H
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Fig. 1. Effect on germination of seed-soaking reagents. A—nontreated, B—distilled water soaked, C—H2 O2 soaked, D—H2 O2 soaked and then distilled water cleaned, E—KNO3 soaked, F—KNO3 soaked and then distilled water cleaned, G—KMnO4 soaked and H—KMnO4 soaked and then distilled water cleaned. Letters on the bars indicated differences subjected to seed-soaking reagents.
samples treated with C. GP and GS of T. latifolia treated with H were significantly higher than others. The average GP and GS, up to 74 ± 3.83 and 16.17 ± 0.80, were about 3 times and 4 times as A, respectively. Seeds of P. australis germinated best treated with F, and its average GP and GS were up to 97% and 28.43 ± 0.71. Multiple comparison results of GP and GS of both species showed differences between the pretreatments of B and D to H were not significant, but those treated with A and C were significantly lower than other rest treatments.
emergence under different water depths. Related data to T. latifolia and P. australis were presented by Table 1. For T. latifolia, SL and RL firstly increased and then declined with water depth increasing. The maximum of SL was 5.94 ± 0.62 mm which appeared at 2 cm water depth treatment, while the maximum of RL, 4.00 ± 0.26 mm, appeared at 8 cm water depth. For P. australis, SL and RL varied with increased water depth. The maximum of SL, 9.33 ± 1.63 mm, and RL, 12.25 ± 9.29 mm, appeared at 0 cm and 2 cm, respectively. The maximum RR of T. latifolia and P. australis appeared at 8 cm and 2 cm, respectively.
3.2. Seed germination under different water depths 4. Discussion 3.2.1. GP under different water depths Results showed water depth had significant effects on GP of T. latifolia (F = 4.503, p = 0.004 < 0.05) and P. australis (F = 30.403, p = 0.000 < 0.05) as Fig. 2. The GP curve of T. latifolia raised quickly and then remained stable with increased water depth. In this experiment of the effect of water depth on germination, the maximum of GP was found at 4 cm (52% ± 1.633, Mean ± SE). GP of P. australis seeds decreased in response with increasing water depth. The maximum of GP was at 0 cm water depth treatment (84% ±2.828), and it failed to germinate at 15 cm. 3.2.2. GS under different water depths Results showed as Fig. 3. Differences analysis results showed water depths had significant effects on GS of P. australis (F = 4.069, p = 0.007 < 0.05), but not on that of T. latifolia (F = 2.067, p = 0.101 > 0.05). GS of T. latifolia varied in an irregular way as water depth increased. The maximum of GS (6.776 ± 0.440) was found at 8 cm water depth. The effects of water depth on GS of P. australis seeds were notable (p < 0.05), and the curve of GS showed a similar trend with that of GP (Figs. 2 and 3). The maximum of GS was at 0 cm water depth treatment. When the water depth increased to 15 cm, P. australis seeds failed to germinate. 3.3. SL and RL under different water depths To some extent, SL, RL and root ratios (RR, the ratio of root to whole plant length) could be as indications to explain seedling
Sexual reproduction of plants is considered the simple and lowcost way to wetland vegetation restoration. Seeds are materials of redevelopment of plant communities and seed germination is the critical phases of sexual reproduction, which is considered the valuable technology in wetland restoration. Each plant species has specific environmental requirements and favorable conditions for germination (Baskin and Baskin, 1989). As so many T. latifolia and P. australis seeds are produced, it would allow ample opportunity for colonization by sexual propagation. However, germination of T. latifolia and P. australis recorded in earlier studies varied greatly, their germination percentages fluctuate from 0% to 100% (Bonnewell et al., 1983; Rivard and Woodard, 1989; Ekstam et al., 1999) due to their local characteristics. In our study, results of experiments showed seed pretreatment and water depth were key influence factors for germination of T. latifolia and P. australis seeds. 4.1. Seed-soaking reagent In the field, seeds can germinate only if they become nodormant (Baskin and Baskin 2014). It is long and difficult to for seeds breaking dormancy, germinating and eventually growing in the nature. It is well known that appropriate environmental conditions, nitrate, or hormonal treatments may favor seeds germination of many species. Potassium permanganate, hydrogen peroxide, potassium nitrate significantly improved the germination rate (Chuanjie et al., 2009). Several studies have showed that species seeds that
Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003
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Fig. 2. GP of T. latifolia and P. australis under different water depths.
Fig. 3. GS of T. latifolia and P. australis under different water depths.
Table 1 SL, RL and RR of T. latifolia and P. australis under different treatments. Treatments
Water depth (cm)
SL (mm)
0 2 4 6 8 10 15
RL (mm)
RR
T.latifolia
P.australis
T.latifolia
P.australis
T.latifolia
P.australis
4.08 ± 0.79 5.94 ± 0.62 5.67 ± 0.86 5.57 ± 0.70 5.50 ± 0.85 4.75 ± 0.74 4.57 ± 0.89
9.33 ± 1.63 6.88 ± 2.30 7.83 ± 1.72 4.40 ± 3.29 2.86 ± 1.68 5.00 ± 2.83 0.00
0.001 1.5 ± 0.27 3.17 ± 0.47 3.29 ± 0.47 4.00 ± 0.26 3.33 ± 0.62 2.14 ± 0.26
3.83 ± 1.17 12.25 ± 9.29 8.17 ± 3.06 4.00 ± 2.35 4.57 ± 3.46 5.50 ± 2.12 0.00
0.00 0.20 0.36 0.37 0.42 0.41 0.32
0.29 0.64 0.51 0.48 0.62 0.52 0.00
“0.001” stands for the smallest value of shoot and root. Bold lettering represents the maximum of statistical indicators.
respond positively to NO3 (Bungard et al., 1997; Cruz et al., 2003; Oliva et al., 2009), similar effects in our study were observed for germination of T. latifolia and P. australis, especial for P. australis. KMnO4 played a vital role in promoting germination of T. latifolia, which is because potassium permanganate can promote seed cap-
sule oxidation, and make starch and protein in seeds absorb fully moisture. Consequently, seeds quickly meet the necessary requirements of germination, and increased germination rate (Chuanjie et al., 2009). From the pretreatment results, we found that T. latifolia pretreated with KMnO4 soaking and rinsing with distilled water
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and P. australis soaking KNO3 and rinsing germinate best. Reagent seed soaking is a simple and reliable effective method of breaking dormancy and promoting germination Therefore, success in establishing T. latifolia and P. australis in wetland restoration project can be greatly enhanced by treating seeds before sowing.
4.2. Water depth Results from the effect of water depth on seed germination, we founded that GP of T. latifolia seeds raised quickly and then remained stable and GS of T. latifolia seeds fluctuated in response with increased water depth. While GP and GS of P. australis seeds both decreased as water depth increased. Several studies suggested water depth was one of the most important factors affecting seed germination in wetlands (McKee and Richards, 1996; Wijte and Gallagher, 1996; Gorai et al., 2010). Water depth may decrease the levels of available oxygen and exposure to light (red light or far-red light), leading to lower levels of dormancy loss compared with those under non-logging conditions (Bonnewell et al., 1983; Weisner and Strand, 1996; Xiuli et al., 2012). It is reported that except 0 cm water depth, lower water depth (4 or 5 cm) was the optimum water level allowing reed germination (Haslam, 1973; Junbao et al., 2012), 2.5% and O2 concentration were sufficient for reed germination (Wijte and Gallagher, 1996). Junbao et al. (2012) also pointed out germination percentage of reed seeds decreased to 2%, it could still germinate at 15 cm water depth. The water depth conditions for germination of T. latifolia is that shallow water warms more quickly than deep water, with conditions of reduced O2 concentrations (Bonnewell et al., 1983). In this paper, GP of T. latifolia increased as increasing water depth, and showed similar trend with previous studies. However, result of that reed seeds failed to germinate at 15 cm water depth, was not coincident with earlier studies (Junbao et al., 2012). Except for function of adaptive physiological characteristics of P. australis seeds, this result may be affected by water quality. In experiment, water used for germination was collected from Songhua River, while in other experiments that was distilled water. The ratio of root to whole plant length is generally used to indicate the morphology of roots relative to the growth of the entire plant (Rivard and Woodard, 1989). In the result, the maximum of SL, RL and RR of T. latifolia and P. australis appeared at different water depths. This suggests seeding establishment would be more successful under the treatments where the maximum appeared, if seed germination activities were the same. We also found that seed germination of P. australis is more seriously restricted by hydrological condition in wetland and T. latifolia seeds have an excellent adaption to germinate under water.
5. Conclusion From the research, we found that success in establishing T. latifolia and P. australis in wetland restoration project can be greatly enhanced by treating seeds before sowing. T. latifolia seeds are more adaptive to aquatic condition, and P. australis seeds are more favorable of wet or moist conditions in wetland plant restoration and establishment. Based on the results, T. latifolia and P. australis seeds would be soaked in an aqueous solution of 0.1% KMnO4 and a solution of 0.1% KNO3 for 8 h, and then rinsed with distilled water before sowing. P. australis seeds are sowed at shallow water (<2 cm). The condition of saturated water is relatively favor of seedling survival of P. australis. T. latifolia seeds are sowed at aquatic condition (about 8 cm). In addition, the sowing time in temperate regions is considered in spring but not autumn, because the climatic features of short fall and long winter are not suitable for plant growth and development.
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Acknowledgments This research was supported by Major Science and Technology Program for Water Pollution Control and Treatment (2012ZX07201004), the National Key Technology R & D Program (2012BAC19B05) and the Natural Science Foundation of China (41401102). We are grateful to Professor Douglas George Watkins from WWF and also to the reviewers for their comments.
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Please cite this article in press as: Meng, H., et al., Seed germination environments of Typha latifolia and Phragmites australis in wetland restoration. Ecol. Eng. (2016), http://dx.doi.org/10.1016/j.ecoleng.2016.03.003