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Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 4: 868 - 879

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.04.019

Revegetation and Management of Mines

Effects of Seedling Methods on Germination and Growth of Sophora japonica L.

  • YAO Jingjing , 1, 2 ,
  • ZHANG Chengliang , 1, 2, * ,
  • HAN Shuang 3 ,
  • LIU Mengfan 1, 2 ,
  • WANG Yan 4 ,
  • CAO Wenbo 5
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  • 1. Institute of Resources and Environment, Beijing Academy of Science and Technology, Beijing 100095, China
  • 2. The National Engineering Laboratory of Circular Economy (Industrial Wastewater Utilization and Industrial Water Conservation), Beijing 100095, China
  • 3. Industry Development and Planning Institute, National Forestry and Grassland Administration, Beijing 100010, China
  • 4. Beijing E20 Environment Co., Ltd, Beijing 100195, China
  • 5. Beijing Clear Water & Blue Sky Environmental Protection Technology Co., Ltd, Beijing 100095, China
*ZHANG Chengliang, E-mail:

YAO Jingjing, E-mail:

Received date: 2022-08-25

  Accepted date: 2023-04-18

  Online published: 2023-07-14

Supported by

Key Research and Development Program of China(2017YFC0504404)

The Key Research and Development Plan Projects of Ningxia Hui Autonomous Region(2018BFG02002)

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Abstract

Bud seedlings were used in this study to overcome the disadvantages of the frequently-used active vegetation restoration methods such as direct seeding and plant seedlings for mining areas. Survival and growth characteristics of Sophora japonica L. by bud seedlings, seedling planting, and direct seeding methods were investigated through field plantation experiments in Changping District of Beijing, China. Nine plots (5 m×1 m) with slope of 25° were conducted and divided into 3 groups according to aspects of west, southwest, as well as south, and seeds were planted by following the three methods in each aspect. Germination, survival, seedling growth, and root parameters of each treatment were analyzed through one-way analysis of variance, paired-sample t test, repeated measures analysis of variance, and multivariate analysis of variance to evaluate the effectiveness of the three seedling methods. The results showed that seedling planting and bud seedlings promoted seeds germination and growth, with a germination percentage of 70.58% and seedling height of 9.97 cm before transplantation, which were 1.48 times and 1.53 times higher than direct seeding, respectively. Moreover, bud seedlings showed the largest survival rate, seedling height, and root biomass under all aspects after transplantation (P<0.05), and at the end of the study, the largest values of the above indicators were 88.33 % in BW (the plot with seedling method of bud seedlings in aspect west), 158.36 cm in BS (the plot with seedling method of bud seedlings in aspect west south), and 131.5 g in BS, respectively. The effect of seedling method on seedling growth was most significant and increased with time, with effect sizes of 0.290 and 0.199 on seedling height and growth rate in 2020, respectively. Overall, bud seedlings could extract the advantages and overcome the disadvantages of seedling planting and direct seeding, which can be considered as a better method for vegetation restoration in the mining areas.

Key words： bud seedlings; seedling planting; direct seeding; germination percentage; seedling height

Cite this article

YAO Jingjing , ZHANG Chengliang , HAN Shuang , LIU Mengfan , WANG Yan , CAO Wenbo . Effects of Seedling Methods on Germination and Growth of Sophora japonica L.[J]. Journal of Resources and Ecology, 2023 , 14(4) : 868 -879 . DOI: 10.5814/j.issn.1674-764x.2023.04.019

1 Introduction

Soil and vegetation in the mining areas have been seriously damaged by excessive coal mining in China (Kuang et al., 2019). Meanwhile, coal gangue, produced through coal mining, washing and processing, accounts for approximately 10%-15% of raw coal production (Liang et al., 2016; Deng et al., 2017). According to a rough estimate, nearly 3 billion tons of coal gangue has been produced in China to date, and has been stacked to form huge gangue dumps, occupying an area of about 15000 km2 (Li et al., 2020a). Coal mining and stacking of coal gangue not only occupy large areas, but also change the physical and chemical properties of soil as well as hydrological process of the mining areas, resulting in serious soil and water erosion (Ahirwal and Maiti, 2016; Wu et al., 2019). In this context, restoration of the active vegetation has been the focus of many scholars, because it can change the physical and chemical properties of coal gangue, effectively prevent soil and water erosion, and improve the ecological environment of the mining areas (Jambhulkar and Kumar, 2019; Li et al., 2020b).
The most frequent used methods for active vegetation restoration of abandoned fields are seedling planting and direct seeding (Ceccon et al., 2016; Souza and Engel, 2018; Xi et al., 2019; Raupp et al., 2020). Seedling planting may be a more favored and developed approach to quickly establish a canopy for higher survival rate and rapid early growth of nursery-raised seedlings (Durigan et al., 2013; Raupp et al., 2020). The natural regeneration can be accelerated by the simultaneous planting of pioneer and later-successional seedling species. However, increased associated costs in terms of equipment, labor, time, etc. owing to the inconvenient transportation, lack of local nurseries, and poor environmental conditions such as low precipitation, limit the implication of this approach at large scales (Lamb et al., 2005; Waiboonya and Elliott, 2020). Thus, it is imperative to develop efficient restoration techniques considering both ecological and economic goals.
Direct seeding ‘sowing seeds directly on the regeneration sites’, is considered a simple and alternatively convenient active restoration method to reduce the initial investments in production and planting (Ceccon et al., 2016; Atondo-Bueno et al., 2018; Raupp et al., 2020). The costs associated with direct seeding are 30%-38% of the cost of seedling planting, since seeds are sown on large areas rapidly by hand or through broadcasting without transportation in the form of seedlings, which reduces the costs in terms of labor and transportation (Balandier et al., 2009; Durigan et al., 2013; Grossnickle and Ivetic, 2017). Additionally, the seedlings produced by this method are generally less prone to toppling, and have unhindered taproot growth compared with container seedlings (Wennström et al., 1999). Moreover, seedlings can be established at high densities, and numerous species can be used as compared to seedling planting (Souza and Engel, 2018; Raupp et al., 2020). For example, Palma and Laurance (2015) found that direct seeding used twice the number of species than seedling planting based on the results of 120 papers published between 1965 and 2013.
Although, direct seeding exhibited higher species richness, germination rate of seeds was found to be significantly lower than that achieved by seedling planting (Palma and Laurance, 2015; Ceccon et al., 2016). Survival and growth rate of seedlings play important roles in measuring the success of vegetation restoration (Grossnickle, 2012; Grossnickle and MacDonald, 2018). Many factors could affect the seedling establishment of direct seeding, making it difficult to be used as a standalone restoration method (St-Denis et al., 2013; Mogilski et al., 2020; Waiboonya and Elliott, 2020). Seed characteristics such as seed size, genetics and source play critical roles in seedling establishment. Larger seeds often show higher germination probability than the smaller ones, while lack of information on optimum sowing time may influence seed germination (Tunjai and Elliott, 2012; St-Denis et al., 2013; Thomas et al., 2014). Difficulties in selecting the quantities of viable seeds lead to failure of direct seeding, which can be solved by optimizing germination through seedling planting. Moreover, seedlings are prone to die in case of unfavourable environmental conditions, especially summer drought (Vickers and Palmer, 2000; Al-Hawija et al., 2015; Guignabert et al., 2020a), which could be avoided by seedling planting (Palma and Laurance, 2015). In addition, previous perturbation of habitat and more management in the first two years after direct seeding may increase the cost (Ceccon et al., 2016). Therefore, costs, seed attributes and environmental characteristics should be carefully identified for seedling establishment (Holl and Aide, 2011; Wortley et al., 2013; Palma and Laurance, 2015; Nunes et al., 2017).
Accordingly, bud seedlings were cultivated in this study to extract the advantages and overcome the disadvantages of seedling planting and direct seeding for vegetation restoration. Bud seedlings are obtained through sowing the seeds in the seedling cups after accelerating germination, and the taproot grows to the edge of the cup without extending out of it. The objectives of this study were to 1) investigate the survival and growth characteristics of bud seedlings, seedling planting, and direct seeding, and 2) evaluate whether bud seedlings method was the best method approach as compared to seedling planting and direct seeding for vegetation restoration in the mining areas. For that purpose, Sophora japonica L. was selected as a test plant owing to its strong resistance to cold, drought, and air pollution, remarkable effects on soil and water conservation, effectiveness during windbreak and sand fixation, as well as economic values. It exhibits a well developed root system, and is widely distributed in China and hence, was used in the current study to check the impacts of these three methods on its growth and survival by cultivating it in soil taken from gangue dump.

2 Materials and methods

2.1 Site description

The experiments were conducted from May 2018 to September 2020 in ecological restoration experimental base of Institute of Resources and Environment, Beijing Academy of Science and Technology. The area is located in Changping District of Beijing, China (40°09′57″N, 116°09′01″E) with altitude of 57 m above the mean sea level. This area is characterized by typical warm temperate sub-humid continental monsoon climate with an average annual temperature of 11.8℃. The mean annual precipitation is 538.7 mm, which is mainly concentrated in July and August. The growing degree-days and frost-free days are about 200 and 180, respectively. Nine plots (5 m×1 m) were established to investigate the effects of seedling methods on survival and growth characteristics of Sophora japonica L. (Table 1). Aspect was considered in this study because light and moisture varied with aspect, affecting the growth of Sophora japonica L..
Table 1 Plots characteristics
Plots/Treatment Slope (°) Aspect Seedling methods
DW 25 West Direct seeding
BW 25 West Bud seedlings
SW 25 West Seedling planting
DSW 25 Southwest Direct seeding
BSW 25 Southwest Bud seedlings
SSW 25 Southwest Seedling planting
DS 25 South Direct seeding
BS 25 South Bud seedlings
SS 25 South Seedling planting

2.2 Experimental design

2.2.1 Sowing

Seeds of Sophora japonica L. produced by Beijing Zhengdao Eco-Technology Co., Ltd., China, were selected in this study. For seedling experiment, eighteen hundred seeds with uniform size were selected, which were soaked in water at an initial temperature of 85 ℃ for 24 hours before sowing. Furthermore, for direct seeding, DW, DSW, and DS were irrigated to saturated water content on May 30, 2018. Two hundred seeds were sowed evenly into each plot. Corresponding to bud seedlings and seedling planting, 600 seedling cups with 12 cm in height and 13 cm in diameter were filled with soil from experimental plots to a depth of 10 cm, and saturated with water before sowing. Two seeds were sown into each seedling cup and covered with soil at a depth of 4-5 times that of seed size. The seedling cups were placed on flat ground beside experimental plots during sowing. Finally, a sunshade net was covered over the seedling cups to decrease water evaporation, and removed after the seeds sprout out of the ground.

2.2.2 Transplant seedlings

Germination of seeds and the growth of seedlings were recorded every 5 days after sowing. Germination percentage was calculated as the number of seeds germinated divided by the number of seeds sown. Three seedlings were dug out from seedling cups to measure the length of taproots. The taproots of seedlings grew to the edge of the cups on June 19, 2018. Sixty holes (13 cm×13 cm×14 cm) were excavated by a shovel in BW, BSW, and BS, respectively with row spacing (25 cm×30 cm). One seedling was planted in each hole as bud seedlings. Meanwhile, seedlings in DW, DSW, and DS were thinned with the same row spacing (25 cm×30 cm), leaving 60 seedlings in each plot. Seedling were planted in SW, SSW and SS under seedling planting method with reference to the method of bud seedlings transplantation on August 1, 2018 when their taproots grew out of the cups.

2.2.3 Field measurements

Survival and growth of each seedling were surveyed each year in September from 2018 to 2020. Survival rate of each plot was calculated as the number of seedlings that survived divided by the number of initially planted seedlings. Three seedlings closest to the mean seedling height of each plot were dug out on September, 2020 to determine root properties. Roots were cleaned cautiously and divided into different parts of < 1 mm, 1-2 mm, 2-5 mm, 5-10 mm and > 10 mm to measure their lengths and biomass. Root length was measured with a steel ruler. Roots were put in envelopes, and numbered to determine biomass after root length measurement. Root dry biomass was determined after oven drying at 80 ℃ for at least 48 h (Al-Hawija et al., 2015).

2.2.4 Statistical analysis

All analyses and computations were performed with Microsoft office Excel (Microsoft Corp.; Redmond, WA, USA), and IBM SPSS Statistics 25.0 software (IBM Corp.; Armonk, NY, USA). One-way analysis of variance (ANOVA), paired-sample t test, and repeated measures analysis of variance were used to analyse the germination, survival, seedling growth, and root parameters of each treatment. Meanwhile, multivariate analysis of variance was used to evaluate the effectiveness of the three seedling methods.

3 Results

3.1 Germination characteristics

Germination percentage and seedling height of direct seeding, bud seedlings and seedling planting were calculated every 5 days from May 30 to June 19, 2018 (Fig. 1). One-way analysis of variance was used to analyze the effect of sowing time on germination percentage and seedling height, while their differences at a given time across sowing methods were compared by paired-sample t test (Table 2).
Fig. 1 Plant germination percentage and seedling height of different seedling methods

Note: (a) Germination percentage, and different letters of a given seedling method indicate that germination percentage varies significantly (0.05 level) with time; (b) Seedling height, and different letters of a given seedling method indicate that seedling height varies significantly (0.05 level) with time.

Table 2 Paired-sample t test results of germination percentage and seedling height at a given time across sowing methods
Days after sowing P
Germination percentage Seedling height
5 0.032 0.015
10 0.010 0.003
15 0.007 0.004
20 0.003 0.005
Germination percentage and seedling height increased with time, and were higher in bud seedlings and seedling planting than that in direct seeding (P<0.05). The final germination percentage of direct seedling was 47.83 % with more seeds germinating 10-15 days after sowing. While, for bud seedlings and seedling planting methods, germination percentage increased more rapidly after 5-10 days of sowing with a final germination percentage of 70.58%, indicating their conduciveness to seed germination. The seedlings of the two seedling methods began to grow rapidly 10 days after sowing attaining heights of 6.50 and 9.97 cm, respectively.

3.2 Survival and growth

3.2.1 Survival rate and seedling height

Survival rate and seedling height of seedlings that survived until 2020 and in test year were summarized in Table 3. Repeated measures analysis of variance was performed using each year’s height data of seedlings surviving in 2020 to determine the variation of seedling growth with time among all the 9 treatments (Table 4 and Fig. 2).
Table 3 Seedling height and survival rate of different seedling methods
Treatment Seedling height (cm) Survival rate (%)
2018 2019 2020 2018 2019 2020
All Surviving in
September, 2020		 All Surviving in
September, 2020		 Surviving in
September, 2020
DW 47.47±9.00a 47.94±9.33aA 73.78±9.01a 73.73±9.10aB 100.71±12.61aC 95.00 83.33 81.67
BW 55.48±13.21b 56.21±13.42bA 94.38±17.94bc 94.38±17.94bcB 133.58±25.70dC 96.67 88.33 88.33
SW 48.87±9.32a 49.10±9.47aA 77.24±13.81a 77.38±13.92aB 107.06±17.76aC 90.00 81.67 80.00
DSW 47.58±7.50a 48.93±7.38aA 78.51±7.47a 78.68±7.61aB 104.52±10.59aC 91.67 78.33 73.33
BSW 58.31±11.89bc 60.18±11.89bA 102.51±18.39d 103.42±18.75dB 136.56±24.37dC 91.67 81.67 75.00
SSW 47.79±9.21a 49.51±9.09aA 89.04±15.11b 89.91±15.59bB 117.26±19.56bC 86.67 80.00 71.67
DS 48.73±8.22a 50.24±8.17aA 93.17±14.85bc 95.15±13.89bcB 123.80±16.63bcC 85.00 76.67 68.33
BS 61.98±16.04c 66.30±14.29cA 115.13±25.37e 117.48±24.00eB 158.36±35.57eC 90.00 78.33 73.33
SS 57.74±11.34bc 60.61±10.04bA 97.22±20.17cd 99.68±19.36cdB 131.90±26.76cdC 83.33 75.00 68.33

Note: (a) Different lowercase letters indicate that seedling height of a given year varies significantly (0.05 level) with treatments. (b) Different capital letters indicate that seedling height of a given plot varies significantly (0.05 level) with time.

Table 4 Multivariate tests for the effects of time and treatment on seedling height based on repeated measures analysis of variance a
Effect Inspection methods Multivariate tests F Hypothesis df Error df Sig. Partial eta squared
Time Pillai’s Trace 0.949 3681.474b 2.000 398.000 <0.001 0.949
Wilks’ Lambda 0.051 3681.474b 2.000 398.000 <0.001 0.949
Hotelling’s Trace 18.500 3681.474b 2.000 398.000 <0.001 0.949
Roy’s Largest Root 18.500 3681.474b 2.000 398.000 <0.001 0.949
Time × Treatment Pillai’s Trace 0.524 17.702 16.000 798.000 <0.001 0.262
Wilks’ Lambda 0.535 18.239b 16.000 796.000 <0.001 0.268
Hotelling’s Trace 0.757 18.778 16.000 794.000 <0.001 0.275
Roy’s Largest Root 0.558 27.845c 8.000 399.000 <0.001 0.358

Note: The within-subjects variables are seedling height data in 2018, 2019, and 2020 of seedlings surviving in 2020. The between-subjects variable is treatment. a. Design: Intercept + treatments, and within subjects design: time. b. Exact statistic. c. The statistic is an upper bound on F that yields a lower bound on the significance level.

Fig. 2 Estimated marginal means of seedling height based on repeated measures analysis of variance
As shown in Table 3, survival rate decreased with time in all treatments and varied among them. The survival rate of bud seedlings was the highest, followed by direct seeding, and the smallest was seedling planting under a given aspect. The highest survival rate was observed in BW in all years, leaving 88.33% in 2020. Seedlings that survived until the end of the study generally exhibited higher height in all treatments. Although seedling height increased significantly with time, the trend of each treatment was different due to the interaction of time and treatment (Tables 3, 4, and Fig. 2). Seedling height varied significantly among treatments in each year, and the largest seedling height was observed in BS among all years. Under a given aspect, the seedlings height of bud seedlings was the largest, generally followed by seedling planting, and the smallest was direct seeding.
Seedling method and aspect varied among the 9 treatments. Multivariate analysis of variance was performed using each year’s height data of seedlings surviving in 2020 to determine the effects of seedling method and aspect on seedling growth. As shown in Table 5 and Fig. 3, seedling method and aspect both had pronounced impacts on seedling growth, where the effect of former was more significant. Moreover, significant interaction between seedling method and aspect only appeared in 2018 (P<0.05). Moreover, effect size of seedling method increased with year, whereas, effect size of aspect first increased and then decreased with time, leaving 0.290 and 0.178, respectively at the end of study.
Table 5 Tests of between-subjects effects for the effects of seedling method and aspect on seedling height based on multivariate analysis of variance
Source Sig. Partial eta squared
2018 2019 2020 2018 2019 2020
Corrected model <0.001 <0.001 <0.001 0.260a 0.406b 0.388c
Intercept <0.001 <0.001 <0.001 0.964 0.970 0.969
Seedling method <0.001 <0.001 <0.001 0.181 0.261 0.290
Aspect <0.001 <0.001 <0.001 0.093 0.244 0.178
Seedling method×Aspect 0.011 0.562 0.775 0.032 0.007 0.004

Note: The dependent variables are seedling height data in 2018, 2019, and 2020 of seedlings surviving in 2020, respectively. The fixed variables are seedling method and aspect. a. R2=0.260 (adjusted R2=0.245). b. R2=0.406 (adjusted R2=0.394). c. R2=0.388 (adjusted R2 = 0.376).

Fig. 3 Estimated marginal means of seedling height in 2018, 2019, and 2020 based on multivariate analysis of variance

3.2.2 Growth rate

The same data analysis methods were used to determine the effects of seedling method, aspect and time on growth rate of seedlings (Tables 6-8, Figs. 4, 5). Similar to seedling height, seedlings that survived until the end of the study exhibited higher annual growth in almost all treatments (Table 6). Both time and treatment could affect annual growth of seedlings, and significant interaction between them was also found based on the results of repeated measures analysis of variance (Table 7 and Fig. 4). As shown in Table 6 and Fig. 4, annual growth of seedlings surviving in 2020 decreased with time, and the value of 2018 was significantly higher than that of 2019 in each treatment. For example, annual growth of 2018 in DW was 1.94 times higher than that of 2019. The decline rate of annual growth decreased with time, leaving no significant difference of annual growth between 2019 and 2020 in DW, BW, SW, and DSW. Annual growth of seedlings varied significantly among treatments in each year where the largest and smallest annual growths were always observed in bud seedlings and direct seeding methods respectively. Moreover, significant difference between direct seedlings and seedling planting was usually only exhibited in aspect south. The largest annual growth was observed in BS among all years.
Table 6 Annual growth (cm) of seedlings under different seedling methods
Treatment 2018 2019 2020
All Surviving in September, 2020 All Surviving in September, 2020
DW 47.47±9.00a 47.94±9.33aB 25.76±6.52a 25.80±6.58aA 26.98±7.36aA
BW 55.48±13.21b 56.21±13.42bB 38.17±11.70b 38.17±11.70bA 39.21±11.54dA
SW 48.87±9.32a 49.10±9.47aB 28.43±8.76a 28.27±8.78aA 29.69±7.91abcA
DSW 47.58±7.50a 48.93±7.38aB 29.79±6.00a 29.75±5.69aA 25.84±5.53aA
BSW 58.31±11.89bc 60.18±11.89bC 42.80±12.06bc 43.24±12.49cdB 33.13±8.87cA
SSW 47.79±9.21a 49.51±9.09aC 40.35±10.60bc 40.40±11.10bcdB 27.35±6.42aA
DS 48.73±8.22a 50.24±8.17aB 43.63±9.77c 44.90±9.30dB 28.66±7.17abA
BS 61.98±16.04c 66.30±14.29cC 50.00±17.55d 51.18±17.29eB 40.89±13.91dA
SS 57.74±11.34bc 60.61±10.04bC 38.27±13.33b 39.07±13.64bcB 32.22±10.47bcA

Note: (a) 2018 annual growth values are equal to seedling height values in Table 3. (b) Different lowercase letters indicate that annual growth of seedlings in a given year varies significantly (0.05 level) with treatments. (c) Different capital letters indicate that annual growth of seedlings in a given plot varies significantly (0.05 level) with time.

Table 7 Multivariate tests for the effects of time and treatment on annual growth based on repeated measures analysis of variancea
Effect Inspection methods Multivariate tests F Hypothesis df Error df Sig. Partial eta squared
Time Pillai’s Trace 0.831 979.207b 2.000 398.000 <0.001 0.831
Wilks’ Lambda 0.169 979.207b 2.000 398.000 <0.001 979.207b
Hotelling’s Trace 4.921 979.207b 2.000 398.000 <0.001 979.207b
Roy’s Largest Root 4.921 979.207b 2.000 398.000 <0.001 979.207b
Time×Treatment Pillai’s Trace 0.291 8.477 16.000 798.000 <0.001 0.145
Wilks’ Lambda 0.726 8.649b 16.000 796.000 <0.001 0.148
Hotelling’s Trace 0.355 8.821 16.000 794.000 <0.001 0.151
Roy’s Largest Root 0.273 13.638c 8.000 399.000 <0.001 0.215

Note: The within-subjects variables are annual growth data in 2018, 2019, and 2020 of seedlings surviving in 2020. The between-subjects variable is treatment. a. Design: Intercept + treatments, and within subjects design: time. b. Exact statistic. c. The statistic is an upper bound on F that yields a lower bound on the significance level.

Table 8 Tests of Between-Subjects Effects for the effects of seedling method and aspect on annual growth based on multivariate analysis of variance
Source Sig. Partial eta squared
2019 2020 2019 2020
Corrected model <0.001 <0.001 0.341a 0.242
Intercept <0.001 <0.001 0.921 0.923
Seedling method <0.001 <0.001 0.148 0.199
Aspect <0.001 <0.001 0.219 0.049
Seedling method× Aspect <0.001 0.325 0.057 0.012

Note: The dependent variables are annual growth data in 2018, 2019, and 2020 of seedlings surviving in 2020, respectively. The fixed variables are seedling method and aspect. Values in 2018 are by definition identical to those in Table 5. a. R2= 0.341 (adjusted R2 = 0.328). b. R2= 0.242 (adjusted R2=0.227).

Fig. 4 Estimated marginal means of annual growth based on repeated measures analysis of variance
Multivariate analysis of variance was performed using each year’s annual growth data of seedlings surviving in 2020 to determine the effects of seedling method and aspect on seedling growth rate. Seedling method and aspect both had significant effects on annual growth, and the former was more significant in 2018 and 2020 (Tables 5, 8, Figs. 3, 5). Moreover, significant interaction between seedling method and aspect only appeared in 2018 and 2019 (P<0.05). Effect size of seedling method first decreased and then increased with time, while the effect size of aspect first increased and then decreased with time, leaving 0.199 and 0.049 respectively in the end of the study.
Fig. 5 Estimated marginal means of annual growth in 2019 and 2020 based on multivariate analysis of variance
Note: Values in 2018 are by definition identical to those in <a href="javascript:;" class="mag_content_a mag_xref_fig" onclick="clickFigXref(this,'F3')" rid="F3">Fig. 3</a>.

3.3 Root parameters

The length and biomass of roots were different with treat- ments (Fig. 6). The root length of < 1 mm was the highest under a given treatment. Accompanied by a significant dif- ference, SS brought the highest value of 1414.6 cm (One-way analysis of variance, P<0.05). Moreover, seed planting showed the largest root length of 1-2 mm under a given aspect, and the highest value of 366.4 m was also found in SS. No significant difference in root length of 1-2 mm was observed between direct seeding and bud seedlings, although a larger value was induced for bud seedlings. Compared with the root length of 1-2 mm, the difference in root length of 2-5 mm and 5-10 mm were smaller among the three seedling methods, although the highest value was still found in seedling planting. However, the root length of > 10 mm in bud seedlings was the highest, followed by direct seeding, and the smallest was seedling planting under a given aspect.
Fig. 6 Biomass and length of roots under different seedling methods

Note: (a) Root length of < 1 mm under different seedling methods; (b) Root length of 1-2 mm, 2-5 mm, 5-10 mm and > 10 mm under different seedling methods; (c) Biomass of below-ground, and different letters indicate that biomass above-ground varies significantly (0.05 level) with treatments.

The greatest root biomass of BW, BSW, and BS under a given aspect (One-way analysis of variance, P<0.05) indicated that bud seedlings had the highest effect in promoting root growth. Moreover, root biomass in direct seeding was generally larger than that of seedling planting. Similar so seedling height, the largest root biomass (131.5 g) was also shown in BS. As can be seen in Fig. 6, root biomass of different diameter ranges gradually increased with root diameter. Root biomass of >10 mm accounted for 72.63%- 90.15% of the total root biomass in all treatments, with the maximum and minimum values taken from SSW and DW, respectively.

4 Discussion

4.1 Germination characteristics

It was observed from Fig. 1 and Table 2 that seedling planting could improve the survival and early growth of seedlings, which was consistent with previous findings (Palma and Laurance, 2015; Ceccon et al., 2016). Germination characteristics of seedling planting and bud seedlings were identical because of the same sowing method. The germination percentage and seedling height of seedling planting and bud seedlings were 70.58% and 9.97 cm, which were 1.48 and 1.53 times greater than direct seeding, respectively. These results might be attributed to the soil moisture stored by the sunshade net in seedling planting and bud seedlings (Howe et al., 2020). Soil moisture was one of the main drivers of germination (Castro et al., 2005; Guignabert et al., 2020a). Furthermore, soil moisture was a critical factor and bottleneck of vegetation restoration in arid and semiarid areas (Ruiz-Yanetti et al., 2016; Gao et al., 2018; Wang et al., 2021), where most of mining areas in China were located. Seeds covered with soil at a depth of 4-5 times that of seed size in seedling planting and bud seedlings could also increase establishment rates (Silva and Vieira, 2017). In addition, physical protection of seeds such as wood veneer and bottomless could increase germination percentage through creating a helpful germination microenvironment (Mattei, 1997; Cerdà and García-Fayos, 2002; Wang et al., 2012), which was provided by seedling cup in this study. All the above factors can improve the adaptability of seeds to mining environment on germination stage.

4.2 Survival and growth

Survival and growth are known to be related, and individual seedling growth as well as its mortality drive forest stand dynamics (Fien et al., 2019). As expected, bud seedlings had a positive impact on survival and growth of Sophora japonica L. (Table 3), illustrating its better viability compared to seedling planting and direct seeding, which could be explained by its helpful growth microenvironment and no damage to the roots while transplantation (Lamhamed et al., 1997). The survival rate of direct seeding was slightly higher than that of seedling planting under a given aspect, but the difference between them was not significant, which was inconsistent with the result demonstrated by Palma and Laurance (2015), that survival of seedling planting was three times higher compared to direct seeding. This could be explained by different calculation methods. The impact of seeds that did not germinate was ignored in this study when calculating the survival rate of seedlings. However, in the study conducted by Palma and Laurance (2015), the survival rate of seedling planting was compared to the germination/survival of seeds by direct seeding. Seedling planting would also show higher survival rate through same calculation method used by Palma and Laurance (2015) because of the significant lower germination of direct seeding in this study. Furthermore, no predation effect as observed in the current study, would enhance the survival rate of direct seeding because browsing by herbivores can kill seedlings (Côté et al., 2014; Ruano et al., 2015; Guignabert et al., 2020b). Although seedling height under seedling planting method was higher as compared to the direct seeding under a given aspect, differences were non-significant, which indicated that the advantage of seedling plating was mainly reflected in higher germination percentage and initial growth during sowing (Palma and Laurance, 2015; Ceccon et al., 2016).
Seedling growth was influenced by seedling method, aspect, and their interaction (Table 5 and Fig. 3). It was worth mentioning that among all the factors, the effect of seedling method was more significant, and it increased with time. Since the difference of seedling height between direct seeding and seedling planting was relatively small, and the value of bud seedlings was significant higher than either of them, it can be inferred that the effect of seedling method on seedling height was mainly explained in bud seedlings method. The sowing method of bud seedlings and seedling planting were almost same, but former had significantly higher seedling height after transplantation, which can be explained by the fact, seedlings under seedling planting method were acclimated to particular environmental conditions in the nurseries (Driessche, 2011). The highest survival rate and seedling height of bud seedlings illustrated that this method could extract the advantages and overcome the disadvantages of seedling planting and direct seeding. On the contrary, the effects of aspect and the interaction between seedling method and aspect decreased with time, and the significant interaction was only found in 2018. The highest seedling height was found in BS with an aspect of south. This might be attributed to its better lighting because light was a key factor in plant growth (Foroughbakhch et al. 2019).
Seedling growth could be also reflected by annual growth (Tables 6-8, Figs. 4-5). The minimum annual growth of direct seeding under a given aspect would be influenced by smaller initial height before transplanting. It is consistent with the conclusion demonstrated by Detsis et al. (2020) who found that initial height has significant positive effect on annual growth. However, the positive impact might be offset by insufficiently developed root systems for seedling planting (Wennström et al., 1999; Mollá et al., 2006). Additionally, root growth would be limited in the first year after planting because roots outgrowing the seedling cup were removed when transplanting for seedling planting, influencing seedling growth (Detsis et al., 2020; Waiboonya and Elliott, 2020).
Overall, smaller containerized seedlings from bud seedlings can be most advantageous, which was also demonstrated by Lamhamed et al. (1997), who found that the use of large seedlings was not necessary compared with smaller containerized seedlings, because the latter was less sensitive to water stress. It was critical for vegetation restoration of arid and semiarid mining areas. Moreover, the cost of long-distance transportation of larger seedlings can be reduced by bud seedlings for vegetation restoration in mining areas.

4.3 Root parameters

The results of seedling planting method on root parameters exhibited that the taproot formation was restricted in seedling planting, with a significant shorter root length of > 10 mm (Fig. 6). The largest root length of 2-5 mm and 5-10 mm under a given aspect was observed in seedling planting, but its advantage was inferior to that of > 10 mm as observed under bud seedlings and direct seeding methods. The results could be that the root development of taproot in direct seeding and bud seedlings was unhindered (Wennström et al., 1999). Longer and larger taproot allowed seedlings to draw water reserves from deeper layers, surviving short periods of stresses such as drought (Baquedano and Castillo, 2007; Al-Hawija et al., 2015; Ceccon et al., 2016), with largest root lengths of 2-5 mm and > 10 mm in aspect south. Similar to survival and growth, bud seedlings had the longest root length of > 10 mm. In contrast, the highest root lengths of < 1 mm and 1-2 mm were both found in seedling planting, which might also be ascribed to the limitation of taproot growth and transplantation shock (Waiboonya and Elliott, 2020).
It can be seen from the results that bud seedlings had a positive effect on root biomass, with a significant highest root biomass value under a given aspect. The maximum root biomass was found in BS under south aspect. Conversely, the minimum value was shown in seedling planting. These results might be attributed to the restriction in root growth by seedling cup and transplantation (Wennström et al., 1999; Waiboonya and Elliott, 2020). Root development of bud seedlings was not be restricted, because seedlings were transplanted when the taproot grew to the edge of the cups without extending out of them, and the cups were removed before planting. Consequently, the sufficiently developed root systems of bud seedlings and direct seeding enabled their roots to explore to explore larger soil volume, improving their ability to use water and nutrients (Tremblay et al., 2013). However, root development in seedling planting was restricted because of seedling cup and transplantation shock, losing the ability to use water efficiently (Baeza et al., 1991).
In conclusion, bud seedlings had the highest germination percentage, growth of above- and underground plant parts, and water utilization efficiency as compared to seedling planting and direct seeding, which can well adapt to the harsh environment of mining area.

5 Conclusions

Direct seeding should not be recommended as a useful restoration technique because of associated low germination percentage and growth. The advantages of seedling planting over direct seeding can be nullified by insufficiently developed root systems and transplantation shock. However, bud seedlings could extract the advantages and overcome the disadvantages of seedling planting and direct seeding. It was confirmed in this study, that bud seedlings had a beneficial effect on promoting the seed germination and improving the survival rate of seedlings. Meanwhile, the highest seedling height, growth rate and root biomass were also shown in bud seedlings method. Although seedling method, aspect and their interaction have a pronounced effect on seedling growth, among them, the effect of seedling method was most significant. Therefore, bud seedlings can be considered as a better method for vegetation restoration in the mining areas.

References

Publishing order | Descend order by publishing year | Descend order by cited within
[1]
Ahirwal J, Maiti S K. 2016. Assessment of soil properties of different land uses generated due to surface coal mining activities in tropical Sal (Shorea robusta) forest, India. CATENA, 140: 155-163.

DOI

[2]
Al-Hawija B N, Lachmuth S, Welk E, et al. 2015. Performance of seedlings from natural and afforested populations of Cupressus sempervirensunder different temperature and moisture regimes. Plant Species Biology, 30(4): 257-271.

DOI

[3]
Atondo-Bueno E J, Bonilla-Moheno M, López-Barrera F. 2018. Cost-efficiency analysis of seedling introduction vs. direct seeding of Oreomunnea mexicana for secondary forest enrichment. Forest Ecology and Management, 409: 399-406.

DOI

[4]
Baeza M J, Pastor A, Ibáñez M, et al. 1991. Post-planting mortality in plantations of Pinus halepensis, Quercus ilex, Ceratonia siliqua and Tetraclinis articulata in Alicante Province . Studia Oecologica, 8: 139-146.

[5]
Balandier P, Frochot H, Sourisseau A. 2009. Improvement of direct tree seeding with cover crops in afforestation: Microclimate and resource availability induced by vegetation composition. Forest Ecology and Management, 257(8): 1716-1724.

DOI

[6]
Baquedano F J, Castillo F J. 2007. Drought tolerance in the Mediterranean species Quercus coccifera, Quercus ilex, Pinus halepensis, and Juniperus phoenicea. Photosynthetica, 45(2): 229-238.

[7]
Castro J, Zamora R, Hódar J A, et al. 2005. Ecology of seed germination of Pirus sylvestris L. at its southern, Mediterranean distribution range. Forest Systems, 14(2): 143-152.

[8]
Ceccon E, González E J, Martorell C. 2016. Is direct seeding a biologically viable strategy for restoring forest ecosystems? Evidences from a meta-analysis. Land Degradation & Development, 27(3): 511-520.

DOI

[9]
Cerdà A, García-Fayos P. 2002. The influence of seed size and shape on their removal by water erosion. CATENA, 48(4): 293-301.

DOI

[10]
Côté S D, Rooney T P, Tremblay J P, et al. 2014. Ecological impacts of deer overabundance on temperate and boreal forests. Annual Review of Ecology, Evolution, and Systematics, 35(1): 113-147.

[11]
Deng J, Li B, Xiao Y, et al. 2017. Combustion properties of coal gangue using thermogravimetry-Fourier transform infrared spectroscopy. Applied Thermal Engineering, 116: 244-252.

DOI

[12]
Detsis V, Efthimiou G, Theodoropoulou O, et al. 2020. Determination of the environmental factors that affect the growth and survival of Greek Fir seedlings. Land, 9(4): 100. DOI: 10.3390/land9040100.

DOI

[13]
Driessche R. 2011. Influence of container nursery regimes on drought resistance of seedlings following planting. I. Survival and growth. Canadian Journal of Forest Research, 21: 555-565.

DOI

[14]
Durigan G, Guerin N, Costa J N. 2013. Ecological restoration of Xingu Basin headwaters: Motivations, engagement, challenges and perspectives. Philosophical Transactions of the Royal Society of London (Series B, Biological Sciences), 368: 20120165. DOI: 10.1098/rstb.2012.0165.

DOI

[15]
Fien E K P, Fraver S, Teets A, et al. 2019. Drivers of individual tree growth and mortality in an uneven-aged, mixed-species conifer forest. Forest Ecology and Management, 449: 117446. DOI: 10.1016/j.foreco.2019.06.043.

DOI

[16]
Foroughbakhch R, Benavides-Mendoza A, Cruz L, et al. 2019. Ultraviolet radiation effect on seed germination and seedling growth of common species from northeastern Mexico. Agronomy, 9: 269. DOI: 10.3390/agronomy9060269.

DOI

[17]
Gao X D, Li H C, Zhao X N, et al. 2018. Identifying a suitable revegetation technique for soil restoration on water-limited and degraded land: Considering both deep soil moisture deficit and soil organic carbon sequestration. Geoderma, 319: 61-69.

DOI

[18]
Grossnickle S, Ivetic V. 2017. Direct seeding in reforestation—A field performance review. Reforesta, 4: 94-142.

[19]
Grossnickle S C. 2012. Why seedlings survive: Influence of plant attributes. New Forests, 43(5): 711-738.

DOI

[20]
Grossnickle S C, MacDonald J E. 2018. Why seedlings grow: Influence of plant attributes. New Forests, 49(1): 1-34.

DOI

[21]
Guignabert A, Augusto L, Delerue F, et al. 2020a. Combining partial cutting and direct seeding to overcome regeneration failures in dune forests. Forest Ecology and Management, 476: 118466. DOI: 10.1016/j.foreco.2020.118466.

DOI

[22]
Guignabert A, Augusto L, Gonzalez M, et al. 2020b. Complex biotic interactions mediated by shrubs: Revisiting the stress-gradient hypothesis and consequences for tree seedling survival. Journal of Applied Ecology, 57(7): 1341-1350.

DOI

[23]
Holl K D, Aide T M. 2011. When and where to actively restore ecosystems? Forest Ecology and Management, 261(10): 1558-1563.

DOI

[24]
Howe A A, Landhäusser S M, Burney O T, et al. 2020. Exploring seedling-based aspen (Populus tremuloides) restoration near range limits in the Intermountain West, USA. Forest Ecology and Management, 476: 118470. DOI: 10.1016/j.foreco.2020.118470.

DOI

[25]
Jambhulkar H P, Kumar M S. 2019. Eco-restoration approach for mine spoil overburden dump through biotechnological route. Environmental Monitoring and Assessment, 191(12): 772. DOI: 10.1007/s10661-019-7873-6.

DOI PMID

[26]
Kuang X Y, Cao Y G, Luo G B, et al. 2019. Responses of Melilotus officinalis growth to the composition of different topsoil substitute materials in the reclamation of open-pit mining grassland area in Inner Mongolia. Materials, 12(23): 3888. DOI: 10.3390/ma12233888.

DOI

[27]
Lamb D, Erskine P D, Parrotta J A. 2005. Restoration of degraded tropical forest landscapes. Science, 310: 1628-1632.

PMID

[28]
Lamhamed M, Bernier P, Hébert C. 1997. Effect of shoot size on the gas exchange and growth of containerized Picea mariana seedlings under different watering regimes. New Forests, 13(1-3): 209-223.

DOI

[29]
Li B, Liu G, Gao W, et al. 2020a. Study of combustion behaviour and kinetics modelling of Chinese Gongwusu coal gangue: Model-fitting and model-free approaches. Fuel, 268: 117284. DOI:10.1016/j.fuel.2020.117284.

DOI

[30]
Li X H, Lei S G, Liu F, et al. 2020b. Analysis of plant and soil restoration process and degree of refuse dumps in open-pit coal mining areas. International Journal of Environmental Research and Public Health, 17: 1975. DOI: 10.3390/ijerph17061975.

DOI

[31]
Liang Y C, Liang H D, Zhu S Q. 2016. Mercury emission from spontaneously ignited coal gangue hill in Wuda coalfield, Inner Mongolia, China. Fuel, 182: 525-530.

DOI

[32]
Mattei V. 1997. Physical shelters evaluation in field direct sowing of Pinus taeda L. Forestry Science, 7(1): 91-100. (in Portuguese)

[33]
Mogilski M, Fensham R J, Firn J. 2020. Effects of local environmental heterogeneity and provenance selection on two direct seeded eucalypt forest species. Restoration Ecology, 28(6): 1348-1356.

DOI

[34]
Mollá S. 2006. Physiological and transplanting performance of Quercus ilex L. (holm oak) seedlings grown in nurseries with different winter conditions. Forest Ecology and Management, 237(1-3): 218-226.

DOI

[35]
Nunes F S M, Soares-Filho B S, Rajão R, et al. 2017. Enabling large-scale forest restoration in Minas Gerais state, Brazil. Environmental Research Letters, 12(4): 044022. DOI: 10.1088/1748-9326/aa6658.

DOI

[36]
Palma A C, Laurance S G W. 2015. A review of the use of direct seeding and seedling plantings in restoration: What do we know and where should we go? Applied Vegetation Science, 18(4): 561-568.

DOI

[37]
Raupp P P, Ferreira M C, Alves M, et al. 2020. Direct seeding reduces the costs of tree planting for forest and savanna restoration. Ecological Engineering, 148: 105788. DOI: 10.1016/j.ecoleng.2020.105788.

DOI

[38]
Ruano I, del Peso C, Bravo F. 2015. Post-dispersal predation of Pinus pinaster Aiton seeds: Key factors and effects on belowground seed bank. European Journal of Forest Research, 134(2): 309-318.

DOI

[39]
Ruiz-Yanetti S, Chirino E, Bellot J. 2016. Daily whole-seedling transpiration determined by minilysimeters, allows the estimation of the water requirements of seedlings used for dryland afforestation. Journal of Arid Environments, 124: 341-351.

[40]
Silva R R P, Vieira D L M. 2017. Direct seeding of 16 Brazilian savanna trees: Responses to seed burial, mulching and an invasive grass. Applied Vegetation Science, 20(3): 410-421.

DOI

[41]
Souza D C d, Engel V L. 2018. Direct seeding reduces costs, but it is not promising for restoring tropical seasonal forests. Ecological Engineering, 116: 35-44.

DOI

[42]
St-Denis A, Messier C, Kneeshaw D. 2013. Seed size, the only factor positively affecting direct seeding success in an abandoned field in Quebec, Canada. Forests, 4(2): 500-516.

DOI

[43]
Thomas E, Jalonen R, Loo J, et al. 2014. Genetic considerations in ecosystem restoration using native tree species. Forest Ecology and Management, 333: 66-75.

DOI

[44]
Tremblay P, Boucher J F, Tremblay M, et al. 2013. Afforestation of boreal open woodlands: Early performance and ecophysiology of planted black spruce seedlings. Forests, 4(2): 433-454.

DOI

[45]
Tunjai P, Elliott S. 2012. Effects of seed traits on the success of direct seeding for restoring southern Thailand’s lowland evergreen forest ecosystem. New Forests, 43(3): 319-333.

DOI

[46]
Vickers A D, Palmer S C F. 2000. The influence of canopy cover and other factors upon the regeneration of Scots pine and its associated ground flora within Glen Tanar National Nature Reserve. Forestry, 73(1): 37-49.

DOI

[47]
Waiboonya P, Elliott S. 2020. Sowing time and direct seeding success of native tree species for restoring tropical forest ecosystems in northern Thailand. New Forests, 51: 81-99.

DOI

[48]
Wang N, Jiao J Y, Lei D, et al. 2012. Effect of rainfall erosion: Seedling damage and establishment problems. Land Degradation & Development, 25(6): 565-572.

DOI

[49]
Wang Y P, Yan W M, Han X Y, et al. 2021. Changes in deep soil water content in the process of large-scale apple tree planting on the Loess Tableland of China. Forests, 12(2): 123. DOI: 10.3390/f12020123.

DOI

[50]
Wennström U, Bergsten U, Nilsson J-E. 1999. Mechanizsed microsite preparation and direct seeding of Pinus sylvestris in boreal forests—A way to create desired spacing at low cost. New Forests, 18(2): 179-198.

DOI

[51]
Wortley L, Hero J M, Howes M. 2013. Evaluating ecological restoration success: A review of the literature. Restoration Ecology, 21(5): 537-543.

DOI

[52]
Wu Y G, Yu X Y, Hu S Y, et al. 2019. Experimental study of the effects of stacking modes on the spontaneous combustion of coal gangue. Process Safety and Environmental Protection, 123: 39-47.

DOI

[53]
Xi Q, Lai W H, Cui Y Y, et al. 2019. Effect of yeast extract on seedling growth promotion and soil improvement in afforestation in a semiarid chestnut soil area. Forests, 10(1): 76. DOI: 10.3390/f10010076.

DOI

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