Restoration of the Steppe ecosystem through agroforestry: A study of the germination and emergence of Pistacia Atlantica Desf  in the El Bayadh region, Algeria

Mekhloufi Moulay Brahim, Benabdeli Khéloufi¹, Tayeb Nouri² and Mahari Latifa³

University Mustapha Stambouli, Mascara, Institute of Agronomy, Algeria
Agro752002@msn.com
¹ Laboratory of Geo- Environment and Development of Spaces. University Mustapha Stambouli, Mascara, Algeria
² Laboratory of Biodiversity and Conservation of Soils and Waters, University Center Salhi Ahmed Naâma, Algeria
³ Faculty of Sciences, Biology Department, Nouri Bachir El-Bayadh University Center, Algeria

Abstract

The steppe ecosystem can be preserved by introducing Pistacia atlantica Desf., a woody tree species with a socio-economic impact. The treatment of seeds harvested in the sylvopastoral area of the Brezina region (El Bayadh-Algeria) has improved the germination rate and has yielded interesting results. In this study, various physical pre-treatments were carried out such as scarification at different temperatures and chemical treatment with sulphuric acid, ethanol, hydrogen peroxide and gibberellin GA₃. The results obtained show that the various pre-treatments tested make it possible to accelerate the germination rate. The highest germination rate (100%) was recorded in seeds that underwent cold stratification at -4°C for 10 hours, combined with mechanical scarifying and treatment of the seeds with GA₃ at 100 ppm for 30 minutes. Mechanical scarification resulted in high germination rates: 88.88, 74.99%, 84.72%, 90.27%, 80.55%, 70.83%, 80.55%, 100% for the stripped seed, ethanol C₂H₅OH (50 pmm), C₂H₅OH (100 pmm), hydrogen peroxide H₂O₂ (50pmm), H₂O ₂ (100ppm), sulphuric acid H₂SO4b (100ppm), gibberellic acid GA₃ (50ppm) and acid GA₃ (100ppm), respectively. However, stratification of seeds at -4°C with different treatments shows average germination rates of 83.85%.

Keywords: sustainable development, scarification, GA₃ gibberellic acid

Introduction

The sustainable development of the steppe area requires restoration by introducing Pistacia atlantica, which is a fairly resistant species and is influenced by local ecological conditions. This tree-like woody plant is present in the Brezina region. But no longer regenerates due to various pressures (overgrazing, climate).

The multiplication of this plant in the region will have socio-economic and ecological impacts due to its agro-sylvo-pastoral importance. Several authors underline the importance of this species since all parts of the plant are used in local phytotherapy (Benaradj A et al 2015). The bark produces a mastic resin that naturally exudes abundantly in hot weather (Monjauze A 1980).

The tree provides wood for crafts and fire, and it can be used to make charcoal. Furthermore, it is a heavy and well-preserved wood (Ozenda P 1983).

The multiple forms of planting carried out in this area have resulted in failures induced by the use of non-adapted species. In this context, particular attention should be paid to local species with economic and ecological potential as they adapt to soil and climate conditions in arid and semi-arid areas. However, the use of such species requires a better understanding of their biology and mechanisms of regeneration and growth.

Some botanical and ecological factors

The genus Pistacia of the Anacardiaceae family includes many species widely distributed in the Mediterranean region and Middle East (Tutin et al 1968). The Atlas pistachio tree (Pistacia atlantica Desf.), commonly known as El Betoum, Botma in Arabic, is a woody and spontaneous species that can reach 10 m in height. The tree has an individualized trunk with hemispherical foliage (Quézel and Santa 1963).

Its compound leaves consist of seven to nine leaflets; the flowers are in loose clusters, and the fruits, which are about the size of a pea, are drupes (Ozenda 1983) that are referred to as khodiri. These fruits are consumed by the local inhabitants (Belhadj et al 2008). Fruiting begins towards the end of March, and the fruits ripen in September (Yaaqobi et al 2009).

According to Zohary (1952,1987) and Quézel and Médail (2003), this species is common in the Mediterranean and Irano-Turanian regions. However, Manjauze (1980) and Ozenda (1983) describe it as endemic to North Africa (Belhadj et al 2008). It is tolerant to several soil types, including alkalis. It can thrive with rainfall of about 150 mm and sometimes less (Benhssaini and Belkhodja 2004). Pistacia atlantica Desf. regenerates and develops in the driest places where few tree species can survive. Its growth is very slow. In Algeria, it is found in places with Ziziphus lotus, which protects young shoots from animals and strong winds (Belhadj et al 2008). It covers a large area including Morocco, Algeria, Tunisia, Libya, Syria, Jordan, Palestine, Iran and Afghanistan (Kaska et al 1996; Khaldi and Khouja 1996; Sheibani 1996). Pistacia atlantica seems to be the ideal choice for steppe enhancement work.

Materials and methods

The seeds used in the experiment were harvested at maturity in September from a seed-carrying stand located in the Brezina region (i.e., Guerar: 01°28'24.26E'' 33°11'47.55N''). The average altitude is 97 m and the rainfall regime is of the AHPE type with a 300 mm rainfall range. After harvesting, the seeds were air-dried and carefully sorted to eliminate those infected and damaged by insects. They were placed in paper bags and stored under ambient conditions and protected from light until they were used. Before use, the seeds were soaked in water for 24 hours to remove the pericarp; empty seeds were also removed.

Results

Pre-treatments

Natural exposure to cold can end seed dormancy. Furthermore, seed dormancy can also be ended by physical treatments such as stratification and scarification or the use of growth regulating hormones. Stratification is a technique used mainly to end primary morphological, physiological and morphophysiological dormancy (Geneve 2003). Stratification is effective in ending secondary dormancy. The stratification process consists of incubating the seeds in humid conditions and at low temperatures (0-10°C). The optimal temperature is 4°C for many species (Baskin and Baskin 1998). The effectiveness of stratification varies by species (Andersson and Milberg 1998; Vincent and Roberts 1977).

Seeding was carried out in cells; three repetitions of 24 seeds were carried out for each germination test. The germinated seeds were counted daily and the cumulative percentages of germination were also determined daily. A seed was considered to have germinated when the radicle became visible (Come D 1968). Mechanical scarification was done by making a small cut in the integument with green paper while respecting the integrity of the kernel. For the chemical treatment, the seeds have been soaked in the different solutions. 100 ppm and 50 ppm for 30 minutes. The seeds of Pistacia atlantica were divided into two blocks, A and B. Each batch suffered mechanical and thermal shock. The treatment method for block A consisted of immersing the seeds in boiling water for one minute and then putting them in a tank at -4°C for 12 hours. Block B underwent the opposite treatment (i.e. the seeds were placed in a cold tank at -4°C for 12 hours and immersed in a boiling water tank for one minute). Both Device A and Device B underwent the same physicochemical and hormonal treatments.

Influence of processing differences

The two pre-treated seed lots were germinated in cells for two months after sowing. The mechanically scarified seeds germinated from day 17, and the germination rate improved for bare seeds and became higher until day 47 after sowing. The mechanical scarifying clearly improved germination, as the rate increased by 88.88%. The treatment of seeds with gibberellic acid significantly increased the germination rate.

The seeds soaked for 30 min had an optimum germination interval between 12 and 20 days after sowing. However, the high germination rates were obtained after treatment with 100 ppm sulphuric acid after 12 days of sowing.

The comparison of germination rates obtained after mechanical and chemical scarifications of the seeds showed that the germination rate of seeds soaked in gibberellic acid for 30 min was significantly higher than that obtained after mechanical scarifying.

Seeds germinated and treated with gibberellic acid (GA₃ at 100 ppm) had the best germination rate (100%); this rate was more than 10% higher than any other treatment.

The influence of the treatments on germination kinetics is presented in Fig. 1 where the curves represent the cumulative germination rates for a 60-day period. The species' sensitivity to different types of treatment where germination kinetics displays three phases: latency, exponential acceleration of germination after reaching maximum germination capacity. The germination rate varied according to the type of treatment; there were two doses (50ppm, 100ppm) with emergence rates of 88.88, 74.99%, 84.72%, 90.27%, 80.55%, 70.83%, 80.55%, 100% for stripped seeds, C₂H₅OH (50 pmm), C₂H₅OH (100 pmm), H ₂O₂ (50 pmm), H₂O (100 ppm), H₂ SO₄ (100 ppm), GA₃ (50 ppm) and GA₃ (100 ppm), respectively.

Figure 1. Germination kinetics of Pistacia atlantica seeds under the effect of the different treatments germinating at room temperature (25–30°C). N: number of germinated seeds

The results were analyzed with Stat Box software (version 6.4), and an analysis of variance was conducted at the 5% probability level. The averages are compared with the Tukey test to determine homogeneous groups at α=0.05.

Only seeds that underwent cold pre-treatment germinated. Therefore, calculations were only performed on the results of germinations of cold pre-treated seeds (Block B).

Table 1 presents the results of the variance analyses with one factor. They show that the variability of germination is highly significant. Interactions between factors are significant only for germination rate calculations, and the interaction between the control and treated grain factors is the most significant. Natural seeds had a lower germination rate and a slower median response than treated seeds. Table 2. shows that the germination rate of seeds varies according to the different treatments. GA ₃ was used to end embryonic dormancy; the seeds that were treated have the highest germination rate but a relatively longer average time. Our results agree with those obtained by Ayfer and Serr (1961) and Crane and Forde (1974).

Scarification succeeded in increasing the germination rate over a shorter period of time. The same results were obtained by Abu-Qaoud (2007). In order to classify the lifting potential, a comparison of germination rates and average germination times was carried out using the Newman-Keuls test (Table 2). It can be seen that as soon as C₂H₅OH was applied, the germination capacity is slightly reduced.

Fig. 2 illustrates the variations in the average germination rates according to the different pre-treatments of scarification for two months. It shows that scarification with sulfuric acid allows a faster start of germination with higher germination rates of 70.83%. Scarification is more or less inferior to the other pre-treatments tested, namely mechanical scarification or gibberellic acid. The best average germination time, 15 days, is noted for pre-treatment with C₂H₅OH (100 ppm) (Table 2). These results are confirmed by the analysis of variance, which revealed a highly significant pre-treatment effect on germination rates and average germination times. They also show that there is a significant effect of the treatments on the germination rate (p < 0.05).

Figure 2. Average germination rate (%) of Pistacia atlantica under the effect of the different treatments

Discussion

The results obtained for the germination behavior of Pistacia atlantica seeds showed that the germination rate of seeds treated with GA₃ reached 100%; this was the highest rate. These low germination rates are believed to be due to the presence of pericarp in fruits, which, on the one hand, prevents the integrity of the seeds from being assessed and, on the other hand, constitutes, in addition to the seed teguments, an additional barrier that limits the access of water and oxygen to the embryo. If this hypothesis is correct, the seeds would thus have an integumentary inhibition linked to the seed integuments, which would be impermeable to air and water.

However, it should be noted that this impermeability of the seed coat would also be an advantage because it would protect it from rapid germination under conditions unfavorable to the development of the plants (Grouzis M 1987; Nongonierma A 1978; penning de vries FW T 1982; Tybirk K 1991).

Mechanical scarification and GA₃ seed treatment significantly increased the germination rate and speed of the Pistacia atlantica seeds compared to intact seeds (controls). The main obstacle to seed germination seems to therefore be of integumentary origin. Indeed, all pre-treatments applied to the seeds weakened the integuments and facilitated, on the one hand, the access of water and air to the embryo and, on the other hand, the root exit

The best germination rate, which was obtained after 30 minutes of immersion of the seeds in GA₃, was higher than that obtained after mechanical scarification. This may be partly explained by the effect of GA ₃ on abscisic acid (ABA), which is the primary inhibitor of germination in many seeds (Pinfield and Gwarazimba 1992). Embryonic dormancy is directly related to ABA production (Hilhorst and Karsseen 1992).

The synthesis of ABA is accelerated in response to stress factors such as water stressors (Yoshioka et al 1995). Lack of oxygen increases the amount of endogenous ABA and decreases the amount of GA₃ and cytokinin in maize seeds (Prasad et al 1983), thus facilitating the absorption of water and oxygen that are essential for germination. However, since mechanical scarification is only sectarian, it does not facilitate the imbibition and expansion of the embryo as much. Optimal germination temperatures vary from one species to another. For Pistacia atlantica, the optimal germination temperature is between 25 and 30°C, which was confirmed by our experience. Although the germination rate is slightly higher at 25°C, the germination rate is higher at 30°C. These results are relatively consistent with those of Grouzis et al (1986), who found the optimal seed temperature of Pistacia atlantica to be 30°C.

Conclusion

• This comparative study of the germination capacity of Pistacia atlantica seeds showed that they have an interesting germination capacity that should be harnessed to improve the success of nursery plant breeding. Mechanical scarification and chemical and especially hormonal scarification significantly increased the germination rate. For chemical scarification with 98% sulphuric acid, the germination rates obtained were a function of the duration of immersion of the seeds in the acid.
• After 12 days, a germination rate of 50% was achieved. With GA₃, it reached 82% after 30 days. Pistacia atlantica seeds seem to have an integumentary inhibition due to the impermeability of the integuments to water and air. If this is true, thermal optimum for germination would be between 25 and 30°C. Above that, the germination rates decrease and cancel each other out at 45°C. If temperatures were raised in such a way as to cause thermal shocks of limited duration, average to low temperatures would have a greater effect on the speed than on the germination capacity. However, high temperatures would inhibit the germination of Pistacia atlantica seeds (The case of non-germination of grains in device (A) in our experiment).
• To succeed in direct seeding in sites with protection or in nurseries, Pistacia atlantica seeds must undergo mechanical or chemical and hormonal scarification in order to remove integumentary inhibition at an optimal germination temperature between 25 and 30°C. The results obtained in this study suggest that Pistacia atlantica seeds should not have difficulty germinating in arid or semi-arid regions, allowing the use of this species for the restoration of the steppe area.
• However, the restoration measures and techniques to be undertaken have yet to be defined through long-term studies considering the dynamics of the species' development from the preliminary stock of viable seeds contained in the soil, and through the introduction of new seeds, or even seedlings, to improve the species' regeneration process.

Acknowledgments

I would like to express my thanks to the staff of the laboratory of Faculty of Sciences, Biology Department of the Nour Bachir El-Bayadh University Center (Algeria) for its help in carrying out this study.

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Received 4 November 2019; Accepted 4 November 2019; Published 2 December 2019

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