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Chen, Wang, Sui, Jin, Wang and An (2020). Seed Science and Technology, 48, 3, 355-365. https://doi.org/10.15258/sst.2020.48.3.04 Effects of drought and temperature on the germination of seeds of Seriphidium transiliense, a desert xerophytic subshrub of Xinjiang, China Aiping Chen1,2,3, Yuxiang Wang2,3, Xiaoqing Sui2,3, Guili Jin2,3, Kun Wang1* and Shazhou An2,3* 1 College of Animal Science and Technology, China Agricultural University, Beijing, 100193, China 2 College of Pratacultural and Environmental Science, Xinjiang Agricultural University, Nongda East Road 311, Shayibake District, Urumqi, Xinjiang 830052, China 3 Key Laboratory of Grassland Resources and Ecology of Xinjiang, Nongda East Road 311, Shayibake District, Urumqi, Xinjiang 830052, China * Authors for correspondence. (E-mail: [email protected]; [email protected]) (Submitted April 2020; Accepted August 2020; Published online September 2020) Abstract Global warming has led to changes in rainfall patterns in many regions and it has an increasing impact on the availability of water for plants, especially in the arid and semi-arid regions. Seed germination is the most critical stage in the plant life cycle, it determines whether or not the population can successfully establish. Here, we assessed the seed germination characteristics of Seriphidium transiliense under six water potentials and four temperature regimes. S. transiliense seeds could germinate from 5/15°C to 20/30°C, while the optimum temperature regime was 10/20°C. As water potential decreased, the germination percentage, germination index, germination energy, vigour index, plumule length and radicle length increased and then decreased, while mean time to germinate decreased and then increased. The optimum condition for S. transiliense seed germination was -0.2 MPa at 10/20°C. Some seeds that failed to germinate under drought conditions were transferred to distilled water and recovered germination ability. Keywords: germination, germination recovery, polyethylene glycol (PEG)-6000, temperature, Seriphidium transiliense Introduction According to a report, the global average temperature will increase by 1.0-3.0°C by 2050 (IPCC, 2012). Alterations in rainfall patterns in many regions occur, and drought severity and length are increasing dramatically (Dai, 2011). Climate change has an important impact on all stages of plant development (Battipaglia et al., 2014; Elnaggar et al., 2018). © 2020 Chen et al. This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: https://creativecommons.org/licenses/by-nc/4.0 355 AIPING CHEN, YUXIANG WANG, XIAOQING SUI, GUILI JIN, KUN WANG AND SHAZHOU AN Compared with other developmental stages, seed germination is the definitive stage in plant population renewal (Bakhshandeh et al., 2013; Song and Wang, 2015), which directly determines the continuation, dynamics and distribution of a population. At the same time, seed germination is the most sensitive to abiotic stresses (Maraghni et al., 2010; Gurvich et al., 2017). Therefore, studying the effect of abiotic stresses on seed germination is the first step to understand the adaptability of species to adverse environments and the mechanism of plant resistance to stress. Seed germination is a complex process (Hellal et al., 2018). When the external environ ment is suitable, seeds germinate quickly and increase the seedings survival. In contrast, when the external environment is not suitable for seed germination, seeds remain as part of the soil seed bank and escape the fate of death after germination (Bradford, 2002; El-Keblawy et al., 2017), serving as a strategy of self-protection. The germination characteristics of seeds are closely related to precipitation and pre- cipitation cycles in natural distribution areas. Some species cannot germinate at -0.2 MPa (Nascimento et al., 2018), while some species have higher germination capacity when water potential is lower than -1.0 MPa (Lai et al., 2019). Seeds can adapt to water stress by increasing protective enzyme activity and osmotic adjustment substances in vivo to minimise the damage caused by water stress during the germination process. Temperature is a critical ecological factor affecting seed germination (Fakhfakh et al., 2018). Different plant species have different temperature requirements for germination (Gorai et al., 2014). Some plant species only germinate over a narrow temperature range, but others can germinate over a wide range of temperatures (Baskin and Baskin, 1998). Drought and high temperatures are commonly encountered together in arid and semi-arid regions, so it is important to study the interactive effects of water deficiency and temperature on seed germination of desert plants. Understanding the range of suitable water and temperature conditions for seed germination of different species will help to provide information for plant survival strategies in the desert. 7 2 Desert pasture occupies approximately 2.7 × 10 hm in Xinjiang, China, and covers more than 46.9% of Xinjiang grassland (Xu, 1993). There are many excellent annual and perennial grasses in desert pasture. As one of the dominant species of desert pasture, Seriphidium transiliense (Poljakov) Poljakov (Compositae) is a perennial xerophytic subshrub (An, 1999). Because of its good root system, drought resistance and adaptability, it plays an important role in maintaining the stability and sustainability of desert ecosystems (Zheng, 2013), and the production of livestock. Seriphidium tran siliense is an 6 2 important component of Xinjiang desert pasture, occupying 1.14 × 10 hm . S. transiliense is located in the transition zone between plains and mountains at an altitude of 500 to 3200 m a.s.l. However, due to the effects of climate change and over-grazing (Manzano and Návar, 2000), S. transiliense desert has undergone severe degradation, which not only restricts the development of Xinjiang animal husbandry, but also affects the ecological balance and ecological security of the desert region in Xinjiang. Therefore, the restoration of degraded grassland is an extremely urgent problem at present. The most cost-effective method is re-seeding of S. transiliense. Bademuqiqige et al. (2018) studied the effect of harvest time on seed germination, and Sun and He (2007) reported that mature seeds of S. transiliense had non-deep physiological dormancy. However, there are few studies on the 356 SEED GERMINATION OF SERIPHIDIUM TRANSILIENSE interactive effects of drought and temperature on the germination of S. transiliense seeds. The objectives of this study were to assess the effects of water potential, temperature and their interaction on seed germination. We hypothesised that drought stress can promote seed germination, and seed germination will be inhibited by high temperatures and low water potentials. The results will reveal the adaptability of germination of S. transiliense seeds to drought and temperature stress, and provide theoretical reference for desert plant protection and population renewal. Material and methods Seed collection Mature seeds of S. transiliense were collected on 23 October 2017 in the desert pasture in Sangongtan, Changji city, Xinjiang, China (43°50'9''N, 87°11'21''E, 994 m a.s.l.). Seeds were air-dried and stored in brown paper bags at 4°C until used for the seed germination experiments. The climate of this area is a typical temperate continental dry climate. The annual mean temperature and precipitation are 8.5°C and 180 mm, respectively, and annual evaporation is 1790 mm. The soil type is grey desert soil. The vegetation community is dominated by S. transiliense, with local accompanying species at the study area, such as Tulipa iliensis Regel., Geranium transversal (Kar. & Kir.) Vved. ex Pavlov, Ceratocarpus arenarius L., Salsola affinis C.A.Mey., Eremopyrum triticeum (Gaertn.) Nevski, Atriplex sp., Kochia scoparia L. Schrad. and Lappula sp. Seed germination experiments The experiments commenced on 18 April 2018. Seeds were incubated at six levels of water potential (ψ): 0.0 (control), -0.2, -0.4, -0.6, -0.8 and -1.0 MPa, and four alternating temperatures, 5/15°C, 10/20°C, 15/25°C and 20/30°C, in plant growth chambers. According to Michel and Kaufmann’s (1973) equations, the different water potentials were acquired with different concentrations of polyethylene glycol (PEG)-6000. The light regimes were 12 hours of white light (approximately 200 μmol m-2 second-1 of photosynthetically active radiation) and 12 hours of darkness. The highest temperatures corresponded to the period of exposure to light. S. transiliense seeds were surface-sterilised with 75% ethanol for one minute and 5% sodium hypochlorite solution for five minutes, and rinsed three times with sterile water. Fifty randomly selected seeds were placed on double-layers of filter paper (Whatman No. 1) in 90 mm-diameter glass Petri dishes, moistened with 6 mL of distilled water (control) or a solution of PEG-6000. Four replicates were included for each treatment. Seeds were scored as germinated upon 2 mm-long radical emergence The number of germinated seeds was recorded daily for 16 days; no further seeds germinated over the following three days after which the germination trials were finished. To avoid evaporation, glass Petri

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