Temperature effect on seed germination of four plants in sand from coastal sand dunes in Greece
Abstract
In high temperatures of coastal sand dunes, salt may limit seed germination and thus strongly limit plant survival. The relationship between germination and sand dunes soil temperatures has never been evaluated. The effect of coastal dunes sands on plant germination at 20°C and 28°C was studied. Sand samples of coastal dunes from coastline regions in Greece were analyzed and used as substrates. The Si content (89-97%) is the representative one in all soils. The Si, Al and Mg contents in the Aegean Sea sand dunes were higher than the Ionian Sea. Pigweed germination at 28°C in sand from mainland Greece was higher than the corresponding one from insular Greece. Purslane germination at 28°C in sand from the Ionian Sea (52% -57%) was higher than the corresponding one from the Aegean Sea (49% -50%) and at 20°C it remained unaffected by the soil. Chervil and coriander germination at 20°C was very low, while no germination occurred in pigweed at 20°C and chervil and coriander at 28°C in all sand soils. The study has shown that the coastal dune soils favoured germination of pigweed and purslane at 28°C. These results indicate that those plants have adapted to the coastal sand dunes environment.
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Introduction
The sand dunes occurred in rows along the coast. Coastal dunes have an extensive global distribution (Martinez etal. 2004). A variety of abiotic and biotic factors including sand instability, salinity, extreme high or low temperatures, drought, and herbivore predation may limit seed germination and seedling emergence in coastal sand dunes (Sykes & Wilson 1988; Maun 1994; Maun 2009). Major problems faced by seeds are sand accretion and soil salinity.
Seed germination is a critical stage for the establishment of a species. Salt inhibits seed germination in saline soil, and high salinity is injurious to most glycophytes. Ungar (1978) suggested that there is a complex interaction between salinity and temperature, especially for coastal halophytes. Salinity and temperature interact in their control of seed germination (Khan & Ungar 1999), with the greatest inhibition due to salinity usually found at the minimum or maximum limits of tolerance to temperature (Badger & Ungar 1989). In sand dune environments, seed germination is strongly related to available moisture and seedling survival is strongly limited by temporal changes in water availability (Maun 2009). Very small seeds showed a high germination rate because of the small amount of moisture required for inbibition (Stairs 1986; Zheng et al. 2005).
Purslane (Portulaca oleracea) is a spontaneous wild forb, herbaceous annual plant, from the Portulacaceae family. It is one of the world's most aggressive and worst weeds, a unique plant that has the ability to adapt to many diverse environments (Rahdari et al. 2012). It is more tolerant to salinity and drought conditions (Hamidov etal. 2007). The plant produces numerous minute see ds, many of which have primary dormancy and require warm temperatures and light for germination (Egley 1984). The plant grows in the wild and is cultivated around almost the whole world. Purslane is a heat - and drought - tolerant plant, and is an importantv egetable crop (Anastácio & Carvalho 2012; Dadkhah 2013). Moreover, purslane is an edible halophyte (Grieve & Suarez 1997) and a promising crop for saline agriculture (Kiliç et al. 2008), which has been studied for its relatively high salinity tolerance (Teixeira & Carvalho 2009). The optimal seed germination occurs at temperatures > 30°C, while poor germination occurs at temperatures < 24°C (Miyanishi & Cavers 1980; Zimmerman 1976). Germination was 96% when seeds were exposed to 35/25°C day/night alternating temperatures, but 25/10°C day/night resulted in 15% germination (Miyanishi & Cavers 1980). In the light/dark regime, the germination was lower at 25/15°C than at 30/20°C (70%, and 81% germination, respectively) (Chauhan & Johnson 2009).
Pigweed ( Amaranth us retroflexus ) is a common annual worldwide weed of 60 crops in 70 countries. It can be found in a wide range of habitats and causes substantial yield reduction in many different agricultural crops through competition (Ghorbani et al. 2000; Holm etal. 19 97). Pigweed is a thermophyte to sub-thermophyte, often highly stress-tolerant, growing in sandy and saline habitats (Costea et al. 2004; Robertson & Clemants 2003). It reproduces by seeds which can only remain viable for at least 6 –10 years (Costea et al. 2004). Seed germination of pigweed differed in its response to temperature. Pigweed had higher germination rates at 35/30°C than at 25/20°C or 45/40°C, and at 15/10°C no seed germination was observed (Guo & Al-Khatib 2003). Ghorbani et al. (1999) found that the minimum temperature for pigweed germination was greater than 5°C, whereas maximum germination occurred between 35 and 40°C. Pigweed was sensitive to Al, Mn, NaCl and Na2SO4.
Chervil ( Anthriscus cerefolium ) is a fragrant, delicate annual herb, belonging to the Apiacae family. Its seeds need light and wet porous soil to germinate. Seeds of chervil have germinated at a 13°C temperature (Bubel 1988). The seed germination percentage of chervil at 22°C in H2O was 44%. In the 80mM NaCl concentration there was an increase in the germination (64%), while in higher NaCl concentrations the germination reduced (Liopa-Tsakalidi & Barouchas 2011).
Coriander (Coriandrum sativum) is an annual herb of the Apiaceae family, grown primarily for its seed and seed oil all over the world (Verma & Sen 2008). It is known as a species moderately tolerant to salinity. Zidan & Elewa (1995) mentioned that during germination, coriander tolerated salinity up to 200mm NaCl. Liopa-Tsakalidi etal. (2011) reported that no seeds germinated in high salt concentrations (0.5 and 1.5 mol/l NaCl). In addition to this, the seed germination of coriander showed a progressive decrease as salinity levels increased (Ewase et al. 2013; Fredj et al. 2013). The salinity effect appears mainly during germination and plant growth (Aymen & Cherif 2013).
Little research has been conducted about the application of seed germination on coastal sand dunes and the studies on their relationship with seedlings are still inadequate. For example, the growth charact eristics of seedlings in Greek coastal sand dunes have not been investigated with respect with to initial seed germination.
The focus of the current study was to provide knowledge on the germination behavior of pigweed ( Amaranthus retroflexus ), purslane ( Portulaca oleracea ), chervil ( Anthriscus cerefolium ), and coriander ( Coriandrum sativum ) in two temperatures and different sand soils of coastal sand dunes in Greece, and to ascertain the effects of different characteristics of sand soils on germination .
Conclusion
The study has shown differences between the percentage of various sand elements in the dunes of the mainland and insular coastline of the Ionian Sea and the insular coastline of the Aegean Sea of Greece. Moreover, the study has shown that there was no germination of chervil and coriander seeds in coastal dune soils and sand soils favoured germination of pigweed and purslane at 28°C. These results indicate that the two plants, pigweed and purslane, have adapted to the coastal sand dunes environment .
