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Vol. 2 No. 2
2011

Germination studies in Juncus acutus L. (Juncaceae), Schoenus nigricans L. (Cyperaceae) and Arthrocnemum macrostachyum (Moric.) Moris (Chenopodiaceae) for salt-marshes restoration

E. Conesa 1, M.J. Vicente 1, J. Álvarez-Rogel 2, J.A. Franco 1 and J.J. Martínez-Sánchez 1 *
1 Departamento de Producción Vegetal, Instituto de Biotecnología Vegetal, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain
2 Departamento de Ciencia y Tecnología Agraria. Escuela Técnica Superior de Ingeniería Agronómica, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain
*Corresponding author, to whom more information request should be addressed (e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).
Additional keywords
: germination recovery, halophytes, salinity, salt marshes, seed ecology

INTRODUCTION

Since the 1970’s, salt marshes have been reduced in area by a great antropogenic pressure derived from agriculture, and more recently, from demand for tourist urban facilities. Therefore, restoration and preservation of plant communities in salt marshes are needed. Among the perennial species that appear typically in maritime sands, on the Mediterranean region and western Europe Juncus acutus L.(Juncaceae), Schoenus nigricans L. (Cyperaceae) and Arthrocnemum macrostachyum (Moric.) Moris (Chenopodiaceae) frequently occur (Álvarez-Rogel et al., 2000; Vicente et al., 2007). On other hand soil salinity has traditionally been considered one of the most important physical factors in plant zonation of salt marshes (Fig.1). Álvarez-Rogel et al. (2006) related the increase in soil salinity in summer to a higher content in Cl, Na+, SO42−, Ca2+, Mg2+ and K+. However, the relative percentages of Ca2+ and K+ decreased when salinity rose, leading to an imbalance in favour of the most toxic cations, such as Na+ and Mg2+. The same authors showed that the highest correlation coefficients for ions were between Cl and Na+ and between Cl and Mg2+.

The use of the above mentioned species in restoration programs require to know the germination responses to light and temperature and their salinity tolerance during germination.

 
GERMINATION RESPONSE

In order to know the effects of photoperiod and temperature conditions on germination, lots of seeds of  Juncus acutus and S. nigricans were obtained from the “Arenales y Salinas de San Pedro del Pinatar”  Regional Park (Murcia  SE  Spain,  N 37º 46’-37º 52’ W 0º 44’-0º 48’)  and  put  on germination. The germination response of A. macrostachyum was not studied due to the existence of scientific information available about this. This area is a semiarid region, with typically Mediterranean climate characterised by irregular rainfall events and a harsh dry summer period. Annual rainfall is around 340 mm and mean annual evapotranspiration 1019 mm and mean annual temperature is 17ºC.

Seeds were placed in growth chambers in two light conditions (12 h photoperiod at 400- 700 nmol, 35 nmol photon m-2 s-1, and total darkness) and seven temperature regimes: five constant temperatures of 10, 15, 20, 25, or 30ºC and two alternating temperatures of 15:25 or 20:30ºC dark:light cycle, and then final germination percentage and mean time to germination (MTG) were determined. 

Final germination in J. acutus was significantly affected by temperature, light and their interaction, obtaining germination percentages higher than 95% at some light and temperature conditions. The germination of S. nigricans was not dependent by light but was affected by temperature. The final germination of this species did not exceed the average value of 37% at any light condition and temperature under study. The low germination percentages obtained from S. nigricans suggests it belongs to a species with seed dormancy (Martínez-Sánchez et al., 2006).

None of the two species is totally dependent on light to germinate. The results might indicate that neither species is specialized in colonizing exclusively bare soils, but that they could also germinate in areas where plant cover is high (Martínez-Sánchez et al., 2006).


SALINITY TOLERANCE

In order to determine the salinity tolerance, four 25-seed replicates of each species were placed on filter paper in 9 cm tight-fitting Petri dishes and submerged in 4 mL of each solution. Solutions of the most common salts in the salt marshes of the area (NaCl, MgCl2, MgSO4 and Na2SO4) (Álvarez-Rogel et al., 2007) were used at concentrations of 1, 2, 3, 4 or 5%. Distilled water was used as control. The dishes were placed in growth chambers and maintained at 30:20ºC with a 12 h photoperiod, for 30 days. This temperature/light regime has been reported to be optimal for germination in these species (Martínez-Sánchez et al., 2006). At the end of the germination period, the germination percentage and the mean time to germination (MTG) under salinity were calculated.

The results showed that A. macrostachyum was the most salt tolerant species (Vicente et al., 2007, 2009). Although maximum germination was obtained under non-saline conditions (84%), its seeds had the ability to germinate at 3% NaCl, although at 2%, germination significantly decreased (64%) and was drastically inhibited at 4% NaCl. On the other hand, none of the MgSO4 concentrations used had a significant effect on the germination of A. macrostachyum, while higher concentrations of MgCl2 and NaSO4 solutions decreased progressively its germination. However, S. nigricans was unable to germinate in the presence of any chloride concentrations and it could only do so in fresh water (26%) or low sulphate concentrations. Juncus acutus showed an intermediate type of behaviour, germinating at 1% both NaCl and MgCl2, although with a decreased percentage (15% and 45%, respectively) compared with the control (95%). When sulphates were used as salt, J. acutus germinated better than in chlorides (Vicente et al., 2007, 2009).

This differential behaviour of seeds according to the salt type is presumably due to the fact that the same concentration of salt generates different osmotic potentials and the osmotic effect may well have a greater influence on germination than specific ion toxicity, as has been suggested by several authors in other halophytes

As these results demonstrate, the salt tolerance of the three species studied in the germination phase differed substantially, especially in the case of A. macrostachyum, varying greatly in their ability to germinate under hypersaline conditions (Vicente et al., 2007).


GERMINATION RECOVERY

Germination recovery of seed lots incubated in 1, 2, 3, 4, or 5% saline solutions of NaCl, MgCl2, MgSO4, and Na2SO4 for 30 days was studied by transferring ungerminated seeds to distilled water.

Seed germination of A. macrostachyum was only inhibited at the highest salinity (4% NaCl, 5% MgCl2) but these ungerminated seeds showed a high germination recovery in distilled water (81% and 83%, respectively) (Vicente et al., 2009). Seed germination of S. nigricans was totally inhibited by salts and only 26% of them germinated in the control treatment. However, the germination recovery of this species could be stimulated by high salt concentrations (germination of ungerminated seeds incubated at 5% Na2SO4 reached 66% in distilled water). Juncus acutus germinated well without salt (95% in the control treatment) but high salt concentrations inhibited them from germination (Vicente et al., 2007, 2009). However, ungerminated seeds were not damaged by salt, showing a high level of recovery (100% in all salt types and concentrations). The chlorides were more inhibitory to germination than sulphates at equivalent concentrations.

The germination-related characteristics of J. acutus and S. nigricans mean that both species may be considered halophytes although neither of them can tolerate such high salinity levels as A. macrostachyum. Juncus acutus and A. macrostachyum produce nondormant seeds, whereas a high proportion of S. nigricans seeds are dormant (Martínez-Sánchez et al., 2006; Vicente et al., 2007, 2009).

Based on the results obtained, and following the classification Boorman, 1968 (Vicente et al., 2009), J. acutus and S. nigricans can be classified as halophytes type 2 (Dune hollows or low lying areas that are occasionally inundated. Germination is strongly inhibited even in very low salinities. Recovery: germination is usually equal to that in freshwater or only slightly reduced), since their germination is strongly inhibited even in very low salinities but after recovery in distilled water germination is equal to that in freshwater. Arthrocnemum macrostachyum fits halophytes type 3 (Marsh habitat that is subject to frequent long-lasting periods of inundation. Seeds germinate to high percentages even at high salinities and show high viability rates after exposure to any salinity. Recovery: germination is enhanced after pretreatment in saline solutions), since their seeds can germinate in high salinities (Vicente et al., 2009). These results are in accordance with the conceptual model proposed by Álvarez-Rogel et al. (2006) for monitoring hydrological and saline gradients in coastal dune salt marshes of southeast Spain (Vicente et al., 2007; 2009).

Of the three species studied, S. nigricans is the one that germinates to the lowest percentage. Thus, perhaps dormant seeds should be used from the soil seed bank to re-establish populations following fluctuations of the salinity gradient. In fact, our results demonstrate that exposure to salt can break dormancy in seeds of S. nigricans (Vicente et al., 2009).


LITERATURE CITED

ÁLVAREZ-ROGEL, J., MARTÍNEZ-SÁNCHEZ, J. J., CARRASCO, L. and MARÍN, C. M. (2006). Vegetal bioindicators for monitoring hydrological and saline gradients in a coastal dune salt marsh of southeast Spain: A conceptual model.Wetlands, 26: 703–717.

ÁLAREZ-ROGEL, J., CARRASCO, L., MARÍN, C.M., and MARTÍNEZ-SÁNCHEZ, J.J. (2007). Soils of a dune coastal salt marsh system in relation to groundwater level, micro-topography and vegetation under a semiarid Mediterranean climate in SE Spain. Catena, 69: 111–121.

MARTÍNEZ-SÁNCHEZ, J. J., CONESA, E. VICENTE, M. J., JIMÉNEZ, A. and FRANCO, J. A. (2006). Germination responses of Juncus acutus (Juncaceae) and Schoenus nigricans (Cyperaceae) to light and temperature. Journal of Arid Environments, 66: 187–191.

VICENTE, M. J., CONESA, E., ÁLVAREZ-ROGEL, J., FRANCO, J. A. and MARTÍNEZ-SÁNCHEZ, J. J. (2007). Effects of various salts on the germination of three perennial salt marsh species. Aquatic Botany, 87: 167–170.

VICENTE, M. J., CONESA, E., ÁLVAREZ-ROGEL, J., FRANCO, J. A. and MARTÍNEZ-SÁNCHEZ, J.J. (2009). Relationships between salt type and seed germination in three plant species growing in salt marsh soils of semi-Arid Mediterranean environments. Arid Land Research and Management, 23: 103–114.