| The eelgrass Zostera marina L.is a dominant seagrass species circumglobally distributed in temperate coastal environments in the North Hemisphere.Two sites were selected in Swan Lake(SLL)and Huiquan Bay(HQB)for monitoring based on historical cover and previous studies in Shandong Peninsula.This study was focused on the characteristics of the seed life cycle of Z.marina in the two sites to analyze the difference in the seed life cycle between the two populations.In addition,the influence of salinity and temperature on seed germination,seedling establishment,and seedling growth of eelgrass was studied.In this study,the seed ecology of Z.marina was investigated,and the main results were as followed:1.The difference in plant reproductive effort between SLL and HQB populations was compared.The flowering shoots in HQB were firstly observed in the middle of April;while in SLL they was firstly observed in the beginning of May,and both peaked in June(SLL: 517.27 ± 504.29 shoots m-2;HQB: 203.04 ± 116.50 shoots m-2).Flowering shoot density decreased in July and disappeared in early August and the potential seed productions were 29000.88 seeds m-2 in SLL and 53623.66 seeds m-2 in HQB,respectively.The number of spathes per flowering shoot was significantly higher in HQB(21.5 ± 5.32 spathes flowering shoot-1)than that in SLL(10.83 ± 3.31 spathes flowering shoot-1).The number of seeds per spathe was significantly higher in SLL(9.57±3.44 seeds spathe-1)than that in HQB(7.98 ± 3.73 seeds spathe-1).The potential seed production in SLL(53623.66 ± 19628.11 seeds m-2)was significantly higher than that in HQB(29000.88 ± 10657.89 seeds m-2).In addition,the values of seed weight and size(length,diameter and volume)in HQB were significantly larger than those in SLL.The seeds in HQB(8.81 ± 0.03 mg)were significantly heavier than those in SLL(5.78 ± 0.34 mg),and the seed length and diameter in HQB were also larger than those in SLL.Eelgrass seed bank increased from July and peaked in SLL and HQB with 386.55 ± 247.19 seeds m-2 and 254.35 ± 613.34 seeds m-2,respectively,Whereas seed banks both in SLL and HQB declined after October.2.Seed germination was documented in spring in SLL,while that was documented in autumn in HQB.The seeds germination and seedling density increased dramatically and peaked in April with the maximum value 377.60 ± 260.09 seedlings m-2 in SLL,and the seed germination percentage was 68.38%.The seedling began clonal growth in May and the number of shoots per seedling was 1.16 ± 0.41 in May and 1.57 ± 0.53 in June,respectively.The density of seedling and seedling shoots were 156.25±71.32 seedlings m-2 and 245.54 ± 112.07 seedling shoots m-2 in June 2015,thus the seedling survival percentage was 41.38%.For HQB most of seeds were mainly germinated during October and November,and the seedling density in HQB is lower than 10 seedlings m-2.The clone growth of seedlings began on 23 March,and about 2 shoots per seedling occurred at 26 June.The data based on the tracing observation of the permanent quadrats showed the process of seedlings growth in HQB,and the average height of seedlings increased from 12.49 cm(April)to 33.05 cm(June).3.Seed source(SLL and HQB)and temperature(10 °C and 15 °C)had significant influence on germination percentage(GP)and germination rate(GR).For SLL and HQB,germination percentage(GP)and germination rate(GR)differed significantly at different temperatures;GP and GR also differed significantly between the two populations.The germination percentage(GP)and germination rate(GR)for eelgrass population in HQB were significantly higher than those in SLL at each temperature.4.Z.marina seeds were classified by seed color(white,cyan,and black),representing various degrees of seed maturity(immature,medium,and advanced maturity,respectively).The wet weight and moisture content of seeds at different degrees of maturity exhibited a significant difference.The wet weight of seeds significantly increased with increasing maturity;in contrast,the moisture content of seeds significantly decreased with increasing maturity.Therefore,moisture content,together with seed color and weight,may be a potential indicator of Z.marina seed maturity.The average wet weight of Z.marina mature seeds selected for germination was 12.50 ± 0.04 mg,and the mean moisture content was 37.41 ± 0.74%.5.Salinity and temperature significantly influence seed germination.Seed germination percentages(GP)were significantly higher at higher temperatures and GP decreased with increasing salinities.GP(80.67–88.67%)in freshwater were significantly higher than in artificial seawater at high salinities.The highest GP(88.67±5.77%)among all treatments was recorded at 15 °C in freshwater.At higher salinities(30,35,and 40ppt),GP were below 16%,but increased considerably when salinity decreased below 20 ppt.Generally,GP increased considerably with increasing temperature.Above 10 ppt,GP at 15 °C and 20 °C were significantly higher than at 5 °C.6.Salinity significantly influences seedling growth and establishment at 5 °C.The seedling maximum length,weight,number of leaves,and differentiation of Z.marina differed significantly between the lower salinities(0 and 10ppt)and the higher salinities(20 and 30ppt)at 5 °C.In the low salinities(0 and 10ppt),a significantly higher GP was detected;however,these seedlings had a lower number of leaves,shorter seedling length,and lower wet weight.This suggested that Z.marina seedlings exposed to low salinities exhibited slower development that may reduce their eventual survival over longer exposure times than those tested in the present study.In contrast,the seedling survival percentage was greater at higher salinities.7.Seedling establishment percentages(SEP)for seeds germinated at reduced salinities and transferred to natural seawater were compared,and there were significant difference.The SEP for seeds germinated at 0,1,5,and 15 ppt at 15 °C and then transferred to natural seawater(32ppt)at 15 °C,were 10.00 ± 0.00,28.67 ± 1.15,39.33 ± 4.16,and 90.67 ± 9.02%,respectively.The SEP at 15 ppt was significantly higher than the other levels of salinity and seedling establishment decreased with decreasing salinities.Elevated salinity increased seedling establishment at 15 °C.8.The metamorphosis of Z.marina,at various growth stages during seed germination and seedling establishment,was observed in the seed germination experiment.Seed germination and seedling growth were divided into seven stages.The seven stages included pre-germination,seed germination,cotyledonary elongation,first true leaf differentiation,adventitious root differentiation,second true leaf emergence and cotyledonary wither. |
PDF Full Text Request