苏北海滨湿地互花米草种子特征及实生苗生长

摘　要　在江苏盐城新洋港滩涂由海向陆建立样地：零星互花米草(Spartina alterniflora)斑块(SAP)?稳定互花米草滩下边缘(SAFI)?2003年互花米草定居处(SAF03)?1989年互花米草定居处(SAF89)，对互花米草的种子特征及幼苗生长进行了研究。结果表明：(1) 各样地种子产量有极显著差异(p< 0.01)，大小顺序为SAP > SAF03 > SAFI > SAF89，种子产量与植株结实率、穗长、单穗种子数成正比。(2) 4月份SAP、SAFI、SAF03和SAF89互花米草短暂土壤种子库分别为673.7 /m2、2328.7 /m2、5948.8 /m2和3990.4 /m2，种子保存率分别为0.5%、3.9%、6.9%和15.8%，且在各样地差异极显著(p< 0.01)。(3) 7月份SAP、SAFI、SAF03和SAF89实生苗数分别为72 /m2、5 /m2、0和0。SAP与SAFI种子萌发率显著高于SAF03与SAF89(p< 0.01)。(4)表层土壤水分含量和种群内部光照衰减是影响实生苗生长的关键因素。在表层土壤水分含量高和低光照衰减的生境中种子繁殖对互花米草种群延续和扩张贡献较大。

Seed characteristics and seedling growth of Spartina alterniflora on coastal wetland of North Jiangsu

Spartina alterniflora is a worldwide discussed exotic species. It was introduced into coastal wetland of North Jiangsu in 1982, and has been expanding quickly, influencing the local ecosystem biodiversity and economic activities. In this study, landward sampling sites along an intertidal zone in Xingyanggang(S. alterniflora patch(SAP), S. alterniflora flat infra-edge(SAFI), S. alterniflora flat 2003(SAF03), S. alterniflora flat 1989(SAF89) ) were arranged and (1) the S. alterniflora seed characteristics were investigated; (2) transient soil seed bank and seed preservation were measured; (3) the contribution of sexual reproduction in S. alterniflora population sustainability and expansion were discussed; (4) the seedling growth strategies choice in different habitat during the expansion of S. alterniflora were explored. Six 1 m × 1 m sampling plots were selected randomly to measure the seed characteristics including fruiting culms, seed weight, seed production, spike length and seeds per spike in November 2009 in the four sampling sites. And four soil samples of 25 cm × 25 cm × 6 cm were collected from the sampling sites in April 2010, and then all the seeds in soil samples were collected, to assess transient seed bank and seed preservation in soil. Three 50 cm × 50 cm permanent plots were set in the four sampling sites for observation of seed germination rate, seedling survival rate and seedling growth on 9 April, 28 May, 14 June and 21 July, meanwhile vertical distribution of relative light intensity within S. alterniflora plots were investigated. Statistical analyses were performed under SPSS11.5 to determine the interaction between seeds, seedlings and environmental factors. The results showed that: (1) the seed production was significantly different (P< 0.01) among sampling sites on the order as SAP 126333.3±1687.4 no./m² > SAF03 86385.2±4263.2 no./m² > SAFI 58999.1±1653.3 no./m² > SAF89 25259.1±1822.6 no./m², which is positively correlated with the setting rate, longer spike length and seed number per spike. (2) By April, the transient soil seed bank was significantly different (P< 0.01) among sampling sites as 673.7/m² at SAP, 2328.7/m² at SAFI, 5948.8/m² at SAF03 and 3990.4/m² at SAF89, respectively; and the seed preservation rates was 0.5% at SAP, 3.9% at SAFI, 6.9% at SAF03 and 15.8% at SAF89, respectively. (3) By April, the seed germination rate at SAP and SAFI were significantly higher than those at the SAF03 and SAF89 (P<0.01); the seedling number was 288.0/m² at SAP, 1085.3/m² at SAFI, 538.7/m²at SAF03 and 312.0/m² at SAF89, which decreased as 72/m² at SAP, 5/m² at SAFI, 0 at SAF03 and 0 at SAF89 by July, respectively; height of seedling in SAFI was significantly different (P< 0.05) with other sampling sites as SAFI > SAP > SAF03 > SAF89 by June. (4) The relative intensity near the ground was 46.1% at SAP, 36.0% at SAFI, 10.4% at SAF03, 3.9% at SAF89 by May, but it was 26.3% at SAP, 32.5% at SAFI, 16.4% at SAF03, 0.9% at SAF89 by June. The water content of topsoil and light attenuation within populations affected seedling growth vitally. The results from this study indicated that the seed propagation played more important role in the continuation and spreading of this invasive plant at habitat with higher topsoil water content and lower light attenuation.