潮间带盐沼植物种子及实生苗漂浮起动临界剪切应力研究

Study on the critical shear stress of floating initiation for the seeds and seedlings of intertidal salt marsh plants

盐沼是分布在海陆过渡区域,以大型草本植物为优势种的潮间带生态系统。在潮间带生态系统中,盐沼植物的种子和实生苗在潮流作用下的漂浮起动是盐沼植物自然扩散的重要前提,决定了盐沼植物能否实现有效扩散和长距离传播。然而,目前缺乏有关盐沼植物繁殖体在复杂潮滩环境下漂浮起动扩散过程的定量研究。以长江口典型盐沼先锋物种海三棱藨草(Scirpus mariqueter)为研究对象,应用U-GEMS微观侵蚀系统,测定了在不同沉积物底质条件下,海三棱藨草种子及不同萌发阶段实生苗漂浮起动时的临界剪切应力,定量分析不同萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的影响。研究结果表明:(1)不同种子萌发阶段和沉积物底质对海三棱藨草种子和实生苗漂浮起动的临界剪切应力均有极显著影响(P<0.01);(2)随着萌发阶段的进展,海三棱藨草实生苗漂浮起动所需的临界剪切应力逐渐减小,因而随潮流漂浮起动进而扩散的机会也相应增大;(3)相比于淤泥质潮滩底质,海三棱藨草种子和实生苗在粉砂质潮滩更易于漂浮起动。研究结果丰富了盐沼植物在潮间带自然扩散过程和机理的研究,也为今后长江口及其他区域开展高效、低成本、以种子为修复材料的大规模盐沼修复提供了科学依据。

Salt marshes are the transition zones of land and ocean which are intertidal ecosystem dominated by large herbaceous plants.The floating initiation of salt marsh seeds and seedlings under the tidal current is an important prerequisite for the natural dispersal of saltmarsh plants in the intertidal ecosystem,which determines whether saltmarsh plants can disperse effectively over long distance.Unfortunately,there are few quantitative studies on the floating initiation and diffusion of salt marsh propagules in the complex tidal flat environment.Here,we focused a typical saltmarsh pioneer species Scirpus mariqueter in the Yangtze estuary,aiming to explore the critical shear stress of floating initiation for S.mariqueter seeds and seedlings at the different germination stages and on the different sediment substrates.The critical shear stress of floating initiation for S.mariqueter seeds and seedlings under experimental gradients were measured by U-GEMS micro erosion system,and the effects of different germination stages and sediment substrates on the floating initiation of S.mariqueter seeds and seedlings were quantitatively analyzed.The results showed that:(1)the germination stages and sediment substrates had significant effects on the critical shear stress of floating initiation for S.mariqueter seeds and seedlings(P<0.01);(2)the critical shear stress of floating initiation for S.mariqueter seedlings decreased gradually with the increase of germination stage,and the chance of dispersal with tidal current increased accordingly;(3)compared with the sediment substrate of muddy tidal flat,the seeds and seedling of S.mariqueter were easier to float in the silty tidal flat.This study enhances the understanding of the process and mechanism of saltmarsh natural dispersal,and provides a scientific basis for efficient low-cost and large-scale saltmarsh restoration in the Yangtze estuary and other regions using seeds as restoration materials,which has important theoretical significance and practical application prospects.