2．大叶藻有性生殖以生殖枝的产种能力和种子库大小为前提。本研究在荣成月湖和青岛汇泉湾同步进行，对月湖大叶藻种群从2014年7月-2015年8月进行了逐月跟踪调查，在此期间对青岛汇泉湾进行了重点月份采样。实验通过随机取样的方法，在两个地区进行调查，结果显示，由于水温存在差异，青岛汇泉湾大叶藻生殖枝形成较月湖早1个月，出现在4月；两个区域的生殖枝密度在6月份达到峰值（月湖517.27 shoots·m-2，汇泉湾995.02 shoots ·m-2），同时种子开始成熟；7月份两个地区的种子逐渐脱落，埋藏进入底质中；两个地区的生殖枝在8月初完全消失。2015年月湖和汇泉湾大叶藻种子产量估计分别为37991.49、76478.23 seeds·m-2。两个地区种子库从7月份开始增加，10月份种子埋藏结束，达到峰值（月湖472.49± 408.29 seed·m-2，汇泉湾399.93± 770.14 seeds· m-2），随后种子死亡率增加，种子库大小降低。
3. 春季随着水温增加，月湖大叶藻种子在3月中旬开始萌发，并逐渐生长。在月湖内划分的三个研究区域：大叶藻床中心区域、边缘区域以及大叶藻斑块区，调查了种苗的密度变化、生长状况、克隆生长情况。结果显示月湖大叶藻种子从3月份中旬开始萌发，4月份大量萌发，种苗密度达到峰值，密度最大值出现在大叶藻边缘区为481.77± 303.42 shoots·m-2。5月种子萌发邻近结束，种苗死亡率增加，种苗密度出现下降，同时开始克隆生长；6月份种苗快速生长，种苗密度稳定，并出现有性生殖枝。在三个研究区域内，大叶藻海草床边缘区种苗密度最大，大叶藻斑块区密度最小，但三个区域在密度、株高、叶鞘高、叶数等并不存在显著性差异（p>0.05）。
4.无性生殖即克隆生长，是大叶藻重要的繁殖方式。本实验通过在月湖大叶藻斑块区和大叶藻海草床边缘区、中心区（依次为THE-1，THE-2和THE-3）设置固定样方进行实验，研究大叶藻克隆生长规律，结果显示，3-4月大叶藻开始克隆生长，但生长速率缓慢，5月份之后克隆生长加快。这种快速生长并没有持续太久，到6月低，营养枝密度出现下降。到8、9月份，月湖大叶藻营养枝密度急剧降低，在三个研究地点中THE-1，THE-2样框内的大叶藻全部消失，而9月份后THE-3样框内的大叶藻密度仅为21.88± 24.20 shoots·m-2，几乎降为零。三个研究区域内营养枝的生长状况没有显著差异，随着8、9月份大叶藻衰退，叶片数迅速减少，茎枝高度也开始下降，在此期间6-9月份硬毛藻（Chaetomorpha linum Kutz）爆发，导致大叶藻因被覆盖，缺乏光照有关。爱莲湾不同水深大叶藻生长状况显示，在设置的5个深度梯度（1m、2m、3m、4m、6m）中，大叶藻在1m，2m的生长、繁殖状况最好，水深为2m处光照强度损失率仍在30%以上，而在水深为4m，6m时，光照强度迅速衰减，小于100 μphotons·m-2·s-1。
5.月湖大叶藻春季生长加速，受水体温带升高的影响，也与湖内营养元素的补充密切相关。本实验通过对春季月湖大叶藻碎屑和大天鹅粪便降解情况进行研究，探索湖内营养物质释放情况。结果显示，春季湖内水温升高，大天鹅粪便和大叶藻碎屑有机物的C、N、P营养元素降低迅速，在5月初降解完全，与对照组无差异，其C、N、P的平均值分别为2.05± 0.19, 0.26± 0.02, 4.02± 0.30 %。大叶藻植株不同部位C、N、P含量可以反映大叶藻元素组成的差异，实验结果显示，大叶藻三种元素含量总体呈现出地上部分大于地下部分，新生部分大于成熟部分的趋势。C含量季节变化平稳，最低值出现在5月为40.07± 0.75 %；N含量变化趋势先增后减，有缓慢增加的趋势，最低值出现在6月初为1.60± 0.23 %；P含量则呈现出逐渐降低的趋势，峰值在3月份，为0.66± 0.07 %，最低值在9月份为0.07± 0.06 %。植物中的C/N、C/P、N/P反应植物对N、P元素的利用情况，其中大叶藻各器官的C/N、C/P、都呈现出地上部分较地下部分低的现象，反应地上部分P含量在其器官的比重中占的比例更大。
|其他摘要||Zostera marina L. (eelgrass), a widespread seagrass in North Hemisphere, dominates the temperate regions in North China. Eelgrass meadows in Swan Lake (Rongcheng) and in Huiquan Bay (Qingdao), acting as typical eelgrass meadows in Shandong Peninsula, can propagate by sexual and vegetative reproduction and represent the natural and recovered populations. In this study we focused on the population recruitment under natural circumstances in both two areas. Combining with the observation of clonal growth under the different depth gradient in Ailian Bay (Rongcheng), we aimed to explore eelgrass natural population recruitment, and the main results were as followed:|
1. A review has been finished on seagrass research. Seagrass beds providing important ecosystem service functions are now facing serious degradation. The current restoration methods including natural recovery, transplantation and seeding, are based on sexual and vegetative reproduction. However, there are few relative studies on the whole recruitment process of eelgrass.
2. Eelgrass sexual reproduction ability was depended on potential seed production and seed bank size. We conducted our studies in both eelgrass meadows in Swan Lake and Huiquan Bay from July 2014 to August 2015. We surveyed density, shoot height, spathe number and seed number of per spathe of flowering shoot and seed bank size using random samples in both two areas. The results showed that flowering shoot appeared one month earlier in Huiquan Bay(started from April) than in Swan Lake, but both peaked in June with 517.27 shoots·m-2 in Swan Lake and 995.02 shoots·m-2 in Huiquan Bay. Flowering shoot degraded in early July and disappear in early August in both two areas and the potential seed productions were 37991.49 and 76478.23 seeds·m-2, respectively. Matured seeds, fell off and were buried in sediment from July and ended in October when seed bank peaked in both areas with 472.49 ± 408.29 and 399.93 ± 770.14 seeds· m-2, respectively. Whereas seed banks in both areas declined after October due to natural mortality and seed predation.
3. With the increase of water temperature, eelgrass seeds germinated from the mid of March and then seedlings grew. We conducted a survey on seed germination and seedling growth in Swan Lake where we chose three stands, the center stand, the margin stand along eelgrass meadow and the patch stand of eelgrass, to measure the density, shoot height, sheath height, leaf number, and clonal growth of seedlings. The results showed that seed germinated from the mid of March and peaked in April (481.77±303.42 shoots·m-2), ending in May when seedling clonal growth commenced. Seedling grew with the rise of water temperature and could not be distinguished with overwintering vegetative shoots after June.
4. Vegetative reproduction is a vital approach for eelgrass propagation. We utilized stable following-up samples in Swan Lake where we chose three strands (THE-1，THE-2 and THE-3) to measure shoot density of seedlings and vegetative shoots. The result showed that clonal growth was slow during March and April, and vegetative shoot density never increased apparently until May when the density peaked, while vegetative shoot density declined slowly after June. The dramatic declines occurred in August and September, with vegetative shoots disappearing in THE-1,2 and seldom remaining in THE-3 (21.88±24.20 shoots·m-2). There was no significant difference between the three stands in shoot height, with the decline in same time after August and September due to Chaetomorpha linum Kutz bloom in Swan Lake. Eelgrass at different depth (1m, 2m, 3m, 4m and 6m) in Ailian Bay showed that eelgrass propagated and grew well only at the depth of 1-2m where the relative light intensity was still above 30% of water surface. However, eelgrass at the depth of 4m and 6m where the relative light intensity was under 100 μphotons·m-2·s-1, degenerated gradually.
5. Eelgrass rapid growth owing to the rise of water temperature may also be the result of release of nutrient element from sediment in spring. Thus we conducted aan in-situ decomposition experiment of organic sediments in Swan Lake, which included faeces of Cygnus cygnus and detritus of eelgrass. The percentages of Carbon, Nitrogen and Phosphorus in sediments were measured. We found that the organic nutrient content declined rapidly with the rise of water temperature in spring and reached almost the same degree as contracted one in organic nutrient content in May. After that, the percentages of C, N and P turned to stable until August when field survey ended with the mean content were 2.05 ± 0.19, 0.26 ± 0.02, 4.02 ± 0.30%, respectively. Organic nutrients including C, N and P percentage content in different organs and parts of eelgrass can interpret the difference composition of nutrient elements, and were measured in Swan Lake to evaluate eelgrass health and growth there. There were significant differences between above- and below-ground parts with values of three elements all higher in above-ground parts. C content increased with a small decline in May with the minimum 40.07 ± 0.75 % and the same tendency with N minimized in June with 1.60 ± 0.23 %. P content declined straightly and minimized with 0.07 ± 0.06 % in September. C/N, C/P and N/P in plants can response the utilization of the N, P elements. C/N and C/P in eelgrass different organs showed an obvious seasonal change with higher value in below-ground parts than above-ground parts, indicating that the above-ground parts utilized more N and P in spring when eelgrass started grow again.
6. Eelgrass propagation including sexual and vegetative reproduction which play an importance role in its recruitment involved 4 processes, seed germination and seedling growth; vegetative shoot clonal growth; occurrence of flowering shoots and seed burial; senescence of shoots to overwinter. The difference between two areas was the seed germination time and flowering shoot commencing time, but the contribution of seedling to population recruitment both ranged from 20-30 %.
|王朋梅. 山东半岛典型海草床大叶藻种群补充机制研究[D]. 北京. 中国科学院大学,2016.|