梁子湖优势沉水植物冬季种子库的初步研究

初步研究了梁子湖6种优势沉水植物如黄丝草、金鱼藻、菹草、黑藻、苦草和穗状狐尾藻等在冬季的广义种子库（种子、芽苞、断枝等），包括它们的繁殖特性、种子在小、结构及萌发时的衰减曲线等问题，主要结果为：（1）在梁子湖不同区域内，种子库大小不相同，满江湖、前江大湖、中湖和管理局网围内种子库分别为714.4粒／m^2、107.5粒／m^2、331.9粒／m^2和159.3粒／m^2。种子库的大小受到现实的种群数量、投鱼强度、人类干扰等因素的影响。（2）黄丝草、金鱼藻、菹草种九的种子库占有明显优势，全湖平均分别为198.8粒／m^2、91.7粒／m^2和21.4粒／m^2。（3）每一种植物种群广义种子库的构成和比例具有差异，金鱼藻、菹草、苦草、黑藻四种植物种子库中，无性繁殖体占有主要的地位；黄丝草、穗状狐尾藻两种植物种子库中，种子占有很大的比例，上述六种植物均可用种子和无性繁殖体来产生幼苗，补充到肿群中去。（4）种子库一般存在冬季休眠（菹草为夏眠），春季种子库萌发，尤其在3月和4月是种子库萌发的高峰期。     

Hydrologic and anthropogenic influences on aquatic macrophyte development in a large,shallow lake in China

1. Macrophyte composition and abundance affect the overall ecological structure and function of lakes, and information on the nature and timing of changes in macrophyte assemblages is therefore crucial for understanding their impact on the lake ecosystem.
2. We examined plant macrofossils, diatoms, cladocerans, and physical and geochemical proxies in two sediment cores from Lake Liangzi, a large shallow lake located on the Yangtze floodplain in south‐east China, in order to assess recent and historical trajectories of ecological and environmental change. We also used archival records of environmental changes (i.e. hydrological, climatic, fishery, and social factors) in the lake and its catchment. Lake Liangzi is of particular interest as it, unlike most other lakes in the region, has maintained a macrophyte‐dominated state.
3. The results revealed a shift in the lake during the past ca. 160 years from a clear water, low‐growing submerged macrophyte community (e.g. Najas minor, charophyte species), dominated by planktonic diatoms and planktonic cladocerans, towards a more pollutant‐resistant, tall‐growing macrophyte community (Potamogeton spp., Ceratophyllum demersum and Myriophyllum spicatum) and dominance by benthic and epiphytic diatoms and littoral cladocerans. However, a pronounced increase in the abundance of planktonic Bosmina spp. at the expense of true littoral cladoceran species and a decline in plant macrofossil assemblages in the surface samples suggest that the lake recently entered into a new unprecedented state.
4. Redundancy analysis indicated major changes in hydrology and moderate inputs of anthropogenic pollutants as well as climate warming as the main drivers of ecological and environmental changes in the lake.
5. Our study demonstrated that plant macrofossils from radionuclide‐dated short sediment cores provide reliable information on the nature and timing of changes in the macrophyte community in Lake Liangzi. Furthermore, our study provided information on the composition of the plant community before recent strong perturbations and also showed the trajectories and suggested the drivers of ecological and environmental change, thereby offering valuable information for lake managers in the Yangtze region and elsewhere.
6. Our study identifies a relatively resistant community of submerged macrophytes, which may be an initial restoration target for managers when restoring the many lakes in the region where submerged vegetation coverage has declined during the last few decades.

     

梁子湖浮游甲壳动物的生物多样性

基于2006年8月至2008年3月对梁子湖浮游甲壳动物的采样调查,记录了该湖区浮游甲壳动物22种,隶属9科18属,其中枝角类(Cladocera)16种,桡足类(Copepoda)6种,包括9属新记录.物种多样性季节性动态变化明显:枝角类优势种在春、夏和秋冬季依次为透明溞(Daphnia hyalina,优势度Y = 0.80±0.01),小栉溞(Daphnia cristata,Y = 0.50±0.03)和长额象鼻溞(Bosmina longirostris,Y = 0.58±0.04);而桡足类优势种在夏、秋和冬春季依次为长江新镖水蚤(Neodiaptomus yangtsekiangensis,Y = 0.41±0.01)、近邻剑水蚤(Cyclops vicinus,Y = 0.46)和特异荡镖水蚤(Neutrodiaptomus incongruens,Y = 0.65±0.18).浮游甲壳类个体密度以春季最高((292±85) ind/L),夏、秋、冬季渐低(依次为(169±104)、(140±53)、(120±0) ind/L).物种多样性冬春季较低(物种数S≤12,丰富度指数D = 0.77和0.71,香农-威纳指数H = 1.79和1.45),夏秋季较高(S≥17,D = 0.98和0.88,H = 1.78和1.83).梁子湖浮游甲壳类动物多样性年际差异不显著,表明湖区环境条件较为优越、稳定.