植物克隆性在生态修复中的意义：鄂尔多斯高原赖草和沙鞭的案例

克隆植物通过克隆生长能够很好的适应异质性的生境。在进行植被修复的研究和实践中，注意发扬或引进具有重要资源价值的克隆植物是重要的恢复生态学思考和途径。本文主要应用实验生态学的方法，通过对鄂尔多斯高原不同克隆植物克隆性及其对水分条件的反应的比较，以及对不同克隆植物抵抗风蚀和风蚀坑修复的能力的比较，探讨克隆植物对干旱(水分条件)及风蚀的适应机制，从而对克隆植物的克隆性在生态修复中的意义进行了研究和阐述。 　　对不同水分条件下赖草(Leymus secalinus (Georgi.) Tzvel)和沙鞭(Psammochloa villosa (Trin.) Bor)克隆性的研究表明：克隆生长开始时间和克隆生长率二者与克隆植物新产生子代分株数量之间存在着显著的相关关系，说明克隆生长开始时间和克隆生长率能够作为准确评价克隆性的指标;相对于沙鞭来说，赖草具有更强的克隆性，表现在它的早的克隆生长开始时间、高的克隆生长率，并且这种差异可以被水分条件所修饰;植物的克隆性对水分条件具有较强的可塑性，这种可塑性具有种间差异。相对赖草来说，沙鞭能更好地适应干旱条件。 　　克隆植物植株有两种繁殖体类型，分株和种子。本研究对分别从分株来源和种子来源的赖草与沙鞭植株在不同水分条件下生长状况及克隆性进行了比较，结果表明：水分的增加，有利于赖草的生长;而对于沙鞭来说，水分抑制了分株来源的沙鞭植株的生长，但对种子来源的沙鞭植株的生长有着促进作用。克隆植物的克隆性在水分条件较好的情况下能够得到更好的表达。不同来源有赖草植株之间克隆性没有明显差异;对于沙鞭来说，分株来源的沙鞭植株克隆性受水分条件的影响不明显，但水分有利于种子来源的沙鞭植株克隆性的表达。说明不同繁殖体类型来源的植株，克隆性对水分的反应格局存在着一定的差异。分株来源的沙鞭植株对干旱条件具有比种子来源的植株更强的适应性。 　　通过对沙鞭和赖草实生幼苗在不同风蚀程度下生长状况的比较，结果表明二者幼苗在抵抗风蚀时采取不同的策略。风蚀显著降低了赖草产生新生分株的能力，而对沙鞭潜在分株数没有显著影响。赖草实生幼苗生长状况在轻中度风蚀条件下与对照处理没有显著差异，说明对风蚀具有较强的抵抗能力，其策略可能是风险分担，赖草具有的强克隆性使之能快速产生新的子代分株，从而分担了风蚀造成的风险;沙鞭实生幼苗的生长状况受风蚀影响较为明显，但风蚀没有能对其产生潜在分株(芽)的能力产生显著的影响，说明沙鞭实生幼苗对风蚀可能采取的是通过芽的产生贮存资源、逃避风险、等待机会的策略。赖草和沙鞭对风蚀所采用的不同适应策略，可能会影响到二者在自然条件下种群更新方式的选择。 　　为了探讨克隆植物对风蚀坑修复能力及机理，研究了沙鞭和赖草对种群内风蚀坑的修复过程，结果表明：合轴型克隆草本赖草具有比单轴型克隆草本沙鞭更强的植被修复能力，能够在风蚀坑中产生更多的新生分株，这主要归功于赖草的强克隆性，而赖草间隔子的可塑性反应也有利于将更多的新生分株放置在风蚀坑内。二者进行植被修复的机理有所差异，赖草对风蚀坑的修复主要是通过周围根茎扩展进入坑中，然后产生新的分株;而沙鞭不仅可以通过周边根茎进入产生新的分株，同时也可以通过刺激深层休眠芽来产生新的分株。二者都能在风蚀坑中产生比自然条件下更多的分株，以更好利用风蚀坑中充足的光照;但同时这些分株的生长也受到风蚀坑中养分条件的制约，生物量和生长状况都不如自然条件下形成的分株。 　　 　　

Moderate mutation rate in the SARS coronavirus genome and its implications

Background: The outbreak of severe acute respiratory syndrome (SARS) caused a severe global epidemic in 2003 which led to hundreds of deaths and many thousands of hospitalizations. The virus causing SARS was identified as a novel coronavirus (SARS-CoV) an

High rate of chimeric gene origination by retroposition in plant genomes

Retroposition is widely found to play essential roles in origination of new mammalian and other animal genes. However, the scarcity of retrogenes in plants has led to the assumption that plant genomes rarely evolve new gene duplicates by retroposition, de

Estimation of the natural purification rate of a eutrophic lake after pollutant removal

Pollution resulting from increased human activities is threatening Lake Donghu, its effects being characterized by serious eutrophication. A steady increase of phosphorus loading is the most important factor of the lake eutrophication. Pollution external control projects are being implemented and will be accomplished before the year 2010. In order to predict the restoration rate by the lake's self-purification after the projects of external control, a model of predicting the removal rate of total phosphorus (TP) from lake water is developed, and a brief method of estimating the release and export rate of sediment phosphorus is suggested. Results show that, on the premise of external loading fully controlled. The restoration needs about 55 years or more. Obviously, the great P pool in the sediment will be a limiting factor of preventing the improvement of water quality after the external loading is under control. Based on the estimation we conclude that after the external control projects before 2010, in order to restore the lake in a few years, although highly cost, the first step must be the sediment dredging to remove internal loading. The second step is diverting water of River Changjiang into the lake to accelerate the improvement of lake water. Otherwise, removal of pollutant sources will become meaningless. (c) 2006 Elsevier B.V. All rights reserved.

Effects of feeding rate on growth performance of white sturgeon (Acipenser transmontanus) larvae

Four 1-week trials were conducted to determine the effects of feeding rates on growth performance and body proximate composition of white sturgeon larvae during each of the first 4 weeks after initiation of feeding. Feeding rates (% body weight day(-1)) were 10, 20, 30, 40, 50, and 60 for trial I; 5, 10, 15, 20, 25, and 30 for trial II; and 2.5, 5.0, 7.5, 10.5, 12.5, and 15.0 for trials III and TV Four tanks with 200 larvae each were randomly assigned to each of the six feeding rates. Average initial body weights of the larvae were 49, 94, 180, and 366 mg, respectively, for trials I-IV. The larvae were kept at 19-20 degreesC in circular tanks and fed continuously one of two commercial salmonid soft-moist feeds using automatic feeders. Proximate composition (%) of the feeds for trials I-III and IV were 13.9 and 14.9 moisture, 52.5 and 50.0 crude protein, 10.3 and 12.9 crude fat, and 8.1 and 8.7 ash, respectively. Except mortality in trial I, gain per food fed in trial III, and body ash in all trials, growth performance and body composition were significantly (P<0.05) affected by all feeding rates. Broken line analysis on specific growth rates indicated the optimum feeding rates of white sturgeon larvae to be 26%, 13%, 11%, and 6% body weight day-respectively, for weeks 1, 2, 3, and 4 after initiation of feeding. (C) 2003 Elsevier Science B.V. All rights reserved.

The precocious Chinese mitten crab: Changes of gonad, survival rate, and life span in a freshwater lake

Changes of the gonad. survival rate, and life span of the precocious (i.e., sexually mature in their first October-November, at the age of 5 or 6 months) Chinese mitten crab (Eriocheir sinensis) were studied in a small, shallow, macrophytic, freshwater lake along the middle reaches of the Changjiang River, China. The gonosomatic index (GSI) reached peak during the next March when the female GSI was 12.32 +/- 1.75 SD% and the male GSI A as 4.24 +/- 0.19%. The sexual glands degraded from then on. In the first ten-day period of the following July, there was no complete ovum in the ovary. and the sperm became thin and lost adhesion. The population declined sharply from November to July, and the last one (a female) died in the middle of July, which indicated that the life span of the precocious crab was about 12 months (from larval hatching in June to death in July of next year). The survival curve might be expressed as Y = 1.09exp(-0.018x) (Y survival rate; x: days) for the precocious crabs stocked in experimental cages.