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摘要5 温度对一年生植物大茨藻在其分布边界的种子成熟和休眠周期

已有 4673 次阅读 2011-1-1 23:17 |个人分类:文献摘要|系统分类:科研笔记

Blackwell Publishing, Ltd.
温度对一年生植物大茨藻在其分布边界的种子成熟和休眠周期的影响
概述
1 大茨藻是浅水湖泊的夏季一年生植物,在英格兰东部Norfolk Broads湖到达其分布边界。种子于秋季脱落并在湖泊沉积物种过冬。
2 我们调查了生长季节长短对种子成熟和发芽力的影响以及冬季温度对发芽模式的积累效应。采用1年以内的种子进行为期4周的发芽实验。利用数据采集器在野外样点和冷房中同时记录数据。用阈限(热时间thermal time)以下的积温将冷库中的行为和生物气候学进行相关。
3 绝大多数在采集时为休眠状态。冷藏吸胀种子导致休眠解除。去休眠种子的比例在相当于一个冬季的低温(例如与野外发芽的理想温度一致)处理后达到高峰。持续的低温层化引发了第二次休眠周期以及随后的解休眠;热时间是第二次更短的发芽高峰的特征,与首次采集种子后第二个春季的野外发芽情况大致一致。
4 通过手收集自然衰亡完成前的材料来缩短大茨藻的生长季节,减少了成熟种子的比例,降低了平均发芽率且增加了发芽时间。
5 水体较大的比热容导致了春季回暖相对于气温的滞后,而秋季逐渐变短的光照时间则成为限制因素。大茨藻极其需要一个足够长的生长季来产生足够多的可育性种子。解除休眠需要低温这一特性阻止了不适宜的秋季发芽,而如果冬季太过漫长(需要紧接着一个较短的生长季),则会有相当比例的种子进入二次休眠,留在种子库中直到第二个春天。
6 一年生植物中,这种对温暖夏季和寒冷冬季的需求可能是造成英格兰北部大陆性气候分布的原因之一。就大茨藻而言,这可能解释了其分布边界在英格兰东端和其较为稀少的现象。
 
Temperature effects on seed maturity and dormancy cyclesin an aquatic annual,Najas marina, at the edge of its range
RICHARD J. HANDLEY and ANTHONY J. DAVY
Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich,NR4 7TJ, UK
Summary
1 Najas marina is a summer annual of shallow lakes that reaches its distributional limit in the Norfolk Broads of eastern England. Seeds are shed in autumn and overwinter in lake sediments.
2 We investigated the influence of growing-season length on seed maturity and germinability and the cumulative effects of winter temperatures on patterns of germinability. Seeds were stratified for up to 1 year and tested for germinability at 4-week intervals. Data-loggers recorded temperatures simultaneously at the field site and in the cold room. Cumulative temperature below a threshold (thermal time) was used to relate behaviour in cold storage to phenology.
3 Most seeds were dormant at collection. Cold storage of imbibed seed resulted in loss of dormancy. The proportion of non-dormant seeds peaked after a cold treatment equivalent to one winter, i.e. coinciding with favourable temperatures for germination in the field. Continued cold stratification resulted in a cycle of secondary dormancy and its subsequent relief; the thermal time characterizing the second, lower, peak in germinability coincided approximately with that attained in the field in the second spring after collection.
4 Shortening the growing season of Najas marina , by collecting material before natural senescence was complete, reduced the proportion of mature seeds, lowered average germinability and increased germination times.
5 The thermal capacity of water bodies causes a lag in spring warming, whereas declining light becomes limiting in autumn. Najas marina is crucially dependent on the length of growing season to produce sufficient viable seed. A low-temperature requirement to break seed dormancy prevents inappropriate autumn germination. In a prolonged winter (necessarily followed by a shorter growing season), a significant proportion of seed would go into secondary dormancy and remain in the seed bank until the second spring.
6 In annual plants, such requirements for warm summers and cold winters could contribute to a continental-climate distribution in northern Europe. In the case of Najas marina this might explain its limit at the eastern extremity of England and thus its rarity.
Key-words : aquatic macrophyte, cold stratification, continental distribution, dormancy cycles, Najas marina , Norfolk Broads, seed dormancy, shallow lake, summer annual, rarity
Journal of Ecology (2005) 93 , 1185–1193
doi: 10.1111/j.1365-2745.2005.01062.x


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