热带稀树草原的火与豆科植物的萌发：生态和历史因素。
Fire and legume germination in a tropical savanna: ecological and historical factors.
机构信息
Universidade Estadual Paulista (UNESP), Instituto de Biociências, Lab of Vegetation Ecology, Rio Claro, Brazil.
Centro de Investigaciones sobre Desertificación (CIDE/CSIC), Montcada, Valencia, Spain.
出版信息
Ann Bot. 2019 Jul 8;123(7):1219-1229. doi: 10.1093/aob/mcz028.
BACKGROUND AND AIMS
In many flammable ecosystems, physically dormant seeds show dormancy-break patterns tied to fire, but the link between heat shock and germination in the tropical savannas of Africa and South America remains controversial. Seed heat tolerance is important, preventing seed mortality during fire passage, and is usually predicted by seed traits. This study investigated the role of fire frequency (ecological effects) and seed traits through phylogenetic comparison (historical effects), in determining post-fire germination and seed mortality in legume species of the Cerrado, a tropical savanna-forest mosaic.
METHODS
Seeds of 46 legume species were collected from three vegetation types (grassy savannas, woody savannas and forests) with different fire frequencies. Heat shock experiments (100 °C for 1 min; 100 °C for 3 min; 200 °C for 1 min) were then performed, followed by germination and seed viability tests. Principal component analysis, generalized linear mixed models and phylogenetic comparisons were used in data analyses.
KEY RESULTS
Heat shocks had little effect on germination, but seed mortality was variable across treatments and species. Seed mortality was lowest under the 100 °C 1 min treatment, and significantly higher under 100 °C 3 min and 200 °C 1 min; larger seed mass decreased seed mortality, especially at 200 °C. Tree species in Detarioideae had the largest seeds and were unaffected by heat. Small-seeded species (mostly shrubs from grassy savannas) were relatively sensitive to the hottest treatment. Nevertheless, the presence of physical dormancy helped to avoid seed mortality in small-seeded species under the hottest treatment.
CONCLUSIONS
Physical dormancy-break is not tied to fire in the Cerrado mosaic. Heat tolerance appears in both forest and savanna species and is predicted by seed traits (seed mass and physical dormancy), which might have helped forest lineages to colonize the savannas. The results show seed fire responses are better explained by historical than ecological factors in the Cerrado, contrasting with different fire-prone ecosystems throughout the world.
背景与目的
在许多易燃生态系统中，处于物理休眠状态的种子表现出与火相关的休眠打破模式，但在非洲和南美洲的热带稀树草原中，热冲击与种子萌发之间的联系仍存在争议。种子的耐热性很重要，它可以防止种子在火通过时死亡，通常可以通过种子特性来预测。本研究通过系统发育比较（历史效应），调查了火频（生态效应）和种子特性在决定塞拉多热带稀树草原-森林镶嵌体中豆科植物的火后萌发和种子死亡率中的作用。
方法
从三种具有不同火频的植被类型（草本稀树草原、木本稀树草原和森林）中采集了 46 种豆科植物的种子。然后进行热冲击实验（100°C 1 分钟；100°C 3 分钟；200°C 1 分钟），随后进行萌发和种子活力测试。在数据分析中使用了主成分分析、广义线性混合模型和系统发育比较。
主要结果
热冲击对萌发影响不大，但种子死亡率因处理和物种而异。在 100°C 1 分钟的处理下，种子死亡率最低，在 100°C 3 分钟和 200°C 1 分钟的处理下显著更高；较大的种子质量降低了种子死亡率，特别是在 200°C 下。Detarioideae 中的树种种子最大，不受热影响。小种子物种（主要来自草本稀树草原的灌木）对最热的处理相对敏感。然而，物理休眠的存在有助于避免小种子物种在最热处理下的种子死亡。
结论
在塞拉多镶嵌体中，物理休眠的打破与火无关。耐热性出现在森林和稀树草原物种中，并且可以通过种子特性（种子质量和物理休眠）来预测，这可能有助于森林谱系在稀树草原中殖民。结果表明，在塞拉多，种子对火的反应更多地是由历史因素而不是生态因素来解释的，这与世界各地不同的火灾多发生态系统形成对比。
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