University of South Bohemia, Branišovská 31, 370 05 Ceské Budejovice, Czech Republic.
Am J Bot. 2012 Jun;99(6):1020-32. doi: 10.3732/ajb.1100503. Epub 2012 Jun 5.
Both abiotic and biotic factors shape species distributions. Orchids produce minute seeds with few nutrient reserves, thus requiring mycorrhizal fungi for germination. Therefore, both environmental conditions and mycorrhizal fungi distribution affect their germination success, but these ecological requirements and their congruence with habitat preferences of adults remain poorly understood. We investigated the importance of these factors during germination in four forest orchid species of the genus Epipactis.
We sowed seeds of three habitat specialists and one generalist in different forest types at sites harboring adults of at least one of these ecologically diverging species. We analyzed germination pattern and identified mycorrhizal fungi of both seedlings and adults.
Habitat conditions had little influence on germination pattern as seedlings grew in more habitats than expected from the adults' ecology. Ectomycorrhizal fungi availability did not limit germination. Suitable mycorrhizal fungi, mostly pezizalean ascomycetes, were recruited in various forest types, though the fungal communities differed according to habitat type. Finally, orchids with divergent ecological preferences shared similar mycorrhizal fungi.
Limited adult distribution contrasted with successful seed germination at diverse sites and indicates existence of niche differentiation between adults and seedlings. Ecological specialization may thus be determined by factors other than mycorrhizal fungi that act later in the ontogeny, perhaps during the transition to above-ground development.
非生物和生物因素共同塑造了物种的分布。兰花产生的种子微小，营养储备少，因此需要菌根真菌来帮助其发芽。因此，环境条件和菌根真菌的分布都会影响它们的发芽成功率，但这些生态需求及其与成体栖息地偏好的一致性仍知之甚少。我们调查了这四个属的兰花物种在发芽过程中这些因素的重要性。
我们在至少有一个生态分化物种的成年个体存在的地点，在不同的森林类型中播种了三种生境专化种和一种广生态幅种的种子。我们分析了发芽模式，并鉴定了幼苗和成体的菌根真菌。
由于幼苗在比成体生态学预期更多的生境中生长，因此生境条件对发芽模式的影响很小。外生菌根真菌的可用性并不限制发芽。在各种森林类型中都招募到了适宜的菌根真菌，主要是子囊菌门的盘菌，但根据生境类型，真菌群落有所不同。最后，生态偏好不同的兰花共享相似的菌根真菌。
有限的成年个体分布与在不同地点成功的种子发芽形成对比，表明成体和幼苗之间存在生态位分化。因此，生态特化可能不是由菌根真菌以外的因素决定的，这些因素可能在个体发育的后期，也就是在向地上发育的过渡阶段起作用。
