BackgroundDensity in inter and intraspecific plant-plant interactions affects the action modes of allelopathy (autotoxicity, negative and positive allelopathy). Some seeds exude compounds that inhibit the germination of others. Ipomoea murucoides and I. pauciflora are sympatric tree species that form patches at the local scale where one or the other dominates, possibly due to allelopathy in the seeds. The objective of this study was to determine the possible density-dependence of the allelopathic effect among seeds of these species through the measure of seed germination and seedling emergence.MethodsIn both species, allelopathy was measured as: a) germination in mixed sowing of both species at different proportions, b) germination in single-species trials at different densities after adding seed extracts of both species, and c) seedling emergence in seed mixtures of both species sown at different proportions beneath canopies of the two Ipomoea species.ResultsSeed germination of I. murucoides was increased by the presence of I. pauciflora and diminished at higher densities of its own seeds; however, seed germination of I. pauciflora was not affected by the presence of I. murucoides seeds. The addition of extracts (either from conspecifics or congeneric) diminished the germination of both species and at higher seed densities the germination was lower. Seedling emergence did not depend on the species under which the seeds were sown nor on the density of the seeds.ConclusionsThe germination experiments evidenced positive allelopathy and/or autotoxicity, while there was no evidence of allelopathic effects in seedling emergence. The allelopathic activity is reported in the seeds of these species for the first time.

中文翻译：

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化感作用对两种番薯种萌发和出苗的密度依赖性影响

背景在种间和种内植物-植物相互作用中的密度影响化感作用的作用模式（自毒作用、负性和正性化感作用）。一些种子散发出抑制其他种子发芽的化合物。Ipomoea murucoides 和 I. pauciflora 是同域树种，它们在局部范围内形成斑块，其中一个或另一个占主导地位，可能是由于种子的化感作用。本研究的目的是通过测量种子萌发和幼苗出苗来确定这些物种种子间化感作用的可能密度依赖性。方法在两个物种中，化感作用测量为：a) 两种物种混合播种时的萌发以不同的比例，b) 在添加两种物种的种子提取物后，在不同密度的单一物种试验中发芽，c) 以不同比例播种在两种番薯树冠下的两种物种的种子混合物中的幼苗出现。结果 I. murucoides 的种子萌发因 I. pauciflora 的存在而增加，并在其自身种子密度较高时减少；然而，I. pauciflora 的种子萌发不受 I. murucoides 种子的影响。添加提取物（来自同种或同类）减少了两种物种的发芽，并且在较高的种子密度下发芽率较低。出苗不依赖于种子播种的物种，也不取决于种子的密度。结论发芽实验证明了阳性化感作用和/或自体毒性，而没有证据表明出苗具有化感作用。