Department of Experimental Plant Biology, Faculty of Science, Charles University, Viničná 5, 12844, Prague, Czech Republic.
Institut Systématique, Muséum National D'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, CP 39, 57 rue Cuvier, Biodiversité, 75005, Évolution, Paris, France.
Mycorrhiza. 2021 Mar;31(2):231-241. doi: 10.1007/s00572-021-01021-w. Epub 2021 Jan 25.
Many orchid species are threatened, while some disappear from their natural habitats without obvious reasons. Eutrophication has been suggested as a possible factor and nitrate, which is able to suppress non-symbiotic orchid seed germination even at very low concentrations, and could pose a serious threat for natural orchid populations. Early ontogenesis of all orchids entirely depends on orchid mycorrhizal symbiosis, and at this initial mycoheterotrophic stage, many terrestrial green orchids associate with polyphyletic fungal symbionts (i.e., mycobionts), collectively called "rhizoctonias." We asked whether these fungi might also have some non-nutritional roles, i.e., whether they might confer resistance to eutrophication. To test this hypothesis, we co-cultivated seeds of the terrestrial orchid Dactylorhiza majalis with five rhizoctonias (two Tulasnella, two Ceratobasidium and one Serendipita isolate) at various ecologically meaningful nitrate concentrations (0 to 100 mg/L). With the exception of one Tulasnella isolate, all mycobionts supported the growth of protocorms and formed orchid mycorrhiza, i.e., intracellular hyphal pelotons, in the protocorms. Nitrate suppressed asymbiotic, as well as symbiotic, seed germination in all but one fungal treatment; the seeds co-cultivated with one of the Ceratobasidium isolates were indeed insensitive to nitrate. We conclude that nitrates also negatively affect symbiotic orchid germination, depending on the available compatible mycobionts. Thus, eutrophication with nitrate may decrease the number of orchid mycobionts capable of supporting seed germination.
许多兰花物种受到威胁，而有些兰花则在没有明显原因的情况下从其自然栖息地消失。有人认为富营养化可能是一个因素，而硝酸盐即使在非常低的浓度下也能抑制非共生兰花种子的萌发，这可能对自然兰花种群构成严重威胁。所有兰花的早期个体发育完全依赖于兰花菌根共生关系，在这个初始菌根异养阶段，许多陆生绿色兰花与多系真菌共生体（即菌根真菌），统称为“Rhizoctonia”。我们想知道这些真菌是否可能具有一些非营养作用，即它们是否可能赋予植物对富营养化的抗性。为了检验这一假设，我们在各种具有生态学意义的硝酸盐浓度（0 至 100mg/L）下，将陆生兰花 Dactylorhiza majalis 的种子与五种 Rhizoctonia（两种 Tulasnella、两种 Ceratobasidium 和一种 Serendipita 分离株）共培养。除了一种 Tulasnella 分离株外，所有菌根真菌都支持原球茎的生长，并在原球茎中形成兰花菌根，即细胞内菌丝球。硝酸盐抑制了非共生和共生种子的萌发，除了一种真菌处理外；与一种 Ceratobasidium 分离株共培养的种子确实对硝酸盐不敏感。我们得出结论，硝酸盐也会负面影响共生兰花的萌发，具体取决于可用的相容菌根真菌。因此，硝酸盐的富营养化可能会减少能够支持种子萌发的兰花菌根真菌的数量。
