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.

许多兰花受到威胁，而有些兰花则在没有明显原因的情况下从自然栖息地消失。富营养化被认为是可能的因子和硝酸盐，即使在非常低的浓度下也能抑制非共生兰花种子的发芽，并且可能对天然兰花种群构成严重威胁。所有兰花的早期本体发育完全取决于兰花的菌根共生关系，并且在这个最初的菌杂营养化阶段，许多陆生绿色兰花与多系真菌共生菌（即，霉菌共生菌）结合在一起，统称为“根瘤菌”。我们问这些真菌是否也可能具有非营养作用，即它们是否可能赋予对富营养化的抗性。为了验证这一假设，我们共同培育了陆地兰花Dactylorhiza majalis的种子。具有五个具有不同生态意义的硝酸盐浓度（0至100 mg / L）的根瘤菌（两个Tulasnella，两个Ceratobasidium和一个Serendipita分离株）。随着一个例外Tulasnella分离，所有mycobionts支持球茎生长和形成菌根兰花，即细胞内的菌丝pelotons，在球茎。除一种真菌处理外，硝酸盐抑制了种子发芽的共生和共生；种子与一种角柏科植物共同培养分离物确实对硝酸盐不敏感。我们得出的结论是，硝酸盐还会对共生兰花的萌发产生负面影响，具体取决于可用的相容性霉菌。因此，用硝酸盐富营养化可以减少能够支持种子发芽的兰花霉菌的数量。