Arbuscular mycorrhizas (AM) prevail in warm and dry climates and ectomycorrhizas (EM) in cold and humid climates. We suggest that the fungal symbionts benefit their host plants especially in the corresponding conditions. The hypothesis tested was that AM plants are more drought resistant than EM or non-mycorrhizal (NM) plants.

Gray alder (Alnus incana) seedlings were inoculated with two species of either AM or EM fungi or none. In one controlled-environment experiment, there was a watering and a drought treatment. Another set of seedlings were not watered until permanent wilting.

The AM plants were somewhat smaller than EM and NM, and at the early stage of the drought treatment the soil-moisture content was slightly higher in the AM pots. Shoot water potential was highest in the AM treatment during severe drought, while stomatal conductance and photosynthesis did not show a mycorrhizal effect. In the lethal-drought set the AM maintained their leaves longer than EM and NM plants, and the AM seedlings survived longer than NM seedlings. Foliar phosphorus and sulfur concentrations remained higher in AM plants than EM or NM but potassium, copper and iron increased in EM during drought. The root tannin concentration was lower in AM than EM and drought doubled it.

Although the difference to EM plants was not large, the hypothesis was supported by the better performance of AM plants during a severe short-termed drought. Sustained phosphorus nutrition during drought in AM plants was a possible reason for this. Moreover, the higher foliar sulfur and lower metal-nutrient concentrations in AM may reflect differences in nutrient uptake or (re)translocation during drought, which merit further research. The much larger tannin concentrations in EM root systems than AM did not appear to protect the EM plants from drought. The differential tannin accumulation in AM and EM plants needs further attention.

中文翻译：

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丛枝菌根的Al木幼苗比外生菌根和非菌根的幼苗更耐干旱吗？

丛枝菌根（AM）在温暖和干燥的气候中流行，而外生菌根（EM）在寒冷和潮湿的气候中流行。我们建议真菌共生菌有益于其寄主植物，特别是在相应条件下。测试的假设是AM植物比EM或非菌根（NM）植物更耐干旱。

用两种AM或EM真菌或不接种两种方法接种灰al木（Alnus incana）幼苗。在一个受控环境实验中，进行了浇水和干旱处理。直到永久枯萎，再浇水。

AM植物比EM和NM小一些，在干旱处理的早期，AM盆中的土壤水分含量略高。在严重干旱期间，AM处理中的枝条水势最高，而气孔导度和光合作用没有表现出菌根作用。在致死性干旱条件下，AM的叶片比EM和NM植物更长，AM幼苗的存活时间比NM幼苗长。在干旱期间，增效植物中叶面的磷和硫的浓度仍高于EM或NM，但EM中钾，铜和铁的含量增加。AM中的根单宁浓度低于EM，干旱使它倍增。

尽管与EM植物的差异不大，但该假设得到了AM植物在严重短期干旱中的更好表现的支持。造成AM植物干旱期间磷营养持续的可能原因。此外，AM中较高的叶面硫含量和较低的金属养分浓度可能反映了干旱期间养分吸收或（重新）转运的差异，值得进一步研究。EM根系中单宁浓度比AM高得多，似乎不能保护EM植物免受干旱侵害。AM和EM植物中单宁积累的差异需要进一步关注。