School of Forest Sciences, University of Eastern Finland, Yliopistokatu 7, PO Box 111, 80101 Joensuu, Finland.
Natural Resources Institute Finland (Luke), Yliopistokatu 6, Joensuu, Finland.
Tree Physiol. 2020 May 30;40(6):782-795. doi: 10.1093/treephys/tpaa035.
Arbuscular mycorrhizas (AMs) prevail in warm and dry climates and ectomycorrhizas (EMs) 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 nonmycorrhizal (NM) plants. Grey alder (Alnus incana (L.) Moench) 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 plants 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 in drought resistance was not large, the hypothesis was supported by the better performance of AM plants during a severe short-term 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.
丛枝菌根（AM）在温暖和干燥的气候中占优势，外生菌根（EM）在寒冷和潮湿的气候中占优势。我们认为真菌共生体特别在相应的条件下对其宿主植物有益。我们检验的假设是 AM 植物比 EM 或非菌根（NM）植物更耐旱。灰桤木（Alnus incana (L.) Moench）幼苗接种了两种 AM 或 EM 真菌或不接种真菌。在一个受控环境实验中，有浇水和干旱处理。另一组幼苗在永久萎蔫之前不浇水。AM 植物比 EM 和 NM 植物略小，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 处理的植物具有最高的茎水势，而气孔导度和光合作用没有表现出菌根效应。在致死干旱组中，AM 植物比 EM 和 NM 植物保持叶子的时间更长，并且 AM 幼苗比 NM 幼苗存活的时间更长。AM 植物的叶片磷和硫浓度仍然高于 EM 或 NM，但钾、铜和铁在 EM 中在干旱期间增加。AM 植物的根单宁浓度低于 EM 植物，干旱使其浓度增加了一倍。虽然抗旱性的差异不大，但 AM 植物在严重短期干旱下表现更好支持了该假设。在 AM 植物中，干旱期间持续的磷营养可能是导致这种情况的原因。此外，AM 植物中较高的叶片硫和较低的金属养分浓度可能反映了干旱期间养分吸收或（再）转运的差异，这值得进一步研究。EM 根系中比 AM 植物大得多的单宁浓度似乎并没有保护 EM 植物免受干旱。AM 和 EM 植物中差异积累的单宁需要进一步关注。
