Department of Biology, Lewis and Clark College, 0615 SW Palatine Hill Rd, Portland, OR, 97219, USA.
Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith, NSW, 2751, Australia.
New Phytol. 2014 Apr;202(1):287-296. doi: 10.1111/nph.12638. Epub 2013 Dec 10.
Alnus trees associate with ectomycorrhizal (ECM) fungi and nitrogen-fixing Frankia bacteria and, although their ECM fungal communities are uncommonly host specific and species poor, it is unclear whether the functioning of Alnus ECM fungal symbionts differs from that of other ECM hosts. We used exoenzyme root tip assays and molecular identification to test whether ECM fungi on Alnus rubra differed in their ability to access organic phosphorus (P) and nitrogen (N) when compared with ECM fungi on the non-Frankia host Pseudotsuga menziesii. At the community level, potential acid phosphatase (AP) activity of ECM fungal root tips from A. rubra was significantly higher than that from P. menziesii, whereas potential leucine aminopeptidase (LA) activity was significantly lower for A. rubra root tips at one of the two sites. At the individual species level, there was no clear relationship between ECM fungal relative root tip abundance and relative AP or LA enzyme activities on either host. Our results are consistent with the hypothesis that ECM fungal communities associated with Alnus trees have enhanced organic P acquisition abilities relative to non-Frankia ECM hosts. This shift, in combination with the chemical conditions present in Alnus forest soils, may drive the atypical structure of Alnus ECM fungal communities.
桤木与外生菌根（ECM）真菌和固氮弗兰克氏菌共生，尽管其 ECM 真菌群落通常具有宿主特异性且物种较少，但尚不清楚桤木 ECM 真菌共生体的功能是否与其他 ECM 宿主不同。我们使用外生酶根尖测定法和分子鉴定来测试与非弗兰克氏菌宿主西洋杉上的 ECM 真菌相比，红桤木上的 ECM 真菌在获取有机磷（P）和氮（N）方面的能力是否存在差异。在群落水平上，红桤木 ECM 真菌根尖的潜在酸性磷酸酶（AP）活性明显高于西洋杉，而在两个地点中的一个地点，红桤木根尖的潜在亮氨酸氨肽酶（LA）活性明显较低。在种间水平上，在任一种宿主上，ECM 真菌的相对根尖丰度与相对 AP 或 LA 酶活性之间均无明显关系。我们的结果与以下假设一致，即与非弗兰克氏菌 ECM 宿主相比，与桤木相关的 ECM 真菌群落具有增强的有机 P 获取能力。这种转变，再加上桤木森林土壤中存在的化学条件，可能会导致桤木 ECM 真菌群落的非典型结构。
