Ecology and Evolutionary Biology, University of California, Santa Cruz, California, 95064, USA.
Biological Sciences and Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, Arizona, 86011, USA.
Ecol Appl. 2019 Apr;29(3):e01867. doi: 10.1002/eap.1867. Epub 2019 Feb 27.
Reforestation is challenging when timber harvested areas have been degraded, invaded by nonnative species, or are of marginal suitability to begin with. Conifers form mutualistic partnerships with ectomycorrhizal fungi (EMF) to obtain greater access to soil resources, and these partnerships may be especially important in degraded areas. However, timber harvest can impact mycorrhizal fungi by removing or compacting topsoil, removing host plants, and warming and drying the soil. We used a field experiment to evaluate the role of EMF in Douglas-fir reforestation in clearcuts invaded by Cytisus scoparius (Scotch broom) where traditional reforestation approaches have repeatedly failed. We tested how planting distance from intact Douglas-fir forest edges influenced reforestation success and whether inoculation with forest soils can be used to restore EMF relationships. We used an Illumina DNA sequencing approach to measure the abundance, richness and composition of ectomycorrhizal fungi on Douglas-fir roots, and assessed differences in Douglas-fir seedling survival and growth near to and far from forest edges with and without forest soil inoculum. Planting Douglas-fir seedlings near forest edges increased seedling survival, growth, and EMF root colonization. Edge proximity had no effect on EMF richness but did change fungal community composition. Inoculations with forest soil did not increase EMF abundance or richness or change community composition, nor did it improve seedling establishment. With Illumina sequencing, we identified two to three times greater species richness than described in previous edge effects studies. Of the 95 EMF species we identified, 40% of the species occurred on less than 5% of the seedlings. The ability to detect fungi at low abundance may explain why we did not detect differences in EMF richness with distance to hosts as previous studies. Our findings suggest that forest edges are suitable for reforestation, even when the interiors of deforested areas are not. We advocate for timber harvest designs that maximize edge habitat where ectomycorrhizal fungi contribute to tree establishment. However, this study does not support the use of inoculation with forest soil as a simple method to enhance EMF and seedling survival.
当采伐区退化、被非本地物种入侵或本身适宜性较差时，重新造林具有挑战性。针叶树与外生菌根真菌（EMF）形成互利共生关系，以更有效地获取土壤资源，而这些共生关系在外生菌根真菌退化区可能尤为重要。然而，采伐可能会通过去除或压实表土、去除宿主植物以及使土壤变暖变干来影响菌根真菌。我们使用野外实验来评估外生菌根真菌在 Douglas-fir 重新造林中的作用，该实验在 Cytisus scoparius（Scotch broom）入侵的皆伐迹地进行，而传统的重新造林方法在此处反复失败。我们测试了与完整的 Douglas-fir 林缘的种植距离如何影响重新造林的成功率，以及是否可以使用森林土壤接种来恢复外生菌根真菌的关系。我们使用 Illumina DNA 测序方法来测量 Douglas-fir 根系上外生菌根真菌的丰度、丰富度和组成，并评估了有无森林土壤接种的情况下，靠近和远离林缘的 Douglas-fir 幼苗的存活和生长差异。在林缘附近种植 Douglas-fir 幼苗会增加幼苗的存活率、生长率和外生菌根真菌根的定植。林缘的接近度对外生菌根真菌的丰富度没有影响，但确实改变了真菌群落的组成。土壤接种并没有增加外生菌根真菌的丰度或丰富度，也没有改变群落组成，也没有改善幼苗的建立。通过 Illumina 测序，我们确定的物种丰富度比以前的边缘效应研究中描述的要高两到三倍。在所鉴定的 95 种外生菌根真菌中，有 40%的物种仅出现在不到 5%的幼苗上。在低丰度下检测真菌的能力可能解释了为什么我们没有像以前的研究那样检测到距离宿主的外生菌根真菌丰富度的差异。我们的研究结果表明，即使在森林砍伐区内部不适宜重新造林的情况下，森林边缘也是适合重新造林的。我们提倡采用最大限度地增加外生菌根真菌有助于树木建立的边缘生境的木材采伐设计。然而，这项研究并不支持使用森林土壤接种作为一种简单的方法来增强外生菌根真菌和幼苗的存活率。
