Department of Biological Sciences, University of Alberta, B717a, Biological Sciences Building, Edmonton, Alberta, T6G 2E9, Canada.
Department of Biology, University of Nebraska at Kearney, Kearney, NE, 68849, USA.
Mycorrhiza. 2020 May;30(2-3):173-183. doi: 10.1007/s00572-020-00940-4. Epub 2020 Feb 22.
For tree seedlings in boreal forests, ectomycorrhizal (EM) fungal networks may promote, while root competition may impede establishment. Thus, disruption to EM fungal networks may decrease seedling establishment owing to the loss of positive interactions among neighbors. Widespread tree mortality can disrupt EM networks, but it is not clear whether seedling establishment will be limited by the loss of positive interactions or increased by the loss of negative interactions with surrounding roots. Depending upon the relative influence of these mechanisms, widespread tree mortality may have complicated consequences on seedling establishment, and in turn, the composition of future forests. To discern between these possible outcomes and the drivers of seedling establishment, we determined the relative importance of EM fungal networks, root presence, and the bulk soil on the establishment of lodgepole pine and white spruce seedlings along a gradient of beetle-induced tree mortality. We manipulated seedling contact with EM fungal networks and roots through the use of mesh-fabric cylinders installed in soils of lodgepole pine forests experiencing a range of overstorey tree mortality caused by mountain pine beetle. Lodgepole pine seedling survival was higher with access to EM fungal networks in undisturbed pine forests in comparison with that in beetle-killed stands. That is, overstorey tree mortality shifted fungal networks from being a benefit to a cost on seedling survival. In contrast, overstorey tree mortality did not change the relative strength of EM fungal networks, root presence and the bulk soil on survival and biomass of white spruce seedlings. Furthermore, the relative influence of EM fungal networks, root presence, and bulk soils on foliar N and P concentrations was highly contingent on seedling species and overstorey tree mortality. Our results highlight that following large-scale insect outbreak, soil-mediated processes can enable differential population growth of two common conifer species, which may result in species replacement in the future.
对于北方森林中的树木幼苗，外生菌根（EM）真菌网络可能会促进其生长，而根系竞争则可能阻碍其生长。因此，EM 真菌网络的破坏可能会由于失去邻居之间的积极相互作用而导致幼苗生长受阻。广泛的树木死亡可能会破坏 EM 网络，但尚不清楚幼苗的建立是会受到失去正相互作用的限制，还是会受到与周围根系失去负相互作用的促进。根据这些机制的相对影响，广泛的树木死亡可能会对幼苗的建立产生复杂的影响，进而影响未来森林的组成。为了区分这些可能的结果和幼苗建立的驱动因素，我们确定了 EM 真菌网络、根系存在和土壤基质在山松甲虫引起的树木死亡率梯度上对黑云杉和白云杉幼苗建立的相对重要性。我们通过在经历不同程度林冠树死亡率的黑云杉林中使用安装在土壤中的网布圆筒来操纵幼苗与 EM 真菌网络和根系的接触，这些林冠树死亡率是由山松甲虫引起的。与在山松甲虫致死林中相比，在未受干扰的云杉林中，接触 EM 真菌网络的黑云杉幼苗存活率更高。也就是说，林冠树木死亡率将真菌网络从对幼苗生存的有利因素转变为不利因素。相比之下，林冠树木死亡率并没有改变 EM 真菌网络、根系存在和土壤基质对白云杉幼苗存活率和生物量的相对强度。此外，EM 真菌网络、根系存在和土壤基质对叶片氮和磷浓度的相对影响高度取决于幼苗物种和林冠树木死亡率。我们的研究结果表明，在大规模昆虫爆发之后，土壤介导的过程可以使两种常见针叶树种的种群生长产生差异，这可能导致未来的物种更替。
