Yuan Yongge, van Kleunen Mark, Li Junmin
School of Advanced Study, Taizhou University, Taizhou, 318000, China.
Zhejiang Provincial Key Laboratory of Plant Evolutionary Ecology and Conservation, Taizhou University, Taizhou, 318000, China.
Ecology. 2021 May;102(5):e03339. doi: 10.1002/ecy.3339. Epub 2021 Apr 10.
Cascading effects are ubiquitous in nature and can modify ecological processes. Most plants have mutualistic associations with mycorrhizal fungi, and can be connected to neighboring plants through common mycorrhizal networks (CMNs). However, little is known about how the distribution of nutrients by CMNs to the interconnected plants is affected by higher trophic levels, such as parasitic plants. We hypothesized that parasitism would indirectly drive CMNs to allocate more nutrients to the nonparasitized neighboring plants rather than to the parasitized host plants, and that this would result in a negative-feedback effect on the growth of the parasitic plant. To test this, we conducted a container experiment, where each container housed two in-growth cores that isolated the root system of a single Trifolium pratense seedling. The formation of CMNs was either prevented or permitted using nylon fabric with a mesh width of 0.5 or 25 μm, respectively. In each container, either both T. pratense plants were not parasitized or only one was parasitized by the holoparasite Cuscuta australis. To quantify the nutrient distribution by CMNs to the host and neighboring plants, we used N labeling. Growth and N concentrations of C. australis and T. pratense were measured, as well the arbuscular mycorrhizal fungi-colonization rates of T. pratense. We found that parasitism by C. australis reduced the biomass of T. pratense. In the absence of the parasite, CMNs increased the N concentration of both T. pratense plants, but did not affect their biomass. However, with the parasite, the difference between host and neighboring T. pratense plants in N concentration and biomass were amplified by CMNs. Furthermore, CMNs decreased the negative effect of C. australis on growth of the host T. pratense plants. Finally, although CMNs did not influence the N concentration of C. australis, they reduced its biomass. Our results indicate that when T. pratense was parasitized by C. australis, CMNs preferentially distributed more mineral nutrients to the nonparasitized neighboring T. pratense plant, and that this had a negative feedback on the growth of the parasite.
级联效应在自然界中无处不在，并且能够改变生态过程。大多数植物与菌根真菌存在共生关系，并且可以通过共同菌根网络（CMNs）与邻近植物相连。然而，关于较高营养级（如寄生植物）如何影响CMNs向相互连接的植物分配养分，我们却知之甚少。我们推测，寄生作用会间接促使CMNs将更多养分分配给未被寄生的邻近植物，而非被寄生的宿主植物，并且这会对寄生植物的生长产生负反馈效应。为了验证这一点，我们进行了一项盆栽实验，每个花盆中有两个内生长芯，将单一红车轴草幼苗的根系隔离开来。分别使用网宽为0.5或25μm的尼龙布来阻止或允许CMNs的形成。在每个花盆中，要么两株红车轴草都未被寄生，要么只有一株被全寄生植物南方菟丝子寄生。为了量化CMNs向宿主植物和邻近植物分配的养分，我们使用了氮标记法。测定了南方菟丝子和红车轴草的生长情况以及氮浓度，还有红车轴草的丛枝菌根真菌定殖率。我们发现，南方菟丝子的寄生降低了红车轴草的生物量。在没有寄生虫的情况下，CMNs增加了两株红车轴草的氮浓度，但并未影响它们的生物量。然而，在有寄生虫的情况下，CMNs放大了宿主红车轴草和邻近红车轴草在氮浓度和生物量上的差异。此外，CMNs降低了南方菟丝子对宿主红车轴草生长的负面影响。最后，虽然CMNs没有影响南方菟丝子的氮浓度，但降低了它的生物量。我们的结果表明，当红车轴草被南方菟丝子寄生时，CMNs优先将更多矿质养分分配给未被寄生的邻近红车轴草，并且这对寄生虫的生长产生了负反馈。
