Root and mycorrhizal responses to nutrient additions in a tropical mountain forest and in pastures after forest conversion

该项目的目标是加强对丛枝菌根和热带山地森林系统中的根的一般较差的了解，特别是将菌根反应纳入研究组正在进行的营养操作中(森林中的Numex和牧场中的FERFAST)。在这个框架内，我们询问有关AM真菌在根和土壤(茎外菌丝)中的丰度的问题，假设即使是低水平的施肥也会导致菌根真菌丰度下降。我们还假设在根外AM菌丝丰度和细根之间存在权衡，这两个结构具有部分重叠的功能。使用分子生态学工具(焦磷酸测序和末端限制性片段长度多态分析)，我们测试了土壤中AM真菌组合对营养操作的响应和沿海拔梯度的差异。结合AM真菌的潜在丰度和组合组成的变化，我们最后提出了一个关键问题，即施肥是否有利于出现互动性较差的AM真菌组合。这将使用温室接种方法来实现。我们研究的菌根功能之一是植物生长，但我们也将研究土壤聚集的生态系统过程。

The goal of this project is to enhance the comparatively poor knowledge about arbuscular mycorrhizas (AM) and roots in tropical mountain forest systems in general, and in particular to integrate mycorrhizal responses into ongoing nutrient manipulations (NUMEX in the forest and FERFAST in the pasture) of the Research Unit. Within this framework, we ask questions about the abundance of AM fungi in roots and in the soil (extraradical hyphae), hypothesizing that even low levels of fertilization will cause decreased mycorrhizal fungal abundance. We also hypothesize that there are tradeoffs between extraradical AM hyphal abundance and fine roots, two structures with partially overlapping functions. Using molecular ecology tools (pyrosequencing and terminal restriction fragment length polymorphism analysis) we test for differences in AM fungal assemblages in the soil in response to nutrient manipulations and along an elevation gradient. Integrating both potential abundance and assemblage composition changes of AM fungi, we finally ask the pivotal question if fertilization can favor the occurrence of less mutualistic AM fungal assemblages. This will be accomplished using a greenhouse inoculation approach. One of the mycorrhizal functions examined will be plant growth, but we will also examine the ecosystem process of soil aggregation.