Understanding how the community structures and functions of soil microbes respond to environmental changes is essential for predicting the dynamics of ecosystem functions. Elevational gradients are an ideal setting for “natural experiments” on the relationships between soil microbes and environmental factors. However, little is known about elevational patterns of soil microbial functions and their interactions with aboveground vegetation. We examined community structures and nitrogen cycling gene abundance of soil bacteria in 20 vegetation survey quadrats in cool-temperate and sub-alpine forests along an elevational gradient (1050–2000 m above sea level) in central Japan. The diversity of soil bacterial communities was investigated based on terminal restriction fragment length polymorphisms (T-RFLP) in the 16S rRNA gene. The abundance of soil bacteria and key functional groups involved in nitrogen cycling was determined by quantifying the 16S rRNA and bacterial genes related to nitrogen fixation (nifH), ammonia oxidation (amoA), and denitrification (nosZ). The terminal restriction fragment (T-RF) richness of soil bacteria showed no relationship with elevation, but was negatively associated with soil nitrate-nitrogen and the species richness of understory vegetation. The abundance of all bacteria and nitrogen functional groups showed hump-shaped relationships with elevation, and was positively associated with soil water content and understory stem density. These results highlight that community structures and nitrogen cycling gene abundance of soil microbes along the elevational gradient can be explained by soil properties associated with understory vegetation. This suggests that vegetation decline caused by environmental changes, such as climate warming, land use change, and increased herbivore density, may deteriorate soil ecosystem functions through aboveground–belowground interactions.

了解土壤微生物的群落结构和功能如何响应环境变化对于预测生态系统功能的动态至关重要。海拔梯度是土壤微生物与环境因素之间关系的“自然实验”的理想设置。然而，人们对土壤微生物功能的海拔模式及其与地上植被的相互作用知之甚少。我们在日本中部沿海拔梯度（海拔 1050-2000 米）的冷温带和亚高山森林的 20 个植被调查样方中检测了土壤细菌的群落结构和氮循环基因丰度。基于 16S rRNA 基因的末端限制性片段长度多态性 (T-RFLP) 研究了土壤细菌群落的多样性。nifH )、氨氧化 ( amoA ) 和反硝化 ( nosZ)）。土壤细菌末端限制片段（T-RF）丰富度与海拔无关，但与土壤硝态氮和林下植被物种丰富度呈负相关。所有细菌和氮官能团的丰度与海拔呈驼峰状关系，与土壤含水量和林下茎密度呈正相关。这些结果强调，沿海拔梯度的土壤微生物的群落结构和氮循环基因丰度可以通过与林下植被相关的土壤特性来解释。这表明气候变暖、土地利用变化和食草动物密度增加等环境变化引起的植被减少可能通过地上-地下相互作用使土壤生态系统功能恶化。