Abstract Tropical mountains support a variety of vegetation types that are threatened by global change, but our understanding of these threats is limited by our scarce knowledge of nutrient constraints on belowground processes in these sensitive ecosystems. To address this, we quantified chemical and microbiological properties at five sites associated with four vegetation types at high elevations (>3000 m a.s.l.) on Volcan Baru, the highest mountain in Panama. At each site we quantified total and extractable soil nutrients, microbial biomass nutrients, and the activities of hydrolytic enzymes involved in nutrient cycling. We found high heterogeneity among vegetation types in soil and microbial nutrients. Phosphorus (P) was mainly in organic form (>70%) in high organic matter soils under forest and grassland, but mostly in inorganic form (≥68%) in shrublands. Inorganic nitrogen (N) concentrations were low to moderate in all soils (0.7–8.7 mg N kg-1), whereas extractable P measured by anion-exchange resins was relatively high (5–54 mg P kg-1) compared with tropical lowlands. We found marked variation in microbial N (51–199 mg N kg-1), microbial P (40–170 mg kg-1), and hydrolytic enzyme activities (e.g. s-glucosidase from 202 to 1399 nmol product g-1 h-1). Stoichiometric ratios in microbial biomass and between enzymes provided further evidence of shifts in the relative investment in N vs P acquisition among vegetation types. For example, the enzymatic N:P ratio (N-acetyl-s-D-glucosaminidase (NAG) to phosphomonoesterase (PME)) pointed to greater investment in microbial acquisition of N relative to P in bamboo-oak forest (NAG:PME = 0.55) compared to grassland and shrublands (NAG:PME ≤0.30). In conclusion, our results show that tropical mountains can be highly heterogeneous within a relatively narrow elevation range, indicating the likelihood of contrasting responses of plant and microbial communities to global change drivers such as cloud base, precipitation, and nitrogen deposition in tropical mountains.

中文翻译：

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新热带山脉海拔带内的土壤和微生物营养状况是异质的

摘要 热带山脉支持受全球变化威胁的多种植被类型，但我们对这些威胁的理解受限于我们对这些敏感生态系统中地下过程的营养限制的缺乏了解。为了解决这个问题，我们量化了与巴拿马最高山火山巴鲁火山高海拔（> 3000 m asl）的四种植被类型相关的五个地点的化学和微生物特性。在每个地点，我们量化了土壤总养分和可提取的土壤养分、微生物生物量养分以及参与养分循环的水解酶的活动。我们发现土壤中植被类型和微生物养分之间存在高度异质性。磷（P）主要以有机形式（>70%）存在于森林和草地下的高有机质土壤中，但在灌木丛中主要以无机形式（≥68%）。与热带低地相比，所有土壤中的无机氮 (N) 浓度为低至中等 (0.7–8.7 mg N kg-1)，而通过阴离子交换树脂测量的可提取 P 相对较高 (5–54 mg P kg-1) . 我们发现微生物 N (51–199 mg N kg-1)、微生物 P (40–170 mg kg-1) 和水解酶活性（例如 s-葡萄糖苷酶从 202 到 1399 nmol 产物 g-1 h- 1）。微生物生物量和酶之间的化学计量比进一步证明了植被类型之间 N 与 P 获取的相对投资发生变化。例如，酶促 N:P 比率（N-乙酰基-sD-氨基葡萄糖苷酶（NAG）与磷酸单酯酶（PME））表明竹栎林中微生物获取 N 相对于 P 的投资更大（NAG:PME = 0。55) 与草地和灌木丛相比 (NAG:PME ≤0.30)。总之，我们的研究结果表明，热带山脉在相对狭窄的海拔范围内可能具有高度异质性，这表明植物和微生物群落对全球变化驱动因素（如热带山脉的云底、降水和氮沉降）的不同反应的可能性。