Ecosystems adapted to low nitrogen (N) conditions such as Calluna-heathlands are especially sensitive to enhanced atmospheric N deposition that affects many aspects of ecosystem functioning like nutrient cycling, soil properties and plant-microbial-enzyme relationships. We investigated the effects of five levels of experimentally-simulated N deposition rates (i.e., N fertilization treatments: 0, 10, 20 and 50 kg N ha^− 1 yr^− 1 for 3 years, and 56 kg N ha^− 1 yr^− 1 for 10 years) on: plant, litter, microbial biomass and soil nutrient contents, soil extracellular enzymatic activities, and plant root ericoid mycorrhizal colonization. The study was conducted in marginal montane Calluna-heathlands at different developmental stages resulting from management (young/building-phase and mature-phase). Our findings revealed that many soil properties did not show a statistically significant response to the experimental addition of N, including: total N, organic carbon (C), C:N ratio, extractable N-NO₃⁻, available phosphorus (P), urease and β-glucosidase enzyme activities, and microbial biomass C and N. Our results also evidenced a considerable positive impact of chronic (10-year) high-N loading on soil extractable N-NH₄⁺, acid phosphatase enzyme activity, Calluna root mycorrhizal colonization by ericoid fungi, Calluna shoot N and P contents, and litter N content and N:P ratio. The age of heathland vegetation influenced the effects of N addition on ericoid mycorrhizal colonization, resulting in higher colonized roots in young heathlands at the control, low and medium N-input rates; and in mature ones at the high and chronically high N rates. Also, young heathlands exhibited greater soil extractable N-NO₃⁻, available P, microbial biomass N, Calluna shoot N and P contents, and litter N content, compared to mature ones. Our results highlighted that accounting for the N-input load and duration, as well as the developmental stage of the vegetation, is important for assessing the effects of added N, particularly at the heathlands' southern distribution limit.

中文翻译：

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与时间和年龄相关的实验模拟氮沉降对山地荒地生态系统功能的影响

适于低氮（N）的条件诸如生态系统Calluna酒店-heathlands是增强的大气氮沉积，影响等营养物循环，土壤性质和植物微生物酶的关系起作用的生态系统的各个方面特别敏感。我们研究了五个水平的模拟氮沉降速率的影响（即，氮肥处理：3年内分别为 0、10、20和50 kg N ha ^-1 yr ^-1以及56 kg N ha ^-1  yr ^-1（持续10年）：植物，凋落物，微生物生物量和土壤养分含量，土壤细胞外酶活性以及植物根类胡萝卜素菌根定殖。这项研究是在边缘山区卡卢纳群岛进行的管理带来的不同发展阶段的荒地（年轻/建筑阶段和成熟阶段）。我们的研究结果表明，许多土壤性质没有表现出对实验加入N统计学显著反应，包括：总N，有机碳（C），C：N比，可提取的N-NO ₃ ^- ，可用的磷（P），尿素酶和β-葡萄糖苷酶活性以及微生物生物量C和N。我们的研究结果还表明，长期（10年）高氮负荷对土壤可提取N-NH ₄ ⁺，酸性磷酸酶活性，愈伤组织根有相当大的积极影响。类固醇真菌，Calluna的菌根定植拍摄N和P含量，以及凋落物N含量和N：P比率。荒地植被的年龄影响氮的添加对类固醇菌根定殖的影响，在控制，低和中等输入氮的情况下，在年轻的荒地中定植的根较高。而在成熟的国家，氮含量较高且长期较高。此外，年轻荒野表现出更大的土壤提取N-NO ₃ ^- ，有效磷，微生物生物量N，Calluna酒店拍摄N，P含量，和垫料N含量，相对于成熟的。我们的结果强调，考虑氮输入的负荷和持续时间以及植被的发育阶段，对于评估添加的氮的影响（尤其是在荒地的南部分布极限处）非常重要。