Bogs and fens cover 6% and 21%, respectively, of the 140,329 km² Oil Sands Administrative Area in northern Alberta. Development of the oil sands has led to increasing atmospheric N deposition, with values as high as 17 kg N·ha⁻¹·yr⁻¹; regional background deposition is <2 kg N·ha⁻¹·yr⁻¹. Bogs, being ombrotrophic, may be especially susceptible to increasing N deposition. To examine responses to N deposition, over five years, we experimentally applied N (as NH₄NO₃) to a bog near Mariana Lake, Alberta, unaffected by oil sands activities, at rates of 0, 5, 10, 15, 20, and 25 kg N·ha⁻¹·yr⁻¹, plus controls (no water or N addition). Increasing N addition: (1) stimulated N₂ fixation at deposition <3.1 kg N·ha⁻¹·yr⁻¹, and progressively inhibited N₂ fixation as N deposition increased above this level; (2) had no effect on Sphagnum fuscum net primary production (NPP) in years 1, 2, and 4, but inhibited S. fuscum NPP in years 3 and 5; (3) stimulated dominant shrub and Picea mariana NPP; (4) led to increased root biomass and production; (5) changed Sphagnum species relative abundance (decrease in S. fuscum, increase in S. magellanicum, no effect on S. angustifolium); (6) led to increasing abundance of Rhododendron groenlandicum and Andromeda polifolia, and to vascular plants in general; (7) led to increasing shrub leaf N concentrations in Andromeda polifolia, Chamaedaphne calyculata, Vaccinium oxycoccos, V. vitis‐idaea, and Picea mariana; (8) stimulated cellulose decomposition, with no effect on S. fuscum peat or mixed vascular plant litter decomposition; (9) had no effect on net N mineralization rates or on porewater NH₄⁺‐N, NO₃⁻‐N, or DON concentrations; and (10) had minimal effects on peat microbial community composition. Increasing experimental N addition led to a switch from new N being taken up primarily by Sphagnum to being taken up primarily by shrubs. As shrub growth and cover increase, Sphagnum abundance and NPP decrease. Because inhibition of N₂ fixation by increasing N deposition plays a key role in bog structural and functional responses, we recommend a N deposition critical load of 3 kg N·ha⁻¹·yr⁻¹ for northern Alberta bogs.

中文翻译：

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实验氮的添加改变了北方沼泽的结构和功能：临界负荷和阈值揭示

在艾伯塔省北部140,329 km ^2的油砂行政区中，沼泽和fen分别占6％和21％。油砂的开发导致大气中氮的沉积增加，其值高达17 kg N·ha ^-1 ·yr ^-1；区域背景沉积<2 kg N·ha ^-1 ·yr ^-1。混养的沼泽可能特别容易增加N的沉积。为了检查到N沉降的响应，在五年内，我们通过实验应用N（如NH ₄ NO ₃），以接近马里亚纳湖，艾伯塔沼泽，不受油砂的活动，在20 0速率，5，10，15日，和25 kg N·ha ^-1 ·yr ^-1，加上控件（不加水或不添加N）。增加氮的添加：（1）在沉积物<3.1 kg N·ha ^-1 ·yr ^-1时刺激N ₂固定，并随着N沉积量增加到该水平以上而逐渐抑制N ₂固定；（2）在第1、2和4年对紫茎泽兰净初级生产力（NPP）没有影响，但在第3和第5年抑制了紫菜链霉菌的NPP；（3）刺激性优势灌木和云杉云杉NPP；（4）导致根生物量和产量增加；（5）泥炭藓物种相对丰度发生了变化（紫红色葡萄球菌减少，麦哲伦葡萄球菌增加，对S. angustifolium）; （6）导致了罗汉杜鹃和仙女座小叶的丰度增加，并且导致了维管植物的普遍生长；（7）导致Andromeda polifolia，Chamaedaphne calyculata，Vaccinium oxycoccos，V。vitis ‐idaea和Picea mariana中的灌木叶N浓度增加；（8）刺激的纤维素分解，对镰刀泥炭或混合维管植物凋落物的分解没有影响；（9）对净氮矿化速率或孔隙水上NH没有影响₄ ⁺ -N，NO ₃ ^-‐N或DON浓度；（10）对泥炭微生物群落组成的影响最小。实验性氮的添加量增加导致从新的氮主要由泥炭藓吸收变为主要由灌木吸收。随着灌木的生长和覆盖率的增加，泥炭藓的丰度和NPP下降。由于增加N沉积对N ₂固定的抑制作用在沼泽的结构和功能响应中起着关键作用，因此我们建议北部艾伯塔省沼泽的N沉积临界负荷为3 kg N·ha ^-1 ·yr ^-1。