Phospholipid Fatty Acid Profiles of Bacteria and Fungi in Peat Exposed to Experimentally Increased N Deposition, 2015

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 levels <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 NH 4 NO 3 ) to a bog
near Mariana Lakes, Alberta, at rates of 0, 5, 10, 15, 20, and 25 kg N
ha -1 yr -1 , plus
controls (no water or N addition). In July of 2015 we measured PLFA
markers in two depths in each plot. For the most part, microbial group
abundances were not affected by increasing N input (Fig. 16). However,
actinomycete abundance decreased with increasing N deposition at rates
that were similar in 0-5 and 5-10 cm peat. Gram-negative bacteria
increased slightly with increasing N input and were more abundant in
0-5 cm than in 5-10 cm peat; correspondingly the Gram-positive to
Gram-negative bacterial ratio decreased with increasing N input and
was lower in 0-5 cm than in 5-10 cm peat. Total microbial abundance
and total bacterial abundance were significantly higher in 0-5 cm peat
than in 5-10 cm peat. It may be that more sensitive/targeted
techniques, such as high-throughput pyrosequencing, 16s RNA clone
library analysis and rRNA-targeted fluorescence in
situ hybridization (FISH) or whole genome shotgun
sequencing may be required to reveal bog microbial community responses
to N loading.

油砂开发引发大气氮沉降持续攀升，最高沉降速率可达17 kg N ha⁻¹ yr⁻¹；区域背景氮沉降速率则低于2 kg N ha⁻¹ yr⁻¹。雨养型泥炭沼泽（ombrotrophic）仅依赖大气降水获取养分，因此对氮沉降增加尤为敏感。为探究其对氮沉降的响应机制，研究团队在5年周期内，对加拿大阿尔伯塔省马里亚纳湖附近的一处雨养型泥炭沼泽开展野外控制实验：以硝酸铵（NH₄NO₃）为氮源，设置0、5、10、15、20、25 kg N ha⁻¹ yr⁻¹共6个氮添加梯度，另设无水分与氮添加的空白对照组。2015年7月，研究人员在每个样地的两个泥炭土层（0-5 cm与5-10 cm）中测定了磷脂脂肪酸（PLFA）标志物丰度。整体而言，多数微生物类群的丰度未随氮输入量增加产生显著变化（图16）。但放线菌丰度随氮沉降水平升高呈下降趋势，且该变化规律在0-5 cm与5-10 cm泥炭土层中表现一致。革兰氏阴性菌丰度随氮输入增加略有上升，且在0-5 cm土层中的丰度显著高于5-10 cm土层；与之对应，革兰氏阳性菌与革兰氏阴性菌的丰度比值随氮输入增加而降低，且0-5 cm土层的该比值低于5-10 cm土层。总微生物丰度与总细菌丰度在0-5 cm泥炭土层中均显著高于5-10 cm土层。未来或需采用灵敏度更高、靶向性更强的技术手段，例如高通量焦磷酸测序、16S rRNA克隆文库分析、靶向rRNA的荧光原位杂交（FISH）或全基因组鸟枪测序，方能揭示泥炭沼泽微生物群落对氮负荷增加的响应特征。