Environmental Studies Department, Mount Holyoke College, 50 College Street, South Hadley, MA, 01075, USA.
Glob Chang Biol. 2013 Dec;19(12):3729-39. doi: 10.1111/gcb.12328. Epub 2013 Oct 11.
To study vegetation feedbacks of nutrient addition on carbon sequestration capacity, we investigated vegetation and ecosystem CO2 exchange at Mer Bleue Bog, Canada in plots that had been fertilized with nitrogen (N) or with N plus phosphorus (P) and potassium (K) for 7-12 years. Gross photosynthesis, ecosystem respiration, and net CO2 exchange were measured weekly during May-September 2011 using climate-controlled chambers. A substrate-induced respiration technique was used to determine the functional ability of the microbial community. The highest N and NPK additions were associated with 40% less net CO2 uptake than the control. In the NPK additions, a diminished C sink potential was due to a 20-30% increase in ecosystem respiration, while gross photosynthesis rates did not change as greater vascular plant biomass compensated for the decrease in Sphagnum mosses. In the highest N-only treatment, small reductions in gross photosynthesis and no change in ecosystem respiration led to the reduced C sink. Substrate-induced microbial respiration was significantly higher in all levels of NPK additions compared with control. The temperature sensitivity of respiration in the plots was lower with increasing cumulative N load, suggesting more labile sources of respired CO2 . The weaker C sink potential could be explained by changes in nutrient availability, higher woody : foliar ratio, moss loss, and enhanced decomposition. Stronger responses to NPK fertilization than to N-only fertilization for both shrub biomass production and decomposition suggest that the bog ecosystem is N-P/K colimited rather than N-limited. Negative effects of further N-only deposition were indicated by delayed spring CO2 uptake. In contrast to forests, increased wood formation and surface litter accumulation in bogs seem to reduce the C sink potential owing to the loss of peat-forming Sphagnum.
为了研究养分添加对碳封存能力的植被反馈作用，我们在加拿大 Mer Bleue 沼泽的施肥样地（氮[N]或氮磷钾[NPK]添加 7-12 年）中调查了植被和生态系统的 CO2 交换。使用气候控制室，于 2011 年 5 月至 9 月期间每周测量总光合作用、生态系统呼吸和净 CO2 交换。采用基质诱导呼吸技术来确定微生物群落的功能能力。与对照相比，最高的 N 和 NPK 添加导致净 CO2 吸收减少了 40%。在 NPK 添加中，由于生态系统呼吸增加了 20-30%，因此 C 汇潜力降低，而总光合作用速率没有变化，因为较大的维管植物生物量补偿了 Sphagnum 苔藓的减少。在仅 N 最高处理中，总光合作用略有减少，而生态系统呼吸没有变化，导致 C 汇减少。与对照相比，所有 NPK 添加水平下的基质诱导微生物呼吸都显著更高。随着累积 N 负荷的增加，样地中呼吸的温度敏感性降低，表明呼吸 CO2 有更多的易变来源。较弱的 C 汇潜力可以通过养分可用性的变化、较高的木本：叶比值、苔藓损失和分解增强来解释。灌木生物量生产和分解对 NPK 施肥的响应强于对仅 N 施肥的响应，表明沼泽生态系统是 N-P/K 共限制而不是 N 限制。由于形成泥炭的 Sphagnum 的损失，进一步的仅 N 沉积的负面影响表现为春季 CO2 吸收的延迟。与森林相反，沼泽中木质形成和表面凋落物积累的增加似乎由于丧失了形成泥炭的 Sphagnum 而降低了 C 汇潜力。
