Biogeochemistry and ecology of peatlands: response to global change and linking the C, N and P cycles

泥炭地覆盖了加拿大约12%的陆地表面，储存了约100 Gt的C，每年排放5 - 10 Tg的CH 4，是水体DOC（约10 Tg/年）的重要来源。虽然我们已经取得了显着的进展，在测量和模拟这些通量，很明显，进一步的进展取决于更好地识别营养物质的作用，如N和P，在影响碳循环在泥炭地，通过增加大气负荷，通过排水和加速矿化速率。我们在Mer Bleue泥炭地进行的长期NPK施肥实验表明，苔藓灌木替代，尽管吸收了N，但光合作用没有增加，呼吸作用增加导致C吸收减少或可能损失，与施肥的预期相反。叶组织分析表明，蓝色海洋是N/P共同限制，并以保守的方式增加施肥。从植物通过衰老的叶片和凋落物到泥炭剖面的C、N和P的化学计量级联表明，大部分N被保存，导致泥炭中相对窄的C：N比和大的N积累速率（0.5 - 1.0 g m2/yr），然而C：P随着泥炭的形成而增加- P从泥炭中被抽出（C：P 1500至2000：1）并保持在上部0.5 m，积累仅为15 mg m2/yr。泥炭地化学计量的P是非常不同的加拿大森林凋落物/土壤，但负责的过程仍然未知，这是我的建议的重点。大量的氮积累在泥炭地的来源是未知的，我们估计N2固定蓝藻在Mer Bleue是小的积累率相比。我们的施肥实验提供了一个机会，以测试是否增加氮沉降（或磷添加）影响固氮率。我们将测试苔藓和泥炭从施肥地块和根际的固氮潜力;甲烷氧化菌是已知的具有固氮潜力，我们将量化这一实验室培养的泥炭剖面不同的水位位置和甲烷浓度。凋落物和泥炭分解速率是泥炭地生态地球化学的重要控制因素，也是DOC、CO2和CH 4的重要来源。我们正在使用蒙特利尔附近的泥炭地，西北地区的永久冻土融化，北卡罗来纳州的pocosins和新西兰的restiad沼泽，以扩大我们对控制凋落物和泥炭分解速率以及N和P释放的理解。

Peatlands cover ~12% of the land surface of Canada, store ~100 Gt of C, emit 5 - 10 Tg CH4 /yr and are significant sources of DOC (~10 Tg/yr) to water bodies. Although we have made significant progress in measuring and modeling these fluxes, it is clear that further advances depend on a better identification of the role of nutrients, such as N and P, in influencing C cycling in peatlands, through increased atmospheric loading and through drainage and accelerated rates of mineralization. Our long-term NPK fertilization experiment at the Mer Bleue peatland has shown shrub replacement of mosses, no increase in photosynthesis despite N uptake, and increased respiration resulting in reduced C uptake or possibly loss, contrary to the expectation of fertilization. Analysis of foliar tissues shows that the Mer Bleue is N/P co-limited and responds in a conservative manner to increased fertilization. The stoichiometric cascade of C, N and P from plants through senescent leaves and litter to the peat profile shows that much of the N is conserved, resulting in a relatively narrow C:N ratio in peat and large rates of N accumulation (0.5 – 1.0 g m2/yr), yet the C:P increases as peat forms - P is drawn out of the peat (C:P 1500 to 2000:1) and maintained in the upper 0.5 m, accumulating at only 15 mg m2/yr. The peatland stoichiometry of P is very different from Canadian forest litter/soils, but the processes responsible remain unknown and this is a focus of my proposal. The sources of the large amount of N accumulated in peatlands are unknown and our estimates of N2 fixation by cyanobacteria at Mer Bleue are small compared to the accumulation rate. Our fertilization experiment provides an opportunity to test whether increasing N deposition (or P addition) affects N2 fixation rates. We shall test mosses and peat from the fertilization plots and rhizospheres for N2 fixation potential; methanotrophs are known to have N2 fixation potentials and we shall quantify this by laboratory incubations of peat profiles varying in water table position and CH4 concentration. Rates of litter and peat decomposition are important controls on peatland biogeochemistry and sources of DOC, CO2 and CH4. We are using peatland sites near Montreal, thawing permafrost in the NWT, pocosins in North Carolina and restiad bogs in New Zealand to broaden our understanding on the controls of litter and peat decomposition rates and release of N and P.