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

泥炭覆盖了加拿大约12%的陆地表面，储存了约100GT的碳，每年排放5-10Tg CH4，是水体DOC(~10Tg/年)的重要来源。尽管我们已经在测量和模拟这些通量方面取得了重大进展，但很明显，进一步的进展取决于更好地识别N和P等营养物质在通过增加大气负荷和通过排水和加速矿化速率影响泥炭地碳循环中的作用。我们在Mer Bleue泥炭地进行的长期NPK施肥试验表明，灌木取代了苔藓，尽管吸收了N，但光合作用没有增加，呼吸增加导致C吸收减少或可能损失，这与施肥的预期相反。对叶片组织的分析表明，Mer Bleue是N/P共限制的，并以一种保守的方式对增加的施肥作出反应。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，导致泥炭中的C：N比相对较小，N的积累速率较大(0.5-1.0gm2/年)，但C：P随着泥炭的形成而增加-P从泥炭中提取出来(C：P1500：2000：1)并保持在0.5m以上，仅以15mgm2/年的速度积累。泥炭地磷的化学计量学与加拿大森林凋落物/土壤非常不同，但相关过程仍不清楚，这是我建议的一个重点。泥炭地积累的大量氮的来源尚不清楚，我们对Mer Bleue蓝藻固定氮气的估计与积累速度相比很小。我们的施肥实验提供了一个测试增加氮沉积(或磷添加)是否影响氮固定速率的机会。我们将测试化肥区和根际的苔藓和泥炭的固氮潜力；甲烷氧化菌已知具有固氮潜力，我们将通过实验室培养不同地下水位和CH4浓度的泥炭剖面来量化这一点。凋落物和泥炭分解速率是控制泥炭地生物地球化学和DOC、CO2和CH4来源的重要因素。我们正在利用蒙特利尔附近的泥炭地、西北部融化的永久冻土、北卡罗来纳州的Pocoins和新西兰的restiad沼泽来扩大我们对凋落物和泥炭分解速率以及N和P释放的控制的理解。

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.