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的碳，排放5 - 10 Tg的CH4 /年，是水体DOC（约10 Tg/年）的重要来源。虽然我们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确定营养物质，如氮和磷，通过增加大气负荷以及通过排水和加速矿化速率，在影响泥炭地碳循环方面的作用。我们在Mer blue泥炭地进行的长期氮磷钾施肥试验表明，灌木取代了苔藓，尽管氮吸收没有增加光合作用，呼吸增加导致碳吸收减少或可能损失，与施肥预期相反。叶面组织分析表明，紫花苜蓿是氮磷共同限制的，对增加施肥反应保守。碳、氮和磷从植物通过衰老的叶片和凋落物到泥炭剖面的化学计量级降表明，大部分氮被保存下来，导致泥炭中碳氮比相对较低，氮积累速率较大（0.5 - 1.0 g m2/年），然而碳磷比随着泥炭的形成而增加——磷被从泥炭中提取出来（碳磷比1500 - 2000:1），并保持在0.5米以上，仅以15 mg m2/年的速度积累。泥炭地P的化学计量学与加拿大森林凋落物/土壤有很大不同，但负责的过程仍然未知，这是我建议的重点。泥炭地积累的大量氮的来源尚不清楚，我们估计蓝藻在Mer blue的固氮量与积累速率相比很小。我们的施肥试验提供了一个测试增加N沉降（或P添加）是否影响N2固定速率的机会。我们将从施肥区和根际测试苔藓和泥炭的固氮潜能；众所周知，甲烷氧化菌具有固定N2的潜能，我们将通过对地下水位和CH4浓度变化的泥炭剖面的实验室培养来量化这一点。凋落物速率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、西北地区融化的永久冻土、北卡罗来纳州的沼泽和新西兰的沼泽来扩大我们对控制凋落物和泥炭分解率以及氮和磷释放的理解。

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.