互花米草盐沼土壤有机碳固定潜力对富营养化响应机制研究

More N and P will be discharged into marine and coastal ecosystems in the coming decades, while the assessment of the effect of eutrophication on soil organic carbon (SOC) pool sequestration potential of salt marsh will contribute to decrease greenhouse effect, to keep coastal wetlands ecosystem health and to reduce nitrogen (N) and phosphorus (P) in coastal region. S. alterniflora saltmarsh is selected as the object of the research to determine the biomass carbon allocation, carbon contribution fraction from S. alterniflora litter (above ground and below ground) decomposition to SOC, SOC pool sequestration potential (labile and recalcitrant fraction) responses to eutrophication. Eutrophication and contrast study area on S. alterniflora salt marsh will be designed and microcosm systems built for culturing collected salt marsh soils; while applying stable carbon isotope labeling and tracing, compound specific isotope GC-C-IRMS and 13C nuclear magnetic resonance (NMR) scanning analysis to study the impacts of eutrophication on S. alterniflora vegetation above / belowground carbon allocation and transformation procession in SOC, the coupling interaction processes between vegetation carbon pool input/output to soil and SOC pool sequestration potential, and to explain the functioning mechanism of the key processions. We aim at assessing the effective concentration of eutrophication (N, P) on S. alterniflora biomass carbon allocation strategy, SOC pool transformation and SOC sequestration potential; evaluating the SOC sequestration potential loss/accretion under effective concentration of eutrophication (N, P); determining the sink/source function of S. alterniflora salt marsh under the effective concentration of eutrophication (N,P). Finally sound proofs will be provided for predicting the tendency of SOC pool sequestration potential of S. alterniflora salt marsh under eutrophication condition, and supporting policy decision on managements of salt marsh utilization and protection.

未来几十年，全球沿海地区富营养化加剧，盐沼土壤有机碳固定潜力对富营养化响应机制研究对减缓温室效应、保护海滨湿地生态系统健康、削减沿海氮磷营养负荷意义重大。项目以互花米草盐沼为研究对象，拟测定富营养化环境下互花米草植物碳分配、互花米草地上/地下凋落物对土壤有机碳库贡献、盐沼土壤有机碳分解转化、土壤有机碳（活性/顽固性有机碳）固定潜力。依托长期盐沼定位站，设置富营养化样地，构建室内盐沼培养系统，应用稳定碳同位素标记示踪、单体分析、13C核磁共振波谱分析，分析富营养化对互花米草地上\地下生物量碳在土壤有机碳库之间的分配、转化过程的影响，研究不同富营养化水平下互花米草盐沼土壤有机碳固定潜力与植被生物碳库输入\输出耦合关系，阐明其作用机制。明确植物生物量碳分配策略、土壤有机碳转化、土壤有机碳固定潜力对富营养化效应水平，估算土壤有机碳固定潜力变化量，评估富营养化对盐沼碳汇功能的影响，提供管理决策依据。

全球沿海富营养化加剧的背景下，盐沼土壤有机碳固定潜力对富营养化响应机制研究对减缓温室效应和实现双碳战略意义重大。项目研究了富营养化对互花米草植被碳分配、转化的影响，富营养化对盐沼土壤有机碳固定潜力效应水平，揭示互花米草盐沼土壤有机碳固定潜力与植被碳库对富营养化的响应机制。研究结果显示，中低水平富营养化提高植被光合固碳潜力，增加植被碳库存量；提高土壤有机碳库稳定性，降低凋落物分解速率，降低微生物量碳库，促进土壤有机碳的转化重组，从而提高盐沼土壤有机碳库固碳潜力。（1）富营养化改变互花米草植被碳分配，低氮、低磷以及高氮磷复合添加提高植物地上生物量碳分配。低水平氮磷复合添加（10.53 kgN·ha-1·a-1+1.45 kgP·ha-1·a-1）处理下，互花米草植被年光合固碳量6765.64 mg 13C·m-2·a-1，提高215.8%。（2）夏冬季节氮磷添加提高土壤有机碳库存量，在春秋季节则降低其存量。夏季中等水平氮磷复合添加（52.75 kgN·ha-1·a-1+7.25 kgP·ha-1·a-1）处理下土壤有机碳提高188.6%。春季低氮磷复合添加下，土壤有机碳含量下降46.7%。其中土壤惰性有机碳含量增加，冬季低氮磷添加处理下提高480%。活性有机碳含量下降，春季低氮处理时下降94%。土壤烷基碳/烷氧碳比增加，惰性指数增加，土壤有机碳稳定性提高。土壤有机碳烷基碳相对含量在氮磷复合添加处理下提高可达7.55%。（3）优势细菌门是变形菌门和拟杆菌门，优势属是Muricauda属，主要承担有机质的分解作用。碳水化合物代谢相关微生物基因占比高，促进土壤有机碳转化重组。土壤微生物量碳库降低，微生物代谢活动改变。秋季高氮磷复合（263.76 kgN·ha-1·a-1配合36.27 kgP·ha-1·a-1）添加处理下，最高降幅85.0%。（4）凋落物分解速率降低。中等水平氮添加处理下，地上部分凋落物分解速率下降82.2%；凋落物分解50%所需时间增加1.18年，分解95%所需时间增加4.98年。（5）建议夏季输入中低水平氮磷复合营养盐，促进光合，植被固碳潜力增加215.8%；土壤有机碳含量最高增加188.6%。冬季输入低磷营养盐，土壤有机碳含量增加168.5%，惰性有机碳库含量增加480%。春秋季限制营养盐输入，维持土壤有机碳库的稳定。