氮磷输入对长白山泥炭地土壤有机碳影响的酶学机理研究

Soil enzymes play critical roles in regulating soil biogeochemical cycles and organic carbon stocks. The substantially increased input of reactive nitrogen to peatland ecosystems due to anthropogenic activities has greatly reduced their ability to sequester carbon, and consequently threatened the global carbon stocks. Through stoichiometric interactions, phosphorus can mediate the impact of nitrogen deposition on the structure and functioning of peatland ecosystems. Nevertheless, there remains a dearth of knowledge of how the interaction between nitrogen and phosphorus, particularly in the long-term, will affect the activity of key soil enzymes and the subsequent organic matter decomposition and soil organic carbon. In this study, we conduct a short-term and a long-term nitrogen and phosphorus fertilization experiment in Hani Peatland in the Changbai Mountains to better understand the direct effect of nitrogen, phosphorus and their interactions, as well as the indirect effect of shift in species composition in response to long-term fertilization, on soil enzymatic activities and their further influences on organic matter decomposition and soil organic carbon. Our results will advance the understanding of how enzymatic activities vary in the context of human-induced nitrogen-phosphorus imbalance, which would be invaluable in predicting the fate of peatland carbon stocks in response to anthropogenic disturbance. In addition, we attempt to provide some scientific basis for considering the potential of phosphorus addition as an effective approach to ameliorate the negative impact of nitrogen deposition on peatland carbon stocks.

土壤酶是调控泥炭地物质循环和土壤有机碳库的核心。人类活动排放的大量活性氮通过影响泥炭地土壤酶活性而削弱其固碳能力，对全球碳库造成威胁。磷可通过和氮之间的交互作用修饰氮输入对泥炭地结构和功能的影响。然而，氮磷交互如何通过改变土壤关键酶活性而影响泥炭地有机质分解和土壤有机碳的机理尚不清楚，尤其缺乏长期野外研究。本项目拟选取长白山哈泥泥炭地为研究地，依托该台站已连续运行十年的长期氮磷施肥实验，结合短期氮磷输入模拟实验，探讨氮磷输入及其交互作用对泥炭地土壤关键酶活性的直接影响，阐明因持续的氮磷输入引发的植物群落结构改变对土壤酶活性及有机质分解的间接影响，通过综合分析揭示人类活动加剧的氮磷输入失衡对典型北方泥炭地土壤关键酶特性的调控机制。本研究有助于深入理解和预测泥炭地物质循环和碳库功能的变化，可为减缓氮沉降对泥炭地碳库功能的威胁提供科学思路和理论依据。

土壤酶是调控泥炭地物质循环的核心。人类活动排放的活性氮可能通过影响泥炭地土壤关键酶活性而威胁其固碳能力，对全球碳库造成威胁。磷可通过和氮之间的交互作用修饰氮输入对泥炭地关键生物地球化学过程的影响。然而，氮磷交互作用通过改变土壤关键酶活性进而影响泥炭地有机碳库的机理尚不清楚。本项目以长白山哈泥泥炭地为研究对象，对比分析短期（一年）和长期（十年）氮磷输入及其交互作用对泥炭地土壤关键酶活性的直接和间接影响，探讨由酚氧化酶通过改变酚类化合物含量从而影响关键水解酶活性以调控泥炭地有机碳库的潜在机制（即“酶闩效应”）。研究结果表明，短期氮磷输入虽然会抑制酚氧化酶活性，但并未显著改变酚类化合物的浓度和三种水解酶的活性，即未对“酶闩”过程产生显著影响。然而，长期氮磷输入对土壤酶特性的影响存在显著的交互作用：虽然氮添加会显著提高酚氧化酶、β-葡萄糖苷酶和N-乙酰-β-D-葡糖氨糖苷酶的活性而抑制磷酸酶的活性，但添加磷后，氮的输入对酶活性的影响则未表现出一致性的规律，“酶闩”机制在长期氮磷输入后被极大削弱。植物生长和凋落物分解实验的结果表明，由于长期氮磷输入引起地上植被群落结构的改变，使得输入泥炭中的凋落物的化学特性（主要是多酚和木质素）发生变化，这种由于富含多酚的灌木凋落物输入的增强从而抵消施氮对水解酶活性促进效应的现象进一步说明了，氮磷输入间接造成的凋落物初始组成的改变对调控土壤酶活性起到至关重要的作用。综上所述，相对于氮而言，长期的磷输入在调控土壤酶活性方面发挥更重要的作用，其通过改变地上植物群落组成、促进富含多酚的凋落物输入而间接调控“酶闩效应”，最终通过氮磷的交互作用使北方泥炭地的有机碳库保持相对稳定。本研究结果进一步佐证了磷限制在泥炭地中绝非偶见，对于深入理解和预测泥炭地物质循环和碳库功能的变化具有重要意义，可为减缓氮沉降对泥炭地碳库功能的威胁提供科学思路和理论依据。