Abstract:

In this study, soil degradation and nitrogen limitation in alpine meadows were addressed, and the effects of organic acids in plant root exudates on soil carbon and nitrogen mineralization were clarified. In an incubation experiment, the response of common organic acids in Kobresia myosuroides (Villars) Foiri, Gueldenstaedtia diversifolia Maxim, and Anemone rivularis Buch-Ham. were investigated for soil carbon and nitrogen mineralization in southeastern Tibet. Acetic, lactic, and fumaric acids significantly increased the content of soil available nitrogen and phosphorus but had no effect on soil total nitrogen and phosphorus. The rate of soil carbon mineralization gradually decreased with increasing cultivation time under the influence of the different organic acids. Lactic acid and 10 mg·L⁻¹ acetic acid first promoted and then inhibited the soil carbon mineralization rate over time, whereas fumaric acid generally inhibited soil carbon mineralization. In addition, except for 10 mg·L⁻¹ lactic acid, which significantly reduced cumulative soil carbon mineralization, the other concentrations of organic acids had no significant effect on cumulative soil carbon mineralization. Correlation analysis showed a significant negative correlation between acetic acid and cumulative soil carbon mineralization (r=−0.796*). The different organic acids had no significant effect on the net ammonification rate of the soil, whereas medium-to-high concentrations of acetic acid inhibited net nitrification and net nitrogen mineralization. The addition of lactic and fumaric acids had no significant effect on the net nitrification rate or the net nitrogen mineralization rate. Correlation analysis showed that acetic acid was significantly negatively correlated with the net nitrogen mineralization rate (r=−0.785*). Soil carbon mineralization was positively correlated with pH and total nitrogen, whereas the correlation between soil nitrogen mineralization and soil environmental factors differed significantly, depending on the presence of organic acids. In summary, acetic acid is the main organic acid affecting soil carbon and nitrogen mineralization, and the organic acids in root exudates, combined with soil environmental factors, regulate soil carbon and nitrogen mineralization. This study provides a scientific basis for determining carbon and nitrogen sequestration and the development of soil management strategies in ecologically fragile areas.

Key words: alpine meadow, root exudates, organic acids, organic carbon mineralization, organic nitrogen mineralization, soil environmental factors

摘要：

针对高寒草甸土壤退化及植被氮限制的问题，为明确高寒草甸植物根系分泌物有机酸对土壤碳氮矿化特征的影响，以藏东南典型的优势植物嵩草、米口袋和草玉梅共有有机酸为研究目标，采取室内培养法分析不同有机酸添加对土壤碳、氮矿化过程的影响。结果显示：乙酸、乳酸和富马酸等3种有机酸均可显著提高土壤速效氮和速效磷的含量，而对土壤总氮和总磷含量没影响。不同有机酸作用下，土壤碳矿化速率随培养时间的增加，均表现为逐渐下降而最后趋于平缓的变化趋势，乳酸和10 mg·L⁻¹的乙酸对土壤碳矿化速率的影响随培养时间增加呈现由促进转为抑制，富马酸总体上抑制土壤碳矿化速率，另外，除了15 mg·L⁻¹的乳酸明显抑制了土壤累积碳矿化量，其余浓度的有机酸对土壤累积碳矿化量影响不显著，但相关性分析显示乙酸与土壤累积碳矿化量显著负相关（r=−0.796^*）。不同有机酸添加对土壤净氨化速率无显著影响，中高浓度乙酸对土壤净硝化速率和净氮矿化速率有抑制作用，乳酸和富马酸添加对土壤净硝化速率和净氮矿化速率均无显著影响，相关性分析显示乙酸与土壤净氮矿化速率显著负相关（r=−0.785^*）。不同有机酸作用下，土壤碳矿化过程与土壤环境因子pH呈正相关，而土壤氮矿化过程与土壤环境因子相关性差异显著。综上，乙酸是影响土壤碳氮矿化的主要有机酸，根系分泌物有机酸与土壤环境因子共同作用调控土壤碳氮矿化过程。研究结果对于生态脆弱区土壤的增碳固氮效应及科学管理具有重要指导意义。

关键词: 高寒草甸, 根系分泌物, 有机酸, 有机碳矿化, 有机氮矿化, 土壤环境因子