热带亚热带土壤氮素反硝化研究进展

摘要

Denitrification has been extensively studied in soils from temperate zones in industrialized countries. However, few studies quantifying denitrification rates in soils from tropical and subtropical zones have been reported. Denitrification mechanisms in tropical/subtropical soils may be different from other soils, due to their unique soil characteristics. The identification of denitrification in the area is crucial to understand the role of denitrification in the global nitrogen (N) cycle in terrestrial ecosystems, and in the interaction between global environmental changes and ecosystem responses. We review the existing literature on microbially-mediated denitrification in tropical/subtropical soils, attempting to provide a better understanding about and new research directions for denitrification in these regions. Tropical and subtropical soils might be characterized by generally lower denitrification capacity than temperate soils, with greater variability due to land use and management practices varying temporally and spatially. Factors that influence soil water content and the nature and rate of carbon (C) and N turnover are the landscape and field scale controls of denitrification. High redox potential in the field, which is mainly attributed to soil oxide enrichment, may be at least one critical edaphic variable responsible for slow denitrification rates in the humid tropical and subtropical soils. However, soil pH is not responsible for these slow denitrification rates. Organic C mineralization is more important than total N content and C/N in determining denitrification capacity in humid subtropical soils. There is increasing evidence that the ecological consequence of denitrification in tropical and subtropical soils may be different from that of temperate zones. Contribution of denitrification in tropical and subtropical regions to the global climate warming should be considered comprehensively since it could affect other greenhouse gases, such as methane (CH4) and carbon dioxide (CO2), and N deposition. Tropical/subtropical soils have developed several N conservation strategies to prevent N losses via denitrification from the ecosystems. However, the mechanisms involved in the biogeochemical regulation of tropical and subtropical ecosystem responses to environmental changes are largely unknown. These works are important for accurately modeling denitrification and all other simultaneously operating N transformations.%热带亚热带独特的土壤性质可能使得反硝化机理有别于温带土壤。文章综述了热带亚热带地区土壤氮素生物反硝化的研究进展，试图更好地了解该地区土壤反硝化在全球氮（N）循环以及在全球环境变化和生态系统响应互作中的角色。热带亚热带土壤反硝化强度普遍较温带地区弱，且随着土地利用方式和耕作管理措施的不同而呈现较大的时空变异性。影响土壤水分状况和土壤碳（C）、N 转化特性和速率的因素即为区域和农田尺度上的反硝化影响因素。湿润型热带亚热带土壤由于含有丰富的氧化物而致使土壤氧化还原势较高，这也是导致该地区土壤反硝化势较温带地区较低的关键土壤因素之一。然而土壤pH值不是该地区土壤反硝化势较低的主要限制因素。有机C矿化过程较土壤全氮含量和土壤C/N比在决定湿润型亚热带土壤反硝化势方面更为重要。愈来愈多的证据表明热带亚热带土壤反硝化的生态环境效应不同于温带地区，热带亚热带地区土壤反硝化对全球变暖的贡献应综合考虑其对其它温室气体（如CH4，CO2）排放和氮沉降的影响。热带亚热带土壤生态系统具有一些防止土壤氮素反硝化损失的机制和保氮策略。然而，热带亚热带生态系统对全球变化的响应机制及其生物地球化学调控机制仍然不清楚，这些研究对于反硝化和其它同时发生的氮转化过程模型的精确构建至关重要。