土地利用变化对土壤有机碳的影响研究进展

土壤有机碳是陆地碳库的重要组成部分,也是当前全球碳循环和全球变化研究的热点。土地利用/覆被变化及土地管理变化通过影响土壤有机碳的储量和分布,进而影响温室气体排放和陆地生态系统的碳通量。研究土地利用变化影响下的土壤有机碳储量及其动态变化规律,有助于加深理解全球气候变化与土地利用变化之间的关系。在阅读国内外有关文献的基础上,分别从土地利用及其管理方式变化的角度,概括了土地利用变化对土壤有机碳的影响过程与机理;针对当前研究的两大类方法,即实验方法和模型方法,分类详细介绍了它们各自的特点以及存在的一些问题。在此基础上,提出今后土地利用变化对土壤有机碳影响研究的发展趋势。

Effects of land use change on soil organic carbon:a review

As the largest carbon pool of terrestrial ecosystems and is the main container and carrier of carbon sequestration in the terrestrial ecosystem, soil plays an important role in the global carbon cycling. Soil organic carbon (SOC) covering more than half of the carbon storage in the soil carbon pool is an important contributor to the variation of atmospheric CO₂ concentration. To measure and evaluate the quantity and dynamic change of SOC is essential for understanding soil carbon sequestration processes, and thus the global carbon balance. Land use/cover change affects not only the concentration and distribution of SOC directly, but also the characteristics of SOC indirectly by influencing the factors of SOC formation and transformation, and further influence greenhouse gas emissions and carbon flux in the terrestrial ecosystem. Literature results reveal that conversion of farmland to forest or grassland usually leads to the net SOC sequestration, while reclamation of grassland or forestland generally decreases the SOC concentration. Conversion of forestland to grassland is most likely to decrease the net SOC sequestration rate. Land management activities affect SOC balance due to fertilization, irrigation, direct additions of C in organic amendments, and the amount of carbon left after biomass removal activities, such as crop harvest, timber harvest, fire, or grazing. Decomposition largely controls C outputs, as highly influenced by changes in moisture and temperature regimes, and the level of soil disturbance resulting from the management activities. In most major agricultural, silvicultural and pastoral systems, recommended or good management practices such as fertilisation, irrigation, conservation tillage (minimum and no-tillage), and retention of plant residue, commonly led to the SOC increasing. On the contrary, traditional management measures such as conventional tillage, cleaning for natural vegetation, whole tree harvest practices, severe fires, long-term heavy grazing, and pest outbreaks, decrease C inputs and thus SOC storage in most cases. Land use changes at present or in the past are critical in determining the distribution and size of global or regional terrestrial carbon sources and sinks. Accurate estimations of land use/cover composition and changes in the terrestrial ecosystem are increasingly important not only for estimating the carbon balance but also for mitigating climate changes and guaranteeing food security. Studies on SOC storage and its dynamic change caused by land use change are important to deepen the understanding of relationship between land use and global climate change. By literature review, this paper summarizes major research progresses on the effects of land use change on SOC at home and abroad, explaining the process and mechanism of SOC change induced by changes of land use and land management mainly in farmland, forest and grassland ecosystems. Further, it summarized characteristics, applications and existing problems of two principal research methods, i.e., experimental methods and model approaches. Finally, research trends on the effects of land use change on SOC are overviewed.