由于人类活动的干扰,通过沉降和施肥形式进入陆地生态系统的氮素持续增加,中国已经成为继欧洲和北美之后的第三大氮沉降区,同时也是最大的化肥消费国。氮输入与陆地生态系统生物地球化学循环的一系列过程都相互联系,碳循环及其格局也受到氮输入的影响。土壤有机碳库在全球碳循环中具有重要作用,氮输入能否或在多大程度上对土壤碳库产生影响已经成为全球变化和氮沉降研究中不可回避的问题。东北地区是世界三大黑土带之一,土壤碳的变化不仅对于土壤肥力维持具有重要意义,而且对区域碳收支具有重要影响。利用生态系统过程模型CEVSA2模型,基于我国能源消费、施氮数据和降水数据生成了一套中国大气氮沉降的时空网格数据,结合大气CO_2浓度、气候、土地覆被、土壤类型和质地的时空数据,模拟评估了19612010年氮输入对中国东北地区土壤碳蓄积的影响。结果表明:(1)19612010年东北地区的平均氮沉降速率为1.00 gN m~(-2) a~(-1),年增长率为0.047 gN m~(-2) a~(-1)。东北农田总氮输入速率达到5.78 gN m~(-2) a~(-1),从20世纪80年代开始显著增加。(2)氮输入促进了东北地区土壤碳的蓄积,东北陆地生态系统的土壤碳密度平均增加了135 gC/m~2,50a氮输入共增加土壤碳蓄积0.16 PgC。(3)氮输入引起的东北地区土壤碳蓄积量的变化呈现出东高西低、南高北低的空间格局,辽河平原、松嫩平原和三江平原的土壤碳密度增加量超过了300 gC/m~2。(4)不同植被类型下的土壤碳密度对氮输入的响应存在较大差异,农田土壤碳密度平均增加了230 gC/m~2,森林、灌丛和草地则分别增加了76、169 gC/m~2和89 gC/m~2。氮输入的空间差异和不同植被类型对氮输入响应的差异共同决定了东北地区土壤碳增加量的空间格局。通过本研究阐明了氮输入对东北农田土壤碳蓄积的影响,从而为农田生态系统的固碳减排和农田土壤碳氮管理提供了决策依据。
英文摘要:
Anthropogenic activities have altered the global nitrogen (N) cycle,leading to increased N input into the ecosystem through N deposition and N fertilizer. China consumes the highest amount of fertilizer globally,and it has become the third largest N deposition region in the world. N input is an important factor in the terrestrial carbon (C) sink, and N input is implicated in a series of biogeochemical cycles that then influence the C cycle and its spatial pattern. The soil C pool plays an important role in the global C cycle ; therefore,the question of whether and to what extent N input affects the soil C pool must be addressed in relation to global change and N deposition. Northeast China has the third-largest black belt in the world and it is an important commodity grain base of China. Cropland is the most prominent manner of land use in the Northeast, and the change in its soil C pool is an essential factor in explaining the regional C budget and maintaining soil fertility. Using a process-based carbon-water-nitrogen coupling model, CEVSA2, we simulated the spatial patterns of N deposition in China between 1961 and 2010. With the N deposition and environment data collected, we also used CEVSA2 to explore the effect of enhanced N input on soil C storage in Northeast China in this period. The results show that the N deposition in Northeast China (1.00 gN m~(-2) a~(-1)) is higher than the average for the whole country,and increases annually by 0.047 gN m~(-2) a~(-1) . From the 1980,the N input began to increase significantly. The model simulations indicated that enhanced N deposition has resulted in a net increase of soil C density by 135 gC/m~2 in Northeast, and the total soil C storage increased by 0.16 PgC over the past 50 years. The soil C sequestration induced by N input decreased from east to west and from south to north. In the Songliao Plain and the Sanjiang Plain, the soil C sequestration induced by N input was >300 gC/m~2. The change in soil C density induced by N input varies significantly among the major biome types in the Northeast. Model simulations indicated that the increase in soil C density in cropland was 230 gC/m~2. However, those in the forest, shrubland, and grassland were 76 gC/m~2,169 gC/m~2 and 89 gC/m~2,respectively,and the spatial heterogeneity of .N input as well as the different responses of vegetation types to it determined the spatial pattern of the increase in soil C storage. Elucidation of the effect of N input on soil C storage will provide a scientific foundation for C fixation as well as C and N management in cropland.