摘要
氮沉降和放牧是影响草地碳循环过程的重要环境因子,但很少有研究探讨这些因子交互作用对生态系统呼吸的影响。在西藏高原高寒草甸地区开展了外源氮素添加与刈割模拟放牧实验,测定了其对植物生物量分配、土壤微生物碳氮和生态系统呼吸的影响。结果表明:氮素添加显著促进生态系统呼吸,而模拟放牧对其无显著影响,且降低了氮素添加的刺激作用。氮素添加通过提高微生物氮含量和土壤微生物代谢活性,促进植物地上生产,从而增加生态系统的碳排放;而模拟放牧降低了微生物碳含量,且降低了氮素添加的作用,促进根系的补偿性生长,降低了氮素添加对生态系统碳排放的刺激作用。这表明,放牧压力的存在会抑制氮沉降对高寒草甸生态系统碳排放的促进作用,同时外源氮输入也会缓解放牧压力对高寒草甸生态系统生产的负面影响。
Both nitrogen （N） deposition and livestock grazing are important factors influencing species composition, soil nutrient availability, plant productivity and allocation pattern in grassland ecosystems. However, little is known about their interactive effects on alpine ecosystem carbon cycling process such as ecosystem respiration. In 2010 we started a long-term factorial experiment in an alpine meadow in Damxung County in northern Tibet, China, to examine the interactive effects of N addition and grazing on plant biomass allocation, soil microbial carbon and N and ecosystem CO2 fluxes. The experiment had two N treatments crossed with two grazing treatments, resulting in a total of four treatments coded as CK （control, no N addition and no simulated grazing）, N （with N addition but no grazing）, G （no N addition but with grazing） and NG （with both N addition and grazing）. For N addition, we added 40 kg N hm-2 a-1, and to simulate livestock grazing, we selectively clipped palatable grasses and sedges. We analyzed the available data collected during the growing seasons in 2011 and 2012. Compared with CK, N significantly increased ecosystem respiration by 82% and 72% and soil respiration by 53% and 65% in August 2011 and 2012, respectively, but G had no significant effect on ecosystem respiration or soil respiration. Moreover, ecosystem respiration or soil respiration did not differ significantly between CK and NG, indicating that simulated grazing partially counteracted the stimulating effect of N addition on ecosystem CO2 fluxes. Compared to CK, N addition stimulated plant aboveground growth by 82% and 84% in August 2011 and 2012, respectively, NG promoted plant root compensatory growth and increased plant allocation to belowground by 127% and 116% in August 2011 and 2012, respectively, and G had no effect on belowground biomass. G inhibited soil microbial carbon and did not affect soil microbial N, while N addition increased soil microbial N and soil microbial metabolic activity. Furthermore, com
出处
《生态学报》
CAS
CSCD
北大核心
2013年第19期6191-6201,共11页
Acta Ecologica Sinica
基金
国家重点基础研究发展计划(2010CB833502)
国家重点基础研究发展计划(2010CB951704)资助
中国科学院战略性先导科技专项(XDA05060700)
关键词
氮素添加
模拟放牧
生态系统呼吸
生物量分配
微生物碳氮
高寒草甸
nitrogen enrichment
simulated grazing
ecosystem respiration
plant biomass allocation
soil microbial carbon and nitrogen
alpine meadow
