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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。  相似文献
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A 40-day incubation experiment was carried out in order to evaluate the microbial activities and heavy metal availability in long-term contaminated arable and grassland soils after addition of EDTA (ethylenediaminetetraacetic acid) or EDDS ([S,S]-ethylenediaminedisuccinic acid). Soils with similar contamination of heavy metal from the vicinity of a lead smelter were used in the experiment. The soil microbial carbon (Cmic) decreased significantly after addition of EDTA in the arable soil (CM1); lesser effects were observed in the grassland soil (CM2). Addition of EDDS caused a decrease of Cmic during the first 10 days of incubation. In the later phases of the experiment, Cmic increased, and even exceeded the amounts found in the control soils. Respiratory activities and metabolic quotients (qCO2) increased after the addition of the chelating agents into the soils. Higher respiratory activities and qCO2 were observed in the EDTA-treated soils. The readily available heavy metal fractions were extracted with NH4NO3 solution. Readily mobilizable heavy metal fractions of Cd, Pb, Zn, and (in part) Cu increased during the first 3-10 days of incubation in the presence of EDTA. The addition of EDDS particularly increased concentrations of available Cu. Significant correlations between NH4NO3-extractable metals, soil respiratory activities, and qCO2 were found in both soil treatments with EDTA and EDDS. This indicates that enhanced metal mobility seriously affects the microbial processes in experimental soils. In addition, the relationships between NH4NO3-extractable Cd, Cu, and the microbial biomass were found in the CM1 soil amended with EDTA.  相似文献
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