Department of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, China ; Key Laboratory for Urban Habitat Environmental Science and Technology, Peking University Shenzhen Graduate School, Shenzhen, China.
Department of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, China.
PLoS One. 2014 Feb 3;9(2):e87975. doi: 10.1371/journal.pone.0087975. eCollection 2014.
Nitrogen (N) deposition and its ecological effects on forest ecosystems have received global attention. Plantations play an important role in mitigating climate change through assimilating atmospheric CO2. However, the mechanisms by which increasing N additions affect net ecosystem production (NEP) of plantations remain poorly understood. A field experiment was initialized in May 2009, which incorporated additions of four rates of N (control (no N addition), low-N (5 g N m⁻² yr⁻¹), medium-N (10 g N m⁻² yr⁻¹), and high-N (15 g N m⁻² yr⁻¹) at the Saihanba Forestry Center, Hebei Province, northern China, a locality that contains the largest area of plantations in China. Net primary production (NPP), soil respiration, and its autotrophic and heterotrophic components were measured. Plant tissue carbon (C) and N concentrations (including foliage, litter, and fine roots), microbial biomass, microbial community composition, extracellular enzyme activities, and soil pH were also measured. N addition significantly increased NPP, which was associated with increased litter N concentrations. Autotrophic respiration (AR) increased but heterotrophic respiration (HR) decreased in the high N compared with the medium N plots, although the HR in high and medium N plots did not significantly differ from that in the control. The increased AR may derive from mycorrhizal respiration and rhizospheric microbial respiration, not live root respiration, because fine root biomass and N concentrations showed no significant differences. Although the HR was significantly suppressed in the high-N plots, soil microbial biomass, composition, or activity of extracellular enzymes were not significantly changed. Reduced pH with fertilization also could not explain the pattern of HR. The reduction of HR may be related to altered microbial C use efficiency. NEP was significantly enhanced by N addition, from 149 to 426.6 g C m⁻² yr⁻¹. Short-term N addition may significantly enhance the role of plantations as an important C sink.
氮（N）沉降及其对森林生态系统的生态影响受到了全球关注。通过同化大气中的 CO2，人工林在缓解气候变化方面发挥着重要作用。然而，增加 N 添加对人工林净生态系统生产力（NEP）的影响机制仍知之甚少。2009 年 5 月，在中国河北省塞罕坝林业中心启动了一项田间实验，该实验在该地区添加了四种不同的 N 浓度（对照（不添加 N）、低 N（5 g N m⁻² yr⁻¹）、中 N（10 g N m⁻² yr⁻¹）和高 N（15 g N m⁻² yr⁻¹）），该地区是中国最大的人工林种植区。测量了净初级生产力（NPP）、土壤呼吸及其自养和异养成分。还测量了植物组织碳（C）和 N 浓度（包括叶片、凋落物和细根）、微生物生物量、微生物群落组成、胞外酶活性和土壤 pH。与中 N 相比，高 N 处理显著增加了 NPP，这与凋落物 N 浓度的增加有关。与中 N 相比，高 N 处理增加了自养呼吸（AR），但降低了异养呼吸（HR），尽管高 N 和中 N 处理之间的 HR 没有显著差异。增加的 AR 可能来自菌根呼吸和根际微生物呼吸，而不是活根呼吸，因为细根生物量和 N 浓度没有显著差异。虽然 HR 在高 N 处理中显著受到抑制，但土壤微生物生物量、组成或胞外酶活性没有显著变化。施肥导致的 pH 降低也不能解释 HR 的模式。HR 的减少可能与微生物 C 利用效率的改变有关。NEP 随着 N 添加而显著增加，从 149 增加到 426.6 g C m⁻² yr⁻¹。短期 N 添加可能会显著增强人工林作为重要 C 汇的作用。
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