Environmental Pollution重要综述 | 氮沉降对森林生态系统土壤氮素转化的影响

文献信息：

Cheng Yi, Wang Jing, Chang Scott X, Cai Zucong, Müller Christoph, Zhang Jinbo*. Nitrogen deposition affects both net and gross soil nitrogen transformations in forest ecosystems: A review. Environmental Pollution, 2019, 244: 608-616. DOI: 10.1016/j.envpol.2018.10.054

摘  要：氮（N）沉降迅速增加，并在全球范围内影响森林生态系统的进程和功能。了解森林土壤中响应氮沉降的特定氮素转化过程如总氮素转化，对于了解全球氮沉降与森林土壤氮素有效性或损失之间的联系具有重要意义。本文综述了氮素矿化、硝化作用和固氮作用的控制因素，特别是与氮沉降有关的因素，讨论了净氮素转化研究的局限性，并整合了有关森林生态系统中氮沉降对总氮素转化影响的文献。研究发现，超过97%的发表论文通过测定净矿化速率和硝化速率的方式评估了氮沉降（包括模拟氮沉降的氮添加实验）对土壤氮循环的影响，并发现氮沉降显著提高了净矿化速率（24.9%）和硝化速率（153.9%）。然而，关于净氮素转化的研究并不能从机理上理解氮沉降对氮循环的影响。到目前为止，很少有研究（总发表论文不到20篇）直接量化了氮沉降对总氮素转化速率的影响，这限制了我们对土壤氮循环对氮沉降响应的理解。对于自养硝化、异养硝化、异化硝酸盐还原成铵、氮矿化、氮固持等特定氮素转化过程对氮沉降的响应研究较少。未来的研究需要用更全面系统的方法来研究氮沉降对总氮素转化速率、氮素损失和固持的影响以及它们的微生物驱动机制，以便更好地理解氮素转化过程，并了解森林和其他生态系统之间的响应差异。

Fig. 1. A schematic diagram illustrating the response of soil C and N, pH and microbial properties to N deposition based on the meta-analysis by Lu et al. (2011); Carey et al., 2016; Zhou et al., 2017; Chen et al., 2018. ↑ represents an increase in response to N deposition; ↓ represents a decrease in response to N deposition. ? Represents a response that is not clear. Net M is net N mineralization rate; Net N is net nitrification rate; Gross M is gross N mineralization rate; Gross N is gross nitrification rate; I is gross immobilization rate. SOC is soil organic C; TN is total N; C/N is soil organic C to total N ratio; MBC is microbial biomass C; MBN is microbial biomass N; C/Nm is microbial biomass C to microbial biomass N ratio; F/B is the fungi to bacteria ratio; AOB is ammonia-oxidizing bacteria; AOA is ammonia-oxidizing archaea. GA is glycine aminopeptidase.

Table 1. Summary of published estimates of N deposition effects (% increase or decrease) on soil microbial activity related indices.

B, bacterial; F, fungal; F/B: fungal/bacterial; Rm, microbial respiration; AMF, arbuscular mycorrhizal fungi; Abu, abundance; Fun, function; Act: actinomycetes abundance; N-AE, nitrogen acquisition enzymes; G+/G-, gram-positive/gram-negative bacteria; Shan, Shannon index; No, no effect or;/, not determined.

Table 2. Summary of directions of N deposition effects on soil gross N transformation rates in forest ecosystems.

Org and Min represent organic and mineral layer, respectively; “+“, “-“, “0“and “/“denote positive, negative, no significant effect and not determined, respectively; GM, gross mineralization rates; GN, gross nitrification rates; GIA, gross NH₄⁺ immobilization rates; GIN, gross NO₃⁻ immobilization rates.

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