Soil aggregate size influences the impact of inorganic nitrogen deposition on soil nitrification in an alpine meadow of the Qinghai–Tibet Plateau

PeerJ

article

Jingjing Li¹  Chao Yang²  Xiaoli Liu¹  Hanzhong Ji³  Xinqing Shao¹ 

[1] College of Grassland Science and Technology, China Agricultural University;Grassland Agri-Husbandry Research Center, College of Grassland Science, Qingdao Agricultural University;Institute of Haibei Tibetan Autonomous Prefecture Animal Husbandry and Veterinary Science;Technical Platform for Adaptive Management of Livestock System in Alpine Grassland;Key Laboratory of Restoration Ecology of Cold Area in Qinghai Province, Northwest Institute of Plateau Biology, Chinese Academy of Sciences

关键词: Soil aggregate;    Alpine meadow;    Soil nitrification;    Inorganic nitrogen deposition;    Soil porosity;   

DOI  :  10.7717/peerj.8230

学科分类：社会科学、人文和艺术（综合）

来源: Inra

【 摘 要 】

Background Ammonium (NH4+) and nitrate (NO3−) are two inorganic forms of nitrogen (N) that are deposited from the atmosphere into soil systems. As the substrate and product of soil nitrification, these two forms of inorganic nitrogen will affect or be affected by the soil net nitrification rate (Nr). Our knowledge regarding soil nitrification is mainly derived from studies with bulk soil. However, soil is composed of different aggregate fractions, which may have an important impact on Nr. Methods In 2017, we collected soil samples from an alpine meadow of the Qinghai–Tibet Plateau and separated them into four soil aggregates (2–4, 1–2, 0.25–1, and <0.25 mm) using the dry sieving method. The four soil aggregate sizes amended with the 2 N deposition forms (NH4+-N and NO3−-N) were then incubated at 25 °C for 28 days, and the soil aggregates for each treatment were collected on day 0, 7, 14, 21, and 28 to determine the NO3−-N concentration. The soil Nr and contribution of soil aggregates to the nitrification rate in the bulk soil were calculated. Results There were differences in the physicochemical properties of the soil aggregates. The addition of N and aggregate size had strong effects on soil Nr, which were significantly increased under high levels of NH4+ addition across all soil aggregates. The Nr during the 4 week incubation period differed among aggregate sizes. Nr in the 2–4 mm aggregates was higher than in the other aggregates, which was correlated with the maximum values of the soil porosity observed in the 2–4 mm aggregates. Furthermore, almost half of the soil was composed of aggregates of <0.25 mm, indicating that the <0.25 mm aggregates made a higher contribution to the nitrification rate in the bulk soil than the other aggregates, even though these aggregates had a lower nitrification ability. Overall, our study revealed that the soil nitrification rate was influenced by both the N addition and soil aggregates, and that the 2–4 mm aggregates had a dominant effect on the response of soil N transformation processes to future nitrogen deposition in the alpine meadow.

【 授权许可】

CC BY