Seasonal and Spatial Variations of Bulk Nitrogen Deposition and the Impacts on the Carbon Cycle in the Arid/Semiarid Grassland of Inner Mongolia, China.

Xianglan Li,Linghao Li,Wei Liu,Hua Xu,Fei Feng,Wenping Yuan,Wenfang Xu,Huiqiu Shi,Xiujun Wang,Longyu Hou,Wenju Liang

doi:10.1371/journal.pone.0144689

Xianglan Li, Linghao Li + Show 9 more

Open Access

https://doi.org/10.1371/journal.pone.0144689

Copy DOI

Abstract

Atmospheric nitrogen (N) deposition is an important component that affects the structure and function of different terrestrial ecosystem worldwide. However, much uncertainty still remains concerning the magnitude of N deposition on grassland ecosystem in China. To study the spatial and temporal patterns of bulk N deposition, the levels of N (NH4 +-N and NO3 --N) concentration in rainfall were measured at 12 sites across a 1200 km grassland transect in Inner Mongolia, China, and the respective N deposition rates were estimated. The inorganic N deposition rates ranged from 4.53 kg N ha-1 to 12.21 kg N ha-1 with a mean value of 8.07 kg N ha-1 during the entire growing season, decreasing steadily from the eastern to the western regions. Inorganic N deposition occurred mainly in July and August across meadow steppe, typical steppe, and desert steppe, which corresponded to the seasonal distribution of mean annual precipitation. A positive relationship was found between inorganic N deposition and mean annual precipitation (R2 = 0.54 ~ 0.72, P < 0.0001) across the grassland transect. Annual estimation of inorganic N deposition was 0.67 Pg yr-1 in Inner Mongolia, China based on the correlation between N deposition rates and precipitation. N deposition was an important factor controlling aboveground biomass and ecosystem respiration, but has no effect on root biomass and soil respiration. We must clarify that we used the bulk deposition samplers during the entire sampling process and estimated the dissolved NH4 +-N and NO3 --N deposition rates during the entire growing season. Long-term N deposition monitoring networks should be constructed to study the patterns of N deposition and its potential effect on grassland ecosystem, considering various N species, i.e., gaseous N, particle N, and wet N deposition.

Highlights

Nitrogen (N) deposition, an important component in the global N cycle, significantly impacts the structure and function of terrestrial ecosystems [1]
Lower inorganic N concentration was found in August in typical and desert steppe, while higher values occurred in June, July, September, and October
Seasonal patterns of inorganic N deposition rates (NH4+-N, NO3--N, and NH4+-N plus NO3--N) fluctuated dramatically during the grass growing season, with peaks occurred in July and August across different steppe types (Fig 3)

Summary

Introduction

Nitrogen (N) deposition, an important component in the global N cycle, significantly impacts the structure and function of terrestrial ecosystems [1]. Human activities in the past few decades, including fossil fuel combustion, fertilizer production, cultivation, and urban development, have led to substantial increases in atmospheric N deposition [2]. 60% of reactive N was removed from the atmosphere to the terrestrial and aquatic ecosystems via N deposition [3]. Excessive atmospheric N deposition has negative impacts on terrestrial ecosystems, such as a loss of biodiversity and soil acidification [9,10]. Excess N deposition has become an important public concern due to its close relationship with human health, biodiversity, and climate change

Objectives

Methods

Results

Discussion

Conclusion