10.1 Introduction
Atmospheric N deposition has increased more than ten-fold in the last 150 years and
will continue to increase by another two- to three-fold in the coming decades
globally (Galloway et al. 2004). The amount of N deposition to grassland in broad
areas of Europe, North America, and part of Asia over the past 50 years has exceeded
the critical load (Bobbink and Roelofs 1995). As a result, grassland ecosystem
exposure to elevated N deposition has been influenced with both enhancement and
inhibition of biogeochemical processes (Stevens et al. 2015). In the nutrient poor
ecosystems, atmospheric N deposition can be regarded as an important nutrient
source to plant growth (Wang et al. 2018). Otherwise, the excessive N input may
lead to eutrophication stage, which is associated with shifts in community structure,
increases or losses in diversity, changes in primary productivity, and enhanced
greenhouse gas emissions (Boutin et al. 2017; Lind et al. 2017; Anderson et al.
2018; Stevens et al. 2018).
In many parts of developed countries, it was expected to decrease reactive N
emission and deposition in the coming decades; however, the threat of N deposition
to grassland ecosystem is severe and is unlikely to be quickly reversed (Payne et al.
2017). Excess N deposition may affect plant through many pathways, such as direct
toxicity, soil acidification, nutrient imbalance, and interspecific competition (Stevens
et al. 2018). Nitrogen deposition is considered as the third greatest threat to terrestrial
biodiversity, after land use change and climate change. The loss of plant biodiversity
will also influence soil microbial and faunal biodiversity through trophic cascades
and impact ecosystem services (Erisman et al. 2013). In China, atmospheric N
deposition was projected to increase continuously in the coming decades (Liu
et al. 2013, 2017), and the impacts of N deposition on grassland ecosystem have
been increasingly recognized. In this chapter, we reviewed previous studies to
elucidate the effects of N deposition on grassland ecosystems in China synthetically.
10.2 Overview of N Enrichment Experiments in China’s
Grasslands
10.2.1 Grasslands in China
China’s grasslands are an important component of the grasslands on the earth, as it
constitutes an integral part of the Eurasian Steppe to the east end of the continent.
The total area of natural grasslands in China is about 400 million hectares, accounting for ~40% of the national land area (Kang et al. 2007; Ren et al. 2008). Grassland
ecosystems play important roles in servicing economic development and ecological
environment of China, e.g. providing livestock forage, modulating regional climate,
and fixing atmospheric carbon dioxide. Majority of the grassland ecosystems in
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X. Lü et al.
Atmospheric N deposition has increased more than ten-fold in the last 150 years and
will continue to increase by another two- to three-fold in the coming decades
globally (Galloway et al. 2004). The amount of N deposition to grassland in broad
areas of Europe, North America, and part of Asia over the past 50 years has exceeded
the critical load (Bobbink and Roelofs 1995). As a result, grassland ecosystem
exposure to elevated N deposition has been influenced with both enhancement and
inhibition of biogeochemical processes (Stevens et al. 2015). In the nutrient poor
ecosystems, atmospheric N deposition can be regarded as an important nutrient
source to plant growth (Wang et al. 2018). Otherwise, the excessive N input may
lead to eutrophication stage, which is associated with shifts in community structure,
increases or losses in diversity, changes in primary productivity, and enhanced
greenhouse gas emissions (Boutin et al. 2017; Lind et al. 2017; Anderson et al.
2018; Stevens et al. 2018).
In many parts of developed countries, it was expected to decrease reactive N
emission and deposition in the coming decades; however, the threat of N deposition
to grassland ecosystem is severe and is unlikely to be quickly reversed (Payne et al.
2017). Excess N deposition may affect plant through many pathways, such as direct
toxicity, soil acidification, nutrient imbalance, and interspecific competition (Stevens
et al. 2018). Nitrogen deposition is considered as the third greatest threat to terrestrial
biodiversity, after land use change and climate change. The loss of plant biodiversity
will also influence soil microbial and faunal biodiversity through trophic cascades
and impact ecosystem services (Erisman et al. 2013). In China, atmospheric N
deposition was projected to increase continuously in the coming decades (Liu
et al. 2013, 2017), and the impacts of N deposition on grassland ecosystem have
been increasingly recognized. In this chapter, we reviewed previous studies to
elucidate the effects of N deposition on grassland ecosystems in China synthetically.
10.2 Overview of N Enrichment Experiments in China’s
Grasslands
10.2.1 Grasslands in China
China’s grasslands are an important component of the grasslands on the earth, as it
constitutes an integral part of the Eurasian Steppe to the east end of the continent.
The total area of natural grasslands in China is about 400 million hectares, accounting for ~40% of the national land area (Kang et al. 2007; Ren et al. 2008). Grassland
ecosystems play important roles in servicing economic development and ecological
environment of China, e.g. providing livestock forage, modulating regional climate,
and fixing atmospheric carbon dioxide. Majority of the grassland ecosystems in
216
X. Lü et al.