soil acidification with increased leaching of nitrate and base cations (e.g. Ca
2+ and
Mg
2+ ) and higher exposure to toxic metals (e.g. Al
3+ and Fe
3+ ) (Bowman et al.
2008). By synthesizing observed data of acid deposition, a recent assessment
indicates the occurrence of urban acid islands in southern China (Du et al. 2015).
In view of stricter control of SO 2 emissions, the contribution of N deposition to soil
acidification is growing in importance (Zhao et al. 2009), following similar trends to
those in Europe and the United States in the early 1980s (Galloway 1995).
By inducing significant changes in soil properties, such as increased N availability, soil acidification and nutrient imbalance, N deposition is expected to change the
structure and function of both microbial and plant communities. Experimental
results indicate that N deposition can alter biomass, stoichiometry and biodiversity
of microbial organisms (Treseder 2008). Key responses of plant physiology to N
deposition include changes in N assimilation and stoichiometry, biomass allocation
(e.g. root to shoot ratio) and root-mycorrhizal associations (Wallenda and Kottke
1998; Liu et al. 2013b; Chen et al. 2015). As a result of species-specific response to
increased N availability (e.g. competitive exclusion) and consequent stresses
(e.g. soil acidification and toxic ions), N deposition has been frequently reported
to alter species composition and even exert negative impacts on plant biodiversity
(Bobbink et al. 2010; Sala 2000), thus weakening the function of forest ecosystems.
In view that N limitation is widespread in terrestrial ecosystems (Elser et al. 2007),
N deposition is expected to stimulate biomass C accumulation via increasing net
primary production (De Vries et al. 2014; Du and De Vries 2018) and increase soil
C sequestration via increasing litterfall inputs (Lu et al. 2011c) and reducing decomposition of organic matter (Berg and Matzner 1997). The response of ecosystem C
sequestration to increased N deposition is likely constrained by multiple environmental factors. For instance, the imbalance of N and P deposition in China’s forests may
result in a shift towards P limitation especially in southern China (Du et al. 2016). In
that case, N-induced forest growth acceleration can be partially diminished with
aggravated phosphorus limitation (Li et al. 2016). Moreover, high levels of acid
deposition significantly contribute to soil acidification in southern China, potentially
reducing plant growth, especially in and near large cities (Lu et al. 2014; Du et al.
2015). Other factors such as co-limitation of water availability and ozone pollution
may also constrain the growth stimulation by N deposition (Tian et al. 2011).
China has diverse forest types, including a transect from boreal forest in Greater
Khingan Mountains in Northeast China to tropical forest in Hainan Island. These
forests cover more than one fifth of the national land area in China and provides
fundamental ecosystem services. In the context of high-level N deposition, there are
emerging experimental and modelling efforts to assess the impacts of N deposition
on various ecosystems in China (Liu et al. 2011; Tian et al. 2018). This chapter
compiled the results of manipulated N deposition experiments in China’s forests and
summarized the key findings, focusing on the effects of N deposition on soil
biogeochemical properties, microbial activities, plant biodiversity and C sequestration. We also discussed current knowledge gaps and future research prospects with
changing atmospheric N deposition in China.
9 Impacts of Nitrogen Deposition on Forest Ecosystems in China
187
2+ and
Mg
2+ ) and higher exposure to toxic metals (e.g. Al
3+ and Fe
3+ ) (Bowman et al.
2008). By synthesizing observed data of acid deposition, a recent assessment
indicates the occurrence of urban acid islands in southern China (Du et al. 2015).
In view of stricter control of SO 2 emissions, the contribution of N deposition to soil
acidification is growing in importance (Zhao et al. 2009), following similar trends to
those in Europe and the United States in the early 1980s (Galloway 1995).
By inducing significant changes in soil properties, such as increased N availability, soil acidification and nutrient imbalance, N deposition is expected to change the
structure and function of both microbial and plant communities. Experimental
results indicate that N deposition can alter biomass, stoichiometry and biodiversity
of microbial organisms (Treseder 2008). Key responses of plant physiology to N
deposition include changes in N assimilation and stoichiometry, biomass allocation
(e.g. root to shoot ratio) and root-mycorrhizal associations (Wallenda and Kottke
1998; Liu et al. 2013b; Chen et al. 2015). As a result of species-specific response to
increased N availability (e.g. competitive exclusion) and consequent stresses
(e.g. soil acidification and toxic ions), N deposition has been frequently reported
to alter species composition and even exert negative impacts on plant biodiversity
(Bobbink et al. 2010; Sala 2000), thus weakening the function of forest ecosystems.
In view that N limitation is widespread in terrestrial ecosystems (Elser et al. 2007),
N deposition is expected to stimulate biomass C accumulation via increasing net
primary production (De Vries et al. 2014; Du and De Vries 2018) and increase soil
C sequestration via increasing litterfall inputs (Lu et al. 2011c) and reducing decomposition of organic matter (Berg and Matzner 1997). The response of ecosystem C
sequestration to increased N deposition is likely constrained by multiple environmental factors. For instance, the imbalance of N and P deposition in China’s forests may
result in a shift towards P limitation especially in southern China (Du et al. 2016). In
that case, N-induced forest growth acceleration can be partially diminished with
aggravated phosphorus limitation (Li et al. 2016). Moreover, high levels of acid
deposition significantly contribute to soil acidification in southern China, potentially
reducing plant growth, especially in and near large cities (Lu et al. 2014; Du et al.
2015). Other factors such as co-limitation of water availability and ozone pollution
may also constrain the growth stimulation by N deposition (Tian et al. 2011).
China has diverse forest types, including a transect from boreal forest in Greater
Khingan Mountains in Northeast China to tropical forest in Hainan Island. These
forests cover more than one fifth of the national land area in China and provides
fundamental ecosystem services. In the context of high-level N deposition, there are
emerging experimental and modelling efforts to assess the impacts of N deposition
on various ecosystems in China (Liu et al. 2011; Tian et al. 2018). This chapter
compiled the results of manipulated N deposition experiments in China’s forests and
summarized the key findings, focusing on the effects of N deposition on soil
biogeochemical properties, microbial activities, plant biodiversity and C sequestration. We also discussed current knowledge gaps and future research prospects with
changing atmospheric N deposition in China.
9 Impacts of Nitrogen Deposition on Forest Ecosystems in China
187