plant physiological processes, and community processes, their findings propose a
novel mechanism for N-induced species loss in the grasslands.
Consistent with results from global herbaceous ecosystems, studies from Chinese
grasslands get robust evidence for the negative impacts of N deposition on biodiversity. It has been unclear whether plant diversity will recover when nitrogen
deposition is reduced. In a semiarid temperate steppe, Hao et al. (2018) examined
the cumulative and recoverable impacts of nitrogen addition on species diversity.
They carried out N addition experiments since 2005 with six different addition rates.
After 2008, the treatment with the highest addition rate (480 kg N ha
À1 year
À1 ) was
ceased. They found that N addition reduced plant species richness, but its effects
depended on the rate of N addition. The low N addition (30 and 60 kg N ha
À1 year
À1 )
had no effect on species richness, whereas the high N addition rates (120 and
240 kg N ha
À1 year
À1 ) significantly reduced species richness by 22% and 41%.
Species richness showed a rapid recovery after the cessation of N addition since
2008. After cessation for 3 years, they found no significant difference in species
richness between the cessation treatment and the control. During the 11 years of this
experiment, they found no significant decline of species richness in the treatments
with low rate of N addition, indicating that the critical load of N deposition for
species loss in this ecosystem would be between 60 and 120 kg N ha
À1 year
À1 .
Furthermore, the reduction of species loss following N enrichment is partially
reversible. In the third year after addition cessation, the species richness was 75%
of that in the control plots and remained 50–70% level in the later years (Fig. 10.7).
Their results are consistent with that from the Park Grass Experiment at Rothamsted
Research, UK, which also showed that biodiversity could recover after the cessation
of nutrient addition (Storkey et al. 2015). In contrast, results from the N addition
experiment in Cedar Creek in the USA showed limited recovery of plant species
richness 20 years after the cessation of N addition (Isbell et al. 2013). Furthermore,
Hao et al. (2018) found other evidence for the ecosystem recovery after cessation of
N addition, including the decline of foliar N concentrations and soil inorganic N
concentrations. Together, their results indicate the impacts of N addition on ecosystem properties are potentially reversible.
10.5.2 Biodiversity of Belowground Community
Soil supports huge amounts of organisms, with most of them being unknown.
Belowground community contributes to many fundamental ecological processes
and functioning, including decomposition, nutrient cycling, disease suppression,
and regulation of primary productivity (Wall 2012). The increasing N deposition
would have great influences on belowground community through both direct and
indirect pathways. Importantly, belowground microbial and fauna communities are
more sensitive to N-induced soil acidification than plant communities (Chen et al.
2013). Moreover, changes in belowground communities following N enrichment
might have consequences on the alteration of plant communities.
234
X. Lü et al.
novel mechanism for N-induced species loss in the grasslands.
Consistent with results from global herbaceous ecosystems, studies from Chinese
grasslands get robust evidence for the negative impacts of N deposition on biodiversity. It has been unclear whether plant diversity will recover when nitrogen
deposition is reduced. In a semiarid temperate steppe, Hao et al. (2018) examined
the cumulative and recoverable impacts of nitrogen addition on species diversity.
They carried out N addition experiments since 2005 with six different addition rates.
After 2008, the treatment with the highest addition rate (480 kg N ha
À1 year
À1 ) was
ceased. They found that N addition reduced plant species richness, but its effects
depended on the rate of N addition. The low N addition (30 and 60 kg N ha
À1 year
À1 )
had no effect on species richness, whereas the high N addition rates (120 and
240 kg N ha
À1 year
À1 ) significantly reduced species richness by 22% and 41%.
Species richness showed a rapid recovery after the cessation of N addition since
2008. After cessation for 3 years, they found no significant difference in species
richness between the cessation treatment and the control. During the 11 years of this
experiment, they found no significant decline of species richness in the treatments
with low rate of N addition, indicating that the critical load of N deposition for
species loss in this ecosystem would be between 60 and 120 kg N ha
À1 year
À1 .
Furthermore, the reduction of species loss following N enrichment is partially
reversible. In the third year after addition cessation, the species richness was 75%
of that in the control plots and remained 50–70% level in the later years (Fig. 10.7).
Their results are consistent with that from the Park Grass Experiment at Rothamsted
Research, UK, which also showed that biodiversity could recover after the cessation
of nutrient addition (Storkey et al. 2015). In contrast, results from the N addition
experiment in Cedar Creek in the USA showed limited recovery of plant species
richness 20 years after the cessation of N addition (Isbell et al. 2013). Furthermore,
Hao et al. (2018) found other evidence for the ecosystem recovery after cessation of
N addition, including the decline of foliar N concentrations and soil inorganic N
concentrations. Together, their results indicate the impacts of N addition on ecosystem properties are potentially reversible.
10.5.2 Biodiversity of Belowground Community
Soil supports huge amounts of organisms, with most of them being unknown.
Belowground community contributes to many fundamental ecological processes
and functioning, including decomposition, nutrient cycling, disease suppression,
and regulation of primary productivity (Wall 2012). The increasing N deposition
would have great influences on belowground community through both direct and
indirect pathways. Importantly, belowground microbial and fauna communities are
more sensitive to N-induced soil acidification than plant communities (Chen et al.
2013). Moreover, changes in belowground communities following N enrichment
might have consequences on the alteration of plant communities.
234
X. Lü et al.