11.5.2 Above- and Belowground Biomass Allocation
In most cases, the N addition can stimulate the growth of the shoot and root (Zhou
et al. 2010). For some species, the root biomass and length decreased under N
addition, such as Zygophyllum fabago and Plantago maritima (Zhou et al. 2011c).
Nitrogen addition did not affect the plant phonology and aboveground biomass on a
desert steppe but enhanced belowground biomass (Li 2014). In contrast, the shoot
and root ratios were found to increase with N supply (Zhou et al. 2011a) in the
Gurbantunggut Desert, while the sensitivity of shoot and root ratio was different
between different life-forms of plants (Zhou et al. 2010). These results suggest that
different life-forms behave differently under increasing N treatments although interspecific scaling relationships were nearly isometric (Zhou et al. 2014).
11.6 Impacts on Biodiversity Loss
11.6.1 Richness and Species Dominance
The community structure is often affected by N addition, such as richness, density,
and diversity indices. Nitrogen addition significantly affected the α-diversity index
and important value in the desert steppe (Bai et al. 2013). N addition reduced
species richness during a 4-year study period from a typical desert steppe (Su et al.
2010, 2013a). Similarly, reduction in richness of herbaceous plants was observed
under high N addition (60 and 240 kg N ha
À1 year
À1 ) in the Gurbantunggut Desert
(Zhou et al. 2018). Additionally, a higher level of N addition than 110 kg N ha
À1
year
À1 in a desert steppe, a clear reduction in diversity, was found (Tang et al.
2017). The dominant species and species composition in the community were
altered by N addition, with the vegetation height and coverage increased, and
vegetation light penetration decreased (Li et al. 2009). Compare to perennial
grasses, the forbs had more chances to lose under N addition in the desert steppe
(Su et al. 2012). In another study on the desert steppe, N addition reduced the
richness and Shannon-Wiener and Margalef indices of the plant community,
increased the ratio of perennial grasses such as Stipa breviflora and Cleistogenes
songorica, and decreased the proportion of semishrub Kochia prostrate (Li 2014).
For the seeds, the N addition did not affect the density of seeds, while the diversity
indices were unaffected by N addition (Li 2014). However, small effects of N on
community structure were also found. N additions increased the diversity indices
(Simpson and Shannon) and evenness, while no significant effects were found
compared with the controls (Zhao et al. 2013).
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
255
In most cases, the N addition can stimulate the growth of the shoot and root (Zhou
et al. 2010). For some species, the root biomass and length decreased under N
addition, such as Zygophyllum fabago and Plantago maritima (Zhou et al. 2011c).
Nitrogen addition did not affect the plant phonology and aboveground biomass on a
desert steppe but enhanced belowground biomass (Li 2014). In contrast, the shoot
and root ratios were found to increase with N supply (Zhou et al. 2011a) in the
Gurbantunggut Desert, while the sensitivity of shoot and root ratio was different
between different life-forms of plants (Zhou et al. 2010). These results suggest that
different life-forms behave differently under increasing N treatments although interspecific scaling relationships were nearly isometric (Zhou et al. 2014).
11.6 Impacts on Biodiversity Loss
11.6.1 Richness and Species Dominance
The community structure is often affected by N addition, such as richness, density,
and diversity indices. Nitrogen addition significantly affected the α-diversity index
and important value in the desert steppe (Bai et al. 2013). N addition reduced
species richness during a 4-year study period from a typical desert steppe (Su et al.
2010, 2013a). Similarly, reduction in richness of herbaceous plants was observed
under high N addition (60 and 240 kg N ha
À1 year
À1 ) in the Gurbantunggut Desert
(Zhou et al. 2018). Additionally, a higher level of N addition than 110 kg N ha
À1
year
À1 in a desert steppe, a clear reduction in diversity, was found (Tang et al.
2017). The dominant species and species composition in the community were
altered by N addition, with the vegetation height and coverage increased, and
vegetation light penetration decreased (Li et al. 2009). Compare to perennial
grasses, the forbs had more chances to lose under N addition in the desert steppe
(Su et al. 2012). In another study on the desert steppe, N addition reduced the
richness and Shannon-Wiener and Margalef indices of the plant community,
increased the ratio of perennial grasses such as Stipa breviflora and Cleistogenes
songorica, and decreased the proportion of semishrub Kochia prostrate (Li 2014).
For the seeds, the N addition did not affect the density of seeds, while the diversity
indices were unaffected by N addition (Li 2014). However, small effects of N on
community structure were also found. N additions increased the diversity indices
(Simpson and Shannon) and evenness, while no significant effects were found
compared with the controls (Zhao et al. 2013).
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
255