addition of biocide (to prevent microbial transformations between Nr species) are
recommended to prevent sample deterioration due to bacterial or chemical action.
3.2.3 Biomonitoring of N Deposition
Apart from combining measurements of dry and wet deposition from the methods
above, N deposition also can be quantified by using bioindicators, such as epiphytic
lichen and mosses (Hicks et al. 2000; Solga et al. 2005). For example, mosses, which
have no root system, absorb N exclusively through deposition from the atmosphere
and, as a result, are very sensitive to environmental pollution. N levels in moss are
used to indicate the amount and spatial variation of N deposition in areas (Liu et al.
2008; Pitcairn et al. 2006). Various species were found to be first-rate bioindicators
of indigenous N deposition, including Pleurozium schreberi and Scleropodium
purum (Xiao and Liu 2011), Sphagnum from ombrotrophic mires (Pitcairn et al.
1995), Haplocladium microphyllum (Liu et al. 2007; Xiao et al. 2010) and also other
varieties of species (Pearson et al. 2000; Qu et al. 2016). Based on tissue N content in
Haplocladium microphyllum and its relationship with N deposition, Xiao et al.
(2010) demonstrated that overall N deposition varied from 13.8 to 47.7 kg N
ha
À1 year
À1 at five sites in the Yangtze River Basin. Similarly, Qu et al. (2016)
combined moss monitoring and kriging interpolation to estimate overall 28 kg N
ha
À1 year
À1 deposition across Guiyang City.
Along with mosses, vascular plants have also been employed for surveying total
N deposition. In an initial effort to measure N flux in vascular plants, Sommer (1988)
grew ryegrass (Lolium perenne) using artificial irrigation, which is known as the
integrated total nitrogen input (ITNI) method. Sommer and Jensen (1991) enhanced
the technique in their next experiments by applying
15 N as a tracer in the fertilizer,
which was then further improved by Mehlert et al. (1995). Using a similar technique
with cotton grass (Eriophorum angustifolium) and ryegrass, Hurkuck et al. (2014)
achieved similar properties for N deposition to moorland vegetation, and He et al.
(2007, 2010) found overall atmospheric N input for a maize-wheat rotation in
northern China to be 80–90 and close to 100 kg N ha
À1 year
À1 when the monitoring
plant was ryegrass. In a survey based in China, Liu et al. (2013) reported that
non-fertilized soils can be used as bioindicators of enriched N deposition based on
leaf N content and crop N uptake.
The methods used to extrapolate values on the field scale are significant because
15 N isotope dilution and pot experiments are used (He et al. 2010). Most extrapolations use the vessel surface area (Böhme et al. 2002, 2003), together with measurements made with maize and sunflower, which need a lot of space per plant. Even
though several plants were tried to surmount this problem, and means determined to
calculate overall atmospheric N input annually, the method may result in overestimations for deposition if the data are not extrapolated for field conditions.
Recently, the TONIS (Total Nitrogen Input Biomonitoring System), which combines biomonitoring with plants with collector methods, was developed to offer a
48
X. Liu et al.
recommended to prevent sample deterioration due to bacterial or chemical action.
3.2.3 Biomonitoring of N Deposition
Apart from combining measurements of dry and wet deposition from the methods
above, N deposition also can be quantified by using bioindicators, such as epiphytic
lichen and mosses (Hicks et al. 2000; Solga et al. 2005). For example, mosses, which
have no root system, absorb N exclusively through deposition from the atmosphere
and, as a result, are very sensitive to environmental pollution. N levels in moss are
used to indicate the amount and spatial variation of N deposition in areas (Liu et al.
2008; Pitcairn et al. 2006). Various species were found to be first-rate bioindicators
of indigenous N deposition, including Pleurozium schreberi and Scleropodium
purum (Xiao and Liu 2011), Sphagnum from ombrotrophic mires (Pitcairn et al.
1995), Haplocladium microphyllum (Liu et al. 2007; Xiao et al. 2010) and also other
varieties of species (Pearson et al. 2000; Qu et al. 2016). Based on tissue N content in
Haplocladium microphyllum and its relationship with N deposition, Xiao et al.
(2010) demonstrated that overall N deposition varied from 13.8 to 47.7 kg N
ha
À1 year
À1 at five sites in the Yangtze River Basin. Similarly, Qu et al. (2016)
combined moss monitoring and kriging interpolation to estimate overall 28 kg N
ha
À1 year
À1 deposition across Guiyang City.
Along with mosses, vascular plants have also been employed for surveying total
N deposition. In an initial effort to measure N flux in vascular plants, Sommer (1988)
grew ryegrass (Lolium perenne) using artificial irrigation, which is known as the
integrated total nitrogen input (ITNI) method. Sommer and Jensen (1991) enhanced
the technique in their next experiments by applying
15 N as a tracer in the fertilizer,
which was then further improved by Mehlert et al. (1995). Using a similar technique
with cotton grass (Eriophorum angustifolium) and ryegrass, Hurkuck et al. (2014)
achieved similar properties for N deposition to moorland vegetation, and He et al.
(2007, 2010) found overall atmospheric N input for a maize-wheat rotation in
northern China to be 80–90 and close to 100 kg N ha
À1 year
À1 when the monitoring
plant was ryegrass. In a survey based in China, Liu et al. (2013) reported that
non-fertilized soils can be used as bioindicators of enriched N deposition based on
leaf N content and crop N uptake.
The methods used to extrapolate values on the field scale are significant because
15 N isotope dilution and pot experiments are used (He et al. 2010). Most extrapolations use the vessel surface area (Böhme et al. 2002, 2003), together with measurements made with maize and sunflower, which need a lot of space per plant. Even
though several plants were tried to surmount this problem, and means determined to
calculate overall atmospheric N input annually, the method may result in overestimations for deposition if the data are not extrapolated for field conditions.
Recently, the TONIS (Total Nitrogen Input Biomonitoring System), which combines biomonitoring with plants with collector methods, was developed to offer a
48
X. Liu et al.