The Effect of Nitrogen Deposition on Soil Enzyme A

Journal of Landscape Research 2018,10(4): 93-98
The Effect of N itrogen Deposition on Soil Enzym e A ctivity in th e F o res t-Grassland Landscape Boundary of Tibet
HAN Yanying1, LIU Yunlong1, YE Yanhui1,2*, DA Buqiong1, GAO Y i1, ZHAO Yalei1, LI Linw ei1, LIU Shuanghao3
(1. Tibet Agriculture & Animal Husbandry University, Linzhi, Tibet 860000, China; 2. China Agricultural University, Beijing 100193, China; 3. Hunan University of Chinese Medicine, Changsha, Hunan 410208, China)
A bstract The simulated nitrogen deposition [control check (CBQ, 0 kg'hm2/a; low nitrogen (LN),
25 kg-hm2/a; medium nitrogen (MN), 50 kg-hm2/^ high nitrogen (HN), 150 kg*hm2/a] was performed
from July 2014 to August 2015 in the fotest-gtassland boundary in Zhuqudeng Village, Bujiu Township,
Iinzhi City, Tibet Autonomous Regioii to analyze the activity of enzymes (invertase, catalase, ufease,
amylase, cellukse, polyphenol oxidase, and p-glucosidase) in soil layers of 0-20 cm and 20-40 cm and
explore die effect of different levels of nitrogen deposition on enzyme activity different layers of soiL
The results showed tiiat' 0different levels of simulated nitrogen deposition had rematkable effects on
sucrase, amylase, cellukse, polyphenol oxidase and p-gjucosidase in the soil layer of 0-20 cm (p < 0.05) and
unrematkable effects on catalase and urease (p > 0.05); in the soil layer of 2CM0 cm, the response made
by suctase, catalase, urease, amylase, cellulase, polyphenol oxidase and p-glucosidase to nitrogen deposition
reached a significant l evel < 0.05). (2) In the soil layer of 0-20 cm, the activity of ufease and polyphenol
oxidase reduced under LN treatment and enhanced under HN treatment, and the activity of invertase,
catalase, amylase, cellulose, and p-glucosidase was inhibited by nitrogen deposition. ® In the soil layer of
2CM0 cm, the activity of polyphenol oxidase and p-glucosidase reduced under under LN treatment and
enhanced under HN treatment, and the activity of invertase, catalase, urease, amylase, and cellulase was
inhibited by nitrogen deposition. @ With the deepening of the boundary soil layer (from 0-20 cm to
20-40 cm), urease and p-^ucosidase made different r esponses to the different l evels of nitrogen deposition,
while invertase, catakse, amylase, cellulose, and polyphenol oxidase showed the same response to nitrogen
deposition.
Keywords Nitrogen deposition, Iinzhi, Boundary soil, Soil enzyme activity, Forest-grassland
D O I 10.16785/jissn 1943-989x.2018.4.021
Nitrogen deposition has attracted much attention in recent decades. Since the mid^O* century, influenced by human activities such as the burning of fossil fuels, the production and use of chemical nitrogen fertilizers，and the booming of animal husbandry, active nitrogen compounds released into the atmosphere sharply increased, and atmospheric nitrogen deposition also shot up[1], leading to the accumulation of nitrides in the atmosphere and settlement in terrestrial and aquatic ecosystems[2]. The subtropical region in cential and southern China has been predicted to be one of the regions with the most severe atmospheric nitrogen deposition in the next few decades[S4l However that region has now become the regions with themostseverenittogendepositioninChW51. With the increase of nitrogen deposition, the natural environment, plants and animals, and human activities have been increasingly affected. Therefore, it is particukdy important to explore the effects of nitrogen deposition.
Landscape boundaries that are widespread
at the ecosystem and landscape scales are an
important component of spatially heterogeneous
regions^. At landscape boundaries, environmental
stress is the most prone to enrichment, the
exchange of matter and energy flow are the
most frequent, and biological regulation is the
most active, so that landscape boundaries have
become the focus of attention of ecologistsR.
Because of the hi^i environmental heterogeneity,
biodiversity, and sensitivity to environmental
changes within landscape boundaries, changes
in landscape boundaries can serve as an early
warning of environmental changes. Therefore,
landscape boundaries have important theoretical
significance In global change research. Due to
their special geography and climate environment,
landscape boundaries have become typical
ecologically fragile zones and zones that
are sensitive to climate change, which have
advanced response to climate change and human
disturbance. For these reasons, they are ideal
places to study global change[8_14].
Soil enzymes，which participate in various
biological and chemical reactions in soil as
catalysts，are important substances for driving the
normal operation of soil systems11^1. The rate of
material cycle conversion is directly constrained
by the level of soil enzyme activity. Whether
or not the ecosystem functions are normally
performed can be greatly affected by the enzyme
activity. The level of biological activity i s reflected
in the soil en2yme activity level in the soil[16]. Soil
enzymes can regarded as indicators for evaluating
the development of soil systems because they
can sensitively perceive a series of changes
caused by external environmental factors. At
present, studies on nitrogen deposition in
China mainly focus on the southern subtropical
evergreen broad-leaved forests[17], Chinese fir
plantation[18], temperate broad-leaved korean
pine forest[19], forests in West China[20'21], and
temperate grasslands[22 23]. Nitrogen deposition
will probably change the status of available
Received: J une 28,2018 Accepted: J uly 23,2018
Sponsored by N ational Natural Science Fund of China (31360119,31460112); 2015 Pilot Project of Excellent A griculture and Forestry T alents Culdvadon P rogram Reform.
* Corresponding a uthor. E-mail* yeyanhiii3554@
93
The Effect of Nitrogen Deposition on Soil Enzyme Activity in the Forest-Grassland Landscape Boundary of Tibet
nitrogen in terrestrial ecosystems, thus affecting the cycle and accumulation of carbon and nitrogen in ecosystems[24]. Studies of nitrogen deposition have been widely carried out abroad. However, research on nitrogen deposition has just started in China, and nitrogen deposition research in Tibet is in the immature stage.
With an average elevation of more than 4.000 m, the Tibet Autonomous Region has unique natural ecological and geographical conditions. It is not only a “source of rivers” and an “ecological source” in South Asia and Southeast Askj but a “starter^，and a “regulatory region” of climate in China and the Eastern Hemisphere[25]. Thus it is appropriate for studying the effect of nitrogen deposition on soil enzyme activity. In this study, a one-year short­term nitrogen deposition simulation experiment was conducted at the forest-grassland landscape boundary in linzhi, Tibet, to study the response of soil enzyme activity to increased nltxogen deposition, so as to provide a reference for the study on the effect of atmospheric nitrogen deposition on soil enzyme activity in the forest- grassland landscape boundary.
1M aterials and M ethods
1.1 Study area
linzhi (29°21,-30°15, N, 93027'-95017' E) is located in the southeast of the Nyenchen Tanglha Mountains in the Qinghai-Tibet Plateau, in which the Brahmaputra and Niyang River meet It borders on Motuo County to the east, Milin County to the south, Gongbo’gyamda County to the west and northwest, and Bomi County to the north and northeast The southern part of Linzhi is the extension of Gangdisi Moimtains, while its northern part is in the offset of the Nyenchen Tanglha Mountains. Measuring 177.2 km long and 98.6 km wide, linzhi has an average elevation of 3,000 m. It has a temperate humid monsoon climate. Annually, its average temperature is 8.5 ^ . The coldest month is January, with the average temperature of -2^; the hottest month is July, with the average temperature of 20 . The fix>st-free period is about 175 days or so. Annually, the total hours of sunshine are 2,022 h. The annual precipitation is 654 mm. The raining mainly occurs from May to September, and the total number of the raining accounts for about 90% of the annual precipitation. The study area is an alpine shrub meadow composed of Quercus aquifolioides, Berbeds julianae, Rosa multi£ora, Cotoneaster microphyllus, Prunella vulgaris, Festuca rubra, Potentilla. chinensis, Phntago depressa,and Heteropappus hispidus.1.2 Research methods
1.2.1Simulated nitrogen deposition. In 2014,
twelve 5 m X 5 m sample plots were set in the
forest-grassland boundary of Zhuquden Village,
Bujiu Township, linzhi Qty, with 10-m intervals
reserved for each plot to prevent mutual
interference. A total of four kinds of treatments
were set, namely control check (CK, 0 kg*hm2/a),
low nitrogen (LN, 25 kg ■hm2/a), medium
nitrogen (MN, 50 kg-hm2/a) and high nitrogen
(HN, 150 kg-hm2/a), which repeated three times
respectively. In July 2014, a simulated nitrogen
deposition test was conducted. At the beginning
of each month, NH4NOs was dissolved in
water and sprayed uniformly on the plots, and
the same amoirnt of water was sprayed on the
control plots.
1.2.2Sample collection and determination. In
August 2015, the soil was collected and sampled
using earth boring auger. Random sampling was
performed along the diagonal line in the sample
plots, and the litter layer was removed. Five
drilled soils were randomly collected and mixed
to form a sample. The sample -\ras brought back
to laboratory for analysis. Fiae roots and gravel
were quickly picked after picking soil out, and
the sample was air-dried, so as to measure soil
enzyme activity.
1.23 Determination of enzyme activity. (1) Soil
invertase activity. It was determined by the 3,
5-dimtrosalicylic add colorimetric method, and
expressed as milligrams of glucose produced by
per gram of soil after 24 hr.
(2) Soil cellulase activity. It was determined
by the 3, 5-dinitrosalicyllc acid colorimetric
method, and expressed as milligrams of glucose
produced by per gram of soil after 72 hr.
(3) Soil amylase activity. It was determined
by the 3, 5-dinitrosalicyllc acid colorimetric
method, and expressed as milligrams of glucose
produced by per gram of soil after 24 hr.
(4) Soil (3-glucosidase activity. It was
determined by colorimetric method with
p-nitrophenyl-p-D-glucoside (PNPG) as a
substrate for enzymatic hydiolysis, and expressed
as the content of p-nitrophenol consumed by
per gram of soil after 1 hr.
(5) Soil polyphenol oxidase activity. It
was determined by the 3,5-dlnitrosalicylic
acid colorimetric method, and expressed as
milligrams of purple pyrogallol produced by per
gram of soil after 2 hr.
(6) Soil catalase activity. It was determined
by potassium permanganate titration, and
expressed as milliliters of 0.02 mol/1 KM n04
solution consumed by per gram of soiL
(7) Soil urease activity. It was determined
by indole-phenol blue colorimetric method, and
expressed as the mass of NH3-N in per gram of
soil after 24 hr.
1.2.4 Data analysis. Microsoft Excel 2010
was used for data analysis and mapping, and
SPSS 20.0 was used to made one-way analysis
of variance (ANOVA) of various indicators
(establishing the significance level as 0.05).
2 Results and analysis
2.1 Effect of simulated nitrogen depo­
sition on invertase
For soil in the soil layer of 0—20 cm,
nitrogen deposition had a significant effect
on invertase activity (p < 0.05) (Fig.l). In all
treatments, there was no significant difference
between LN and MN (p > 0.05), and there
was a significant difference between the other
treatments (p < 0.05). After one year of
simulated nitrogen deposition, invertase activity
showed a significantly suppressed response with
the deepening of nitrogen deposition (CK >
MN > LN> HN). For soil in the soil layer of
20-40 cm, invertase activity was significantly
affected by nitrogen deposition {p < 0.05), and
the difference between treatments reached a
significant level (p < 0.05). In general, invertase
activity was significantly inhibited by nitrogen
deposition under three different levels of
treatments (CK > MN > LN > HN).
In the same treatment, with the deepening
of the soil layer，invertase activity was signi­
ficantly reduced. With the deepening of
simulated nitrogen deposition, invertase activity
showed the same variation trend in different soil
2.2 Effect of simulated nitrogen de­
position on catalase
Catalase activity in different soil layers
varied with different levels of nitrogen
deposition. For soil in the soil layer of 0-20 cm,
nitrogen deposition had no significant effect on
catalase activity > 0.05) (Fig.2). There was no
significant difference between treatments except
for between CK and MN (p < 0.05). After the
one-year simulated nitrogen deposition, catalase
activity showed no significant inhibitory response
to nitrogen deposition (CK > HN > LN >
MN). For soil in the soil layer of 20^1-0 cm,
catalase activity was significantly affected
by nitrogen deposition (p < 0.05), and the
difference between treatments also reached a
significant level (p < 0.05). Broadly speaking,
catalase activity showed a significant downtrend
as the nitrogen deposition deepened (CK > LN
>M N >HN).
In the same treatment of different soil
94
Journal of Landscape Research
layers, catalase activity from CK treatment to HN treatment had been weakened with the deepening of the soil layer. In different soil layers, simulated nitrogen deposition inhibited catalase activity which was significant in the soil layer of 0-20 cm but insignificant in the soil layer of 2CM0 an.
2.3 Effect of simulated nitrogen de­position on urease
For soil in the soil layer of 0-20 cm, nitrogen deposition had no significant effect on urease activity (p >0.05), and there was no significant difference between treatments (p > 0-05) (Fig.3). Specifically, after one year of simulated nitrogen deposition, urease activity was insignificandy inhibited under LN treatment, and insignificandy enhanced under HN treatment (MN > HN > CK > LN). For soil in the soil layer of 20-40 cm, urease activity si^iificantiy affected by nitrogen deposition (p < 0.05). The difference between HN treatment and the other three treatments was significant, and the dififetence between CK, LN, and MN treatments did not reach a significant level (p > 0.0^. In short, utease activity showed an inhibitory response from CK to HN treatment (CK > MN > LN > HN).
In the same tceatment, with the deepening of the soil layer, urease activity changed differently. In different soil layers, with tie deepening of simulated nitrogen deposition, utease activity showed the same change trend, but the overall responses of xireasc activity i n two soil l ayers to nitrogen deposition w ere different
2.4 Effect of simulated nitrogen de­
position on amylase
For soil in the soil layer of 0-20 cm, nit­
rogen deposition had a significant effect on
amylase activity (p < 0,05) (Fig.4). There was a
sigiificant difference between CK treatment and
the othet three treatments (p < 0-05), but no
significant difference between IN, MN，and HN
treatments (p > 0.05). Specifically, after one year
of simulated nitrogen deposition, atri^ase activity
was significantly inhibited (CK > LN > HN >
MN). For soil in the soil kyer of 2(M0 cm, the
effect of nitrogen deposition on amylase activity
reached a significant level (p <0,0^, and there
were significant differences between treatments
(p < 0.05). General^ speaking, amylase activity
was inhibited by nitrogen deposition (CK > HN
>M N>LN).
In the same treatment, with the deepening
of the soilkyo; amjdase activity significantly
weakened. In different soil layers, with the
deepening of the simulated nitrogen deposition,
amylase activity had a tendency to change
2.5 Effect of simulated nitrogen de­
position on cellulase
For soil in the soil layer of 0-20 cm,
nitrogen deposition has a significant effect on
cellulase activity (p < 0.05), and there was a
significant difference between CK treatment
and the other three treatments (jp < 0.05) (Fig.5).
After one year of simulated nitrogen deposition^
cellulase activity was significandy inhibited (CK
> MN > LN > HN). For soil in the soil layer of
2CM0 cm, tbe effect of nitrogen deposition on
cellulase activity also reached a significant level
(p < 0.05). The difference between L N treatment
and HN treatment did not reach a significant
level >0.05), but the difference between
other treatments was significant (p < 0.05). In
summary, cellulase activity made a suppressed
response under nittpgen deposition (CK > UN
>LN>M N).
In the same treatments for different
soil layers, cellulase activity was significantly
reduced with the deepening of the soil from
CK treatment to HN treatment. In different
soil layers, cellulase activity showed the same
inhibitDry response to nitrogen deposition-
2.6 Effect of simulated nitrogen de­
position on polyphenol oxidase
For soil in the soil kyer of 0-20 cm, the
effect of nitrogen deposition on polyphenol
oxidase activity w as significant (p < 0.0另（Hg6).
There were si^iificant differences between the
MN treatment and the other three treatments
(p < 0.05), but no significant difference between
the three treatments except MN (p > 0.05)*
After one year of simulated nitrogen deposition^
polyphenol oxidase activity was inhibited by LN
treatment and responded positively under HN
treatment (MN > HN > CK > US). For soil in
the soil kyer of 2CM0 cm, polyphenol oxidase
activity was significantly affected by nitrogen
deposition (p < 0.05). The difference between
1.6
0-20 cm 20-40 cm
Fig.1 Effect of nitrogen deposition on boundary soil invertase activity Fig.2 Effect of nitrogen deposition on boundary soil catalase activity
9.0
8.0
7.0
6.0
5.0
4.0
3.0 2.0 1.0 0.0
CK i i i i i ^ i
LN HN CK LN MN HN
20-40 cm
Rg.3 Effect of nitrogen deposition on boundary soil uroaso activity 95Hg.4 Effect of nitrogen deposition on boundary soil am
ylase activity
The Effect of Nitrogen Deposition on Soil Enzyme Activity in the Forest-Grassland Landscape Boundary of Tibet
Fig.7 Effect of nitrogen deposition on boundavv soil p-glucosidase activity Fig.6 Effect of nitrogen deposition on boundary soil polyphenol oxidase activity
did a study on the effect of simulated nitrogen deposition on soil enzyme activity in Pinus tabiJaeformis forest of Taiyue Mountab and foimd that nitrogen deposition inhibits catalase activity^^1, and Xuan Danjuan et al. also found that simulated nitrogen deposition significantly i nhibits soil catalase activity i n P hyllostachys hctcsxKyck foreste135.The results were the same as those in this study. However Gallo et aL[3^ and Du Hoogxia et aL^ also pointed out that nitrogen deposition can increase soil catalase activity.
Research by Luo Shouhua reached the condusion that soil catalase
96
CK treatment and HN treatment did not reach a significant level (p > 0.05), but the differences between the other treatments were significant (p < 0.05). In a word, polyphenol oxidase activity inhibited by LN treatment, and was enhanced from CK treatment to HN treatment (H N>M N>CK>LN).
In the same treatment, polyphenol oxidase activity increased with tbe deepening of the soil kyen In different soil layers, with the deepening of the simulated nitrogen deposition, polyphenol oxidase activity varied similarly. To be specific, it first weakened and then increased and then weakened again, and it was reduced under LN treatment and enhanced under HN treatment 2.7 Effect of simulated nitrogen de­position on p-glucosidase
p-glucosidase activity in different soil layers varied with different levels of nitrogen depositioa For soil in the soil layer of 0-20 cm, nitrogen deposition had a si^iificant efifect on the P-gJucosidase activity (p < 0.05), and there were significant differences among various treatments (p < 0,05) (Fig.7), After one year of simulated nitrogen deposition, P-glucosidase activity \ras inhibited under and showed a downtrend (CK > MN > HN > LN). For soil in the soil layer of 2(M0 cm, P-glucosidase activity w as significantly affected by nittogen deposition (p < 0.0另，and the differences between treatments also reached significant l evels < 0.05). In b rie^ p-glucosidase >M N>LN).
In the same treatment, p-glucosidase activity
was significantly decreased with the deepening
of the soil layei, and p-gjucosidase activity was
affected differently by nitrogen deposition in
diffeent soil l ayers,
3 Discussion
3.1 Effect of simulated nitrogen depo­
sition on invertase
This study found that soil invertase activity
in soil layers of 0-20 cm and 2CM0 cm was
significantly inhibited under various nitrogen
deposition tteatments. Hu Lei et aL pointed out
that invertase enzyme activity is affected by a
series of complex factors induding the content
of organic mattet, nitrogen, and phosphorus
of soil, number of microorganisms, soil
tespiiation intensity^1, and research results about
invemse enzyme activity may be disturbed by
other factors, Yxian Yinghong et al. found that
in the subtropical Cunninghomia lanceolate
plantation, the invertase activity deoeases with
the increase of nitrpgen application level under
the application of nitrogen fertilizer^73.Du
Kun et al conducted a study on the response
of invertase activity to nitrogen deposition and
reached the cx>ndusion that nitrogen deposition
significantly inhibits invertase activity, which
is the same as the results obtained by this
study^. Pan Chaofeog studied on the efifect of
ited nitrogen deposition
on soil enzyme activity
of a Cryptomcm fortrnd plantation, and found
that tiittogeti deposition significantly increases
the soil invertase activity1291. Chun Lei et al
found that invertase activity w as enhanced under
LN treatment, and reduced under under HN
treatment by conducting the research on the
effect of nitrogen deposition on die microbial
population and enzyme activity in the humus
layer of Larix gmelmii forest1^. likewise, Luo
Shouhua drew the same conclusion[31].In
addition, Liu Xing et al. found that simulated
nitrogen deposition reduced invertase activity
in plantation forests but did not affect invertase
activity in natuial forests^. Thete has not been
a unified condusion about the efifect of nitrogen
deposition on i nvertase activity.
3.2 Effect of simulated nitrogen de­
position on catalase
The study found diat the response of soil
catalase activity in the soil layer of 0-20 cm to
nitrogen deposition did not reach a significant
level, and reached a significant level in the soil
layer of 2CM0 o il In the soil layer of 0-20 cm,
the difference between CK treatment and MN
treatment was significant; in the soil layer of
2(M0 cm, the diffeteace between CK treatment
and the other three treatments was significant
Specifically, catalase activity made a negative
response to nitrogen deposition in both soil
layers, that is, nitrogen deposition inhibited
the catalase activity in the two soil layers. At
present, domestic studies has not reached a
xmanimoxis conclusion. For example, Liu Xing
20-40 cm
activity w as inhibited by L N treatment, and mane combination of Simula a positive response to HN treatment (HN > CK and litter composition
45-0
M4〇〇
> 35.0
f 300
125.0
S 20.0 I15.0 110.0 5 5.00.0
i I i i i ^ i
CK LN MN HN CK LN MN HN 0-20 cm20-40 cm
Rg.5 Effect of nitrogen deposition on boundary soil cellulase activity
b
T
i
i
^
—
20-
LN
.0
.8
.6
.4
^
.D
.8
.6
.4
^
.0
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1.
1.
1.
1
1.
0.
0.
0.
0.
3
/
9
日
/
/
I
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awppco
Isaqdxlod
Journal of Landscape Research
activity is enhanced firstly and inhibited later under nitrogen deposition[31]. Fan Houbao found that low nitrogen promotes catalase activity and high nitrogen inhibits catalase activity1183. However, Song Sirui found that in Phyllostachys heterocyck forest, simulated nitrogen deposition significantly reduced soil catalase activity in the soil layer of 0-20 cm, and had no significant effect on soil catalase activity in the soil layer of 20-40 cmp61.
3.3 Effect of sim ulated nitrogen de­position on urease
During the process of deepening nitrogen deposition, soil urease activity in the soil layer of 0-20 cm under CK treatment was not significantly different from that under the three treatments, and did not reach a significant level. Urease activity was inhibited under LN treatment and increased under HN treatment, but not significandy. Soil urease activity in the soil layer of 2CM0 cm was significantly inhibited by nitrogen treatment Song Xuegui et al. found that urease activity in the subtropical evergreen broad-leaved forest increased with the increase of nitrogen application level[37]. Similarly, Wang Jie also found that soil enzyme activity responded positively to nitrogen deposition after conducting the research on the effect of nitrogen and moisture on soil enzyme activity and microbial biomass1381. Nonetheless, Du Kun et al.[28], Song Suiru et al.[36|5 and Sun Yanan et aL[39] found that nitrogen deposition significantly inhibits urease activity in their respective studies. This is consistent with the results of the soil layer of 0-20 cm in this study. In addition, Tu Lihua et al.[21], Wang Shuguang et al.[40], and Xu Fuli et al.[41] also found that low nitrogen promotes urease activity and high nitrogen inhibits urease activity. This is consistent with the results of the soil layer of 20-40 cm in this study. Currently, research in this area has not y et reached a unified conclusion,
3.4 Effect of sim ulated nitrogen de­position on cellulase
The study found that the response of soil cellulase activity to nitrogen deposition in soil layers of 0-20 cm and 20^0cm reached a significant level Specifically, nitrogen deposition significantly inhibited cellulase activity in the two soil layers, and there were significant differences between the results of various nitrogen treatments and CK treatment in the two soil layers. Sun Yanan et al smdied effect of nitrogen and phosphorus nutrient additions to the enzyme activity of the alpine meadow soil, and found that nitrogen addition inhibits cellulase activity1391，which is consistent with research results of this paper. In addition, Song Sirui et al. found that
cellulase activity was significantly affected by-
nitrogen deposition in the soil layer of 0-20 cm,
but was not significantly affected by nitrogen
deposition in the soil layer of 20-40 cm[36].
According to research by Pan Chaofeng et
al., nitrogen deposition significantly increased
soil cellulase activity of Cryptomem fortund
plantations[29]. Research Xuan Danjuan et al.
reached a similar conclusion133] _And Lhi Xing
found that simulated nitrogen deposition reduces
cellulase activity in natural forests, but has no
effect on cellulase in plantation forest1321,
3.5 Effect of sim ulated nitrogen de­
position on polyphenol oxidase
It turned out that polyphenol oxidase
activity in soil layers of 0-20 cm and 2CM0 cm
was inhibited under LN treatment, and was
enhanced under HN treatment. Of particular
note, the effect of nitrogen deposition in
both soil layers reached a significant level. Pan
Chaofeng et aL found that nitrogen deposition
generally inhibits polyphenol oxidase activity in
the soil of Cryptomem fortuned plantation, but
it was not significant^. Deforest et al[42]also
pointed out that soil polyphenol oxidase activity
decreases with the increase of available nitrogen,
which may be due to the inhibition of the fungal
activity of polyphenol oxidase secreted by high
concentrations of N03" a nd NH4+ in the soil1151.
3.6 Effect of simulated nitrogen depo­
sition on amylase and p-glucosidase
The study found that the effect of nitrogen
deposition on soil amylase activity in soil layers
of 0-20 cm and 20-40 cm reached a significant
level, and the effect was n^ative, that is, nitrogen
deposition inhibited amylase activity in both soil
layers. (3-glucosidase activity made a significant
response to nitrogen deposition in soil layers of
0-20 cm and 20-40 cm. To be specific, nitrogen
deposition inhibited (3-glucosidase activity in the
soil layer of 0-20 cm; in the soil layer of 20-40 cm,
nitrogen deposition inhibited (3-glucosidase
activity under LN treatment, and enhanced
j3-glucosidase activity under HN treatment.
Luo Shouhua et al. found that amylase activity
has obvious seasonal dynamic while studying
the effect of simulated nitrogen deposition on
litter decomposition, soil enzyme activity, and
soil respiration in the birch forest of the rainy
zone of West China[31l At present, there are
few studies on the effect of nitrogen deposition
on the activity of amylase and |3-glucosidase
in China. In this paper, a short-term nitrogen
deposition simulation test was conducted to
study the response of the activity of amylase and
(3-glucosidase to increased nitrogen deposition,
in order to provide a reference for better
understanding and evaluating the effect of
atmospheric nitrogen deposition on the activity
of the two enzymes in the landscape boundary
soil
In this study, a one-year nitrogen deposition
experiment was conducted in Tibet. There
are both similarities and differences between
results of this experiment and other research. It
is suggested that future studies focus on long­
term test data and compare field operations
conducted in affected and unaffected areas. And
the speed of atmospheric nitrogen deposition
in the future can be more accurately reflected by
conducting the nitrogen increase test according
to the amount of nitrogen deposition in different
regions. In order to reflect the change gradient
of regulatory factors in different regions,
response conditions of the selected ecosystem
can be detected.
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