全 文 ：Received 28 Oct. 2003 Accepted 20 Nov. 2003
Supported by the National Natural Science Foundation of China (40071085), the Knowledge Innovation Program of The Chinese Academy
of Sciences (KZCX1-SW-01-02).
* Author for correspondence. E-mail: .
http://www.chineseplantscience.com
Acta Botanica Sinica
植 物 学 报 2004, 46 (2): 194-201
N Mineralization and Nitrification in a Primary Lithocarpus xylocarpus Forest
and Degraded Vegetation in the Ailao Mountain, Yunnan Province
LI Gui-Cai1, 2, HAN Xing-Guo1* , HUANG Jian-Hui1
(1. Laboratory of Quantitative Vegetation Ecology, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, China;
2. Laboratory of Remote Sensing Information Science, Institute of Remote Sensing Application,
The Chinese Academy of Sciences, Beijing 100101, China)
Abstract: Using the closed-top tube incubation method, we examined the soil nitrogen (N) mineralization
and nitrification in the primary Lithocarpus xylocarpus forest, a secondary oak forest and a tea plantation
in the Ailao Mountain, Yunnan Province, China. This study was conducted in the dry season from
November 20, 1998 to May 15, 1999. Results showed that there were significant differences among the
three vegetation types in both net N mineralization and nitrification rates, and they also demonstrated
temporal variation. The net ammonification rate (RA) was much higher than net nitrification rate (RN), and
the latter was about 0.5%-10% of the former. Our results indicated that incubation period, vegetation type
and the location of plot all interactively affected RA, RN and net mineralization rate (RM ). We provided
evidence that anthropogenic disturbances could result in changes of ecosystems processes such as N
mineralization and nitrification rates. It is obvious that tea plantation and secondary growth forest have
more physically (mainly temperature and moisture) controlled N transformation processes than the
well-preserved primary L. xylocarpus forest, implying that the conservation of primary forest ecosystems
in the Ailao Mountain region should be emphasized.
Key words: Lithocarpus xylocarpus forest; net mineralization rate (RM); net ammonification rate (RA);
net nitrification rate (RN)
Nitrogen (N) is one of the macronutrients for the growth
and development of plants. Among all the nutrient elements
that plants take up from the soil, the quantity of N is the
largest (Ingestad, 1981). Nitrogen, as a main component of
protein, mainly comes from the soil organic detritus decom-
posed by microorganisms (Rashid and Scheafer, 1988). N
mineralization plays a major role in plant N availability
(Kolberg et al., 1997), and is closely correlated with ground
productivity (Liu and Muller, 1993).
The availability of N limits biomass production in many
forest ecosystems (Chapin, 1996). N can be easily lost from
the soil through leaching and volatilization. NH4+-N and
NO3--N are main N forms that plants take up from the soil.
Soil N availability depends on many transformation
processes, such as mineralization, immobilization,
volatilization, nitrification and denitrification. N
mineralization, a process that the organic N is transformed
to NH4+-N and NO3--N, directly affects the supply of soil
available N. However, immobilization transforms inorganic
N into organic N that consists of the tissues of soil micro-
bial organisms. The two processes exist simultaneously
(Mo and Kong, 1997). The N availability is influenced by
many factors such as soil temperature, humidity, vegeta-
tion type, litter quality, and disturbance regimes (Sulkava
et al., 1996).
Information on N availability is of great significance in
studies of ecosystem function as well as forest manage-
ment schemes. Our study was to examine the temporal dy-
namics of inorganic N pools and net N mineralization and
nitrification rates in three floristically distinct forest types
in the Ailao Mountain region, Southwest China.
1 Site Description
The research site is located at 24°32 N, 101°01 E, which
is in proximity to the Ailao Mountain Forest Ecosystem
Research Station, the Chinese Academy of Sciences, and
ranges from 2 000 m to 2 700 m in elevation. The annual
mean temperature is about 11.3 ℃, with the mean tempera-
ture of 15.4℃ in the hottest month (August), and 5.4 ℃ in
the coldest month (January). The annual accumulated tem-
perature above 10 ℃ is approximately 3 420 ℃. The annual
mean precipitation is about 1 931.9 mm，with 85% of it
occurring in the humid season from May to October. An-
nual evaporation, which is only about 1 485.9 mm, is much
LI Gui-Cai et al.: N Mineralization and Nitrification in a Primary Lithocarpus xylocarpus Forest and Degraded Vegetation in the
Ailao Mountain, Yunnan Province 195
less than annual precipitation. The total solar radiation is
greater than 87.7 k Cal·cm-2·a-1 (Ecology Department of
Kunming Division, The Chinese Academy of Sciences, 1983).
Three vegetation types, including a primary L.
xylocarpus forest, a secondary forest and a tea plantation,
were studied. The primary L. xylocarpus forest is a moun-
tain temperate rain forest dominated by L. xylocarpus, a
typical zonal vegetation type in this area. Castanopsis
rufescens, L. xylocarpus, Schima noronhae, L. hancei and
flourishing Sinarundinaria nitida are major arboreal spe-
cies that dominate the upper-stratum. Plagiogyria commu-
nis and Carex teinogyna are the major herbaceous species.
Disturbances, such as fires and harvests, can have great
impact on the growth and development of the primary L.
xylocarpus forest. After disturbance, the primary forest is
gradually replaced by secondary forest that is distributed
as mosaics in the primary L. xylocarpus forest. The height
of the secondary forest community is approximately 12-18
m, with flourishing sprouts and no apparent stratification.
The dominant arboreal species include L. hancei,
Vaccinium bracteatum, Camellia forrestii, Eurya
obliquifolia, Mechelia floribunda. The secondary growth
forest is characterized by having many sprouting and with-
out apparent herb stratum. After severe disturbances such
as heavy fire or intensive logging, the secondary arboreal
species were replaced by shrub and weed. In this case, tea
was usually planted there. Management practices for the
tea plantation generally include tillage, weed control, and
tea-picking.
Mountain yellow-brown soil, with a litter layer of 3-7
cm and a loose dark humus layer of 10-15 cm, is the typical
soil type found there. The soil is relatively acidic, with a pH
of less than 5 (Table 1).
2 Methods
2.1 Plot design
The primary L. xylocarpus forest, secondary forest, and
tea plantation were chosen for this study because they
represented weak, intermediate and strong disturbance
intensities. Three sampling plots, each with an area of 400
m2 (20 m × 20 m), were positioned. The three plots were at
least 50 m apart. In each sampling plot, we identified five
sampling points. Three paired soil cores in each sampling
point were taken using the polyvinyl chloride (PVC) tube.
The PVC tube was15 cm long and had an internal diameter
of 4.6 cm. For each pair of soil cores, one was used for initial
inorganic N determination, and another was put back to the
hole from which the soil core was taken and then incubated
for 45-60 d. During incubation, the tubes were covered
with plastic films that prevented water penetration and al-
lowed gas exchange. Three incubation periods were sepa-
rated during the entire dry season, representing early,
middle and late period of the dry-season, respectively.
2.2 Soil analysis and rate calculations
All soil samples were oven-dried at 60℃ for 24 h, then
ground and sieved using a 2 mm sieve. NH4+-N and
NO3--N were determined using Segmented Flow Analyzer
manufactured by SKALAR Company, Norway. The net min-
eralization rate (RM), net ammonification rate (RA), and net
nitrification rate (RN) (mg N·kg-1·30 d-1) were respectively
calculated by following equations.
RM = [ ( Tm1 – Tm0 ) / T ] × 30
RA = [ ( Ta1 – Ta0 ) / T ] × 30
RN = [ ( Tn1 – Tn0 ) / T ] × 30
Ta1, Tn1 and Tm1 (mg N/kg) represent respectively val-
ues of NH4+-N, NO3--N, and the both after incubation, and
Ta0, Tn0 and Tm0 represent the initial values. T represents
the total days of incubation.
2.3 Statistical analysis
One way ANOVA and Duncan’s multiple-range test were
used to test the differences of the mineralization rates among
vegetation types, plots and incubation periods, which were
all treated as independent variables (Li and Wang, 1998).
NH4+-N, NO3--N, pH, total C, total N and C/N ratio were
regarded as dependent variables. The statistical analyses
were conducted using ANOVA and POST HOC, two mod-
ules of SPSS software package (Lu et al., 1997). In addition,
to find out the difference between two factors, General
Table 1 Soil properties (0-15 cm) of the three vegetation types
Items Primary Lithocarpus xylocarpus forest Secondary forest Tea plantation
pH 4.39（0 . 1 1）a 4 . 5 1（0 . 1 0）a 4 . 4 7（0 . 0 7）a
Total carbon (C) content（g/kg） 1 4 3（1 2）a 1 3 8（1 9）a 6 2 （ 5 ）b
Total nitrogen (N) content（g/kg） 7 . 8 2（0 . 3 9）a 7 . 7 5（0 . 9 2）a 4 . 1 9（0 . 2 6）b
C/N ratio 1 8 . 1 2（0 . 8 9）a 1 7 . 6 0（0 . 5 7）a 1 4 . 5 5（0 . 6 1）b
NH4+-N (mg/kg） 6 6 . 0 1（2 . 9 9）a 5 2 . 6 3（3 . 2 4）b 30.80（2.58） c
NO3--N (mg/kg） 2 . 2 7（0 . 3 8）a 0 . 3 8（0 . 0 2）b 1 . 4 3（0 . 1 8）a
NH4+-N + NO3--N (mg/kg） 6 8 . 2 8（3 . 0 7）a 5 3 . 0 1（3 . 2 4）b 3 2 . 2 4（2 . 6 0）c
Values in the parentheses indicate standard errors; value in the same row with same superscript letters (a, b or c) indicate no significant
differences (Duncan’s multiple-range test) between vegetation types (P < 0.01)
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004196
Factoria was used to test the interactions among indepen-
dent variables. Vegetation types, plots, and three incuba-
tion periods were considered as independent variables, and
RM, RA, and RN were considered as dependent variables.
3 Results
3.1 Dry-season dynamics of RA and RN
In the dry season, RA showed similar trends for the three
incubations. It was high in the first incubation period (Nov.
20-Feb. 1), then declined in the second period (Feb. 1-
Apr. 1), and apparently increased again in the third period
(Apr. 1-May. 15). Table 2 indicated that there were notable
differences in RA among three incubations (P < 0.00 1).
RN showed a similar pattern compared to RM. For the
three incubations, RN tended to decline, and the differ-
ences among incubations were statistically significant (P <
0.001) (Fig.1B; Table 3). It is obviously clear that the changes
of RM and RN were significantly different in entire dry-
season.
Our results demonstrated that nitrification only ac-
counted for a minor fraction of the N mineralization process.
NH4+-N was the major component of inorganic N, and
NO3--N was only equal to 0.6%-7.4 % of NH4+-N. RA was
much higher than RN (Fig.1A, B). Due to the dominance of
ammonification in the mineralization process, RM could be
even replaced by RA.
3.2 RA and RN among three vegetation types
Results of ANOVA and Duncan’s multiple-range test
indicated that RA in the primary L. xylocarpus forest was
significantly different from that in the secondary forest only
in the third incubation, but not in the first and second
incubations. Significant difference of RA between primary
forest and tea plantation was found only in the first incuba-
tion (P < 0.05) (Fig.1A).
The dynamic pattern of RN differed greatly from that of
RM. In the first and second incubations, RN in the second-
ary forest and tea plantation were very close, and both of
them were significantly lower than that in the primary L.
xylocarpus forest. However, in the third incubation, RN in
the primary L. xylocarpus forest was significantly higher
than that in the secondary forest, which was significantly
higher than in the tea plantation (P < 0.05). RN in the tea
plantation was even negative in the third incubation period
(P < 0.05) (Fig.1B).
The quality of soil organic matter played an important
role in affecting N mineralization process. Generally, soil
organic matter with low C/N ratio has higher net mineraliza-
tion potential (Binkley and Hart, 1989). Our results showed
that the soil C/N ratios in the primary L. xylocarpus forest,
secondary forest and tea plantation were respectively
18.12±0.89, 17.60±0.57 and 14.55±0.61 (mean±1 s).
Our results seemed not to conform to the generality that
the mineralization rate is negatively correlated with the C/N
ratio. For example, in the first incubation, the net N mineral-
ization rate in the primary L. xylocarpus forest, with higher
C/N ratio, was higher than those in the secondary forest
and tea plantation having lower C/N ratios (Fig.1A).
3.3 General Factorial ANOVA of Rm
General Factorial ANOVA was used to compare the in-
tensities of various factors, which act on the dependent
Fig.1. The net ammonification rates (A), the net nitrification
rates (B) and the net mineralization rates (C) of soils under three
vegetation types during three incubations in the dry-season. The
vertical short lines at the top of bars represent the standard errors
(n =15). Different letters marked on bars indicate significant dif-
ferences between the vegetation types (Duncan’s multiple-range
test) (P < 0.01).
LI Gui-Cai et al.: N Mineralization and Nitrification in a Primary Lithocarpus xylocarpus Forest and Degraded Vegetation in the
Ailao Mountain, Yunnan Province 197
variables and the interactions among the biological factors
and environmental factors. Incubation period, vegetation
type, and plot are independent variables, and RA, RN and
RM are dependent variables. The results showed that incu-
bation period exerted the greatest control on RM , being
similar to plots, and vegetation type the least (Table 4).
Being similar to RM, RA was also strongly affected by
the independent variables (Table 2). The factors highly in-
teracted between each other. Differing from RM and RA,
there were significant interactions for RN only between
vegetation types and plots. This indicated that the soil
NO3--N was unstable and/or the low nitrification potential
in soils of low pH. The interaction among the three factors
was also extremely significant.
4 Discussion
4.1 Net N mineralization rate and dry-season dynamic
pattern
RA was determined using the Closed-Top Tube Incuba-
tion method that it isolates incubated soil from plant
uptake and excludes the N input of rainfall (Nadelhoffer
and Aber, 1985). RA reflected the balance among
ammonification, nitrification and microbial immobilization.
Results from laboratory incubation experiment have dem-
onstrated that the humidity fluctuation can increase N min-
eralization (Sahrawat, 1980). For all three communities, RA
was negative in the second period of dry season, indicat-
ing that there was strong microbial immobilization of inor-
ganic N. In the second period of dry season, because the
nitrification rate was much lower than the ammonification
rate, nitrification was only contributed a small proportion
of mineralization (Fig.1A, C).
Obviously, the dynamic patterns between RA and RN
were not accordant, partly due to the fact that different
microbial processes control ammonification and
nitrification. This indicated that the balance among
ammonification, nitrification and immobilization, had differ-
ent responses to the change of environmental factors in
dry season. In other words, the rates at which NH4+-N or
NO3--N is produced by microbial processes are different.
Table 2 General factorial ANOVA results of the soil net ammonification rates (RA) during dry-season (Dependent variable, RA)
Source
Type III sum of
Df Mean square F Significance
Noncent. Observed
squares parameter power a
Corrected model 21 519.915 b 26 827.689 8.211 0.000 213.487 1.000
Intercept 6 923.147 1 6 923.147 68.681 0.000 68.681 1.000
IP c 11 521.494 2 5 760.747 57.149 0.000 114.298 1.000
VT 415.276 2 207.638 2.060 0.132 4.120 0.416
P 582.128 2 291.064 2.887 0.060 5.775 0.554
IP× VT 2 276.310 4 569.078 5.645 0.000 22.582 0.975
IP × P 1 955.666 4 488.916 4.850 0.001 19.401 0.950
VT× P 1 866.914 4 466.728 4.630 0.002 18.521 0.939
IP× VT× P 2 902.127 8 362.766 3.599 0.001 28.790 0.978
Error 10 886.632 108 100.802
Total 39 329.694 135
Corrected total 32 406.546 134
a, computed using alpha = 0.05; b, R2 = 0.664; c, IP, incubation period; P, plot; VT, vegetation type.
Table 3 General factorial ANOVA results of soil net nitrification rates (RN) during dry-season (Dependent variable, RN)
Source
Type III sum of
Df Mean square F Significance
Noncent. Observed
squares parameter power a
Corrected model 67.989 b 26 2.615 10.444 0.000 271.553 1.000
Intercept 42.966 1 42.966 171.607 0.000 171.607 1.000
IP c 4.833 2 2.417 9.652 0.000 19.305 0.979
VT 47.717 2 23.858 95.292 0.000 190.584 1.000
P 1.847 2 0.923 3.688 0.028 7.375 0.667
IP× VT 1.727 4 0.432 1.724 0.150 6.896 0.513
IP × P 2.153 4 0.538 2.150 0.080 8.599 0.619
VT× P 5.734 4 1.434 5.726 0.000 22.902 0.977
IP× VT× P 3.979 8 0.497 1.986 0.055 15.891 0.793
Error 27.040 108 0.250
Total 137.995 135
Corrected total 95.029 134
a, computed using alpha = 0.05; b, R2 = 0.715; c, IP, incubation period; P, plot; VT, vegetation type.
Acta Botanica Sinica 植物学报 Vol.46 No.2 2004198
The immobilization rates, at which NH4+-N or NO3--N is
utilized by microbes, are also different. This explained that
RN was linearly reduced following the decrease of soil mois-
ture (Table 5).
The seasonal patterns of N mineralization are generally
affected by the change of environmental factors (Pekka et
al., 1996). To a greater extent, N mineralization is positively
correlated with temperature and moisture, and there are
positive interactions between them. In our experiment, N
mineralization increased with increasing soil moisture, and
vice versa. This indicated that soil moisture was one of the
important factors influencing N mineralization in the Ailao
Mountain Region. The net N mineralization rate was higher
in the first incubation period than in the second one be-
cause of the higher moisture, despite of the lower
temperature.
The inorganic N pool was lower in the third incubation
period than in the first two incubation periods. Nevertheless,
the mineralization rate was higher. It is generally accepted
the soil inorganic N pools do not necessarily correlate with
N transformation processes. However, in some cases, a
higher initial N content in the soil may impede the N miner-
alization and nitrification rates because of suppression of
microbial activities by accumulated in organic N. The inor-
ganic N generally increases after a period of incubation,
because the losses due to plant absorption, volatilization
and leaching are minimized during the incubation period.
However, due to microbial immobilization, the inorganic N
pool may decrease dramatically after incubation, as reflected
by the results of our second incubation when negative net
N mineralization rates were observed (Fig.1C). Thus, the
size of the soil inorganic N pool was a result from the inter-
actions of various processes mentioned above.
4.2 N mineralization rate and disturbance intensities
Effects of disturbance on soil N transformation have
been reported everywhere. The N mineralization rates with
disturbance and without disturbance are apparently differ-
ent (Raison et al., 1987; Cabrera and Kissel, 1988; Hadas et
al., 1989). In the forest ecosystems, a lot of organic N is
transformed into inorganic N after disturbances such as
clearing-harvesting (Adams and Attiwill, 1991), prescribed
fire (Schoch and Binkley, 1986) and weeding (Vitousek,
1992). Disturbances can lead to increase potential of N loss,
especially the dissolved forms (Bonilla and Roda, 1990;
Adams and Attiwill, 1991). N transformation is also affected
by the ecosystem management practices. Net N mineraliza-
tion and nitrification often increase and the microbial im-
mobilization generally declines after forest harvest due to
the rising of soil temperature and mineralizable organic
matter (Smethurst and Nambiar, 1990a; 1990b). This can
contribute to the different N proportions in soil pool under
different harvest intensities (Emmett, 1991). The level of
available soil N declines after disturbances.
Generally, disturbances result in a decline of vegetation
Table 4 General factorial ANOVA results of soil net mineralization rates (RM) during dry-season (Dependent variable, RM)
Source
Type III sum of
Df Mean square F Significance
Noncent. Observed
squares parameter power a
Corrected model 21 608.161 26 831.083 8.210 0.000 213.449 1.000
Intercept 8 057.368 1 8 057.368 79.592 0.000 79.592 1.000
IP c 11 525.706 2 5 762.853 56.926 0.000 113.853 1.000
VT 198.783 2 99.392 0.982 0.378 1.964 0.217
P 645.459 2 322.729 3.188 0.045 6.376 0.599
IP× VT 2 255.593 4 563.898 5.570 0.000 22.281 0.974
IP × P 1 991.796 4 497.949 4.919 0.001 19.675 0.953
VT× P 2 065.648 4 516.412 5.101 0.001 20.405 0.960
IP× VT× P 2 925.175 8 365.647 3.612 0.001 28.895 0.979
Error 10 933.226 108 101.234
Total 40 598.755 135
Corrected total 32 541.387 134
a, computed using alpha = 0.05; b, R2 = 0.664; c, IP, incubation period; P, plot; VT, vegetation type.
Table 5 The soil temperature and moisture of three vegetation types during dry season at the depth of 5 cm
Date of sampling Nov. 20 Feb. 1 Apr. 1 May 15
Soil temperature Primary L. xylocarpus forest (℃) 10.50 6.90 11.10 12.50
Secondary forest (℃) 12.00 8.10 13.80 14.10
Tea plantation (℃) 13.50 9.30 16.40 15.60
Soil moisture Primary L. xylocarpus forest (%) 105.72 88.34 70.95 80.00
Secondary forest (%) 117.07 87.44 57.81 83.80
Tea plantation (%) 48.59 38.70 28.80 40.00
LI Gui-Cai et al.: N Mineralization and Nitrification in a Primary Lithocarpus xylocarpus Forest and Degraded Vegetation in the
Ailao Mountain, Yunnan Province 199
coverage (Sierra, 1992). The organic matter input decreases,
and, at the same time, the quality of organic matter changes
(Table 1). Scott et al. (1997) found that the net N mineraliza-
tion was controlled by the forest litterfall quality (C/N or
lignin/N) through influencing the soil organic matter quality.
Furthermore, the forest litterfall quality, which is indepen-
dent in relation to climates and soils, is also a good indica-
tor of the net N mineralization rate. Our result is similar to
the study reported by Fyles et al. (1990). In addition, soil
temperature and soil moisture content strongly influence N
release (Powers, 1990). After some disturbances such as
fire and harvest, more sunlight could directly arrive at soil
surface, resulting in the rise of soil temperature and an ac-
companying reduction of soil moisture (Table 5). Excluding
leaching loss and plant uptake, the higher N transforma-
tion rate, especially N mineralization rate, resulted in more
accumulated inorganic N in a definite time.
In the first incubation period of the dry season, the net
N mineralization rate in primary forest was higher than that
in the secondary forest. The latter was higher than that in
the tea plantation (Fig.1A, C). The lower net N mineraliza-
tion rate that we found in the primary L. xylocarpus forest
might have been ascribed to the lower soil temperature. Tea
plantation was very sensitive to the fluctuations of tem-
perature and moisture due to its lower vegetation coverage.
The differences of net N mineralization rates in three veg-
etation types were not statistically significant under lower
soil temperature and moisture (Table 5), because N mineral-
ization was strongly inhibited. These results clearly dem-
onstrate that the disturbances (such as land use change)
not only can result in changes of soil organic matter, but
also changes in the magnitude of temperature and moisture
fluctuations. In other words, ecosystem degradation due
to timber harvest and man-induced fire or land conversion
may render these ecosystems more abiotically controlled.
Thus, it also resulted in the increase of N mineralization
rate and a decline of plant uptake, leading to a subsequent
increase of accumulated available N. However, these de-
graded ecosystems may become more prone to soil N loss
due to the low vegetation coverage and a correspondingly
low N uptake by plants, which may finally result in deple-
tion of soil N stocks.
N mineralization was negatively correlated with the C/N
ratio of forest litterfall (Arunachalam et al., 1998; Ohrui et
al., 1999). When C/N ratio is low, the growth of microbes
usually is limited by the lack of C in the soil organic matter.
However, in this case, the N resource is still sufficient, thus
N immobilization would be limited. Contrarily, if the C/N
ratio is high, the microbes would need more N because of
the lack of N, and the mineralized N would be quickly
immobilized. This indicates that C/N ratio usually plays a
key role in the processes of “mineralization - immobiliza-
tion” (Reich, 1997), and N mineralization links with C flux
through those microbial processes (Sactre, 1998). As an
important indicator of organic matter, C/N ratio strongly
influences the N mineralization, though the effects of other
factors, such as soil temperature and moisture, should not
be ignored. Furthermore, in three vegetation types, the sen-
sitivities of microbial processes to the environmental fac-
tors are different. In our research, C/N ratio of soil decreased
in the order of the primary L. xylocarpus forest, secondary
forest and tea plantation (Table 1). Generally, C/N ratio is
negatively correlated with the N mineralization rates, but
our results do not always conform to this generality, sug-
gesting that an array of other factors in addition to C/N
ratio also exert great controls on N transformation
processes.
In conclusion, we provided evidence that anthropogenic
disturbances could result in changes of ecosystem pro-
cesses such as N mineralization and nitrification rates. It is
obvious that tea plantation and secondary growth forest
have more physically (mainly temperature and moisture)
controlled N transformation processes than the well-pre-
served primary L. xylocarpus forest, implying that the con-
servation of primary forest ecosystems in the Ailao Moun-
tain Region should be emphasized.
Acknowledgements: We appreciate Prof. TANG Jian-
Wei, Dr. HE Yong-Tao, Mr. LI Da-Wen, Mr. YANG Guo-Pin
and Mr. YANG Wen-Zheng for their assistance in the field
experiments.
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(Managing editor: HAN Ya-Qin)