全 文 ：应用与环境生物学报　2002, 8(3):223～ 233 　 　
Chin J Appl Environ Biol=ISSN 1006-687X 　 2002-06-25
　
收稿日期:2001-08-13　　接受日期:2001-11-01
＊中国博士后科研基金 、福建省科委重大基础研究项目(2000F004)、高等学校骨干教师资助计划及福建省自然科学基金(B0110025)资助　
Supported by the Post-doctor Research Foundation of China , the Supporting Project for Key Teachers in Universities of the Ministry of Education , the Major Project
of Basic Research of Fujian Science and Technology Committee , and the Provincial Natural Science Foundation of Fujian , China
＊＊通讯作者　Corresponding author(Tel:0599-8504071;E-mai l:ffcyys@public.npptt.fj.cn)
PRODUCTION , DISTRIBUTION AND NUTRIENT RETURN OF
FINE ROOTS IN A MIXED AND A PURE FOREST IN
SUBTROPICAL CHINA＊
YANG Yusheng
1＊＊ , CHEN Guangshui , He Zongming , CHEN Yinxiu &GUO Jianfen
(Forestry College , Fujian Agriculture and Forestry University , Nanping　353001, China)
(1Post-doctoral Stat ion of Biology , Xiamen University , Xiamen　360005 , China)
Abstract　The studies on production , distribution and nutrient return of fine roots (d <2 mm)in a mixed
Chinese fir(Cunninghamia lanceolata)-Tsoong tree (Tsoongiodendron odorum)forest and a pure Chinese fir
forest at age 27 were carried out in Sanming of Fujian , China.The standing crops of dry matter , N and P in fine
roots of the mixed stand were 5.381 t hm-2 , 48.085 kg hm-2 and 4.174 kg hm-2 , 17.4%, 27.2% and 20.
0%higher than those of the pure stand , respectively.The fine root production in the mixed forest was up to 4.
124 t hm-2 a-1 , 16.9%higher than that in the pure stand.Fine roots of Chinese fir and Tsoong tree in the
mixed forest both concentrated in the surface soil , and showed a vertical stratification in the subsoil.Compared
with those in the mixed forest , fine roots of Chinese fir in the pure forest had a deeper rooting zone , with a lower
root density in the superficial soil.The turnover rates of fine roots for Tsoong tree and Chinese fir in the mixed
stand , and Chinese fir in the pure stand , were 1.16 , 0.96 and 0.95 , respectively.The undergrowth species had
higher root turnover rates than their respective tree layers(1.46 in the mixed forest and 1.52 in the pure stand).
The annual mortality , annual return of N and P of fine roots in the mixed forest amounted to 2.119 t hm-2 , 18.
559 kg hm
-2
and 1.565 kg hm-2 , 1.21 , 1.23 and 1.14 times as much as that in the pure forest respectively.
Bulk density , moisture content , total N and humic C were strongly correlated with fine root density along the soil
profile in the two forests , with total N giving the highest coefficients of determination.Fig 1 , Tab 4 , Ref 32
Keywords　fine root;net production;vertical distribution;nutrient return;soil factor
CLC　S718
杉木观光木混交林和杉木纯林群落细根
生产力 、分布及养分归还＊
杨玉盛1＊＊　陈光水　何宗明　陈银秀　郭剑芬
(福建农林大学林学院　南平　353001)
(1 厦门大学生物学博士后流动站　厦门　360005)
摘　要　研究了福建三明27 a生杉木观光木混交林和杉木纯林群落细根(d<2 mm)的生产力 、分布和养分归还.结果
表明 ,混交林细根生物量 、N、P养分现存量分别为 5.381 t hm-2、48.085 kg hm-2和 4.174 kg hm-2 ,分别比杉木纯林增加
17.4%、27.2%和 20.0%.混交林细根的年净生产力达 4.124 t hm-2 a-1 , 比纯林高出 16.9%.混交林杉木和观光木细根
均在表层土壤富集 , 而在较深层土壤两者分布具镶嵌性;与混交林杉木相比 ,纯林杉木土壤表层细根量较少 , 最大分布
层次下移.混交林中观光木细根的周转速率为 1.16 , 杉木为 0.96 和 0.95;而林下植被层细根周转速率(1.46～ 1.52)均
高于相应的乔木层.混交林细根的年死亡量 、N 和 P 养分年归还量分别达 2.119 t hm-2、18.559 kg hm-2和 1.565 kg
hm-2 , 分别是纯林的 1.21 倍 、1.23倍和 1.14倍 , 其中林下植被细根占有较为重要位置.对细根分布与土壤性质的相关
分析表明 ,细根的垂直分布与土壤全N 的相关性最强(0.87～ 0.89).图 1表 4 参 32
关键词　细根;净生产力;垂直分布;养分归还;土壤因子
CLC　S718
　　Due to the lack of knowledge on their ecological roles
andmany difficulties , study on fine roots has been one of
the weak fields in forest ecology for a long time.Fine roots
represent a functionally important portion of the biomass of
forests and are constant in flux , with death and replacement
taking place simultaneously.Even though fine roots
contribute only a small part of the total stand biomass in
forests , their growth and maintenance use a major part of
total net primary production
[ 1] .In the last two decades , a
large amount of documents on fine root productivities have
been accumulated world-widely .However , study on fine
roots in relation to production and mortality has seldom been
listed on the timetable of Chinese forest ecologists since it is
a very laborious task.
It is well known that , on a similar substrate , different
tree species may differ markedly with respect to not only the
extension of their coarse root system , but also the
abundance and the productivity of their fine roots.Also , to
reduce exploitation competition , spatial or temporal
separation of the fine root systems and their activities is
likely to occur in multi-species communities.However ,
most of the studies were conducted in monospecific tree
stands where intra- but not interspecific competition could
be expected[ 2] .Much less is known about the spatial
separation of root systems in mixed forest stands[ 3] .
Fine roots are important sources and sinks for nutrients
in terrestrial ecosystems.In view of the higher nutrient
concentrations than those in foliage and the relatively
shorter life spans across the range of forests , the
production , death and decomposition of roots are major
processes in the carbon and nutrient dynamics of forest
ecosystems[ 4 , 5] .In forests , for example , the amounts of
carbon and nutrients returned to the soil from fine root
turnover may be equal to or exceed those from leaf litter.
Thus , soil fertility can benefit very much from the
significant amounts of nutrient and organic matter transfers
from fine root mortality.However , studies on organic matter
and nutrient dynamics in forest ecosystems have been
focused mainly on aboveground production , and the role of
fine roots in nutrients and organic matter return and soil
amelioration is poorly understood.
The purposes of this paper are:(1)to determine fine
root biomass , production , mortality and turnover rate , (2)
to characterize possible species differences in the vertical
distribution of fine roots , (3) to quantify the annual
transfers of organic matter and nutrients by fine root
mortality , and(4)to estimate the potential effects of soil
factors on fine root distribution in a mixed Chinese fir
( Cunninghamia lanceolata )-Tsoong tree
(Tsoongiodendron odorum)forest and an adjacent Chinese
fir plantation in Sanming , Fujian , P.R.China.
1　SITE DESCRIPTION
The sites are located at Xiaohu work area of Xinkou
Experimental Forestry Farm of Fujian Agriculture and
Forestry University , Sanming , Fujian(φ(N)26°11′30″, λ
(E)117°26′00″).This area has a subtropical monsoonal
climate with an mean annual temperature of 19.1 ℃, an
annual precipitation of 1 749 mm , an annual evaporation of
1 585.0 mm , a mean annual relative humidity of 81%,
and an frost-free period of around 300 d [ 6].The soil is red
earth derived from shale.The mixed stand of Chinese fir
and Tsoong tree , and the pure stand of Chinese fir , were
both established with seedlings in 1973 , with a planting
density of 3 000 stems per hm2.The mixed pattern is strip
spacing , with three rows of Chinese fir spaced by one row
of Tsoong tree.At time of survey (at age 27), the pure
stand had a density of 1 100 stems per hm2 , with a crown
density of 0.80 and a coverage of 95% for undergrowth.
The mean tree height and diameter at breast height(DBH)
were 19.61 m and 23.6 cm for Chinese fir respectively.
The mixed stand had a density of 907 stems per hm
2
for
Chinese fir and 450 stems per hm2 for Tsoong tree.The
mean tree height and DBH were 20.88 m and 25.1 cm for
224 　　　　　　　　应 用 与环 境生 物学 报　　Chin J Appl Environ Biol　　　　　　　　　　　　　　 　　　8卷
Chinese fir , and 17.81 m and 17.0 cm for Tsoong tree ,
respectively.The crown density was 0.95 and the
undergrowth coverage was 80%.
2　METHODS
2.1　Extraction of roots
Three 20 m ×20 m marked plots were established
within each of mixed and pure stands.On the 26th day of
every other month during January to November in 1999 , 10
soil cores per plot , totaled 30 per stand , were collected
from surface to a depth of 100 cm at random across each
plot using a steel core (6.8 cm diameter).The soil cores
then were divided into the soil depths of 0 ～ 10 , 10 ～ 20 ,
20 ～ 30 , 30 ～ 40 , 40 ～ 60 , 60 ～ 80 and 80 ～ 100 cm.Soil
samples were washed with tap water to remove adhering soil
and accompanying organic debris , then the roots of object
trees and undergrowth(shrubs and herbages)were detached
with magnifying glass , scissors and tweezers etc.At the
same time , fine roots (d <2 mm)were picked up , and
separated into live and dead categories according to their
respective appearance , color , flexibility and the cohesion
between cortex and periderm
[ 7]　.The fine roots of object
trees were further sorted into three diameter classes(1 ～ 2 ,
0.5 ～ 1 and <0.5 mm).All the roots were oven-dried
(80 ℃)to constant weight and weighed.The standing crop
of fine roots was calculated using the following formula:the
standing crop of fine roots (ρA/ t hm-2)= dry weight of
fine roots per core(m/g)×10-6/〔π(6.8(d/cm)/2〕2×
108.
2.2　Collection of soil samples
Soil samples were collected at each time of root coring
at five sampling points following ” sigmoid” route across
each plot.Each time at each sampling site , six soil rings
for determination of soil water-physical properties and three
soil samples for analysis of soil chemical properties were
collected at three depths:0 ～ 20 , 20 ～ 40 and 40 ～ 60 cm.
2.3　Decomposition experiment
Fine roots of Chinese fir , Tsoong s tree and
undergrowth were obtained from the upper 0 ～ 20 cm soil
layer in the mixed and pure forests by excavating.Root
materials of Chinese fir and Tsoong s tree were sorted into
three diameter classes:<0.5 mm , 0.5 ～ 1mm , and 1 ～ 2
mm.Thus , there were 7 categories of root samples for
mixed forest and 4 for pure forest.5 g air-dried root sample
was confined into a nylon bag (18 cm×18 cm , 0.25 mm
mesh size), and there were 100 bags for each category.
The bags were incubated in the soil at a depth of 10 cm in
May 1999 , and 5 to 6 bags for each category were retrieved
after 30 , 60 , 90 , 150 , 210 , 270 , 360 , 450 and 540 d at
random.
2.4　Chemical analysis
For the determination of N , the root materials were
digested in K2Cr2O7-H2SO4 solution and then N was
determined by micro-Kjeldahl technique.Samples for P
analysis were wet digested in a mixture of HNO3 , H2SO4
and HClO4 solution.Concentration of P was analyzed
colorimetrically by a mixture of (NH4)6Mo7O24-KSbOC4
H4O6-C6H8O6[ 8] 　.Determination of soil physical and
chemical properties used the same procedures previously
described by Yang et al.(1994)[ 9]　.
2.5　Calculation
Fine root production was estimated by the Maximum-
Minimum method using these following formulas:M =
Mmax-Mmin+D , P =Pmax-Pmin+M , T =P/Y , Where
M , P , D and T represent annual mortality , production ,
decomposition and turnover rate of fine roots , respectively.
Mmax and Mmin represent the maximum and minimum of
current biomass of dead roots in a year , while Pmax , Pmin
and Y stand for the maximum , minimum and average of the
standing crop of living root in a year , respectively [ 10]　.
The data on the standing crop of fine roots for each
species at all sampling date in 1999 were pooled according
to the same soil depth , then the vertical distribution of fine
roots for each species was analyzed based on the mean value
of each depth.
The standing crop of nutrient in fine roots was
calculated as the product of the standing crop of dry mass
and the nutrient concentration.Annual nutrient return from
fine root turnover was estimated as the product of annual
root mortality and the mean nutrient concentration in fine
roots in a year.
For each sampling date , the data on fine root biomass
and soil properties in each forest were pooled according to
the same depth (0 ～ 20 , 20 ～ 40 and 40 ～ 60 cm)and
225　3期 杨玉盛等:杉木观光木混交林和杉木纯林群落细根生产力 、分布及养分归还 　　
plot.Thus , we got a set of 54 data for root density and for
each soil index in a forest in a year.A linear regression
analysis was then made between root density and each soil
index.
Tab 1　The standing crop of dry matter, N and P in fine roots(x-±s)
Forest
type
Species
Root
diameter
Live root
Dry
weight
(ρA/ t hm-2)
N
　 　　ρA/ kg
P
hm-2　
Dead root
Dry
weight
(ρA/ t hm-2)
N
　 　　ρA/ kg
P
hm-2　
Gross product
Dry
weight
(ρA/ t hm-2)
N
　　　ρA/kg
P
hm-2　
Mixed
stand
Chinese f ir 1～ 2 mm 0.627±0.090
3.604
±0.555
0.210
±0.025
0.232
±0.034
1.261
±0.173
0.071
±0.011
0.859
±0.142
4.865
±0.642
0.281
±0.040
0.5～ 1 mm 0.439±0.051
3.018
±0.380
0.180
±0.018
0.162
±0.020
1.051
±0.118
0.062
±0.008
0.601
±0.081
4.069
±0.439
0.242
±0.028
<0.5 mm 1.623±0.188
14.913
±1.858
0.890
±0.087
0.728
±0.087
6.625
±0.737
0.391
±0.049
2.351
±0.314
21.538
±2.300
1.281
±0.148
subtotal
2.689
±0.371
21.535
±3.196
1.281
±0.149
1.122
±0.161
8.937
±1.184
0.524
±0.078
3.811
±0.606
30.472
±3.876
1.805
±0.249
Tsoong tree 1～ 2 mm 0.110±0.013
0.849
±0.112
0.107
±0.011
0.051
±0.006
0.370
±0.043
0.043
±0.006
0.161
±0.023
1.219
±0.138
0.150
±0.018
0.5～ 1 mm 0.091±0.014
0.987
±0.159
0.078
±0.010
0.039
±0.006
0.409
±0.059
0.029
±0.005
0.13
±0.022
1.396
±0.193
0.107
±0.016
<0.5 mm 0.389±0.053
6.056
±0.890
0.527
±0.061
0.133
±0.019
1.836
±0.241
0.152
±0.022
0.522
±0.082
7.892
±0.994
0.679
±0.093
Subtotal
0.590
±0.071
7.892
±1.016
0.712
±0.072
0.223
±0.028
2.615
±0.301
0.224
±0.029
0.813
±0.112
10.507
±1.160
0.936
±0.112
Underground
vegetation
<2 mm 0.593±0.080
5.593
±0.814
1.149
±0.131
0.164
±0.023
1.513
±0.197
0.284
±0.041
0.757
±0.118
7.106
±0.887
1.433
±0.194
total
5.381
±0.783
48.085
±6.126
4.174
±0.510
Pure stand Chinese f ir 1～ 2 mm 0.635±0.062
3.636
±0.384
0.213
±0.026
0.234
±0.025
1.267
±0.131
0.072
±0.009
0.869
±0.098
4.903
±0.502
0.285
±0.027
0.5～ 1 mm 0.415±0.050
2.858
±0.370
0.171
±0.026
0.181
±0.024
1.175
±0.149
0.069
±0.010
0.596
±0.082
4.033
±0.506
0.24
±0.028
<0.5 mm 1.590±0.177
14.603
±1.752
0.875
±0.123
0.656
±0.080
5.654
±0.664
0.336
±0.045
2.246
±0.286
20.257
±2.355
1.211
±0.132
Subtotal
2.640
±0.329
21.097
±2.835
1.259
±0.197
1.071
±0.147
8.096
±1.065
0.477
±0.072
3.711
±0.530
29.193
±3.801
1.736
±0.211
Underground
vegetation
<2 mm 0.675±0.090
6.707
±0.966
1.374
±0.231
0.198
±0.029
1.907
±0.269
0.368
±0.060
0.873
±0.134
8.614
±1.202
1.742
±0.227
total
4.584
±0.719
37.807
±5.187
3.478
±0.458
3　RESULTS
3.1　Biomass and nutrient content in fine roots
The mixed forest had a higher fine root biomass than
the pure forest (5.381 t hm-2 vs.4.584 t hm-2 , P <
0.01).The fine root biomass/necromass ratios for various
diameter classes of both Chinese fir and Tsoong tree were
about 7/3.The N and P contents in fine roots in the mixed
stand were 48.085 kg hm-2 and 4.174 kg hm-2
respectively , 27.2% and 20.0% higher than that in the
pure stand (Tab 1).The undergrowth vegetations
accounted for 14.1% of dry matter , 14.6% of N amount
and 34.3%of P amount in fine roots in the mixed forest ,
respectively , compared with the corresponding values of
19.0%, 22.8% and 50.1% in the pure stand(Tab 1).
For fine roots of both Chinese fir and Tsoong tree , above
60%of the biomass , N and P contents were contributed by
the roots of less than 0.5 mm in diameter.
3.2　The vertical distribution of fine roots
Fine root density of Chinese fir in the mixed stand
decreased with the increase of soil depth , and 59.7% of
226 　　　　　　　　应 用 与环 境生 物学 报　　Chin J Appl Environ Biol　　　　　　　　　　　　　　 　　　8卷
the fine roots were concentrated in the upper 0 ～ 20 cm
layer but only 5.4% occurred in soil deeper than 80 cm.
Fine roots of Tsoong tree were highly concentrated in the
upper 0 ～ 10 cm layer with a proportion of 56.0%, then
decreased with the increase of soil depth to the minimum in
the depth of 30 ～ 40 cm , and again increased in the soil
layer of 60 ～ 80 cm(Fig 1a).It can be seen that the fine
roots of the two species in the mixed forest show a vertical
stratification in the 10 ～ 80 cm soil layer.The root density
of Chinese fir in the pure stand peaked in the depth of 10 ～
20 cm , and decreased thereafter with the increase of soil
depth , with 47.3% of the fine roots being detected from
the surface to the depth of 20 cm (Fig 1a).
Fig 1　Vertical distribution of fine roots in the mixed and pure forests
(a)Vertical distribution of fine roots of tree species;(b)Vertical distribution of fine roots of shrub species;
(c)Vertical distribution of fine roots of herbage species;(d)Vertical distribution of total fine roots
　　Fine roots of the shrubs in the mixed forest were rare
in soil layer of 0 ～ 30 cm , and reached a maximum in the
30 ～ 40 cm layer , with a percentage of 74.0%, while those
in the pure forest were packed in the soil layer of 0 ～ 10
cm , with a high percentage of 91.1%(Fig 1b).Fine roots
of the herbages in the mixed and pure forests were both
concentrated in the 0 ～ 10 cm layer , with a proportion of
90.9% and 81.3%respectively , then decreased rapidly in
the deeper layer (Fig 1c).
The densities of total fine roots in the mixed and pure
forest were both highest in the depth of 0 ～ 10 cm , and
decreased gradually with the increase of soil depth except for
an increase at the depth of 30 ～ 40 cm in the mixed forest
(Fig 1d).About 49.2%of total fine roots occurred in the
0 ～ 20 cm soil layer in the mixed forest , compared with 44.
5% in the pure forest.
3.3　Annual fine root production and nutrient return
Annual net production of fine roots in the mixed stand
was up to 4.124 t hm-2 , 16.9%higher than that of pure
stand(Tab 2).The annual turnover rate of Tsoong tree
was 1.16 , compared with 0.96 of Chinese fir(P <0.05).
Undergrowth had a higher turnover rate of fine roots than its
227　3期 杨玉盛等:杉木观光木混交林和杉木纯林群落细根生产力 、分布及养分归还 　　
respective tree stratum (P <0.05).The annual turnover
rate of total fine roots in mixed stand was 1.07 , being
similar to that in the pure stand(1.06;P >0.1).
Tab 2　Annual turnover rate , mortality and annual return of nutrients of fine roots(x-±s)
Items
Mixed stand
Tree stratum
Undergrowth Total
Chinese fir Tsoong tree Subtotal
Pure stand
Tree stratum Undergrowth Total
Turnover rate 0.96±0.10 1.16±0.14 1.02±0.10 1.46±0.16 1.07±0.13 0.95±0.09 1.52±0.17 1.06±0.11
Annual prodution 2.569±0.436 0.687±0.101 3.256±0.503 0.868±0.144 4.124±0.579 2.504±0.372 1.024±0.163 3.528±0.533
Annualmortality(ρA/ t hm-2) 1.461±0.209 0.348±0.054 1.809±0.219 0.310±0.046 2.119±0.291 1.519±0.234 0.375±0.062 1.894±0.250
Annual return of N
(ρA/ kg hm-2) 11.529±1.334 4.17±0.520 15.699±.537 2.860±0.344 18.559±2.065 11.503±1.433 3.612±0.482 15.115±1.614
Annual return of P
(ρA/ kg hm-2) 0.675±1.414 0.353±0.551 1.028±1.629 0.537±0.364 1.565±2.189 0.678±1.519 0.697±0.511 1.375±1.711
　　In the mixed stand , annual mortality of fine roots , and
the return of N , P , amounted to 2.119 t hm-2 , 18.559 kg
hm-2 and 1.565 kg hm-2 , being 1.21 , 1.23 and 1.14
times as much as that in the pure stand , respectively (Tab
2).As far as the percentage of nutrient return through fine
roots turnover in mixed stand is concerned , Chinese fir
accounted for 62.1%of total N return and 43.1%of total
P return , and Tsoong tree accounted for 22.5% and 22.
6%, and undergrowth accounted for 15.4% and 34.3%
respectively.Correspondingly , 76.10% of total N return
and 49.3% of total P return were contributed by Chinese
fir , and 23.9% of N and 50.7%of P were contributed by
undergrowth in the pure forest.For both tree species , 70%
of annual nutrient return via fine roots was contributed by
those <0.5 mm in diameter.
Tab 3　Fine root density and soil factors in the mixed and pure forests(x±s)
Stand
Depth(δ/ cm)
Root
density
Bulk
density
ρ/g m-3
Non-
capillary
porosity
>0.25 mm
waterstable
aggeregate
Moisture
content
w/ %
Humic C Total N Total P Hydrolysable N Available P
w/mg kg-1
pH
Mixed
forest
0～ 20 1612±35.2
1.21
±0.05
10.24
±0.50
25.96
±2.37
32.911
±4.461
8.595
±0.416
1.18
±0.02
0.252
±0.005
106.8
±4.9
5.42
±0.40
5.23
±0.25
20～ 40 915.7±22.0 1.336±0.015 9.73±0.603 23.38±2.284 28.529±3.829 5.652±0.702 0.747±0.031 0.238±0.010 73.5±4.041 3.44±0.200 4.88±0.11
40～ 60 341.7±35.4 1.373±0.016 8.45±0.351 21.34±1.249 27.307±3.107 3.67±0.153 0.447±0.010 0.211±0.021 56.91±6.557 2.31±0.150 4.83±0.09
Pureforest 0～ 20 1260.5±76.9 1.221±0.015 6.56±0.351 18.21±2.278 26.488±4.835 6.326±0.251 1.03±0.112 0.195±0.014 86.21±2.646 4.92±0.306 4.87±0.126
20～ 40 748±26.5 1.421±0.038 5.77±0.420 16.85±2.354 24.344±3.451 3.581±0.173 0.58±0.028 0.17±0.005 55.62±5.000 3.28±0.252 4.82±0.081
40～ 60 438±20.0 1.534±0.068 3.83±0.252 14.24±2.133 23.021±3.739 2.745±0.289 0.367±0.013 0.165±0.009 49.2±3.215 1.06±0.500 4.9±0.146
.
Tab 4　Correlation coefficients(r)between soil factors and fine root density in the mixed forest and pure forest
Stand Indice
Bulk
density
Non-capillary
porosity
>0.25 mm
waterstable
aggregate
Moisture
content
Humic C Total N Total P
Hydrolysable
N
Available
P
pH
Mixed r -0.7760 0.6817 0.5768 0.6817 0.8416 0.8904 0.4109 0.6369 0.5566 0.4153
forest F 9.4603＊＊ 6.3073＊ 4.8231＊ 5.5491＊ 13.032＊＊ 17.9287＊＊ 3.9905 4.754＊ 3.505 3.9731
Pure r -0.7216 0.7209 0.6267 0.6542 0.8166 0.8689 0.3769 0.6424 0.4792 0.3301
forest F 7.5875＊＊ 5.9707＊ 5.5993＊ 4.7672＊ 11.0133＊＊ 15.7211＊＊ 3.5457 4.6639＊ 3.9611 3.4493
　　n=54;F 0.05(1 , 54)=4.018;F0.01(1, 54)=7.13;＊P<0.05 , ＊＊P<0.01
228 　　　　　　　　应 用 与环 境生 物学 报　　Chin J Appl Environ Biol　　　　　　　　　　　　　　 　　　8卷
3.4　Effects of soil factors on root distribution
The fine root densities and soil chemical and physical
factors in both of the two forests are listed in table 3.The
fine root density are significantly correlated with the soil
factors except for the total P , available P and pH , and the
highest coefficients are shown with the total N and humic C
(Tab 4).
4　DISCUSSIONS
4.1　Biomass and nutrient content in fine roots
The observation of a higher fine root biomass in the
mixed forest than that in the pure forest was in lined with
the finding of Liao et al.(1995)for a mixed forest of
Chinese fir and Michelia macclurei and a pure Chinese fir
plantation in Huitong
[ 11]　, which may be an important cause
for the higher stand productivity in the mixed forest.
A wide range of standing crop of fine roots from 3 ～
100 t hm-2 has been reported by Vogt et al.(1986)[ 12]
　.However , for forest stands over 10 years of age , the
published fine root biomass values for different forest types
of the world range between 400 and 6 000 kg hm
-2[ 13] .
The annual mean fine root biomass in our study lies in the
middle of the global range.Also , our values are comparable
to those reported for a Chinese fir-Michelia macclurei mixed
forest and a pure Chinese fir forest in Huitong in north
subtropics [ 11]　.With respect to total (above- and below-
ground) stand biomass , fine roots (d <2.0 mm)
represented a relatively small proportion in both of the
forests we studied:2.1% of total biomass in the mixed
forest and 2.3% in the pure forest.Similar values have
been found by numerous other researchers in a wide array of
forest types [ 14 , 15]　　.
The proportions of the dead to total fine root biomass in
our studies were less than those observed in most of
plantations(45% ～ 80%)[ 1 ,16 , 17]　, but they were similar to
those reported by Liao et al.(1995)[ 11]　.Several factors
may explain the observed differences in the proportion of
dead to total fine root biomass:(i) seasonal time of
sampling:dead fine root biomass may fluctuate considerably
throughout the season;(ii)the age of the stand;(iii)
nutrient status of the site; and (iv) moisture and
temperature status of the site.
The contribution of different diameter classes of fine
roots to total fine root biomass and turnover in forests differs
greatly.The percentages of roots <0.5 mm in diameter in
total root (<2 mm)biomass observed in our study are
similar to other studies.Hendrick et al.(1993)reported
that the percentage of the total fine root(<2 mm)biomass
accounted for by roots <0.5 mm in diameter was higher
than 70% [ 15]　;McClaughterty et al.(1982)showed that
the mass of roots <0.5 mm represented about one half to
two thirds of the total mass of all roots <3.0 mm [ 10]　.It
suggested that roots <0.5 mm were the main pool of dry
matter for fine roots.
Observations on fine roots of undergrowth have seldom
been conducted separately , thus , their contributions to root
turnover and nutrient cycle remains unclear.Finer et al.
(1997)found that understorey species accounted for 20%
～ 34% of the root biomass [ 18], which was a little higher than
that in our study (14.1% in mixed forest and 19.0% in
pure forest).The contribution of understorey species to total
fine root biomass is correlated with tree canopy status and
changes in understorey light availability
[ 18].A higher value in
the pure forest might be the result of a higher undergrowth
coverage (0.95 vs.0.80), which is due to the lower
canopy density (0.80 vs.0.95).
4.2　Vertical distribution
Root partitioning among co-existing species is still
poorly understood , but a recent paper by Brisson et al.
(1994)has shown that there exists a strong intraspecific
competition for rooting space for creosotebush (Larrea
tridentate)shrubs in the Chihuahuan desert of New Mexico ,
USA [ 19]　.The spatial distribution of plant roots in the soil is
a complex dynamic process that changes in response to the
changing morphological , physiological and ecological state
of plants and in response to the spatial and temporal
distribution of soil resources
[ 19]　.
Our data show that the two co-existing tree species in
the mixed forest differ clearly with respect to root
distribution along the soil profile in a shared soil volume
(Fig 1a).This is consistent with the findings of a vertical
stratification of the fine roots of two co-existing tree species
in the mineral soil under a mixed Pinus-Picea and a Pinus-
Fagus stands
[ 2]　.In a mixed oak-beech forest , Buttner et
al.(1994)found that oak fine roots were more superficially
distributed than beech roots in the organic layers , indicating
a vertical stratification of the root systems of the two species
[ 3]　.Our results showed that the vertical stratification existed
229　3期 杨玉盛等:杉木观光木混交林和杉木纯林群落细根生产力 、分布及养分归还 　　
not only between trees , but also between trees and
undergrowth species (Fig 1a , b , c ).The different
proportion of roots found in the different soil layers among
species could be seen as an acclimatization for the
coexistence of different plant species in order to minimize
competition for water and nutrients[ 18] .
The fine roots of the two tree species in the mixed
forest were both concentrated at surface soil of 0 ～ 20 cm ,
especially those of Tsoong tree , which may be due to the
more accumulation of nutrient in surface soil of mixed
stand.A reduction in abundance of fine roots for Tsoong
tree in deeper soil indicated the weakness of this species in
competition for nutrients with Chinese fir when there existed
a nutrient depression , especially in 20 ～ 40 cm soil layer.
Numerous studies[ 1 , 2] 　have shown that the majority
of forest tree roots are located in the upper 50 cm of a soil
profile with most of the absorbing roots in the top 20 cm.
Similar results were obtained during this study for Chinese
fir and Tsoong tree in the mixed forest.Several reports
stated that high concentration of fine roots in the surface soil
layers of the forest is related to higher nutrient
concentrations and more moisture retention because of plant
litter on the surface soil , particularly during periods of
active growth
[ 1]　.The leaf litter forms a shelter for the
surface roots by providing a moist microclimate for the
development of new roots.Further , a shallow-rooted system
was adapted for the uptake of nutrients from detritus ,
stemflow and rainfall as implied in the direct nutrient
cycling and nutrient trapping theories.However , Buttner et
al.(1994)reported that the superficial distribution could
be a consequence of the highly acidic soil profile which
forces the trees to concentrate fine root growth in the
nutrient-rich organic horizons [ 3]　.
In the pure forest , however , the bulk of fine roots of
Chinese fir occurred at a deeper depth than those in the
mixed forest.The subsoil colonization of fine roots in the
pure forest may be due to one or more of the following:(i)
the athelopathic substances produced by the litter of Chinese
fir in forest floor;(ii)the competition from fine roots of
shrubs.The decomposition product of the mixture of fallen
litter of Chinese fir and Tsoong s tree was likely to be less
or no harmful to the growth of fine roots in the mixed forest.
A low crown density in the pure forest increased the light
availability for undergrowth shrub species , thus , a strong
belowground competition between shrubs and Chinese fir
occurred in the superficial soil layer.Liao et al.(2001)
found that the distribution of fine roots of Chinese fir got
deeper in the soil layer with the increase of replanting
generations
[ 20]　.They owed this penology to soil degradation
resulted from the management disturbances such as
harvesting , slash , burning , etc.Following a cycle of slash
and burn land preparation , losses of nutrients occurred , and
inorganic ions were susceptible to leaching.Thus , the
development of a superficial fine-root system was certainly
important in nutrient conserving , especially in the repeating
monoculture of Chinese fir.
A negative exponential equation fits the declining
pattern of root density with the increase of soil depth very
well for both of the two forests (Fig 1d).A negative
exponential distribution of fine root biomass density along
the soil profile was also observed in other studies [ 21～ 23 ]　.
4.3　Annual fine root production and nutrient return
Our estimates of fine root production lies in the range
of 1.4 t hm-2 to 11.5 t hm-2 obtained from worldwide
forest ecosystems [ 16]　.Although fine roots contribute only a
very low proportion to total stand biomass , they account for
30%～ 80% of total stand net primary production [ 1 , 12 , 24]　.In
this study , though fine roots occupied only 2.1%～ 2.3%
of the total stand biomass , they accounted for 20.9%～ 22.
9% of the total stand net primary production [ 25]　, which was
higher than those in the broad-leaved Korean pine forest of
Changbai mountain(19.4%)[ 26]　, in monsoon broad-leaved
evergreen forest (16.8%)and in coniferous and broad-
leaved mixed forest in Dinghu mountain(17.4%)[ 27]　.The
variations therein may be related to the difference in site
conditions and tree species.
Fine root turnover was related to a nutrient absorptive
strategy , that is , new roots should occur frequently at a new
position as a substitution for senescing roots to meet with the
variational status of soil water and nutrient in prevention of
excessive respiratory consumption of ineffective roots [ 28]　.It
was reported that differences in turnover rate of fine roots
among species were related to biological characteristics ,
climatic conditions , life span and disturbance from forest
managements [ 11]　.It can be seen from table 2 that the
turnover rates for both Tsoong tree and Chinese fir fell into
the upside of the range of 0.5 ～ 1.20 reported in other
studies [ 29]　, which showed that both of the two species in the
230 　　　　　　　　应 用 与环 境生 物学 报　　Chin J Appl Environ Biol　　　　　　　　　　　　　　 　　　8卷
middle-subtropics had a relative high fine roots turnover
rate.
It is widely recognized that the turnover and
decomposition of fine roots may contribute substantially more
to soil carbon and nutrient pools than those of aboveground
litter-fall [ 12 , 14 , 15]　.Researches showed that annual input of C via
fine roots(d<2 mm)accounted for 25%～ 80% of total
soil C pool [ 10]　.Hendrick et al.(1993)reported that , in
two sugar maple forests , fine root turnover dominated
nutrient inputs to the soil , accounting for approximately
48%～ 58%of N cycled annually [ 15]　.In some ecosystems ,
the input of nitrogen to soil through fine roots turnover had
been reported as 18%～ 58% greater than through litterfall
aboveground
[ 12]　.Li et al.(1998)reported that N return
from fine root accounted for 49.5% of the total annual N
return in stand , 3.1%more than that of litterfall , 42.3%
P and 28.9%Mg , slightly less than those of litterfall [ 30]　.
In this paper , annual fine root mortality in mixed stand
and pure stand were 31.4% and 27.8%of annual litterfall
above ground , respectively.Annual return of N , P from
fine roots of mixed stand accounted respectively for 38.3%
and 67.4% of those from litterfall.It was showed that
nutrient return from fine roots was an important source to the
soil nutrient pool , especially for P.
Surprisingly , roots of <0.5 mm in diameter accounted
for a large proportion of the carbon and nutrients in fine root
standing crops , as well as fine root production and
mortality.These roots played a major role in the carbon and
nutrient cycles of plantation forests , and care should be
taken to fully recover very fine roots in future studies.
4.4　Effects of soil factors on root distribution
Soil conditions can adversely affect root growth and in
some circumstances can reduce crop yield , so much
attention has been directed towards understanding the
mechanisms underlying these responses.This has also led to
a greater recognition of the interactions between soil factors
and root growth.However , the influence of soil factors on
root growth remains unclear.This may be attributable to the
lack of knowledge on soil conditions in different studies.
The soil where fine roots occurred densely might
become more porous because of the mechanical penetration
during growth periods of fine roots and the plenty of small
root pores remained after root disappearance;inversely ,
more porous soil is certainly suitable for fine root growth.In
addition , the soil humus produced by root decomposition
and root excretion is a good agglutinant for soil , especially
for subsoil , to form aggregates.These were confirmed by
the significant correlations of root density with bulk density ,
non-capillary porosity and the content of >0.25mm water-
stable aggregate (Tab 4).A negative correlation between
root density and bulk density was also reported elsewhere.
Shierlaw et al.(1984)reported that the root lengths of
annual ryegrass and maize were decreased by half when the
soil bulk density increased from 1 200 g cm-3 to 1 550 g
cm-3[ 31] 　.
Attempts to correlate tree root activity to soil water
availability have yielded controversial results.Our results
were similar to Persson (1983)and Ares et al.(1992)
who found a negative impact of water shortage on tree root
biomass , root growth [ 1～ 2]　.However , this contrast with
studies that there are minor or no reduction of root activity
or biomass of fine root under the condition of water shortage
[ 21]　.According to Mallonen et al.(1998), soil pH can
exert a great influence on root distribution [ 17]　.They found
that the solubility of Al increases sharply in acid soils at pH
values below 5.5 , and can cause toxic effects and poor root
growth.But no significant correlation between root density
and soil pH value has been observed in our study though
most of the pH values less than 5.0.
Ares et al.(1992)and Heilman et al.(1994)both
found[ 2 ,32] 　 that , among soil factors , the organic matter
content provided the best correlation with root density.A
very strong correlation between root density and humic C
was also detected in our study.This may explain the
frequent occurrence of fine roots in combination with organic
detritus , the relatively dense distribution of fine roots in
cumulic soils as well as the more sharp decrease in soils
with less organic matter content at lower depths.
How the soil nutrients can affect the root distribution
has seldom been done.Heilman et al.(1994)reported
that the distribution of fine roots in the stratified soil profile
was correlated with soil Kjeldahl N with a determination
coefficient of 0.73 [ 32]　.Our study found a correlation of root
density with soil total N and hydrolysable N , with the total
N showing the best correlation(Tab 4).It implied that fine
root had strong tropisms for soil N , and their growth might
be restrained in soils where there is low N availability.
However , no significant effect of soil total P or available P
231　3期 杨玉盛等:杉木观光木混交林和杉木纯林群落细根生产力 、分布及养分归还 　　
on root distribution has been detected in our study.This is
out of expectations in view that P availability has been
usually considered as an important factor that restrict tree
growth.
From our results , it can be deduced that , in general ,
the growth or distribution of fine roots in the subtropical
mountainous area can be predicted by a combination of soil
bulk density , N availability , humic C and moisture
content.However , how can this prediction run well needs a
vast of further studies.
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大读者欢迎及专家好评的学术期刊.1999 年荣获首届中国期刊奖提名奖.被 SCIE、CA等国际权威检索系统收录.ISI最新出版的期
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233　3期 杨玉盛等:杉木观光木混交林和杉木纯林群落细根生产力 、分布及养分归还