Response of Grassland Biomass to Soil Moisture in

Response of Grassland Biomass to Soil Moisture in the Arid Mountainous Area of the Qilian Mountains
W A N G Shunli1, W A N G Rongxin1, JING W enm ao1, ZHAO W eijun1, N IU Yun1, M A Jian1, ZH U Hong2
(1. Academy of Water Resources Conservation Forest of Qilian Mountains of Gansu Province, Zhangye, Gansu 734000, China; 2. Northwest Research Institute of Mining and Metallurgy, Baiying, Gansu 730900, China)
Journal of Landscape Research 2018,10(1): 77-82
Abstract The Pallugou watershed o f the Qilian Mountains in the arid region o f nortiieast China was
selected for research to analyze the species, height, and biomass in typical mountain grassland with an altitude o f 2,700-3,000 m and measure soil moisture, so as to explore the seasonal chatacteiistics of grassland biomass as altitude increases and the felationship between grassland biomass and soil moisture. The results showed that (1) with a mean value o f 135.36 g/m 2, grassland aboveground- biomass showed a unimodal distribution from tise to decline as altitude increased, and reached its maximum o f 176.79 土 28.37 g/m 2 at an altitude o f 2,900 m; with a mean value o f 946.13 g/m 2, grassland underground biomass showed an uptrend as altitude increased^ and reached its maximum of 1，301.19 土 68.24 g/m 2 at an altitude o f 3,000 m; (2) the difference between abovegtound biomass and underground biomass in the grassland at different altitudes was significant; (3) values o f foot shoot ratio o f the arid mountain grassland varied between 4.14—11.95; (4) values o f soil moisture content o f the arid mountain grassland yaned between 9.23%-31.31%; (5) there was a positive correlation between aboveground biomass and mderground biomass and the mean soil moisture content (p < 0.05), with a correlation coefficient of 0.778 4 and 0.784 3respectively, soil layers with different moisture content made different contributions to grassland biomass, and moisture content in the soil layer where ovet-60-cm root systems were located was of significance to grassland biomass.
Keywords Mountain giassknd, Biomass, Soil moistute, Qilian Mountains DOI 10.16785/jissn 1943-989x.2018.1.016
T he Q ilia n M o u ntains, lo cated on the northeastern edge o f the Q inghai-Tibet Plateau, are a “w et island” tha t extends in to the arid re g io n o f n o rth w e st C hina. I t p ro te cts the ecological secunty in northwest Q iirn , and drives the sustainable economic and social development in H exi C o rridor and the downstream regions. As one o f the areas that is m ost sensitive to global clim ate change, the Q ilia n M ountains plays a decisive foie in the overnll development o f the countty. A rid m ountain grassland o f the Q ilian M ountains is a com plex ecosystem w ith large spatial differences o f eco-hydrological variables[1]. In recent years, the phenom enon that a large am ount o f water fo r ecological use has been occupied fo r other uses is common in the arid region o f northwest China, leading to spreading desertification, obviously inadequate c a rry in g ca p acity o f w a te r resources and eco-environm ental cap acity^. Study on the relationship between m ountain grassland and moisture content involves many d iscip lin e s' In order to prom ote the development o f disciplines and meet science and technology needs, it is necessary to fu lly understand issues including the absorption o f soil moisture by vegetation^ plant
transpiration，and soil evaporation in the soil- plant-atmosphere continuum.
D om estic scholars have conducted many studies on grassland s tru c tu re [4_8], species dive i:sit:y[9-10]，and grassland biom a ss[11_13]. M ost o f these studies are short-term o r static obsefvations, and there have been few large- scale regional studies. Ecosystem s o f forest- grassland com posite watershed play a key role in and and semi-arid regions. W atet is a lim iting h c to t fo r the growth, distribution, and restnration
o f vegetation in arid regions. liu Jinrong et a l[141 considered that vegetation in alpine grassland in the Q ilian Mountains is characterized by lowness and adaptation to low temperature environm ent Chang Xuexiang et aL[151 studied the diversity o f spedes a at different altitudes in grassland o f the Q ilk n Mountains. Sheng Haiyan et aL[161 studied the change law o f soil bu lk density, m oisture content, and nutrient content o f Jinlum ei shrub grassland in the Q ilian M ountains by using the g rid m ethod. D a i Shengpei et al.[17] acquired data through RS, G IS, and SPOT V G T -N D V I and used image difference m ethod, trend line analysis method, mean value analysis method, and
o f v^etation cover in the grassland o f the Qilian M ountains bo th tem porally and spatially. Yan YueJ e et a i[18] analyzed the status o f the northern slope o f the Q ilian M ountains and degraded grassland based on the m onitoring data o f the Q ilian Mountains. The purpose o f this paper is to reveal the response o f grassland biomass to soil moisture and find the thresholds o f soil moisture grounded on the data o f Pallugou watershed in the
1 O verview of the study area
and research methods
1.1 Overview of the Qilian Mountains
The Q ilian M ountains (94°24'-103°46, E, 36043'-39042' N ) are located in the center o f Eurasia, It belongs to the alpine valley landscape w ith a varied topography. Its altitude is generally betw een 2,000-4,000 m. T he highest peak KangzeJ gyai, situated in the south o f Jiuquan, rises to 5,826.8 m [19]. The Q ilian Mountains run east-west Ecosystems in the Q ilian M ountains are com plex and there are high levels o f spedes diversity and genetic diversity120'211. O ver there, glaciers, snow-capped m ountains, grassland, and forests add radiance and beauty to each
Received: December 19,2017
Accepted: January 23,2018
Sponsored by N ational Natural Science Foundation of China (91425301,31360201,91225302).
E-maiL Wangshunl23_78@
77
Response of Grassland Biomass to Soil Moisture in the Arid Mountainous Area of the Qilian Mountains
other, form ing a unique ecological safety barrier that nurtures the vast expanse o f fe rtile land in H e xi C o rrid o r. Its n o rth e rn and w estern regions have a w et clim ate, w hile its southern and western regions have a dry climate. Due to differences in topography and climate, obvious vertical distribution can be found in its soil and vegetation types. Picea. crassifo lia, w hich is the only species constituting the arbofous layef，is distributed on the shady and semi-shady slopes in patchy form. The grassland w ith an altitude o f over 3,300 m is a w et shrub forest dominated by P o te n tilla fru tic a s a, Caragana ju b a ta and
The sunny slope and semi-sunny slope o f the Q ilian M ountains are mainly grassland dominated by Polygonum viviparm n, Carex Carexatmta. m dS tipa.
1.2 Overview of the study area
In this paper, the study area is the Pailugou watershed (lO O^T-lO O0!? E, 38°32-3S°3y N) o f X ishui forest region in the m iddle section o f the Q ilian Mountains, w ith an altitude o f 2,640- 3,796 m. I t covers an area o f 2.74 km2. Annually, its average temperatxife is 1.6 The hottest m onth is July, w ith average m onthly temperature ranging from10.0-14.0^. The coldest m onth is January, w ith average m onthly tem perature ranging fi:om-9.8-12.5 The average annual p re c ip ita tio n is 354.3 m m, and the ra in in g m ainly occurs fro m June to September. A n- nually, the total hours o f sunshine are 1，892.6 h. The annual average relative hu m id ity is 60%. The average amount o f evaporation is annually 1,081.7 mm. The Pailugou watershed features steep terrain, crustal topography, and obvious vertical d istrib u tio n o f vegetation (F ig.l). Soil there may fa ll in to three classes: m ountainous fo re s t gra y-b ro w n s o il, m ou n ta in chestnut soil, and sub-alpine shrub meadow soil. These soils are characteristic o f th in soil kyer, coarse texture, and m edium organic content w ith a pH o f 7.0-8.0. To the class o f parent materials belong peat rock, conglom erate, fuchsia sand shale, etc.
1.3 Arrangement of sample plots
In th is p a p e r, th e ty p ic a l g ra ssla n d com m unity w ith an altitude o f 2,700-3,000 m in the Pailugou watershed was taken as the research object, in w hich 10 m X 10 m fixed sample plots were set up. In the grow th season between M ay and September in 2014 to 2015, five 1m x1m quadrats were laid diagonally in each sample p lot, the latitude and longitude, altitude, and hum idity o f the sample plots were recorded, height, coverage, and abundance o f species in each sample p lo t were surveyed, and biomass o f herbaceous plants in five quackats
100olT0M E100〇18,0"E100o18,30"E •38o33,30"N
38〇33,3〇”N.•38〇33,0，，N
38〇33,〇,，N. -3So3T30^
100。

1谷^"E
-38°32,0nN
Picea crassi f olia
Alpine meadow
Sub-alpine shrubs
Shrubs
High coverage grassland
Middle coverage grassland
Low coverage grassland
Bare rock
Building
Trial
115 0 230 m
10Q°ir〇M E______________100ol；T30，’ E
38o32,0"N-
Fig.1 Distribution of vegetation in the Pailugou watershed
in each sample p lo t were selected. Biomass in 20
quadrats was analyzed per m onth, totaling 100
quadrats. Table 1and Table 2 show the basic
con ditions o f the observation sites and the
m ain plant species respectively. The coverage
o f the com m unity is 56-81%, and the average
height o f the quadrat is 8-15 cm. Sample plots
covered by m ountain chestnut soil have a slope
o f 25-32° and an exposure o f 180-252°.
1.4 Dynamic determination of biomass
and soil moisture
Aboveground and underground biomass in
each quadrat was measured. The aboveground
biomass was measured by the harvest method,
w ith sampling area o f 1m X 1m. The weighed
aboveground biomass was packaged in valve
bags and returned to the laboratory fo r drying at
80 ^ w ith precision o f 0.01 g. The underground
biomass was measured by the trench excavation
method, w ith sampling area o f 50 cm X 50 cm
and excavation depth o f 40 cm. Sundries on the
ground corresponding to aboveground biomass
were removed fo r sampling. Sample processing
w ent throu gh several processes such as the
smashing and g rind ing o f soil，soil sam pling
w ith fine sieve，package o f ro o t system w ith
nylon gau^e, and cleaning w ith branch water.
The sampled herbaceous plants were dried in the
oven at 80 X l fo r 24 h to constant weight, and
weighed fo r the dry weight on an electronic scale
w ith precision o f 0.01 g to calculate the moisture
content o f herbaceous plants. In this study，it
was d iffic u lt to differentiate between dead and
liv in g roots under ground by the ro o t co lo r
78
Journal of Landscape Research
Table 1 Overview of observation sites
Observation sites No. o f sample plots Latitude and longitude Altitude/fm Exposure#。

Slope 夕0Coverage#%Hdght/^m 2,700 m1# above the slope100°iri4.3" E,2,708252°SW30720.09 2# the middle o f the slope38°33,22.2" N600.12
3# below the slope710.14
2,800 m4# above the slope m°\rilA n E,2,811180°S25610.08 5# the middle o f the slope38°33'18.0" N560.09
6# below the slope650.11
2,900 m7# above the slope100〇17'46_2" E,2,917193°SW30670.11 8# the middle o f the slope3B°33,10.3H N810.13
9# below the slope740.15
3,000 m10# above the slope100〇17,58.8" E,2,996210°SW32690.12 11# the middle o f the slope38°33'3.5" N580.13
12# below the slope630.14
Table 2 Main plant species in observation sites at different altitudes
Observation sites Main plant spedes
Mountain-desert grassland with an altitude o f 2,700 m Mountain-desert grassland with an altitude o f 2,800 m Mountain grassland with an altitude o f 2,900 m Mountain grassland with an altitude o f 3,000 m Sdpa breviHora,Agropp:on cdstatamy SteJlera chamaejasmeiM edicago p olpnotpha, Aster tatadcus, PotentiUa bifurcayAchnatherum splendens
Sdpa breviHorayAgropyron cdsta.tumyStellera chamaejasme^M edicagopolymorpha, Oxytropis subfalcata,Leonto-podium leontopodioides, PotentUla discolory A rtemisia capillanes^Ids lactea
Stipa gtandisy Stipa breviSorayAgropyron cnstatumi Pedicuhds reaupinanta, Allium p olyrhizum^ PotendJla multi-caulis, Anaphalis hctea
Stipa. gtandiSf Sdpa bteviBora, Agropyron cnstatum, Stellenz chamaejasine^ Potentilla discolor^ PotentUla bifurca9 Achnatherum inebdons^ Gentiana. macrophyllo, Ids hctea
because there were the perennial herbaceous plants in the grassland, and the underground biomass -W2S calculated with the total biomass of the root systems of herbaceous plants below the surface.
The ratio o f dry weight to fresh weight of samples T was calculated by Formula 1, and biomass in the quadrat were calculated by Formula 2.
iw= iw x y(7\ ^total d ty s a m p l e s w total&e s h s a m p l e s±'v'/'
Soil moisture was determined by drying method Three fixed sites monitoring soil moisture were set around each sample plot On the 1s t, the 11th, and the 21st of each month from May to September in the growth season, soil at layers of 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm and 40-60 cm was sampled by earth boring auger respectively. Soil samples were then took back to the laboratory where soil samples were weighed with a 0.01 g-predsion electronic scale, and the weight of soil samples was recorded as wet weight W P Later, soil samples were dried in an oven at 105 ^ to constant wei^it, and the wei^it of soil samples was recorded as dry w d^it W2. And soil moisture content 6m is defined as follows:
(3).
P recip itatio n in the sam ple p lo t w as determined by the standard rain gauge used by the meteorological statioa
1.5 Data processing
The grassland biomass was analyzed by SPSS19.0 with analysis of variance (ANVOA).
Specifically, ANVOA o f soil moisture content
and grassland community structure at different
altitudes and slope positions was conducted to
compare the differences. The survey statistics
and data processing w ere done w ith Excel
2010, and the results were expressed as mean 土
standard error. SPSS regression analysis was also
used more often in the study of the relationship
between grassland vegetation characteristics and
soil moisture*
2 Results and analysis
2.1 Seasona丨
variation of aboveground
biomass with increase in altitude
The aboveground grassland biomass in
the northern slope o f the Qilian Mountains
with altitudes of 2,700 m, 2,800 m, 2,900 m
and 3,000 m were 80.49 ± 20.52 g/m2, 113.98
± 24.54 g/m2and 176.79 ± 28.37 g/m2, and
170.17 ± 29.52 g/m2(Fig.2). Biomass reached
the maximum in the grassland with an altitude
o f 2,900 m w here w ater and tem perature
conditions were best. The grassland with an
altitude below 2,900 m where temperature was
proper and precipitation was less could meet
herbaceous plants, grow th needs. T he dry
matter mass o f grassland increased first and
then decreased with the elevation increasing.
Aboveground biomass, height, and coverage
o f herbaceous plants all show ed positive
growth before the dry m atter mass reached
the m axim um. A fter the d ry m atter mass
reached the maximum, aboveground biomass
in the grassland decreased. ANVOA showed
significant differences in grassland at different
altitudes 中 < 0.05, R2二 0.923 8).
G reatly affected by tem p eratu re, the
grassland In the Qilian Moimtains turns green
later. Generally, grassland biomass began to
grow and accumulate in early May, and increased
with the increase o f plant growth and rhythm,
temperature, and precipitation. The aboveground
biomass in June was only 86.71 ± 17.73 g/m2.
W ith the increase of temperature and preci­
pitation, the aboveground biomass showed
an uptrend. From July to August when water
and temperature conditions were the best, the
aboveground biomass increased rapidly, reaching
151.98 ± 26.42g/m2 and 162.05 ± 34.42 g/m2,
respectively (Fig.1). At this time, the soil moisture
and temperature in the Qilian Mountains were
sufficient, and the grassland vegetation was fully
grown. As photosynthetic efficiency gradually
maximized, the dry matter accumulation o f
most vegetation significantly increased. M ost
herbaceous plants in this period were in full
flowering stage, with the largest accumulation of
dry matter, forming the peak o f aboveground
biomass of mountain grassland. That is to say,
the aboveground biomass ^^s significantly higher
than that of Jxme (p < 0.05). In September, the
temperature began to decrease in the Qilian
Mountains, and the surface o f the grassland
began to turn yellow. B esides, herbaceous
plants entered the productive phase, and the
79
Response of Grassland Biomass to Soil Moisture in the Arid Mountainous Area of the Qilian Mountains
1,800.001,600.001.400.001.
200.001,000.00800.00600.00400.00200.00
0.00
■ 2,700 m 0 2,800 m
J ：
□ 2,900 m
□ 3,000 m
工
工n i
250.00
200.00150.00100.00 50.000.00
■ 2,700 m
0 2,800 m
□ 2,900m □ 3,000 m
工
M y
工
I
June
A u ：
gust September
July
June
August
September
aboveground biom ass decreased gradually, reaching 140.67 ± 24.38 g/m 2. By October ， the grassland withered over a large area, and herbaceous plants remained dominant until the following year in May to return to green. Over the whole growth season, the aboveground biomass of the arid grassland showed a unimodal distribution with the seasonal variation, and the aboveground biomass peaked in August This is consistent with the results of studies conducted by Yang Futun et al.[22] and Huang Deqlng et al 严.
2.2 Seasonal variation of underground biomass with increase in altitude
In a growth season, the variation trend of aboveground biomass in grassland is mainly imimodal and bimodal, while the later one mainly appeares in the early and late growth stages. How­ever, due to the different utilization methods, the growth cyde of various plants is different The grassland underground biomass in the Qilian the underground biomass increased first and then decreased with increasing altitude ^> < 0,05, R2 二 0.993 8). The underground biomass in the grass­land with altitudes of 2,700 m, 2,800 m, 2,900 m, and 3,000 m was 782.74 ± 60.66 g/m2, 818.30 ± 69.32 g/m2, 882.29 ± 68.24 g/m2,1，301.19 土 86.64 g/m2, respectively. The underground bio­mass reached the maximum in July with an aver- age of 1,334.15 ± 66.91 g /m2 (Fig.3). This may be closely related to the growth rhythm of herba­ceous plants, the unsynchronized growth of root systems of many dominant spedes, and the dif­ferences in climatic conditions and environmental factors. Accurate estimation of undeiground b io mass is key to model predictions and to proper assessment of the role of regional carbon budget in grassland ecosystem. Because of the limitations of sampling methods, howevei; there is a lack of data on the underground biomass. In this study, the measured data of aboveground and under­
ground biomass were obtained based on a unified
sampling method, and there is a good correlation between aboveground biomass and underground biomass. The root shoot ratio of arid mountain grassland in this paper varied from 4.14 to 11.95. The estimation o f biomass carbon pool was grounded on the relationship between the two as well as the relationship between aboveground biomass and NDVI, to a certain extent, which re­duced the uncertainty of estimation of grassland biomass.
2.3 V ariation of soil m oisture w ith increase in altitude
Soil moisture is a necessary condition for plant growth. Under different soil moisture, the growth status of plants is also different, which affects plants’ biomass and bearing capacity In arid and semi-add regions o f the northwest, soil moisture has become the limiting factor for plant growth and development The seasonal variation o f soil m oisture is m ainly affected by such factors as atmospheric precipitation, vegetation types, air temperatxire, and soil evaporation. Meanwhile, differences in altitudes, exposure, and soil structures also have a great impact on the change of soil moisture. The soil moisture change law is very complicated, and is the result o f the interaction o f m any environm ental factors. According to the analysis of the seasonal variation o f soil moisture In the 0-60 cm soil layer of the arid mountain grassland in the study area (Fig.4), the seasonal variation trend of soil moisture o f the grassland at different altitudes was basically the same, namely small fluctuation in the early and late growth seasons and great fluctuation in the middle one. The differences in soil moisture content at different periods of plant growth might be related to factors such as precipitation, precipitation intensity, and vegetation growth. In the early and late growth seasons when precipitation was small, herbaceous plants grew more slowly, resulting in
small evapotranspiration and small fluctuation in soil moisture content. In the mid-growth season, with the increase o f precipitation, the herbaceous plants grew rapidly, leading to great evapotranspiration and great fluctuation in soil moisture content From May to September of the growth season, the soil moisture o f arid mountain grassland fluctuated between 9.23% and 31.31% with an average o f 14.94%. The soil moisture content of the grassland decreased first and then increased at different altitudes of 2,700-3,000 m.
2.4 Response of grassland biomass to soil moisture
Precipitation provides moisture for plant growth and developm ent. W ithin a certain range, precipitation is positively correlated with grassland biomass, but the improvement of grassland productivity is related to whether precipitation in different periods can meet plant growth. The aboveground biomass in the add mountain grassland tended to decrease first and then increase with the increase of monthly precipitation. This may be due to the fact that when the monthly precipitation is small, soil moisture content is also small, and the growth activity o f the plant is blocked obviously with small biomass. There was a significant linear correlation between underground biomass and monthly precipitation (p = 0.042, R2 = 0.918) in the arid mountain grassland. The greater the monthly precipitation was, the larger the biomass o f herbaceous plants was. T he correlation between the biomass and the precipitation in the sunny slope is as follows: aboveground biomass (R2 - 0.991) > underground biomass (R2 - 0.918).
ANOVA. of aboveground biomass, under­ground biomass, and soil moisture content in the grassland from May to September in 2014 (Fig.5) showed that the grassland aboveground biomass and underground biom ass was significantly
Fig.2 Seasonal variation of aboveground biomass of herbaceous plants at different altitudes
80
Fig.3 Seasonal variation of underground biomass of herbaceous plants at different altitudes
^/s//SW B U I .2
q p u n o &3p u n
K
a /8/、w s m n .2q
pxm o&
AoqY
Journal of Landscape Research
—O— 2,700 m ~~ 2,800 m —0—2,900 m
-D -3,000 m
2 500.00
2 000.00
1 500.00
1 000.00
500.00
n nn
I Aboveground biomass Underground biomass
0 ----------------1-----------------1----------------1-----------------1-----------------1
0-10
10-20
20-30 30-40
40-60
0.00
5.00
_
1500
20.00
2500
Soil depth//cm
Soil moisture //%
Fig.4 Variation of moisture content at different soil layers in different Fig.5 Relationship between grassland biomass and soil moisture
altitudes
correlated with soil moisture content (p < 0.05), indicating a significant positive correlation between grassland biomass and soil moisture content. The correlation between aboveground biomass as well as underground biomass and soil moisture was 0.778 4 and 0.784 3, respectively. D uring the growth season, the biom ass o f herbaceous plants increased with the increase of soil moisture content There were differences in soil moisture between soil layers at different altitudes and in the variation of soil moisture. The coefficient of variation of soil moisture of grassland at different altitudes varied from 7.54% to 25.96%, and the coefficient of variation did not show obvious regularity with the increase of soil depth. Despite great change, coefficient of variation in the surface was still a moderate variation. Great changes in soil moisture indicate that soil moisture increases rapidly during the rainfall, and is liable to transpiration during the drought. In the growth season, limited by insufficient water in the arid mountain grassland, grassland biomass was affected by the change of soil moisture, especially the soil moisture at the depth of 0-30 cm, which affected the coefficient of variation of surface soil moisture.
3 Conclusion
(1) Grassland ecosystem plays an important role in the response to future climate change. G rassland biom ass is an im portant part o f the ecosystem. However, due to the limitation o f surface observation data and the spatial heterogeneity of biomass data, w e still lack know ledge o f the variatio n o f grasslan d biomass and its response to climate change in the Q ilian M ountains, and there is still controversy about the dynamics o f grassland biomass[9]. Based on a unified survey method, this paper obtained a large number of field survey data on aboveground and underground biomass. With a mean value of 135.36 g/ni2, the aboveground grassland biomass in the Qilian Mountains increased first and then decreased as the altitude increased, and reached the maximum of 176.79 ± 28.37 g/m2 at an altitude o f 2,900 m; with a mean value of 946.13 g/m2, the underground grassland biomass in the Qilian Mountains increased progressively as the altitude tises，and readied the maximum of 1,301.19 土 68.24 g/m2at an altitude of 3,000 m. There were significant differences between the aboveground biomass and underground biomass at different altitudes (p < 0.05).
(2) The aboveground biomass and under­ground biom ass in the grassland showed a unimodal distribution in the growth season between May and September. The aboveground biomass reached its maximum of 162.05 ± 34.42 g/ m 2 in August, while the underground biom ass reached its m axim um o f 1,334.15 ± 66.91 g/m in July, which might be dosely related to the growth rhythm o f the grassland, the asynchronous growth of the root system of dominant spedes, and the difference o f climatic conditions and environm ental factors. T he accurate estimation of the undeiground biomass is the key to model predictions and to proper as­sessment of the role of regional carbon budget in grassland ecosystem. The spatial distribution o f grassland biom ass is inextricably linked with environmental factors, and envitonmental differences at different altitudes are bound to have an impact on grassland biomass[23].(3) A krge number of studies have shown that w ater and tem perature conditions are the limiting factors that affect the growth of grassland ecosystem, especially those in the arid and semi-arid areas[24'25]. Grassland biomass has a time-lag effect on soil moisture112,221. In this paper, the relationship between grassland biomass and moisture content was analyzed by
means of average moisture content at different
soil layers. During the growth season, there was a positive correlation between grassland biomass and accumulated value of soil average moisture content The contribution of moisture content of different soil layers t» biomass in grassland at different altitudes varied. The moisture content in the soil layer where root systems with a length o f above 60 cm were located was o f great significance to grassland biomass.
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