土壤与环境 2000, 9(4):316~321
Soil and Environmental Sciences
http://www.environment.soil.gd.cn
E-mail: ses@soil.gd.cn
Article ID：1008-181X (2000) 04-0316-06
Effects of Soil Warming on Some Soil Chemical Properties
XIAO Hui-lin1, ZHENG Xi-jian2
( 1: Guangdong Institute of Eco-environmental and Soil Sciences, Guangzhou 510650, China;
2: Guangzhou Station of Environmental Monitoring, Guangzhou 510030, China )
Abstract: Change in soil temperature induces the changes in the microbial community composition and their activity; some
communities at higher temperatures have the ability to access to or metabolize substrates that are not used by members of the
microbial community at lower temperatures; therefore, increases in soil temperature will influence the C, N and S cycling in soil
eco-systems. Most research results indicated that temperature has the effects on concentrations of dissolved organic matter in soil
solution and on composition of soil organic P. These conclusions are significant for predicting the effects of global climate change on
soil.
Key words: soil temperature; soil chemistry; climate change
CLC number: X142; S153
Document code: A
土壤温度上升对某些土壤化学性质的影响
肖辉林 1，郑习健 2
（1：广东省生态环境与土壤研究所，广东 广州 510650；2：广州市环境监测中心站，广东 广州 510030）
摘要：土壤温度变化导致微生物群落组成及其活性产生变化；某些微生物群落成员在较高温度时有能力代谢那些在较低温度
时不能被利用的基质；因此，土壤温度上升将影响土壤生态系统中的 C、N、S 循环。大多数研究结果显示，温度对土壤溶
液中的溶解态有机质和土壤有机磷组分有较大的影响。这些结论对预测全球气候变化对土壤的影响有重要的意义。
关键词：土壤温度；土壤化学；气候变化
中图分类号：X142; S153
文献标识码：A
In the interplay of the soil and the atmosphere, the
soil can be both a contributor to and a recipient of the
impacts of climate change. In the past, land
management has generally resulted in considerable
depletion of soil organic matter and the release into
the atmosphere of such radiatively active gases as
carbon dioxide, methane, and nitrous oxide. Global
climate change, to the extent that it occurs, will
strongly impact all soil process[1].
It is suggested that soil should be a sensitive
indicator of climatic patterns, and it should be
expected to manifest measurable responses to global
warming[2].
1 Soil Warming and Dynamics of Soil C, N
and S
Microbial metabolism in soil is controlled by
substrate availability and by soil temperature and soil
matric potential. The mineralization of soil organic
Biography: XIAO Hui-lin ( 1961-), male, associate-professor.
Received date: 2000-08-26
matter (C or N) conforms to first-order kinetics and
rates can be estimated with knowledge of the substrate
pool size and the response of the first-order rate
constant (k) to soil temperature[3]. The temperature
dependency of this process is often described as an
increase in the first-order rate constant, whereas the
substrate pool metabolized is assumed to be
unaffected by temperature[4]. However, the
tempera-ture dependence of microbial respiration and
net N mineralization appears to involve the access to
or metabolism of larger substrate pools as soil
tem-perature increases[5~7]. One mechanism to explain
this observation is a shift in microbial community
com-position, such that communities at higher
temperatures have the ability to access to or
metabolize substrates that are not used by members of
the microbial community at lower temperatures. Zogg
et al.(1997)[7] incubated soil over a range of
Vol.9 No.4
XIAO Hui-lin et al.: Effects of Soil Warming on Some Soil Chemical Properties
temperatures (5, 15, and 25 ℃ ) and observed
increases in the abundance of Gram-positive bacterial
PLFAs (phospholipid fatty acids) and declines in the
abundance of Gram-negative bacterial and fungal
PLFAs, a change in microbial community composition
that paralleled a temperature-dependent increase in the
amount of C (i.e., increase in substrate pool size)
respired by soil microorganisms. If such a response
occurs under field conditions, then understanding
changes in substrate use by microbial communities in
response to changes in temperature or other
environmental factors is im-portant for predicting in
situ rates of microbial activity (e.g., respiration and
net N mineralization).
Soil-matric potential influences microbial activity
by modifying substrate availability. Consequently,
matric potential alters rates of organic matter
min-eralization at warmer temperatures, especially if
warmer soil temperatures are accompanied by more
negative matric potentials. Rates of microbial
processes are generally most rapid near field capacity
(-0.01 MPa), and they linearly decline as soil matric
potential becomes more negative[8]. This decline in
microbial activity has been attributed to the decreased
diffusion of soluble substrates to microbial cells,
reduced microbial mobility that limits access to
substrates, the lowering of intracellular water potential,
which alters enzyme conformation and inhibits
ac-tivity[9], or a combination of these mechanisms[10].
Therefore, it is likely that declines in soil matric
potential below field capacity (-0.01 MPa) will
mod-ify the temperature-dependent increase in
substrate pools for microbial respiration and net N
min-eralizsation[6, 7].
Soil temperature and matric potential influence the
physiological activity of soil microorganisms.
Changes in precipitation and temperature can alter
microbial activity in soil, rates of organic matter
decomposition, and ecosystem C storage[11].
First-order rate constants (k) for net N mineralization
significantly increase with temperature (at the range of
5, 10, and 25 ℃), but the k for microbial respiration
does not increase in a consistent manner. Matric
potential does not significantly influence k for either
process. Substrate pools for microbial respiration and
net N mineralization decline between –0.01 and –0.30
317
MPa, and the decline is greatest at the highest soil
temperature; this response produces a significant
temperature-matric potential interaction. Zak et
al.(1999)[11] concluded that high rates of microbial
activity at warm soil temperatures (e.g., 25 ℃) are
limited by the diffusion of substrate to metabolically
active cells. This limitation apparently lessens as
physiological activity and substrate demand decline at
relatively cooler soil temperature (e.g., 5 ℃) [11].
Global climatic change could have major impacts
on C, N, and S cycling in forest ecosystems by
increasing soil temperature[12]. For example, CH4
emission from forest soil in mountain is closely and
positively related to soil temperature at the depth of 5
cm[13], and there are similar results from the
researches on paddy soil[14, 15]. But there is a little
difference for CH4 dynamics in sediments of
Bruguiera sexangula mangrove in Hainan where the
seasonal pattern of CH4 fluxes is that of spring > of
summer > of autumn > of winter[16]. This phenomena
should be studied further.
Studies by MacDonald et al. (1995)[6] showed that
cumulative respired C and mineralized N and S
increase with temperature (from 5 to 25 ℃) at all
sites of northern hardwood forests in the Great Lakes
region and are strongly related (r2 = 0.67 to 0.90,
significant at p = 0.001) to an interaction between
temperature and soil organic C. Production of respired
C and mineralized N is closely fit by first-order
kinetic models (r2  0.94, p = 0.001), whereas
mineralized S is best described by zero-order kinetics.
Contrary to common assumptions, rate constants
estimated from the first-order models are not
consistently related to temperature, but apparent pool
sizes of C and N are highly temperature dependent.
Temperature effects on microbial respiration can not
be accurately predicted using temperature-adjusted
rate constants combined with a constant pool size of
labile C. Results suggest that rates of microbial
respiration and the mineralization of N and S may be
related to a temperature-dependent constraint on
microbial access to substrate pools.
Moreover, from some studies, it can be concluded
that increased soil temperature may induce surplus
HNO3 which will increase the concentration of Al3+ in
acid soil and the leaching of basic ions from the soil,
318
Soil and Environmental Sciences
leading to nutrient imbalance and rootlet mortality[17].
Simulation models should rely on a through
understanding of the biological basis underlying
microbially mediated C, N, and S transformations in
soil. For example, correlation analysis indicates that
there are significant relationships between soil
microbial carbon, mineralizable carbon and soil
organic carbon[18].
2 Soil Warming and Dissolved Organic
Matter
Temperature will always be a factors regulating
microbial production of dissolved organic matter
(DOM). Strong correlations between soil organic C
pools and climate[19, 20] imply temperature may affect
DOM release from soils. Although the amount of
SOM is negatively correlated with temperature at both
the global and the local scale[19, 21], the relationship
between temperature and DOM release is equivocal.
DOM prodution in catchments can increase in warmer
climates, but the effect of climate on DOM is probably
small because decomposition rates, which remove
DOM, also increase[22]. Liechty et al. (1995)[23]
estimated that the differences in soil temperatures
(2.1 ℃) could be responsible for as much as 16%
increase in DOC concentrations in forest floor
solutions at the warmer compared with the colder site.
Soil drainage conditions play an important role in
understanding climate effects on DOM release. For
well drained and moderately drained soils, there is
often an inverse correlation between average soil
temperature and DOC concentration in surface soil
leachates[24]. Thus, DOC concentrations generally
increase in cooler environments. In poorly drained
areas, DOC concentrations in surface horizons often
reach very high levels, regardless of the climate from
cool northern peatlands to warm southern blackwater
swamps. These inconsistent data indicate no general
climatic effect on DOC[25].
Numerous field studies show seasonal variability in
DOM concentrations and fluxes. In general, DOC
concentrations in soil solution are higher in summer
than in winter[23]. Mean DOC concentrations increase
by 26% to 32% in shallow soil solution in summer,
but DOC concentrations in deeper soil horizons
remain relatively constant[26, 27]. Differences in
temperature effects between upper and lower soil
Vol.9 No.4
horizons support the hypothesis that DOC
con-centration in the topsoil, is controlled mainly by
microbial process which are, in turn, partly controlled
by temperature. This is also supported by the
observation that hydrophilic compounds (derived
mainly from microbial sources) and carbohydrates[28]
are released preferentially into the soil solution during
the growing season rather than in the dormant season.
However, studies on the seasonality of DOC
concentration also show variable results. Dosskey and
Bertsch (1997)[29] found no seasonal effects on DOC
concentration in soil solution. The lack of seasonality
may be due to relatively short, mild winters with
neither concentrated growth seasons in summer, nor
litterfall periods in autumn[29]. In other words, this
lack of seasonality is caused by a lack of seasons.
Michalzik and Matzner (1999)[30] found a
cor-relation between temperature and both DOC and
DON concentrations in the forest floor of a Norway
spruce stand. However, fluxes of DOC and DON are
not correlated to temperature. They conclued that
abiotic processes supercede biological controls on
DOM release under field conditions. In contrast,
Liechty et al. (1995) [23] found a significant positive
correlation between soil temperature and DOC flux in
forest floors of two hardwood stands. Unfortunately,
studies on the effects of temperature on DOM fluxes
in soil are rare.
The results of laboratory studies are more consistent
than field investigations, with nearly all showing that
an increase in temperature results in increased DOC
concentrations[25]. Only MacDonald et al. (1999) [31]
did not find temperature effects on DOC
con-centrations in soil solution. Decomposition of
DOC was probably enhanced to the same extent as
DOC production.
Kalblitz et al. (2000)[25] suggest that there be a
trend of increasing DOM concentrations with
increasing temperature that is more obvious in
laboratory experiments than in field studies. It seems
unlikely that the release of DOM (DOM fluxes) under
field conditions depends entirely on temperature.
Climatic and hydrological conditions, litterfall and
litter quality, and soil texture and other soil properties
can modify and even mask the temperature response
of DOM in the field.
Vol.9 No.4
XIAO Hui-lin et al.: Effects of Soil Warming on Some Soil Chemical Properties
3 Soil Warming and Composition of
Organic P
Climate and climate-dependent differences in the
composition of organic forms of soil phosphorus (soil
P0) may play an important role in mineralization
rates[32] because, besides substrate supply, temperature
and water supply are the governing factors controlling
microbial activity.
The group of monoester-P comprises mainly
inositol phosphates[33]. Their high stability against
microbial and enzymatic attack is caused by their
strong interactions with soil minerals because of their
high charge density and by precipitation as Al-, Fe-,
and Ca-salts of low solubility[33]. The diester-P
fraction, which contains nucleic acids, phospholipids,
and other compounds, characterizes a labile soil P0
fraction. The occurrence of phosphonates in soils was
explained with the simultaneous absence of bacteria
containing the phosphonatase enzyme[34].
As MAT increases, the proportion of diester-P
increases in both bulk soils and clay fractions,
where-as that of monoester-P decline, although the
decline of monoester-P is only observed in the clay
fraction[35].
Miltner et al. (1998) [36] found that the proportion of
diester-P increases in the course of incubation of
beech litter with various minerals. The authors
concluded that they are synthesized by microbes. The
increase of soil temperature leads to increases of
microbial
productivity[37].
Apparently,
labile
com-pounds are produced at a higher rate and
stabilized by inorganic particles at conditions
favorable for micro-bial and biochemical degradation
such as high tem-peratures. As a consequence, the
clay fractions re-flected a strong relationship between
MAT and soil P0 composition.
The MAT is significantly positively correlated with
diester-P and reflects large microbial production at
higher temperatures and enhances stabilization of
diester-P in the clay fraction[35].
Sumann et al. (1998) [35] investigated the effect of
climate on the composition of organic P in
uncul-tivated soils of the North American prairie.
They present 31P nuclear magnetic resonance (NMR)
spectra of alkaline extracts of bulk samples and clay
fractions along gradients of mean annual temperature
319
(MAT) and mean annual precipitation (MAP) across
the Great Plains. The results show that as MAT
increases, the proportion of diester-P increases,
whereas that of monoester-P decreases. These
statistically significant correlations are more
pro-nounced for both diester-P (r =0.91) and
monoester-P (r =-0.87) in the clay fractions than in the
bulk soils. They believed that temperature and
precipitation strongly influence the organic P in North
American grassland soils through their influence on
microbial activity and plant production.
The experiment by King et al. (1999)[38] shows that
high soil temperature increases rates of
photosynthe-sis (65%) of trembling aspen (Populus
tremuloides Michx), resulting in greater whole-plant
growth (37%) through increases in roots, stems, and
foliage; however these increases generally occurs only
in soil of high N-availability. Root∶ shoot biomass
allocation varies between clones but is unaffected by
the soil temperature or N-availability treatments. Root
length production and mortality increase at elevated
soil temperature, but this response is modified by soil
N-availability. At high soil temperature, soil
N-availability has little effect on root dynamics, while
at low soil temperature, high soil N-availability
increases both production and mortality (turnover) of
roots.
4 Soil Warming and Dynamics of Lignin
A study by Amelung et al. (1997)[39] showed that as
annual temperature increases from 7 to 23 ℃ at sites
with 500 mm precipitation per year, the amount of
polysaccharides decreases from 605 to 422 g/kg SOC
( soil organic sarbon ) in the topsoil ( 0~15 cm ) and
from 516 to 278 g/kg SOC in the subsoil ( 30~40 ).
For various forest subsoils, Zech et al. (1989)[40]
reported decreasing aromaticity of SOM with an
increasing
precipitation/temperature
ratio.
Tempera-ture should affect primarily C turnover
rates[41].
It is known that different C pools control SOC
dynamics in mineral soils[42]. According to Skjemstad
et al. (1986)[43], stabilization of SOC is the essential
factor that controls SOM decomposition, the chemical
resistance of SOC to mineralization being less
important. McDaniel and Munn (1985)[44] suggested
that stabilizing influences of clay minerals are more
320
Soil and Environmental Sciences
important in warmer climates than in cooler ones. This
suggests that climate and texture may interact to affect
SOM properties.
The climate of a site influences the chemical
composition of SOM. Polysaccharides are not
mineralized in preference to lignin in soil profiles.
Thus, in addition to the recycling of carbohydrate
structures by microbes, there must be processes that
protect less stable polysaccharides from decay. These
processes seem to depend on climate. The warmer the
climate, the more quickly microbes decompose SOM
and the less polysaccharides persist. This is probably
accompanied by an enrichment of alkyl structures
relative to other functional groups[39].
A study was conducted by Amelung et al. (1999a)[45]
to investigate influences of climate on the dynamics of
lignin in particle-size fractions. Com-posite samples
were taken from the top 10 cm of 18 native grassland
sites along temperature and pre-cipitation transects
from Central Saskatoon, Canada to South Texas, USA.
Lignin-derived phenols were determined in the 2 m
(clay), 2~20 m (silt), 20~250 m (fine sand) and
250~2 000 m (coarse sand) size separates. With
decreasing particle size the concentration of
lignin-derived phenols decreases significantly from 72
g/kg soil organic carbon (SOC) in the coarse sand
fractions to 12 g/kg SOC in the clay fractions.
Increasing phenolic acids to aldehyde ratios indicates
that side chain oxidation proceeds as particle size
decreases. Moreover, these ratios decrease in fractions
250 m with increasing mean annual temperature
(MAT) at the sites. This suggests that the degree of
lignin decomposition decreases with in-creasing MAT,
possibly because there is a lack of additional C
sources, such as saccharides of root litter, which are
needed for the co-metabolic decay of lignin.
In another experiment related to the above,
Amelung et al. (1999b)[46] summed up that as particle
size decreases, the concentration of monosaccharides
decreases significantly from 297 g/kg SOC in coarse
sand to 174 g/kg SOC in the silt fractions, but
increases to 239 g/kg SOC in clay. Ratios of hexoses
to pentoses increase with decreasing particle size,
indicating that SOM of the finer fractions contains
more microbe-derived saccharides, this effect being
more pronounced at lower MAT. The concentrations
Vol.9 No.4
of neutral saccharides decrease in silt and fine-sand
fractions as MAT decreases. The results suggest that
the temperature regime primarily affects the
sac-charides concentrations of the coarser fractions.
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