| 其他摘要 | Soils have the potential for C release or sequestration，can be affected by vegetation
cover and land management. Many studies found the transformation of cultivated soil to
forest ecosystem can change soil carbon sequestering. However, soil carbon stock change in
forest chronosequence is likely to appear different results. Hence, accurate estimate on the
mechanism of SOC dynamics in forest chronosequences is necessary. The study investigated
the variation patterns of organic matter of four selected Robinia pseudoacacia forests aged 10,
25, 31, 35 years, and explore the rules. On basias of the rules, we made field and labortary
incubational experimentes to explore the effected factors. The main conclusions were showed
as follows:
（1）The study gives a anlysis on indexes such as SOC、Tatol nitrogen、particle size、
CaCO3、CECand pH,etc,in the soil profile of Caragana Korshinskii Kom planted in 1975 、
plowland since 1974 and Robinia pseudoacadia planted in 1978. Soil organic carbon
accumulation in each site has a high correlation with the percent of <0.02mm diameter; some
factors in soil profiles exist unnormal changes in different depths, the <0.002mm clay matrial
has a substantial increase, represents the charactors of illuvial horizon; In the depth of
100cm,it is C78>N75>H74 on SOC content, however, the main difference was reflected in the
upper 30cm depth. The presence of ancient soil lead to 16.684g/m3 error on H74 SOC
assessment, as well as 36.926g/m2 Error on C78 SOC assessment.
（2）We investigated the variation patterns of organic carbon of four selected Robinia
pseudoacacia forests aged 10, 25, 31, 35 years, and a contrastive tillage site in similar
topography condition. On average of 20cm, 40cm, 60cm depth, SOC, active organic carbon
(AOC), DOC gradually increase with the forest growth. Compared with tillage sites,
AOC/SOC ratio, ROC (resistant organic carbon)/SOC ratio show a higher value, and LOC
(slow organic carbon)/SOC ratio shows a lower value. DOC/DON is lower and UV absorption
at 280 nm shows a higher value in all forest sites. During forest restoration, 25-year-old
Robinia pseudoacacia forest shows a special phase in four forest sites represented by depth
distribution. During forest restoration (i) not only AOC, but ROC take an accumulation
process, Robinia pseudoacacia forest restoration contributes to SOC accumulation. (ii) DOC,
DOC/DON, UV-absorbance appear changes but not obviously accordant to SOC, suggesting
different changes during SOC accumulation. (iii) SOC, AOC don’t show a persistent increase in each depth of soil profile and which indicate a depth distribution. Our study found SOC
had compounds-distribution and depth-distribution, but the relative machisms need to be
explore.
（3）Analyzed the quantity of SOC, total nitrogen, particle size, CaCO3 for the diversity
analysis and the correlation ratio in 100cm soil profiles respectly in Caragana Korshinskii
Kom forest planted in 1975(N75) 、tillage since 1974(H74) and Robinia pseudoacadia forest
planted in 1978(N78) . The results suggest that compared with tillage site, though SOC and
total of nitrogen in two restored forest sites show obvious changes, the distinct diversity in
C78 appears mainly in the depth of 0-20cm, and the same state appears at 20-100cm for N75.
At 20-100cm in H74 site, SOC, C/N show remarkable correlations with percent of
0.002-0.02mm particle size. Below 40cm in C78 site, SOC are remarkable correlation with
<0.002mm particle size, the correlation rate between C/N and <0.02mm changes from minus
value for 0-100cm depth to positive value for 40-100cm. Our study indicate that after forest
restoration, changes of SOC and total of nitrogen mainly represent a obvious diversity at 40
cm and 60 cm soil layer for Caragana Korshinskii Kom forest, but diversity appearsat 20 cm
for Robinia pseudoacadia forest. SOC in deep soil layer of tillage and Robinia pseudoacadia
forest is closely adsorbed by fine particle size soil, with a steady quality.
（4）We have observed the dynamics of SOC and it’s relative factors of three depths
(20cm,40cm,60cm) incubation holes, which were backfilled soils mixed with litter rags in
advance, in C78 Robinia pseudoacacia forest, and took samples in March, July and November,
2010. The results represent reasonal changes, at 20cm and 40cm, SOC, POC, TN in July are
highest, but decrease in November, and reverse states represent for DOC. Different with those
at 20 cm, SOC at 60 cm decreases gradually in the process of incubation and TN and POC
have increase trend, DOC in July appears a high value. During C accumulation, SOC
increases but decrease later, represents self-modulation function. DOC has different sources
for deeper soil layer with those at 20 cm, SOC suggests complex sources at 60 cm, the
production of litters decomposition have limited effect.
（5）Took soil and mixed litter samples in 31 year old Robinia Pseudoacacia forest and
determined the accumulative CO2-release of soil samples and DOC-removal soil samples
(100% water content only) at three soil layers (20 cm，40 cm，60 cm), three controlled
litter-mixed soil samples (mixed by complex litters, included Robinia Pseudoacacia litters
and herbage litters), in laboratory under the different soil moisture levels of 100%, 20%, 2%
water content respectively. The results showed that the CO2-release levels in different depths
were suggested by 20 cm>60 cm>40 cm in controlled 100% and 20% water content; In the condition of 100% water content, when DOC were removed, the accumulative CO2-release
quantity of 20 cm soil samples decreased, but obviously increase for samples at 40 cm and
had no marked change at 60 cm; The accumulative CO2-release of complex litter-mixed soil
samples had highest value in the condition of 100% water content, those of simply Robinia
Pseudoacacia litter-mixed samples was obvious higher than that of herbage litter-mixed
samples in 20% and 2%water content, but slightly lower in 100% water content. The
asynchronous effect of water content levels is suggested on the respiratory intensity of the soil
layers with different SOC compositions and litter kinds, heavy precipitation removes DOC
from soil subsurface layers, can weaken the soil respiratory intensity.
（6）In two-year incubation experiment, litter-mixture soil (outside bags) and no
litter-mixture soil (inside bags) were insulated by nylon cloth in incubation holes, changes in
the LDOM portion of the soil were then monitored by comparing the WEOM levels outside
the bags with inside the bags., In July, the ratio of locked WEOC (LDOC) to WEOC outside
bags (LDOC/WEOC) was low in the topsoil, and increased gradually with depth while the
locked WEON (LDON) to WEON ratio outside bags (LDON/WEON) suggested no obvious
rule. At 20 cm In July, LDOC/WEOC were lower and LDON/WEON were higher than those
in March and November, solutions of the soil samples had highest UV-absorbance at 280 nm,
The LDOC:LDON ratio at 20 cm was comparable in July with, but higher in March and
November than WEOC:WEON ratio of samples outside bags, which implied that
LDOC:LDON has little difference compared to that of RDOM in July, but represents higher
value at other times of the year. The study proves that LDOM has seasonal variability and
depth distribution, which brings a difficult to distinguish the difference between WEOM and
DOM (RDOM).
Key Wards：Keywords: soil organic matter; water extractable organic matter;
Robinia pseudoacacia forests; UV-absorbance |
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