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Effects of Thinning and Litter Fall Removal on Fine Root Production and Soil Organic Carbon Content in Masson Pine Plantations
Pedosphere 20(4): 486–493, 2010 ISSN 1002-0160/CN 32-1315/P c 2010 Soil Science Society of China Published by Elsevier Limited and Science Press
Effects of Thinning and Litter Fall Removal on Fine Root Production and Soil Organic Carbon Content in Masson Pine Plantations∗1 TIAN Da-Lun1 , PENG Yuan-Ying2 , YAN Wen-De1,∗2 , FANG Xi1 , KANG Wen-Xing1 , WANG Guang-Jun1 and CHEN Xiao-Yong3 1 Forest Ecology Section, Faculty of Life Sciences, Central South University of Forestry and Technology, Changsha 410006 (China) 2 Biology Program, Department of Health and Science, College of DuPage, IL (USA) 3 Biology Program, College of Arts and Science, Governors State University, IL (USA)
(Received October 2, 2009; revised May 18, 2010)
ABSTRACT Soils play a critical role in the global carbon cycle, and can be major source or sink of CO2 depending upon land use, vegetation type and soil management practices. Fine roots are important component of a forest ecosystem in terms of water and nutrient uptake. In this study the effects of thinning and litter fall removal on fine root production and soil organic carbon content were examined in 20-year-old Masson pine (Pinus resinosa) plantations in Huitong, Hunan Province of China in the growing seasons of 2004 and 2005. The results showed that fine root production was significantly lower in the thinning plots than in the control plots, with a decrease of 58% and 14% in 2004 and 2005 growing seasons, respectively. Litter fall removal significantly increased fine root production by 14% in 2004. Soil temperature (Tsoil ) and soil moisture (Msoil ) were higher in the thinning plots than those in the controls. Litter fall removal had significant effects on Tsoil and Msoil . Soil organic carbon content was higher in the thinning plots but was lower in the plots with litter fall removal compared with that in the controls. Our results also indicated that annual production of fine roots resulted in small carbon accumulation in the upper layers of the soil, and removal of tree by thinning resulted in a significant increase of carbon storage in Masson pine plantations. Key Words:
fine roots, forest management, soil carbon, soil moisture, soil temperature
Citation: Tian, D. L., Peng, Y. Y., Yan, W. D., Fang, X., Kang, W. X., Wang, G. J. and Chen, X. Y. 2010. Effects of thinning and litter fall removal on fine root production and soil organic carbon content in Masson pine plantations. Pedosphere. 20(4): 486–493.
Soils are a major terrestrial carbon reservoir. The amount of carbon in soil in the world estimated between 1 000 and 3 000 Pg (1 Pg = 1015 g), constitutes approximately two-thirds of the carbon in terrestrial ecosystems (Post et al., 1982). Through a variety of ecological processes, soil carbon has a tight interaction with the atmosphere and responds to land use and land cover changes (Jobbagy and Jackson, 2000). The amount and distribution of soil organic carbon (SOC) was affected by fine root production (Chen et al., 2004). Many processes in forest ecosystems, such as nutrient cycling, cation exchange and soil water storage are all strongly influenced by SOC. Carbon storage in soils is a dynamic balance between both aboveground and belowground litter inputs (primarily litter fall and fine root litter) and organic matter outputs in the form of CO2 efflux from the soil. Roots are a major organ of a tree for absorption of water and nutrients. In addition, roots are a key component of the belowground part in forest ecosystems, and are a main source of soil organic matter which influences soil microbial activity and decomposition processes (Janssens et al., 2002). A ∗1 Supported
by the “948” Grant of the National Forestry Administration of China (No. 2007-4-19), the Special Grant of Chinese Forestry Public Benefits (Nos. 200804030 and 2007-4-15), and the Provincial Fund for Distinguished Young Scholars of Hunan, China (No. 07JJ1004). ∗2 Corresponding author. E-mail: [email protected].
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large proportion of forest production is allocated to fine roots, resulting in a large carbon flux into the belowground system (Kurz et al., 1996). Due to their high metabolic activity, fine root production and turnover play a critical role in forest carbon dynamics, representing an important carbon input to the soil and can equal or exceed aboveground detritus production in some plant communities (Fogel, 1983). Fine roots may contribute less than 2% of the total ecosystem biomass, but contribute up to 40% of the total ecosystem production (Vogt et al., 1990). The contribution of roots to the total soil respiration rates ranged from 12.5% to 54.6% in a Betula ermanii-dark coniferous forest of the Changbai Mountains, China (Liu et al., 2005), and 8.3% to 48.6% during seedling growth of Pinus sylvestris var. sylvestriformis (Liu et al., 2007). This means that when examining biomass and carbon allocation in forests, fine root component (similar to the foliage in the aboveground) may be very sensitive to environmental change and thus may respond most strongly to a disturbance (Vogt et al., 1990). Thinning, cutting down and removal of a proportion of trees in a forest, has been a common applied silvicultural practice in forest plantations in southern China for over three decades (Tian, 2005). The purposes of thinning usually are: 1) to redistribute the potential resources available for the remaining trees, 2) to maintain or improve the growth rate of the stand, and 3) to utilize the intermediate source of timber revenue before the final forest is cut down at the end of the rotation. Many studies showed that thinning provided a great deal of benefits to the forest stands, including the short-term raise of tree growth and productivity of Masson pine forest (Liu et al., 1992), the acceleration of nitrogen mineralization rate due to increase of temperature of the surface soli layers (Thibodeau et al., 2000), and the decrease of the vulnerability of trees to insect attack (Coyea and Margolis, 1994). Thinning is expected to change soil environments, the allocation of aboveground and belowground productivity, and root density and turnover (Keith et al., 1997; Bowden et al., 2004). The effects of thinning on aboveground processes of forest ecosystems are relatively obvious, while its effects on belowground processes, such as fine root production and SOC content are still not fully clear. Global climate change was expected to increase the air temperature and change the patterns of precipitation distribution around the world (Raich et al., 2006, Zhang et al., 2007). The alterations of temperature and rainfall in the environments may cause the change of litter fall quantity in a forest, because heat and moisture are most important factors affecting tree growth and altering leafing phenology (Finzi et al., 2001). As litter fall represents a major nutrient input of soils, it seems that changes in aboveground litter production will have direct impacts on belowground processes. However, little is known about the potential impact of changes in litter fall on fine root dynamics and SOC content. Masson pine (Pinus massoniana) is one of the dominant pioneer conifer species in southern China and has been widely planted in this region because of its tolerance for infertile and drought soils, and its capacity to retain water and nutrients (Liu et al., 1992). Thinning of Masson pine has been promoted as a means of ecological stand conversion and as an intensive forest management strategy to promote conifer growth and hardwood recruitment. In the present study the effects of thinning and litter fall removal on fine root production and SOC content were examined in Masson pine plantations. We address the following specific hypotheses: 1) thinning will result in an decrease of fine root production; 2) litter fall removal will increase fine root production due to the decrease of nutrient input from the litter layer; 3) thinning will increase SOC due to providing more litters and stimulating microbial activities; 4) litter fall removal will decrease SOC due to the decrease of nutrient inputs; and 5) soil temperature (Tsoil ) and soil moisture (Msoil ) will be increased following thinning. MATERIALS AND METHODS Study sites The study sites consisted of 20-year-old Masson pine (Pinus resinosa) plantations and were located at the Huitong Ecosystem Research Station of the Central South University of Forestry and Technology in Hunan Province, China (26◦ 50 N and 109◦ 45 E). The study area is a moist subtropical zone
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with a mean annual temperature of 16.8 ◦ C and mean temperatures of 4.4 and 26.3 ◦ C in January and July, respectively. Mean annual relative humidity is > 80%, annual rainfall ranges from 1 000 to 1 600 mm, most of which occurs from April to August, and elevation is 270–400 m. The terrain features a relatively open topography with low slopes and some hills, average site slope being below 10 degrees. The soils at the study sites are a mature mountain yellow soil with a thick mineral layer. The soils are predominantly fine loams and silt loams. Soil pH on the surface (0–10 cm) is acidic with an average pH of 5.0. Masson pine plantations were established in the 1985s with an initial plant density of 2 m × 2 m. Understory vegetation was very sparse. Selective thinning was performed in the study sites in the fall of 2003 with 20% thinning intensity. Relative small and unhealthy trees were cut. Experiment design and measurements It was a nested experimental design for the experiment with three replicate plots per treatment. The thinning and control were the main factors. The sub-plots with control and litter fall removal were nested in both thinning and control plots. All litter fall on the floor including branches and needles were removed. The size of each main plot was 50 m × 50 m. Within a main plot, four sub-plots were established and each sub-plot was 10 m × 10 m. To eliminate the edge effects from each of the sub-plots, about 5 m buffering strip was set up between each sub-plot. The distances between the sub-plot with litter fall removal and the sub-control were at least 10 m away from each other. Therefore, a total of 24 sub-plots were set up in the study. All treatments were completed at the end of 2003 and all measurements were conducted in the whole years of 2004 and 2005. Fine root production was estimated using a modified maximum and minimum root core method (McClaugherty et al., 1982). Samples of fine roots (≤ 2 mm) were taken once a month in 2004 and 2005. Fine root biomass was estimated from 3.5 cm diameter soil cores collected to 60 cm depth. In each sampling point, the soil core was divided into four layers from top to bottom of soil, and each layer was 15 cm (i.e., 0–15, 15–30, 30–45 and 45–60 cm). A total of 12 soil cores were collected in each sub-plot at each sampling time. When the samples were brought back to the laboratory, cores were carefully washed over a 0.2-mm sieve to remove soil. Both living and dead roots were distinguished by analysing their external form and colour. The roots were dried at 60 ◦ C until they reached a constant weight. Soil temperature measurements were performed every two weeks, and Tsoil was determined at 5 cm below the soil surface with an LI-COR 6000-09TC soil probe thermocouple (LI-COR Inc, Lincoln, Nebraska, USA). Soil samples with the depth of 0–15, 15–30, 30–45, and 45–60 cm were taken from the uppermost mineral soil layer using a soil auger, stored in airtight tubes and taken back to the laboratory for determination SOC. Soil moisture was determined by ECHH2 O check (Decagon, USA). Soil organic carbon was determined using an improved Walkley-Black wet digestion method. Approximately 0.5 g air-dry soil samples (particle size < 0.15 mm) were transferred to graduated test tubes with 2 mL of K2 Cr2 O7 and agitated, with 4 mL of 98% H2 SO4 gradually added. The test tubes were then heated in an aluminium block at 135 ◦ C for 30 min, allowed to cool to room temperature and adjusted to a final volume of 20 mL using distilled water. Blank solutions were prepared in the same way. The soil supernatant was centrifuged at 3 000 r min−1 for 15 min. Absorbance of all spun supernatant was then measured at 600 nm and a standard curve of relative absorbency vs. organic carbon was constructed. A series of organic carbon standard solutions were prepared by dissolving 0.4754 g sucrose (Chen et al., 2004). Data analysis Statistical tests were conducted for the effects of thinning and litter fall removal and their combination on fine root production and SOC content. Tsoil and Msoil were performed using analysis of variance (ANOVA). No transformations were necessary for the original Tsoil and Msoil data, which satisfied the normality and homoscedasticity assumptions of ANOVA. We calculated sample means and standard errors (SE) of fine root production, Tsoil and Msoil in the thinning and control plots and sub-plots
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with litter fall removal separately in 2004 and 2005. Pair-wise t-tests were used to examine differences between the thinning and control plots. RESULTS Fine root production Thinning significantly affected soil fine root production, which showed significant differences between the thinning and control plots (P = 0.026, Table I). Overall, fine root production was significantly lower in the thinning plots than that in the control plots in both of 2004 and 2005 (Fig. 1). The fine root production in the thinning and control plots was 1.63 and 2.58 kg m−3 , respectively, on average with a difference of 0.95 kg m−3 , a decrease of 37% in 2004, and was 1.86 and 2.05 kg m−3 with a difference of 0.19 kg m−3 , a decrease of 9% in 2005. There was also a significant effect of litter fall removal on fine root production (P = 0.043, Table I). Overall, fine root production was constantly higher in the sub-plots with litter fall removal than that in sub-control plots within both main factor plots only in 2004, but not in 2005 (Fig. 1). In the control plots, the fine root production in the sub-control plots and the sub-plots with litter fall removal were 1.79 and 1.97 kg m−3 , respectively, with a difference of 0.18 kg m−3 on average, a increase of 10% in 2004, but not in 2005 (Fig. 1). The combination effects of litter fall removal and thinning in the thinning plots compared with the sub-control in the control plots showed a significant difference on fine root production in 2004. The fine root production in the sub-control plots and the sub-plots with litter fall removal in the thinning plots were 1.65 and 1.89 kg m−3 , respectively, with a difference of 0.23 kg m−3 on average, an increase of 14% in 2004, but not in 2005 (Fig. 1). TABLE I Analysis of variance results for fine root production affected by thinning (T), litter fall removal (LR) and their combination (T × LR) in 20-year-old Masson pine (Pinus resinosa) plantations in Huitong, Hunan Province of China Source
Degree of freedom
Mean square
F
P
Experimental error
Corrected total
T LR T × LR
2 5 10
2.42 1.86 5.30
2.20 2.86 2.34
0.026 0.043 0.468
54
71
Fig. 1 Mean fine root production in the sub-control plots and the sub-plots with litter fall removal of the control (C) and thinning plots (T) in 2004 and 2005. CC and CLR represent the sub-control plots and the sub-plots with litter fall removal in the control plots, and TC and TLR represent the sub-control plots and the sub-plots with litter fall removal in the thinning plots, respectively. Error bar indicates standard error.
Tsoil and Msoil Thinning altered the microenvironment, with the obvious effects observed in the first year (Table
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II). Both thinning and litter fall removal had statistically significant effects on Tsoil and Msoil (P < 0.0001 and P = 0.0001, respectively). The interaction of thinning and litter fall removal also significantly affected Tsoil (P < 0.0001) and Msoil (P = 0.0060). Tsoil on average increased from 18.92 to 21.78 ◦ C in response to thinning in 2004, with mean differences of 2.86 ◦ C between the sub-control plots and sub-plots with litter fall removal one year after thinning. The mean values of Msoil were consistently lower in the thinning plots than those in the control plots. The litter fall removal in the thinning plots significantly altered Msoil (P = 0.0001) in 2004, but not in 2005 (P > 0.05). TABLE II Soil temperature and soil moisture in the sub-control plots and sub-plots with litter fall removal of the control and thinning plots in 2004 and 2005 Sub-plot
n
2004 Control
2005 Thinning
Differencea) P
Control
Thinning
Difference P
(◦ C)
Control 12 18.62±0.75 21.28±0.88 −2.66 Litter fall removal 12 19.23±0.91 22.28±0.93 −3.05 Mean 24 18.92±0.41 21.78±0.46 −2.86 Control 12 186.4±0.20 152.5±0.26 34.1 Litter fall removal 12 172.8±0.23 159.7±0.33 18.1 Mean 24 179.6±0.26 156.1±0.27 24.5 a) Difference
Soil temperature < 0.0001 18.30±1.64 0.0001 18.03±1.60 < 0.0001 18.17±0.80 Soil moisture (g kg−1 ) < 0.0001 189.4±0.53 0.0001 192.3±0.55 < 0.0001 193.5±0.33
20.81±1.62 −2.51 18.23±1.53 −0.20 19.52±0.81 −1.35
0.0163 0.4263 0.0001
176.8±0.48 14.6 196.2±0.49 −3.9 197.3±0.26 −1.1
0.0048 0.3655 0.2567
= control − thinning.
Tsoil showed a typical parabolic curve during the studied period of 2004 (Fig. 2). Tsoil peaked in July with a value above 30 ◦ C both in the thinning and control plots, being 32.6 and 30.4 ◦ C, respectively, while the corresponding minimum Tsoil was in January with 5.8 and 6.3 ◦ C, respectively. The overall mean value of Tsoil was higher in the thinning plots than that in the control plots both in 2004 and 2005, and the significant differences (P < 0.05) were also found between the sub-control plots and sub-plots with litter fall removal (Table II, Fig. 2). The average Msoil was significantly different (P < 0.05) between
Fig. 2 Seasonal patterns of soil temperature and soil moisture in the thinning, litter fall removal and control plots in year 2004. C and T represent the control and thinning plots, and CC and CLR represent the sub-control plots and the sub-plots with litter fall removal in the control plots, respectively. Error bar indicates standard error.
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the control and thinning plots throughout the growing season of 2004 and 2005 (Table II). The minimum Msoil was in September with the value of 18.2% and 19.5%, while the maximum value appeared in April of 27.3% and 28.6% in the control and thinning plots, respectively (Fig. 2). Soil organic carbon (SOC) Fig. 3 shows the patterns of SOC content with soil depth affected by thinning and litter fall removal in Masson pine plantations. Comparison of SOC vertical distributions for the Masson pine plantations in each plot showed particularly larger differences in the top layer with the soil depth of 0–15 cm (Fig. 3). Averagely, total SOC content was significantly higher (P < 0.001) in the thinning plots (175.4 t ha−1 ) than that in the control plots (151 t ha−1 ) (Fig. 3, Table III). Litter fall removal significantly decreased SOC content, while total SOC in the sub-plots with litter fall removal in the thinning plots (155.4 t ha−1 ) had no significant difference compared with the sub-control plots in the control plots (158 t ha−1 ) (Table III).
Fig. 3 Comparison of mean soil organic carbon contents (SOC) in the thinning (T) and control (C) plots in 2005 (a) and SOC in the sub-plots with litter fall removal in the control (CLR) and thinning plots (TLR), and the sub-control plots in the control plots (CC) in 2005 (b). Error bar indicates standard error. TABLE III Vertical distribution of soil carbon storage in the thinning, litter fall removal, and control plots in 2005 Soil depth
Ta) Amount
cm 0–15 15–30 30–45 45–60 Total
t
ha−1
70.1 52.6 25.6 27.0 175.4
Cb) Percent % 40.0 30.0 14.6 15.4 100.0
Amount t
ha−1
60.0 46.5 21.3 21.2 151.0
CLRc) Percent % 41.1 30.8 14.1 14.0 100.0
Amount ha−1
t 26.0 27.5 18.2 19.4 91.1
TLRd) Percent % 28.5 30.2 19.5 21.3 100.0
Amount t
ha−1
61.8 48.2 23.8 21.6 155.4
CCe) Percent % 39.8 31.0 15.2 13.9 100.0
a) Thinning plots; b) Control plots; c) Sub-plots with litter fall removal in the control plots; removal in the thinning plots; e) Sub-control plots in the control plots.
Amount t
ha−1
66.1 48.2 21.8 21.9 158.0
d) Sub-plots
Percent % 41.8 30.5 13.8 13.9 100.0
with litter fall
DISCUSSION Fine root production This study showed that thinning resulted in a significant reduction of fine root production (Fig. 1). As a result of removal of trees by thinning, root density and biomass were altered. The death of root systems of cut trees should greatly reduce the root component of biomass and production. Our results from this study are consistent with the findings by other researchers (Mello et al., 2007). They found that fine root dynamics was significantly altered, and about 50% decrease in fine root density was observed 60
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days after harvesting. Thinning effects were also highly related with soil conditions (Tsoil and Msoil ) (Fig. 2). Our results are consistent with the findings that decomposition of fine roots speeded up after harvesting, which were directly related to the environmental conditions (Mello et al., 2007). As canopy gaps were formed in a forest by thinning, microclimatic properties within the forest would be changed. The quantity and quality of substrate inputs into the forest floor and soil were altered as well. Thinning was expected to directly reduce living root biomass by removing trees, and possibly to reduce soil microbial biomass by disturbing the humus layer (Mallik and Hu, 1997). Msoil was lower in the thinning plots than that in the control plots in 2004 and 2005 (P < 0.05, Table II, Fig. 2). It was likely attributed to the increase of forest floor evaporation and plant utilization of soil water through transpiration. By providing more space and reducing competition of soil water and nutrients, thinning stimulated active physiological processes of the remaining trees and increased fine root production of the forest (Fig. 1). Litter fall removal constantly increased the fine root production in both control and thinning plots in 2004 (Fig. 1). Litter fall input was generally the most important nutrient resource of the forest soil (Vitousek et al., 1995; Berg and Meentemeyer, 2001). As a result of direct removal of nutrient source from the exposed soil, fine root would produce more to uptake nutrition from soil for nutrient supply. Litter fall removal combined with thinning mitigated fine root production in 2004, as thinning decreased it. Litter fall removal had no effects on fine root production, Tsoil and Msoil in 2005, which is likely attributed to the increasing new litter fall on the forest floor after the treatments. Soil organic carbon content The amount of SOC in the thinning plots was higher than that in the control plots with the difference of 24.4 t ha−1 , which was possibly contributed to the increasing decomposition of organic matter as a result of the increase of microbial activity by thinning. As the canopy removed by thinning, microclimatic properties were altered, as well as the quantity and quality of substrate inputs into the soil. Thinning increased Msoil and Tsoil by increasing insolation and reducing stand evapotranspiration. As a consequence, the composition of the soil microbial community was likely to be altered and microbial activities may increase because of the increasing decay speed of dead roots (Tang et al., 2005; Maassen and Wirth, 2006). The overall mean amount of SOC in the plots with litter fall removal was lower than that in the control plots with the difference at 66.9 t ha−1 (Table III, Fig. 3). Reduction of SOC is mainly due to suppression of microbial activities and nutrient supply from the humus layer, because litter fall input is generally the most important way of nutrient transfer to forest soil (Berg and Meentemeyer, 2001). Soil is the habitat of plant roots and the home of numerous microflora, including viruses, bacteria, fungi and blue-green algae. The soil microflora and fauna complement each other through the combination of litter, mineralization of essential plant nutrients, and conservation of these nutrients within the soil system (Marshall, 2000). Litter fall removal likely greatly reduced microbial activity as a result of removing the substrate supply to the mineral soil. Combination of thinning and litter fall removal did not change SOC in this study. It is likely due to the offset effects between them. CONCLUSIONS The study showed that thinning and litter fall removal significantly changed fine root production, SOC content, Tsoil and Msoil . Thinning caused a decrease in fine root production and a increase in SOC. The decrease in fine root production is likely a result of the increase in Tsoil and Msoil , while the increase in SOC resulted from the increasing microbial activities following by the thinning treatment. Litter fall removal increased fine root production but decreased SOC in both thinning and control plots, as a result of changes in Tsoil and Msoil and reduced substrate input to the soil. In a word the changes of fine root production and SOC following thinning and litter fall removal were driven by the changes in soil conditions, such as Tsoil and Msoil , soil nutrient input, and bacteria and fungi consumption of fine roots in forest soils. Thinning had long term effects on forest belowground process and environmental conditions while litter fall removal only made a short term effects on them.
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REFERENCES Berg, B. and Meentemeyer, V. 2001. Litter fall in some European coniferous forests as dependent on climate: a synthesis. Can. J. Forest Res. 31: 292–301. Bowden, R. D., Davidson, E., Savage, K., Arabia, C. and Steudler, P. 2004. Chronic nitrogen additions reduce total soil respiration and microbial respiration in temperate forest soils at the Harvard Forest. Forest Ecol. Manag. 196: 43–56. Chen, X., Eamus, D. and Hutley, L. B. 2004. Seasonal patterns of fineroot productivity and turnover in a tropical savanna of northern Australia. J. Trop. Ecol. 20: 221–224. Coyea, M. R. and Margolis, H. A. 1994. The historical reconstruction of growth efficiency and its relationship to tree mortality in balsam fir ecosystem affected by spruce budworm. Can. J. Forest Res. 24: 2208–2221. Finzi, A. C., Allen, A. S., DeLucia, E. H., Ellsworth, D. S. and Schlesinger, W. H. 2001. Forest litter production, chemistry, and decomposition following two years of free-air CO2 enrichment. Ecology. 82: 470–484. Fogel, R. 1983. Root turnover and productivity of coniferous forests. Plant Soil. 71: 75–85. Janssens, I. A., Sampson, D. A., Curiel-Yuste, J., Carrara, A. and Ceulemans, R. 2002. The carbon cost of fine root turnover in a Scots pine forest. Forest Ecol. Manag. 168: 231–240. Jobbagy, E. G. and Jackson, R. B. 2000. The vertical distribution of soil organic carbon and its relation to climate and vegetation. Ecol. Appl. 10: 423–436. Keith, H., Jacobsen, K. L. and Raison, R. J. 1997. Effects of soil phosphorus availability, temperature and moisture on soil respiration in Eucalyptus pauciflora forest. Plant Soil. 190: 127–141. Kurz, W. A., Beukema, S. J. and Apps, M. J. 1996. Estimation of root biomass and dynamics for the carbon budget model of the Canadian forest sector. Can. J. Forest Res. 26: 1973–1979. Liu, X., Xiang, W. and Wen, S. 1992. Influence of thinning on biomass production of different densities of Masson’s pine forests. In Liu, X. (ed.) Long-Term Forest Ecosystem Research (in Chinese). Chinese Forestry Press, Beijing. pp. 274–278. Liu, Y., Han, S. J., Zhou, Y. M. and Li, X. F. 2007. Soil and root respiration under elevated CO 2 concentrations during seeding growth of Pinus sylvestris var. sylvestriformis. Pedosphere. 17: 660–665. Liu, Y., Han, S. J., Zhou, Y. M. and Zhang, J. H. 2005. Contribution of root respiration to total soil respiration in a Betula ermanii-dark coniferous forest ecotone of the Changbai Mountains, China. Pedosphere. 15: 448–455. Maassen, S. and Wirth, S. 2006. The effects of thinning on soil chemical properties, microbial community composition and lignocellulolytic activities—results of a five year monitoring program at a pine forest stand. Geophys. Res. Abstr. 8: 01079. Mallik, A. U. and Hu, D. 1997. Soil respiration following site preparation treatments in boreal mixedwood forest. Forest Ecol. Manag. 97: 265–275. Marshall, V. G. 2000. Impacts of forest harvesting on biological processes in northern forest soils. Forest Ecol. Manag. 133: 43–60. McClaugherty, C. A., Aber, J. D. and Melillo, J. M. 1982. The role of fine roots in the organic matter and nitrogen budgets of two forested ecosystems. Ecology. 63: 1481–1490. Mello, S. L. de M., Gon¸calves, J. L. de M. and Gava, J. L. 2007. Pre- and post-harvest fine root growth in Eucalyptus grandis stands installed in sandy and loamy soils. Forest Ecol. Manag. 246: 186–195. Post, W. M., Emanuel, W. R., Zinke, P. J. and Stangenberger, A. G. 1982. Soil carbon pool and world life zones. Nature. 298: 156–159. Raich, J. W., Russell, A. E., Kitayama, K., Parton, W. J. and Vitousek, P. M. 2006. Temperature influences carbon accumulation in moist tropical forests. Ecology. 87: 76–87. Tang, J., Qi, Y., Xu, M., Misson, L. and Goldstein, A. H. 2005. Forest thinning and soil respiration in a ponderosa pine plantation in the Sierra Nevada. Tree Physiol. 25: 57–66. Thibodeau, L., Raymond, P., Camire, C. and Munson, A. D. 2000. Impact of precommercial thinning in balsam fir stands on soil nitrogen dynamics, microbial biomass, decomposition, and foliar nutrition. Can. J. Forest Res. 30: 229–238. Tian, D. 2005. The Functioning of Chinese Fir Plantation Ecosystem (in Chinese). Science Press, Beijing. Vitousek, P. M., Gerrish, G., Turner, D. R., Walker, L. R. and Mueller-Dombois, D. 1995. Litterfall and nutrient cycling in four Hawaiian montane rainforests. J. Trop. Ecol. 11: 189–203. Vogt, K. A., Vogt, D. J., Gower, S. T. and Grier, C. C. 1990. Carbon and nitrogen interactions from forest ecosystems. In Persson, H. (ed.) Above and Belowground Interactions in Forests Trees in Acidified Soils. Simlangsdalen, Sweden. pp. 203–235. Zhang, X., Zwiers, F. W., Hegerl, G. C., Lambert, H. and Gillett, N. P. 2007. Detection of human influence on twentiethcentury precipitation trends. Nature. 448: 462–465.
Effects of Thinning and Litter Fall Removal on Fine Root Production and Soil Organic Carbon Content in Masson Pine Plantations∗1 TIAN Da-Lun1 , PENG Yuan-Ying2 , YAN Wen-De1,∗2 , FANG Xi1 , KANG Wen-Xing1 , WANG Guang-Jun1 and CHEN Xiao-Yong3 1 Forest Ecology Section, Faculty of Life Sciences, Central South University of Forestry and Technology, Changsha 410006 (China) 2 Biology Program, Department of Health and Science, College of DuPage, IL (USA) 3 Biology Program, College of Arts and Science, Governors State University, IL (USA)
(Received October 2, 2009; revised May 18, 2010)
ABSTRACT Soils play a critical role in the global carbon cycle, and can be major source or sink of CO2 depending upon land use, vegetation type and soil management practices. Fine roots are important component of a forest ecosystem in terms of water and nutrient uptake. In this study the effects of thinning and litter fall removal on fine root production and soil organic carbon content were examined in 20-year-old Masson pine (Pinus resinosa) plantations in Huitong, Hunan Province of China in the growing seasons of 2004 and 2005. The results showed that fine root production was significantly lower in the thinning plots than in the control plots, with a decrease of 58% and 14% in 2004 and 2005 growing seasons, respectively. Litter fall removal significantly increased fine root production by 14% in 2004. Soil temperature (Tsoil ) and soil moisture (Msoil ) were higher in the thinning plots than those in the controls. Litter fall removal had significant effects on Tsoil and Msoil . Soil organic carbon content was higher in the thinning plots but was lower in the plots with litter fall removal compared with that in the controls. Our results also indicated that annual production of fine roots resulted in small carbon accumulation in the upper layers of the soil, and removal of tree by thinning resulted in a significant increase of carbon storage in Masson pine plantations. Key Words:
fine roots, forest management, soil carbon, soil moisture, soil temperature
Citation: Tian, D. L., Peng, Y. Y., Yan, W. D., Fang, X., Kang, W. X., Wang, G. J. and Chen, X. Y. 2010. Effects of thinning and litter fall removal on fine root production and soil organic carbon content in Masson pine plantations. Pedosphere. 20(4): 486–493.
Soils are a major terrestrial carbon reservoir. The amount of carbon in soil in the world estimated between 1 000 and 3 000 Pg (1 Pg = 1015 g), constitutes approximately two-thirds of the carbon in terrestrial ecosystems (Post et al., 1982). Through a variety of ecological processes, soil carbon has a tight interaction with the atmosphere and responds to land use and land cover changes (Jobbagy and Jackson, 2000). The amount and distribution of soil organic carbon (SOC) was affected by fine root production (Chen et al., 2004). Many processes in forest ecosystems, such as nutrient cycling, cation exchange and soil water storage are all strongly influenced by SOC. Carbon storage in soils is a dynamic balance between both aboveground and belowground litter inputs (primarily litter fall and fine root litter) and organic matter outputs in the form of CO2 efflux from the soil. Roots are a major organ of a tree for absorption of water and nutrients. In addition, roots are a key component of the belowground part in forest ecosystems, and are a main source of soil organic matter which influences soil microbial activity and decomposition processes (Janssens et al., 2002). A ∗1 Supported
by the “948” Grant of the National Forestry Administration of China (No. 2007-4-19), the Special Grant of Chinese Forestry Public Benefits (Nos. 200804030 and 2007-4-15), and the Provincial Fund for Distinguished Young Scholars of Hunan, China (No. 07JJ1004). ∗2 Corresponding author. E-mail: [email protected].
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large proportion of forest production is allocated to fine roots, resulting in a large carbon flux into the belowground system (Kurz et al., 1996). Due to their high metabolic activity, fine root production and turnover play a critical role in forest carbon dynamics, representing an important carbon input to the soil and can equal or exceed aboveground detritus production in some plant communities (Fogel, 1983). Fine roots may contribute less than 2% of the total ecosystem biomass, but contribute up to 40% of the total ecosystem production (Vogt et al., 1990). The contribution of roots to the total soil respiration rates ranged from 12.5% to 54.6% in a Betula ermanii-dark coniferous forest of the Changbai Mountains, China (Liu et al., 2005), and 8.3% to 48.6% during seedling growth of Pinus sylvestris var. sylvestriformis (Liu et al., 2007). This means that when examining biomass and carbon allocation in forests, fine root component (similar to the foliage in the aboveground) may be very sensitive to environmental change and thus may respond most strongly to a disturbance (Vogt et al., 1990). Thinning, cutting down and removal of a proportion of trees in a forest, has been a common applied silvicultural practice in forest plantations in southern China for over three decades (Tian, 2005). The purposes of thinning usually are: 1) to redistribute the potential resources available for the remaining trees, 2) to maintain or improve the growth rate of the stand, and 3) to utilize the intermediate source of timber revenue before the final forest is cut down at the end of the rotation. Many studies showed that thinning provided a great deal of benefits to the forest stands, including the short-term raise of tree growth and productivity of Masson pine forest (Liu et al., 1992), the acceleration of nitrogen mineralization rate due to increase of temperature of the surface soli layers (Thibodeau et al., 2000), and the decrease of the vulnerability of trees to insect attack (Coyea and Margolis, 1994). Thinning is expected to change soil environments, the allocation of aboveground and belowground productivity, and root density and turnover (Keith et al., 1997; Bowden et al., 2004). The effects of thinning on aboveground processes of forest ecosystems are relatively obvious, while its effects on belowground processes, such as fine root production and SOC content are still not fully clear. Global climate change was expected to increase the air temperature and change the patterns of precipitation distribution around the world (Raich et al., 2006, Zhang et al., 2007). The alterations of temperature and rainfall in the environments may cause the change of litter fall quantity in a forest, because heat and moisture are most important factors affecting tree growth and altering leafing phenology (Finzi et al., 2001). As litter fall represents a major nutrient input of soils, it seems that changes in aboveground litter production will have direct impacts on belowground processes. However, little is known about the potential impact of changes in litter fall on fine root dynamics and SOC content. Masson pine (Pinus massoniana) is one of the dominant pioneer conifer species in southern China and has been widely planted in this region because of its tolerance for infertile and drought soils, and its capacity to retain water and nutrients (Liu et al., 1992). Thinning of Masson pine has been promoted as a means of ecological stand conversion and as an intensive forest management strategy to promote conifer growth and hardwood recruitment. In the present study the effects of thinning and litter fall removal on fine root production and SOC content were examined in Masson pine plantations. We address the following specific hypotheses: 1) thinning will result in an decrease of fine root production; 2) litter fall removal will increase fine root production due to the decrease of nutrient input from the litter layer; 3) thinning will increase SOC due to providing more litters and stimulating microbial activities; 4) litter fall removal will decrease SOC due to the decrease of nutrient inputs; and 5) soil temperature (Tsoil ) and soil moisture (Msoil ) will be increased following thinning. MATERIALS AND METHODS Study sites The study sites consisted of 20-year-old Masson pine (Pinus resinosa) plantations and were located at the Huitong Ecosystem Research Station of the Central South University of Forestry and Technology in Hunan Province, China (26◦ 50 N and 109◦ 45 E). The study area is a moist subtropical zone
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with a mean annual temperature of 16.8 ◦ C and mean temperatures of 4.4 and 26.3 ◦ C in January and July, respectively. Mean annual relative humidity is > 80%, annual rainfall ranges from 1 000 to 1 600 mm, most of which occurs from April to August, and elevation is 270–400 m. The terrain features a relatively open topography with low slopes and some hills, average site slope being below 10 degrees. The soils at the study sites are a mature mountain yellow soil with a thick mineral layer. The soils are predominantly fine loams and silt loams. Soil pH on the surface (0–10 cm) is acidic with an average pH of 5.0. Masson pine plantations were established in the 1985s with an initial plant density of 2 m × 2 m. Understory vegetation was very sparse. Selective thinning was performed in the study sites in the fall of 2003 with 20% thinning intensity. Relative small and unhealthy trees were cut. Experiment design and measurements It was a nested experimental design for the experiment with three replicate plots per treatment. The thinning and control were the main factors. The sub-plots with control and litter fall removal were nested in both thinning and control plots. All litter fall on the floor including branches and needles were removed. The size of each main plot was 50 m × 50 m. Within a main plot, four sub-plots were established and each sub-plot was 10 m × 10 m. To eliminate the edge effects from each of the sub-plots, about 5 m buffering strip was set up between each sub-plot. The distances between the sub-plot with litter fall removal and the sub-control were at least 10 m away from each other. Therefore, a total of 24 sub-plots were set up in the study. All treatments were completed at the end of 2003 and all measurements were conducted in the whole years of 2004 and 2005. Fine root production was estimated using a modified maximum and minimum root core method (McClaugherty et al., 1982). Samples of fine roots (≤ 2 mm) were taken once a month in 2004 and 2005. Fine root biomass was estimated from 3.5 cm diameter soil cores collected to 60 cm depth. In each sampling point, the soil core was divided into four layers from top to bottom of soil, and each layer was 15 cm (i.e., 0–15, 15–30, 30–45 and 45–60 cm). A total of 12 soil cores were collected in each sub-plot at each sampling time. When the samples were brought back to the laboratory, cores were carefully washed over a 0.2-mm sieve to remove soil. Both living and dead roots were distinguished by analysing their external form and colour. The roots were dried at 60 ◦ C until they reached a constant weight. Soil temperature measurements were performed every two weeks, and Tsoil was determined at 5 cm below the soil surface with an LI-COR 6000-09TC soil probe thermocouple (LI-COR Inc, Lincoln, Nebraska, USA). Soil samples with the depth of 0–15, 15–30, 30–45, and 45–60 cm were taken from the uppermost mineral soil layer using a soil auger, stored in airtight tubes and taken back to the laboratory for determination SOC. Soil moisture was determined by ECHH2 O check (Decagon, USA). Soil organic carbon was determined using an improved Walkley-Black wet digestion method. Approximately 0.5 g air-dry soil samples (particle size < 0.15 mm) were transferred to graduated test tubes with 2 mL of K2 Cr2 O7 and agitated, with 4 mL of 98% H2 SO4 gradually added. The test tubes were then heated in an aluminium block at 135 ◦ C for 30 min, allowed to cool to room temperature and adjusted to a final volume of 20 mL using distilled water. Blank solutions were prepared in the same way. The soil supernatant was centrifuged at 3 000 r min−1 for 15 min. Absorbance of all spun supernatant was then measured at 600 nm and a standard curve of relative absorbency vs. organic carbon was constructed. A series of organic carbon standard solutions were prepared by dissolving 0.4754 g sucrose (Chen et al., 2004). Data analysis Statistical tests were conducted for the effects of thinning and litter fall removal and their combination on fine root production and SOC content. Tsoil and Msoil were performed using analysis of variance (ANOVA). No transformations were necessary for the original Tsoil and Msoil data, which satisfied the normality and homoscedasticity assumptions of ANOVA. We calculated sample means and standard errors (SE) of fine root production, Tsoil and Msoil in the thinning and control plots and sub-plots
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with litter fall removal separately in 2004 and 2005. Pair-wise t-tests were used to examine differences between the thinning and control plots. RESULTS Fine root production Thinning significantly affected soil fine root production, which showed significant differences between the thinning and control plots (P = 0.026, Table I). Overall, fine root production was significantly lower in the thinning plots than that in the control plots in both of 2004 and 2005 (Fig. 1). The fine root production in the thinning and control plots was 1.63 and 2.58 kg m−3 , respectively, on average with a difference of 0.95 kg m−3 , a decrease of 37% in 2004, and was 1.86 and 2.05 kg m−3 with a difference of 0.19 kg m−3 , a decrease of 9% in 2005. There was also a significant effect of litter fall removal on fine root production (P = 0.043, Table I). Overall, fine root production was constantly higher in the sub-plots with litter fall removal than that in sub-control plots within both main factor plots only in 2004, but not in 2005 (Fig. 1). In the control plots, the fine root production in the sub-control plots and the sub-plots with litter fall removal were 1.79 and 1.97 kg m−3 , respectively, with a difference of 0.18 kg m−3 on average, a increase of 10% in 2004, but not in 2005 (Fig. 1). The combination effects of litter fall removal and thinning in the thinning plots compared with the sub-control in the control plots showed a significant difference on fine root production in 2004. The fine root production in the sub-control plots and the sub-plots with litter fall removal in the thinning plots were 1.65 and 1.89 kg m−3 , respectively, with a difference of 0.23 kg m−3 on average, an increase of 14% in 2004, but not in 2005 (Fig. 1). TABLE I Analysis of variance results for fine root production affected by thinning (T), litter fall removal (LR) and their combination (T × LR) in 20-year-old Masson pine (Pinus resinosa) plantations in Huitong, Hunan Province of China Source
Degree of freedom
Mean square
F
P
Experimental error
Corrected total
T LR T × LR
2 5 10
2.42 1.86 5.30
2.20 2.86 2.34
0.026 0.043 0.468
54
71
Fig. 1 Mean fine root production in the sub-control plots and the sub-plots with litter fall removal of the control (C) and thinning plots (T) in 2004 and 2005. CC and CLR represent the sub-control plots and the sub-plots with litter fall removal in the control plots, and TC and TLR represent the sub-control plots and the sub-plots with litter fall removal in the thinning plots, respectively. Error bar indicates standard error.
Tsoil and Msoil Thinning altered the microenvironment, with the obvious effects observed in the first year (Table
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II). Both thinning and litter fall removal had statistically significant effects on Tsoil and Msoil (P < 0.0001 and P = 0.0001, respectively). The interaction of thinning and litter fall removal also significantly affected Tsoil (P < 0.0001) and Msoil (P = 0.0060). Tsoil on average increased from 18.92 to 21.78 ◦ C in response to thinning in 2004, with mean differences of 2.86 ◦ C between the sub-control plots and sub-plots with litter fall removal one year after thinning. The mean values of Msoil were consistently lower in the thinning plots than those in the control plots. The litter fall removal in the thinning plots significantly altered Msoil (P = 0.0001) in 2004, but not in 2005 (P > 0.05). TABLE II Soil temperature and soil moisture in the sub-control plots and sub-plots with litter fall removal of the control and thinning plots in 2004 and 2005 Sub-plot
n
2004 Control
2005 Thinning
Differencea) P
Control
Thinning
Difference P
(◦ C)
Control 12 18.62±0.75 21.28±0.88 −2.66 Litter fall removal 12 19.23±0.91 22.28±0.93 −3.05 Mean 24 18.92±0.41 21.78±0.46 −2.86 Control 12 186.4±0.20 152.5±0.26 34.1 Litter fall removal 12 172.8±0.23 159.7±0.33 18.1 Mean 24 179.6±0.26 156.1±0.27 24.5 a) Difference
Soil temperature < 0.0001 18.30±1.64 0.0001 18.03±1.60 < 0.0001 18.17±0.80 Soil moisture (g kg−1 ) < 0.0001 189.4±0.53 0.0001 192.3±0.55 < 0.0001 193.5±0.33
20.81±1.62 −2.51 18.23±1.53 −0.20 19.52±0.81 −1.35
0.0163 0.4263 0.0001
176.8±0.48 14.6 196.2±0.49 −3.9 197.3±0.26 −1.1
0.0048 0.3655 0.2567
= control − thinning.
Tsoil showed a typical parabolic curve during the studied period of 2004 (Fig. 2). Tsoil peaked in July with a value above 30 ◦ C both in the thinning and control plots, being 32.6 and 30.4 ◦ C, respectively, while the corresponding minimum Tsoil was in January with 5.8 and 6.3 ◦ C, respectively. The overall mean value of Tsoil was higher in the thinning plots than that in the control plots both in 2004 and 2005, and the significant differences (P < 0.05) were also found between the sub-control plots and sub-plots with litter fall removal (Table II, Fig. 2). The average Msoil was significantly different (P < 0.05) between
Fig. 2 Seasonal patterns of soil temperature and soil moisture in the thinning, litter fall removal and control plots in year 2004. C and T represent the control and thinning plots, and CC and CLR represent the sub-control plots and the sub-plots with litter fall removal in the control plots, respectively. Error bar indicates standard error.
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the control and thinning plots throughout the growing season of 2004 and 2005 (Table II). The minimum Msoil was in September with the value of 18.2% and 19.5%, while the maximum value appeared in April of 27.3% and 28.6% in the control and thinning plots, respectively (Fig. 2). Soil organic carbon (SOC) Fig. 3 shows the patterns of SOC content with soil depth affected by thinning and litter fall removal in Masson pine plantations. Comparison of SOC vertical distributions for the Masson pine plantations in each plot showed particularly larger differences in the top layer with the soil depth of 0–15 cm (Fig. 3). Averagely, total SOC content was significantly higher (P < 0.001) in the thinning plots (175.4 t ha−1 ) than that in the control plots (151 t ha−1 ) (Fig. 3, Table III). Litter fall removal significantly decreased SOC content, while total SOC in the sub-plots with litter fall removal in the thinning plots (155.4 t ha−1 ) had no significant difference compared with the sub-control plots in the control plots (158 t ha−1 ) (Table III).
Fig. 3 Comparison of mean soil organic carbon contents (SOC) in the thinning (T) and control (C) plots in 2005 (a) and SOC in the sub-plots with litter fall removal in the control (CLR) and thinning plots (TLR), and the sub-control plots in the control plots (CC) in 2005 (b). Error bar indicates standard error. TABLE III Vertical distribution of soil carbon storage in the thinning, litter fall removal, and control plots in 2005 Soil depth
Ta) Amount
cm 0–15 15–30 30–45 45–60 Total
t
ha−1
70.1 52.6 25.6 27.0 175.4
Cb) Percent % 40.0 30.0 14.6 15.4 100.0
Amount t
ha−1
60.0 46.5 21.3 21.2 151.0
CLRc) Percent % 41.1 30.8 14.1 14.0 100.0
Amount ha−1
t 26.0 27.5 18.2 19.4 91.1
TLRd) Percent % 28.5 30.2 19.5 21.3 100.0
Amount t
ha−1
61.8 48.2 23.8 21.6 155.4
CCe) Percent % 39.8 31.0 15.2 13.9 100.0
a) Thinning plots; b) Control plots; c) Sub-plots with litter fall removal in the control plots; removal in the thinning plots; e) Sub-control plots in the control plots.
Amount t
ha−1
66.1 48.2 21.8 21.9 158.0
d) Sub-plots
Percent % 41.8 30.5 13.8 13.9 100.0
with litter fall
DISCUSSION Fine root production This study showed that thinning resulted in a significant reduction of fine root production (Fig. 1). As a result of removal of trees by thinning, root density and biomass were altered. The death of root systems of cut trees should greatly reduce the root component of biomass and production. Our results from this study are consistent with the findings by other researchers (Mello et al., 2007). They found that fine root dynamics was significantly altered, and about 50% decrease in fine root density was observed 60
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days after harvesting. Thinning effects were also highly related with soil conditions (Tsoil and Msoil ) (Fig. 2). Our results are consistent with the findings that decomposition of fine roots speeded up after harvesting, which were directly related to the environmental conditions (Mello et al., 2007). As canopy gaps were formed in a forest by thinning, microclimatic properties within the forest would be changed. The quantity and quality of substrate inputs into the forest floor and soil were altered as well. Thinning was expected to directly reduce living root biomass by removing trees, and possibly to reduce soil microbial biomass by disturbing the humus layer (Mallik and Hu, 1997). Msoil was lower in the thinning plots than that in the control plots in 2004 and 2005 (P < 0.05, Table II, Fig. 2). It was likely attributed to the increase of forest floor evaporation and plant utilization of soil water through transpiration. By providing more space and reducing competition of soil water and nutrients, thinning stimulated active physiological processes of the remaining trees and increased fine root production of the forest (Fig. 1). Litter fall removal constantly increased the fine root production in both control and thinning plots in 2004 (Fig. 1). Litter fall input was generally the most important nutrient resource of the forest soil (Vitousek et al., 1995; Berg and Meentemeyer, 2001). As a result of direct removal of nutrient source from the exposed soil, fine root would produce more to uptake nutrition from soil for nutrient supply. Litter fall removal combined with thinning mitigated fine root production in 2004, as thinning decreased it. Litter fall removal had no effects on fine root production, Tsoil and Msoil in 2005, which is likely attributed to the increasing new litter fall on the forest floor after the treatments. Soil organic carbon content The amount of SOC in the thinning plots was higher than that in the control plots with the difference of 24.4 t ha−1 , which was possibly contributed to the increasing decomposition of organic matter as a result of the increase of microbial activity by thinning. As the canopy removed by thinning, microclimatic properties were altered, as well as the quantity and quality of substrate inputs into the soil. Thinning increased Msoil and Tsoil by increasing insolation and reducing stand evapotranspiration. As a consequence, the composition of the soil microbial community was likely to be altered and microbial activities may increase because of the increasing decay speed of dead roots (Tang et al., 2005; Maassen and Wirth, 2006). The overall mean amount of SOC in the plots with litter fall removal was lower than that in the control plots with the difference at 66.9 t ha−1 (Table III, Fig. 3). Reduction of SOC is mainly due to suppression of microbial activities and nutrient supply from the humus layer, because litter fall input is generally the most important way of nutrient transfer to forest soil (Berg and Meentemeyer, 2001). Soil is the habitat of plant roots and the home of numerous microflora, including viruses, bacteria, fungi and blue-green algae. The soil microflora and fauna complement each other through the combination of litter, mineralization of essential plant nutrients, and conservation of these nutrients within the soil system (Marshall, 2000). Litter fall removal likely greatly reduced microbial activity as a result of removing the substrate supply to the mineral soil. Combination of thinning and litter fall removal did not change SOC in this study. It is likely due to the offset effects between them. CONCLUSIONS The study showed that thinning and litter fall removal significantly changed fine root production, SOC content, Tsoil and Msoil . Thinning caused a decrease in fine root production and a increase in SOC. The decrease in fine root production is likely a result of the increase in Tsoil and Msoil , while the increase in SOC resulted from the increasing microbial activities following by the thinning treatment. Litter fall removal increased fine root production but decreased SOC in both thinning and control plots, as a result of changes in Tsoil and Msoil and reduced substrate input to the soil. In a word the changes of fine root production and SOC following thinning and litter fall removal were driven by the changes in soil conditions, such as Tsoil and Msoil , soil nutrient input, and bacteria and fungi consumption of fine roots in forest soils. Thinning had long term effects on forest belowground process and environmental conditions while litter fall removal only made a short term effects on them.
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