Plant Ecol (2007) 193:71–84 DOI 10.1007/s11258-006-9249-6
O R I G I N A L A RT I C L E
Soil respiration and carbon balance in a subtropical native forest and two managed plantations Yu-Sheng Yang Æ Guang-Shui Chen Æ Jian-Fen Guo Æ Jin-Sheng Xie Æ Xiao-Guo Wang
Received: 12 July 2005 / Accepted: 5 December 2006 / Published online: 10 January 2007 Springer Science+Business Media B.V. 2007
Abstract From 1999 to 2003, a range of carbon fluxes was measured and integrated to establish a carbon balance for a natural evergreen forest of Castanopsis kawakamii (NF) and adjacent monoculture evergreen plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata, CF) in Sanming Nature Reserve, Fujian, China. Biomass carbon increment of aboveground parts and coarse roots were measured by the allometric method. Above- and belowground litter C inputs were assessed by litter traps and sequential cores, respectively. Soil respiration (SR) was determined by the alkaline absorbance method, and the contribution from roots, above- and belowground litters was separated by the DIRT plots. Annual SR averaged 13.742 t C ha–1 a–1 in the NF, 9.439 t C ha–1 a–1 in the CK, and 4.543 t C ha– 1 –1 a in the CF. For all forests, SR generally peaked in later spring or early summer (May or June). The contribution of root respiration ranged from 47.8% in the NF to 40.3% in the CF. On Y.-S. Yang (&) G.-S. Chen J.-F. Guo Department of Geographical Sciences, Fujian Normal University, Fuzhou 350007, China e-mail:
[email protected] G.-S. Chen e-mail:
[email protected] J.-S. Xie X.-G. Wang Department of Forestry, Fujian Agriculture and Forestry University, Fuzhou 350002, China
average, soil heterotrophic respiration (HR) was evenly distributed between below- (47.3~54.5%) and aboveground litter (45.5%–52.7%). Annual C inputs (t C ha–1 a–1) from litterfall and root turnover averaged 4.452 and 4.295, 4.548 and 2.313, and 2.220 and 1.265, respectively, in the NF, CK, and CF. As compared to HR, annual net primary production (NPP) of 11.228, 13.264, and 6.491 t C ha–1 a–1 in the NF, CK, and CF brought a positive net ecosystem production (NEP) of 4.144, 7.514, and 3.677 t C ha–1 a–1, respectively. It suggests that native forest in subtropical China currently acts as an important carbon sink just as the timber plantation does, and converting native forest to tree plantations locally during last decades might have caused a high landscape carbon loss to the atmosphere. Keywords Soil respiration Carbon balance Carbon sink Native forests Tree plantations
Introduction The role of the world’s forests as a ‘‘sink’’ for atmospheric carbon dioxide is the subject of active debate. Less clear, however, is the extent to which intact or low disturbance forests are currently sinks for carbon dioxide. In recent years considerable progress has been made in understanding the processes which determine forest
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carbon balance, through a combination of physiological, micrometeorological, and mensurational studies (Malhi et al. 1999). Recent micrometeorological research suggests that there is a net C sink in mature Amazonian forests (Grace et al. 1995a, b). However, Saleska et al. (2003) shows very low net carbon storage in Amazonian forests. They believed that the earlier work purporting to show a large sink from micrometeorological (eddy covariance) data was flawed because it did not sufficiently account for the effect of low air turbulence in limiting measured carbon fluxes to below the likely biological flux. Long-term monitoring of plots in mature humid tropical forests concentrated in South America revealed that these forest plots have accumulated 0.71 ton, plus or minus 0.34 ton, of carbon per hectare per year in recent decades (Phillips et al. 1998). However, though these results indicate that mature forests may still act as a significant carbon sink, the role of natural or old-growth forest and tree plantation in C sequestration is unclear at present. As Harmon (2001) points out, there are two contrasting views, and consequently some confusion prevails. On the one hand, young or (newly planted) forests are generally believed to be better than older ones for C sequestration because of their faster growth, higher dry-matter accumulation rates, and fewer dead trees or decomposing parts. On the other hand, replacements of older forests with younger ones are reported to result in net release of C into the atmosphere (e.g., Schulze et al. 2000) when the long-term carbon storage by detritus, soil, and forest products are considered. Due to rapid human population growth, demand for timber, fuel material, and other forest products are increasing. In many areas of South China, native broad-leafed forests have been cleared for the last several decades, and subsequent development has involved the plantation of more productive forest species. Following timber extraction, the forestland is slashed, burned, and planted with economical conifer species, especially Chinese fir (Cunninghamia lanceolata). As an important native conifer, Chinese fir has been widely planted for more than 1,000 years and used for a variety of wood products. Planting area has reached 6 million ha and accounted for 24%
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of all forested land in China (Yu 1996). Currently, it is thought that this conifer will be able to bring great profit of carbon sequestration in addition to timber production. However, our knowledge is limited about the effects of forest conversion to tree plantations on C sequestration in the subtropical China. The establishment of tree species trials during the 1960s at the Xinkou Experimental Station in Sanming, Fujian, China, provided a unique opportunity to examine how tree plantations altered C dynamics in this ecosystem. In this article, a range of measurements on carbon fluxes has been integrated to establish a carbon balance for a subtropical native broadleaved forest and two plantations of southeastern China. The primary objective of this study was to answer three questions: What are the fluxes of carbon to and from these subtropical forests? What are the annual budgets of carbon for these ecosystems? What differences occurred during conversion of native forest to managed plantations?
Materials and methods Site description The study was carried out in the Xiaohu workarea of the Xinkou Experimental Forestry Centre of Fujian Agricultural and Forestry University, Sanming, Fujian, China (2611¢30† N, 11726¢00† E). It borders the Daiyun Mountain on the southeast, and the Wuyi Mountain on the northwest. The region has a middle sub-tropical monsoonal climate, with a mean annual temperature of 19.1C and a relative humidity of 81%. The mean annual precipitation is 1749 mm, mainly occurring from March to August (Fig. 1). Mean annual potential evapotranspiration (Penman– Monteith equation) is 1,585 mm. The growing season is relatively long with an annual frost-free period of around 330 days. The parent material of the soil is sandy shale and soils are classified as red soils (humic Planosols in FAO system). Thickness of the soil exceeds 1.0 m. Selected forest characteristics and some properties of the surface soil (0–20 cm) of the three sites are described in Table 1. NF represents the evergreen, broad-leaved C. kawakamii forest in
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Monthly air temperature (˚C)
Fig. 1 Monthly changes of rainfall and air temperature in the study sites
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Monthly rainfall (mm)
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Table 1 Forest characteristics and soil properties in a natural forest and two plantation forests
a
NF: natural forest of Castanopsis kawakamii; CK: C. kawakamii plantation forest; and CF: Chinese fir (Cunninghamia lanceolata) plantation forest
b
Castanopsis kawakamii is only involved in the NF c
Top 0–20 cm soil
Rainfall in 1999
Rainfall in 2000
Rainfall in 2001
Rainfall in 2002
Rainfall in 2003
Rainfall during 1961-1990
Temperature in 1999
Temperature in 2000
Temperature in 2001
Temperature in 2002
Temperature in 2003
Temperature during 1961-1990
Forest typea
Parameter
Canopy coverage (%) Mean tree height (m)b Mean tree diameter at breast height (cm)b Stand density (stem ha–1) b Stand volume (m3 ha–1)b Biomass of tree layer (t ha–1) Biomass of shrub layer (t ha–1) Biomass of herb layer (kg ha–1) Standing crop of forest floor (t ha–1) Fine-root biomass (t ha–1) Bulk density (g cm–3)c Organic matter (g kg–1)c Total N (g kg–1)c Total P (g kg–1)c Total ecosystem C store (t ha–1)
mid-subtropical China with high purity (85% of total stand basal area for C. kawakamii), old age (~150 years), and large area (~700 ha). In addition to C. kawakamii, the overstory also contained other tree species, such as Pinus massoniana, Schima superba, Lithocarpus glaber, Symplocos caudate, Machilus velatina, Randia cochinchinensis, and Symplocos stellaris. In 1966, part of this NF was clear-cut, slashed, and burned. In 1967, the soil was prepared by digging holes and then 1-year-old seedlings of C. lanceolata (Chinese fir) and C. kawakamii were planted at 3,000 trees per hectare. The area of each plantation is larger than 20 ha. The plantation forests were managed with similar practices, such as weed-controlling and fertilizing during the first
NF
CK
CF
80 24.3 42.2 255 398.3 512.5 10.115 867 7.7 4.94 0.93 46.0 1.88 0.36 399.1
90 18.9 24.2 875 412.4 379.9 0.780 292 7.4 3.20 1.10 29.8 1.12 0.31 300.7
65 21.9 23.3 1117 425.9 237.4 1.993 2 478 3.2 1.49 1.20 29.5 1.12 0.29 217.1
3 years, and thinning twice between 10 and 15year-old. The normal rotation length is 30 years for the CF and 40 years for the CK, respectively. Methods Biomass estimation In January 1999, five 20 m · 20 m plots were located at each site. Diameters at breast height of all trees on each plot were measured. All stems 4 cm d.b.h. and above were identified by species; diameter was determined using standard diameter measuring tapes. In the NF, for trees with epiphytic cover on the trunk, the epiphytes were pulled a short distance away from the trunk,
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sufficient to allow determination of the trunk diameter. Dead stems were inventoried and identified where possible. Biomass components (wood, bark, branch, twig, leaf, and root) were estimated by harvest. A total of 56 trees from eight dominant tree species (including 10 individuals of C. kawakamii, eight of Pinus massoniana, eight of Schima superba, six each of Lithocarpus glaber, Symplocos caudate, Machilus velatina, Randia cochinchinensis, and Symplocos stellaris) in the NF, 12 of C. kawakamii in the CK and 12 of Chinese fir in the CF were felled. The selected tree species in the NF account for over 95% of the total stand basal area. Allometric regression equations (power functions) relating tree DBH and biomass were developed for each species at these sites (Yang et al. 2006). Annual growth rate was determined as the annual ring increment from cores obtained using either a 4.5 mm or 11 mm corer, or from bole slices. Samples for carbon analysis were obtained from each of the harvested species. These samples were derived from material collected during harvests to determine allometric relationships. Four to six branches were removed from each tree; these were selected from different levels of the canopy. Samples of branch wood, twig, and foliage were obtained from each branch. Samples of coarse root wood (further divided into > 40, 20–40, 10–20, 4–10, 2–4 mm in diameter) were obtained from selected four to six root branches of each tree. Samples of trunk wood were obtained from each tree using an 11-mm tree corer or wedges of wood cut using a chainsaw. All samples obtained were field weighed, placed into plastic bags and kept cool until they could be transported to the laboratory. Fine root production Fine root biomass was measured by the sequential core method. On each sampling date, six soil cores (1 m in depth) were randomly collected from each plot (30 per forest) bimonthly during January 1999–January 2004 using a steel corer (6.8 cm diameter, 1.2 m length). To avoid length shrinkage caused by soil compaction, each core
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was taken by three consecutive coring at the same sampling point, viz. 0–40 cm, 40–80 cm, and 80– 100 cm, respectively for each coring. Soil cores were then cut into different depths (0–10, 10–20, 20–30, 30–40, 40–50, 50–60, 60–70, 70–80, 80–90, and 90–100 cm) and stored at 4C in refrigerators until processed. Cores were washed with tap water to remove adhering soil and accompanying organic debris. Fine roots were classified by diameter class ( 0.05). Annual LF was intimately negatively correlated with annual rainfall in the CF (r2 = 0.9,
CO2 efflux rate(mg CO2 m-2 h-1)
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a)
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J F M A M J J A S O N D J F M A M J J A S O N D J F M A MJ J A S O N D 2001 2002 2003
b)
-2
-1
CO2 efflux rate(mg CO2 m h )
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J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 2001 2002 2003
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CO2 efflux rate(mg CO2 m h )
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Fig. 2 Monthly changes of soil respiration and its components (mg CO2 m–2 h–1) in the NF (a), CK (b), and CF (c) s, newly aboveground litter; •, old aboveground litter; M, Root respiration; m, belowground litter; and·, soil respiration
P < 0.01), while this correlation is much poorer in the NF and the CK (r2 = 0.43–0.48, P < 0.01).
forests (P < 0.01). Both significantly lower annual FRP and FRM were found in year 2003 than in the other years (P < 0.01).
Annual fine-root production and mortality Annual fine-root production (FRP) and mortality (FRM) averaged 4.319 and 4.295 t C ha–1 a–1 in the NF, 2.679 and 2.313 t C ha–1 a–1 in the CK and 1.282 and 1.265 t C ha–1 a–1 in the CF, respectively (Table 4). There were significant differences in annual FRP and FRM between
Carbon increment in aboveground biomass and coarse root In 5 years, carbon sequestered from aboveground biomass averaged 2.076, 5.379, and 2.614 t C ha–1 a–1 in the NF, CK, and CF, respectively (Table 4). Annual increment of coarse root carbon averaged
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Table 2 Parameters of different models of soil respiration (SR) in relation to soil temperature (T) and soil water content (W) at 0–10 cm Forest type
NF
CK
CF
Year
2001 2002 2003 Jun–Oct 2003 2001 2002 2003 Jun–Oct 2003 2001 2002 2003 Jun–Oct 2003
SR = aebT
SR = aW+b
SR = aebTWc
r2
r2
A
b
c
r2
0.561 0.533 0.074 0.002 0.713 0.749 0.384 0.060 0.755 0.799 0.198 0.207
0.440 0.490 0.704 0.813 0.431 0.404 0.637 0.791 0.401 0.397 0.688 0.567
45.621 43.703 79.040 143.490 17.254 18.716 25.535 20.467 2.634 2.843 1.717 9.749
0.0265 0.0277 0.0133 –0.0171 0.0423 0.0402 0.0303 0.0047 0.0531 0.0557 0.0444 0.0405
0.641 0.625 0.528 0.568 0.712 0.705 0.669 0.793 0.932 0.967 1.917 0.616
0.894 0.863 0.855 0.802 0.939 0.959 0.878 0.787 0.942 0.926 0.935 0.636
0.352, 0.831, and 0.431 t C ha–1 a–1, respectively, in the NF, CK, and CF, which accounted for 17.0%, 15.4%, and 16.5% those of aboveground (Table 4). Carbon balance budget Annual net primary production (NPP) amounted to 11.228, 13.264, and 6.491 t C ha–1 a–1 in the NF, CK, and CF, respectively (Table 5). The NF and the CF were estimated to have similar net carbon sink (or NEP, net ecosystem production) of 4.144 and 3.677 t C ha–1 in a year, respectively (Table 5). An estimate as high as 7.514 t C ha–1 a–1 was obtained in the CK, almost two times of those in the NF and CF. No significant yearly fluctuation of NEP was found in these forests (P > 0.05).
Discussion Soil respiration Though the soda lime method was used quite frequently before the mid-1990s, there may be an overestimate of soil CO2 flux during low-flux periods using the soda-lime procedure (Raich et al. 1990), although the effect on annual soil respiration estimates may not be large. The soda lime can reduce the CO2 content in the chamber to well below the normal CO2 concentration above the soil surface. This can result in accelerated diffusion of CO2 from the soil into the air
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enclosed by the chamber, compared to the normal situation. The method can therefore overestimate the rate of soil respiration. Thus, the estimates of soil respiration that are presented may be overestimates, due to the soda-lime procedure used for measuring them. Soil surface CO2 efflux at our site (4.543– 13.742 t C ha–1 a–1) approaches the range of published values for tropical and subtropical forests (3.45–15.20 t C ha–1 a–1) (Raich and Potter 1995). Annual SR of the NF was higher than those of other subtropical climatic forests, e.g., monsoon broad-leaved forest (11.5 t C ha–1 a–1) and mixed conifer-broad-leaved forest (10.4 t C ha–1 a–1) in Dinghushan Mt. (Yi et al. 2003), Karst forest (5.3 t C ha–1 a–1) in Maolan (Ran et al. 2002) and Quercus glauca forest (6.6 t C ha–1 a–1) (Huang et al. 1999). Annual SR of the CF was much lower than those of younger Chinese fir plantations, e.g., 10-year-old Chinese fir stand in Huitong (5.9 t C ha–1 a–1) (Fang and Tian 1997) and 14-year-old Chinese fir stand in Qianyanzhou (9.3 t C ha–1 a–1) (Zhou et al. 2002). Many studies (e.g., Raich and Potter 1995; Boone and others 1998; Raich 1998), including those carried out in subtropical China, have related variation in SR to soil temperature. However, the seasonal pattern of SR in these forests did not intimately follow soil temperature across the research period (especially in the dry year of 2003), suggesting that soil temperature alone is not enough to predict SR, even in a
14.232 3.894 15.019 4.682 12.464 3.459 13.742 4.263
±
±
±
±
9.812 3.683 10.451 3.391 8.427 3.179 9.439 3.446
±
±
±
±
4.765 1.196 5.093 1.974 3.993 1.279 4.543 1.845 ±
±
±
±
6.875 2.312 7.296 2.912 5.779 2.121 6.537 2.382 ±
±
±
±
4.056 1.242 4.47 0.798 3.557 0.980 4.013 1.078
CK
NF
CF
NF
CK
Root respiration
Soil respiration
±
±
±
±
1.943 0.556 2.111 0.619 1.545 0.376 1.828 0.561
CF
±
±
±
±
3.406 1.036 3.638 0.846 3.249 0.841 3.431 0.891
NF
±
±
±
±
Mean
2003
2002
2001
2000
1999
Year
2.365 0.536 1.787 0.554 2.088 0.597 2.200 0.513 2.064 0.493 2.076 0.495
±
±
±
±
±
±
5.502 0.943 5.256 0.909 5.198 0.802 5.703 0.970 4.486 0.805 5.379 0.926
±
±
±
±
±
±
2.851 0.525 2.432 0.477 2.559 0.592 2.978 0.539 2.008 0.529 2.614 0.598 ±
±
±
±
±
±
0.401 0.151 0.303 0.105 0.354 0.098 0.373 0.106 0.350 0.092 0.352 0.108 ±
±
±
±
±
±
0.850 0.253 0.812 0.247 0.803 0.212 0.881 0.255 0.693 0.180 0.831 0.240
CK
±
±
±
±
±
±
0.470 0.134 0.401 0.120 0.422 0.136 0.491 0.119 0.331 0.129 0.431 0.132
CF
±
±
±
±
±
±
NF
CF
NF
CK
Biomass C increment of coarse root
Aboveground biomass C increment
4.462 0.411 4.153 0.436 4.557 0.583 4.356 0.414 4.733 0.497 4.452 0.508
NF
±
±
±
±
±
±
Litterfall C
2.89 0.475 3.044 0.532 2.542 0.458 2.825 0.504
CK
4.702 0.536 4.228 0.596 4.612 0.438 4.413 0.627 4.785 0.675 4.548 0.650
CK
±
±
±
±
Respiration of belowground litter
Table 4 Annual NPP components (t C ha–1 a–1) in the NF, CK, and CF (Data are mean ± SD)
Mean
2003
2002
2001
Year
±
±
±
±
±
±
±
±
±
±
2.389 0.222 2.051 0.256 2.013 0.286 2.112 0.285 2.534 0.317 2.22 0.322
CF
1.513 0.515 1.625 0.419 1.354 0.469 1.497 0.517
CF
Table 3 Annual soil respiration and its components (t C ha–1 a–1) in the NF, CK, and CF (Data are mean ± SD)
±
±
±
±
±
±
±
±
±
±
2.205 0.651 2.327 0.516 1.685 0.654 2.072 0.613
CK
±
±
±
±
4.421 0.553 4.053 0.361 4.784 0.646 4.519 0.515 3.819 0.340 4.319 0.687
NF
±
±
±
±
±
±
3.05 0.271 2.771 0.418 2.516 0.287 2.879 0.268 2.179 0.329 2.679 0.405
CK
±
±
±
±
±
±
Fine root production
2.523 0.641 2.603 0.597 2.079 0.585 2.402 0.682
NF
Respiration of newly aboveground litter
±
±
±
±
1.412 0.213 1.165 0.154 1.317 0.122 1.498 0.187 1.019 0.135 1.282 0.172
CF
0.979 0.391 1.047 0.431 0.766 0.301 0.931 0.325
CF
±
±
±
±
±
±
±
±
±
±
0.662 0.459 0.61 0.478 0.643 0.461 0.638 0.480
CK
±
±
±
±
3.973 0.401 4.27 0.517 4.814 0.602 4.678 0.617 3.742 0.479 4.295 0.571
NF
±
±
±
±
±
±
1.992 0.255 2.452 0.324 2.261 0.201 2.769 0.354 2.089 0.198 2.313 0.289
CK
±
±
±
±
±
±
Fine root mortality
1.427 0.478 1.483 0.496 1.357 0.474 1.422 0.489
NF
Respiration of old aboveground litter
1.295 0.123 1.201 0.171 1.267 0.191 1.452 0.138 1.112 0.139 1.265 0.185
CF
±
±
±
±
±
±
±
±
±
±
0.33 0.150 0.31 0.129 0.328 0.141 0.323 0.147
CF
Plant Ecol (2007) 193:71–84 79
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3.489 4.097 3.444 3.677 7.373 7.895 7.273 7.514 4.426 3.725 4.281 4.144 7.122 6.049 6.311 7.079 5.892 6.491 14.104 13.067 13.129 13.876 12.143 13.264 11.649 10.296 11.783 11.448 10.966 11.228 1999 2000 2001 2002 2003 Mean
NF
± ± ± ± ± ±
1.041 1.117 1.506 1.074 1.153 1.277
CK
± ± ± ± ± ±
1.592 1.862 1.267 1.917 1.858 1.921
CF
± ± ± ± ± ±
0.637 0.783 0.905 0.898 0.825 0.949
7.357 7.723 6.685 7.255
± ± ± ±
2.493 2.380 2.095 2.454
5.756 5.981 4.870 5.536
± ± ± ±
1.932 1.656 1.935 1.951
2.822 2.982 2.448 2.751
± ± ± ±
0.862 1.013 0.923 0.969
NF CF CK NF
Soil heterotrophic respiration Total NPP Year
Table 5 Carbon balance budget and annual NEP (t C ha–1 a–1) in the NF, CK, and CF (Data are mean ± SD)
NEP
± ± ± ±
1.452 1.373 1.550 1.545
CK
± ± ± ±
1.875 2.463 2.289 2.478
CF
± ± ± ±
1.337 1.049 1.319 1.354
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normal climatic condition (e.g., year 2002 or 2001). This might be due to that soil water content, in addition to soil temperature, will exert a strong influence on SR. In subtropical China, soil temperature and soil water content often change asynchronically over the year and peaked differently in August and May or June, respectively. A dry period usually occurs during midsummer when soil temperature reaches its maximum while soil water content at a relative low level due to less rain event. Thus, soil respiration will be restricted by soil water content and the maximum SR will not happen during this period. Instead, the maximum SR will occur during May– June when soil temperature does not reach its maximum while soil water content is at its highest. The influence of soil water content on SR will be significant when a long dry period occurs, just as the period from June to October in 2003. SR is intimately correlated with soil water content (R2 = 0.80, P < 0.01) during this period (Table 2), resulting in a higher correlation of SR to soil water content than to soil temperature across the whole year. This is similar to Rout and Gupta (1989) who have found that, in northern India forests, soil moisture alone explained 76% of variation in SR during a long period of high temperature or seasonal dry period. However, soil temperature and soil water content together can be explained over 85% of variation in SR in these forests, which is similar to those in a coppice oak forest in Central Italy (91%), a coniferous forest in the Sierra Nevada mountains (89%), and an Eucalyptus pauciflora forest (97%) in Australia (Rey et al. 2002; Qi and Xu 2001; Keith et al. 1997). Contribution of the components to the total soil respiration Factors controlling relative contributions to total soil respiration in different forests are not well understood. The absolute rate of total soil respiration from forest soils is influenced by a number of factors, including moisture and temperature, soil nitrogen content, litter quality and soil organic matter content, forest development, and management practices (Bowden et al. 1993). These factors may also influence the relative
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contributions to soil respiration. A greater understanding of these factors is needed to predict relative contributions to total soil respiration in different forest ecosystems. There is large variability in the literature with regard to the relative contributions of autotrophic and heterotrophic respiration to total soil CO2 efflux (as reviewed by Hanson et al. 2000), e.g., Rey et al. (2002) reported that, in a coppice oak forest in Central Italy, the overall annual average was: 21.9%, 23.3%, and 54.8% for aboveground litter respiration, root respiration and belowground SOM and detritus decomposition, respectively; Bowden et al. (1993) have reported that, in a temperate mixed hardwood forest, the contributions to total soil respiration by live root respiration, organic matter derived from aboveground and belowground litter were 33%, 37%, and 30%, respectively. In this investigation, root contributions to SR (40.3%–47.8%) is comparable to the mean values of 45.8 for the world forests throughout a growing season, and to a range of 43%–55% for tropical forests that estimated by the component integrated method. The contribution of root respiration was maximum during late spring and early summer and minimum during winter, coinciding with periods of aboveground growth and optimization of both soil temperature and moisture. Similar patterns were also reported by other studies, e.g., Edwards et al. (1977) directly measured the seasonal patterns of 14CO2 efflux from the roots of a white oak tree and found that the rate of root-derived CO2 efflux increased dramatically during the May–June period; Work from Tennessee hardwood forests (Edwards and Harris 1977) and Missouri white oak forests (Joslin 1983) has also shown that the time period from midMay through June is characterized by high root growth and root turnover. A large fraction of heterotrophic respiration in these forests is due to belowground processes, the decomposition of belowground litter and soil organic matter, which accounted for as much as 47.3%–54.5% of the total SR. This is in agreement with studies indicating that root respiration plus belowground litter decomposition combined contribute 70%–80% of total soil respiration across a wide range of forests (Raich
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and Nadelhoffer 1989; Nadelhoffer and Raich 1992). Aboveground litter decomposition accounted for 45.5%–52.7% of the total SR. Newly deposited aboveground litter dominated the carbon dioxide emitted by total aboveground litter, and contributed 17.2%–21.6% of total soil respiration, higher than the 12% measured by Bowden et al. (1993) and the 10.9% by Edwards and Harris (1977). Increased death of roots as a consequence of the trenching treatment should have induced an increase in respiration by the decomposers of root debris that might have continued into the following year, and may have led to underestimation of the proportion of root respiration. To minimize this effect, we waited several months for the initial flush of CO2 resulting from the treatment to dissipate, and this may have obviated the problem as suggested by other studies. Fahey et al. (1988), for example, found that the C content of decomposing, recently killed fine roots, in a mixed hardwood forest in New Hampshire was relatively stable approximately 4 months after decay began. Our estimated root decomposition rate is much faster than the rate reported by Fahey et al. (1988), suggesting that root decomposition probably did not strongly influence our flux measurements begun 4 months after trenching was completed. Additionally, Ewel et al. (1987) found no effects of root decomposition on CO2 effluxes 4 months after trenching was completed in a Florida pine plantation. Another problem associated with removal of roots to enable estimation of their contribution to SR, is the elimination of root water uptake and hence a potential increase in soil water content compared to the control plots. However, we did not measure a significant or consistent increase in soil moisture in the trenched plots. Contribution of the components to NPP In the NF, NPP is clearly dominated by yearly tissues (litterfall plus fine-root production), accounting for 80% of total NPP. While in the CK and the CF, NPP is quite evenly distributed between yearly tissues (53.8% and 53.4%) and woody biomass increment (46.2% and 46.6%).
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The measured annual litterfall fell into the range from tropical forests (0.9–6.0 t C ha–1 a–1) (Clark et al. 2001). Mean annual C returns through litterfall in the NF (4.452 t C ha–1 a–1) and the CK (4.548 t C ha–1 a–1) were both higher than those in natural forest of Lithocarpus xylocarpus in Ailao mountain (3.24 t C ha–1 a–1) (Liu et al. 2002) and mixed forest of Pinus massoniana and Schima superba in Dinghu mountain (4.02 t C ha–1 a–1) (Fang et al. 2003). The carbon input from the CF (2.220 t C ha–1 a–1) was much lower in comparison with old-growth coniferous forest of Picea abies (20 t C ha–1 a–1) (Pedersen and Hansen 1999). The estimated aboveground biomass increment of these forests was comparable with the range for tropical forests (from 0.3 t C ha–1 a–1 in a Hawaiian forest on 3,400-year-old lava at 700 m elevation to 3.8 t C ha–1 a–1 in a lowland moist forest in Ivory Coast (Raich et al. 1997; Clark et al. 2001). A significantly higher proportion of NPP (41.7%) was allocation belowground in the NF than in the plantations (26.1% and 26.2% for the CK and the CF). Fine roots dominate the belowground NPP in these forests, especially in the NF where 92.4% of BNPP was attributed to FRP. Therefore, fine-root production is an important component contributing to NPP for these forests. NEP In this study, NEP was positive (NF: 4.144 t C ha–1 a–1, CK: 7.514 t C ha–1 a–1, and CF: 3.677 t C ha–1 a–1), indicating that the sites studied are a carbon sink. The value for the NF was higher than the estimates for Amazonian rainforest (1 t C ha–1 a–1, Grace et al. 1995b), southern China tropical rainforest (0.373 t C ha–1 a–1) (Li et al. 1998), northern Australian tropical savanna (3.8 t C ha–1 a–1) (Chen et al. 2003), eastern North American deciduous forests (0.7–3.2 t C ha–1 a–1, Curtis et al. 2002) and Japan temperate deciduous forest (1.28 t C ha–1 a–1) (Yamamoto et al. 2001), lower than the estimates for China tropical forests (7.68 t C ha–1 a–1) and broad-leaved forests (7.28 t C ha–1 a–1) (Zhou et al. 2000), and falls in the range for European temperate deciduous forest (2–5 t C ha–1 a–1, Goulden et al. 1996;
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Greco and Baldocchi 1996). The value for the CK was very similar to the estimate for China broad-leaved forests. The value for the CF was also comparable to Northern China temperate Laris gmelinii forest (2.65 t C ha–1 a–1) (Jiang and Zhou 2001) and Siberian Scots pine forests (0.19–1.36 t C ha–1 a–1, Wirth et al. 2002). The positive NEP in the CF contrasts a negative NEP (–0.427 t C ha–1 a–1) in a 10-year-old Chinese fir stand in Huitong (Fang et al. 2002). Though lower than the CK, the NF had a positive NEP similar to the CF, the most important timber plantation in southern China as indicated above, suggesting that this native forest still play an active role in carbon sequestration just as the timber plantation did. Taking into account the fact that the NF had much larger ecosystem carbon storage than the plantations (Table 1), however, one may believe that conversion of a native forest to a tree plantation in subtropical China might have caused a high net release of carbon to the atmosphere. This is similar to Harmon et al. (1990) who had reported that the conversions of old-growth forests to younger plantations in western Oregon and Washington in the last 100 years had added 1.5 · 109 to 1.8 · 109 megagrams of carbon to the atmosphere. Though they may have higher carbon accumulation rates, tree plantations could unlikely compensate for this net release under current management regime (e.g., clear-cutting, slash and burning, and short rotation). For this reason, the NF forests, and the other remaining natural ecosystems must be protected and restored.
Conclusion In this article, the possible changes of carbon fluxes and carbon balance associated with converting a natural forest to plantations grown on the same site were assessed. As compared to the plantations, the NF had a lower biomass C accumulation rate, a higher detritus carbon input (above- plus belowground), and a higher soil respiration not only autotrophic but also heterotrophic. Though the NF had a low NPP relative to soil heterotrophic respiration, it had a positive
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NEP similar to the CF, the most important timber plantation in southern China, suggesting that this native forest currently acts as an important carbon sink just as the timber plantation does. When the high ecosystem carbon storage of the NF is included, converting native forest to tree plantations in subtropical China might have caused a high landscape carbon loss to the atmosphere. In order to maintain carbon stores, preservation of currently existing native forests should be put forward. Acknowledgments This work was funded by the National Natural Science Foundation of China (No. 30170770 and No. 30300272), the Teaching and Research Award program for MOE P.R.C. (TRAPOYT), the Key Basic Research Project of Fujian Province (2000F004), and the Natural Science Foundation of Fujian Province (B0310014).
References Boone RD, Nadelhoffer KJ, Canary JD et al (1998) Roots exert a strong influence on the temperature sensitivity of soil respiration. Nature 396:570–572 Bowden R, Nadelhoffer KJ, Boone RD, Melillo JM, Garrison JB (1993) Contribution of aboveground litter, belowground litter, and root respiration to total soil respiration in a temperate mixed hardwood forest. Can J Forest Res 23:1402–1407 Chen XY, Hutley LB, Eamus D (2003) Carbon balance of a tropical savanna of northern Australia. Oecologia 137:405–416 Clark DA, Brown S, Kicklighter DW, Chambers JQ, Thomlinson JR, Ni J, Holland EA (2001) Net primary production in tropical forests: an evaluation and synthesis of existing field data. Ecol Appl 11(2):371–384 Curtis PS, Hanson PJ, Bolstad P, Barford C, Randolph JC, Schmid HP, Wilson KB (2002) Biometric and eddycovariance based estimates of annual carbon storage in five eastern North American deciduous forests. Agricult Forest Meteorol 113:3–19 Edwards NT, Harris WF (1977) Carbon cycling in a mixed deciduous forest floor. Ecology 58:431–437 Edwards NT, Harris WF, Shugart HH (1977) Carbon cycling in deciduous forest. In: Marshall JK (ed) The belowground ecosystem: a synthesis of plant-associated processes. Range Science Department Science Series No. 26, Colorado State University, Fort Collins, CO, USA, pp 153–157 Ewel KC, Cropper WP Jr, Gholz HL (1987) Soil CO2 evolution in Florida slash pine plantations. II. Importance of root respiration. Can J Forest Res 17:330–333 Fahey TJ, Hughes JW, Pu M et al (1988) Root decomposition and nutrient flux following whole-tree harvest in northern hardwood forest. Forest Sci 34:744–768
83 Fang X, Tian DL (1997) CO2 emission from Chinese fir plantation. Scientia Silvae Sinicae 33(sp. 2):94–103 Fang X, Tian DL, Xiang WH et al (2002) Carbon dynamics and balance in the ecosystem of the young and middle-aged second-generation Chinese fir plantation. J Central South Forest Univ 22:2–6 Fang YT, Mo JM, Huang ZL, Ouyang XJ (2003) Carbon accumulation and distribution in Pinus massoniana and Schima superba mixed forest ecosystem in Dinghushan Biosphere Reserve. J Trop Subtrop Bot 11(1):47–52 Goulden ML, Munger JW, Fan SM et al (1996) Measurements of carbon acquisition by long-term eddy covariance: methods and critical evaluation of accuracy. Global Change Biol 2:169–182 Grace J, Lloyd J, McIntyre J, Miranda AC, Meir P, Miranda H, Moncrieff JB, Massheder J, Wright IR, Gash J (1995a) Fluxes of carbon dioxide and water vapour over an undisturbed tropical rainforest in south-west Amazonia. Global Change Biol 22:1–12 Grace J, Lloyd J, McIntyre J, Miranda AC, Meir P, Miranda H, Nobre C, Moncrieff JB, Massheder J, Malhi Y, Wright IR, Gash J (1995b) Carbon dioxide uptake by an undisturbed tropical rain forest in SouthWest Amazonia 1992–93. Science 22:778–780 Greco S, Baldocchi DD (1996) Seasonal variation of CO2 and water vapor exchange rates over a temperate deciduous forest. Global Change Biol 2:183–198 Grogan P (1998) CO2 flux measurement using soda lime: the appropriate correction for water formed during CO2 adsorption. Ecology 79:1467–1468 Hanson PJ, Edwards NT, Garten CT et al (2000) Special Issue. Controls on soil respiration: implications for climate change. Separating root and microbial contributions to soil respiration: A review of methods and observations. Biogeochemistry 48(1):115–146 Harmon ME (2001) Carbon sequestration in forests: addressing the scale question. J Forest 99(4):24–29 Harmon ME, Ferrell WK, Franklin JF (1990) Effects on carbon storage of conversion of old-growth forests to young forests. Science 247:699–702 Huang CC, Ge Y, Chang J et al (1999) Studies on the soil respiration of three woody plant communities in the east mid-subtropical zone, China. Acta Ecol Sinica 19(3):324–328 Jiang YL, Zhou GS (2001) Carbon equilibrium in Laris gmelinii forest and impact of global change on it. Chin J Appl Ecol 12:481–484 Joslin JD (1983) The quantification of fine root turnover in a white oak stand. PhD dissertation, University of Missouri, Columbia, MO, USA, pp 77–111 Keith H, Jacobsen KL, Raison RJ (1997) Effects of soil phosphorus availability, temperature and moisture on soil respiration in Eucalyptus pauciflora forest. Plant Soil 190:127–141 Kurz WA, Kimmins JP (1987) Analysis of some error in methods used to determine fine root production in forest ecosystems: a simulation approach. Can J Forest Res 17:909–912 Li YD, Wu ZM, Zeng QB et al (1998) Carbon pool and carbon dioxide dynamics of tropical mountain rain
123
84 forest ecosystem at Jianfengling, Hainan Island. Acta Ecol Sinica 18(4):371–378 Liu WY, Fox JED, Xu ZF (2002) Biomass and nutrient accumulation in montane evergreen broadleaved forest (Lithocarpus xylocarpus type) in Ailao Mountains, SW China. Forest Ecol Manag 158:223–235 Malhi Y, Baldocchi DD, Jarvis PG (1999) The carbon balance of tropical, temperate and boreal forests. Plant Cell Environ 22(6):715–740 Nadelhoffer KJ, Raich JW (1992) Fine root production estimates and belowground carbon allocation in forest ecosystems. Ecology 73:1139–1147 Pedersen LB, Hansen JB (1999) A comparison of litterfall and element fluxes in even aged Norway spruce, sitka spruce and beech stands in Denmark. Forest Ecol Manag 114:55–70 Phillips OL, Malhi Y, Higuchi N, Laurance WF, Nunez PV, Vasquez RM, Laurance SG, Ferreira LV, Stern M, Brown S, Grace J (1998) Changes in the carbon balance of tropical forests: evidence from long-term plots. Science 282:439–441 Qi Y, Xu M (2001) Separating the effects of moisture and temperature on soil CO2 efflux in a coniferous forest in the Sierra Nevada mountains. Plant Soil 237(1):15– 23 Raich JW (1998) Aboveground productivity and soil respiration in three Hawaiian rain forests. Forest Ecol Manag 107:309–318 Raich JW, Nadelhoffer KJ (1989) Belowground carbon allocation in forest ecosystems: global trends. Ecology 70:1346–1354 Raich JW, Potter CS (1995) Global patterns of carbon dioxide emissions from soils. Global Biogeochem Cycles 9:23–36 Raich JW, Russell AE, Vitousek PM (1997) Primary productivity and ecosystem development along an elevational gradient on Mauna Loa, Hawaii. Ecology 78:707–721 Raich JW, Bowden RD, Steudler PA (1990) Comparison of two static chamber techniques for determination of CO2 efflux from forest soils. Soil Sci Soc Am J 54:1754–1757 Ran JC, He SY, Cao JH et al (2002) A preliminary research on CO2 release in subtropical karst forest soil. Guizhou Sci 20(2):42–47 Rey A, Pegoraro E, Tedeschi V, De Parri I, Jarvis PG, Valentini R (2002) Annual variation in soil respiration and its components in a coppice oak forest in Central Italy. Global Change Biol 8:851–866
123
Plant Ecol (2007) 193:71–84 Rout SK, Gupta SR (1989) Soil respiration in relation to abiotic factors, forest floor litter, root biomass and litter quality in forest ecosystems of Siwaliks in northern India. Acta Oecol/Oecol Plant 10:229–244 Saleska SR, Miller SD, Matross DM, Goulden ML, Wofsy SC, de Rocha HR, de Camargo PB, Crill P, Daube BC, de Freitas HC, Hutyra L, Keller M, Kirchnoff V, Menton M, Munger JW, Hammond-Pyle E, Rice AH, Silva H (2003) Carbon in Amazon forests: unexpected seasonal fluxes and disturbance-induced losses. Science 302:1554–1557 Schulze ED, Wirth C, Heimann M (2000) Managing forests after Kyoto. Science 289:169–179 Wirth C, Czimczik CI, Schulze ED (2002) Beyond annual budgets: carbon flux at different temporal scales in fire-prone Siberian Scots pine forests. Tellus 54B:611– 630 Yamamoto S, Saigusa N, Murayama S et al (2001) Longterm results of flux measurement from a temperate deciduous forest site (Takeyama). In: Proceedings of international work-shop for advanced flux network and flux evaluation, Sapporo, ASAHI Printing CO., Ltd., pp 5–10 Yang YS, Chen GS, Lin P, Xie JS, Guo JF (2004a) Fine root distribution, seasonal pattern and production in four plantations compared with a natural forest in subtropical China. Annl Forest Sci 61:617–627 Yang YS, Guo JF, Chen GS, Xie JS, Cai LP, Lin P (2004b) Litterfall, nutrient return, and leaf-litter decomposition in four plantations compared with a natural forest in subtropical China. Annl Forest Sci 61:465–476 Yang YS, Chen GS, Wang YX, Xie JS, Yang SH, Zhong XF (2006) Carbon storage and allocation in Castanopsis kawakamii and Cunninghamia lanceolata plantations in subtropical China. Scientia Silvae Sinicae 42(10):43–47 Yi ZG, Yi WM, Zhou GY et al (2003) Soil carbon effluxes of three major vegetation types in Dinghushan Biosphere Reserve. Acta Ecol Sinica 23(8):1673–1678 Yu XT (1996) Silviculture of Chinese-fir in China. Fuzhou, Fujian Science and Technology Press Zhou YR, Yu ZL, Zhao SD (2000) Carbon storage and budget of major Chinese forest types. Acta Phytoecol Sinica 24(5):518–522 Zhou ZT, Cheng SK, Liu YF et al (2002) CO2 emission of soil under different land use types in subtropical red soil hilly areas in China: preliminary exploration. Resour Sci 24(2):83–87
