1. 1 ( N, E) kg Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved. Vol. 22 No. 2 Apr.

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1 SCIENTIA GEOGRAPHICA SINICA Vol. 22 No. 2 Apr : (2002) ( ) : (SL) ( GC) 14 C (m) 0 10 cm (m) m m (T) m CO cm CO 2 98 % SL m CO 2 GC CO 2 : :S :A ( 14 [3 4 C > 0) ] CO 2 14 C CO 2 CO 2 CO 2 / [1 2 ] 1 CO ( N E) CO kg CO 2 14 C 14 C( 14 C) CO 2 : : : ( ) (984105) : ( ) E2mail : net.

2 2 : 197 (SL) 662 m C NE ml 1. 1 m 25 2 mm ( GC) 905 m 10 % 24 NE m 18 ( 1) O 2 (800 ) Table 1 Macroscopic characteristics and sampling designation for mountainous soil profiles at Dinghushan Mt. SL GC (cm) 0 30 (cm) (cm) ( ) CO 2 14 C 650 Li 2 C 2 Li 2 C 2 14 C C 2 H 2 C 2 H C 1200Quantulus 14 C 14 C 14 C 14 C 14 C 14 C ( 14 C) A 0 ( t) : t 14 C C A ABS : 14 C 1963 : = 1/ C 2 [5 ] a C [6 ] 14 C m a [3 ] Cherkinsky : A S (1955) m = (1) A ABS m + ( ) A S ( t) = A S ( t - 1) - ( m + ) A S ( t - 1) + ma 0 ( t) (2) A S (1955) : C A S ( t) : t 14 C t : C 0 ( 2) A S ( t - 1) : ( t - 1) 14 C m : a - 1 m ( T) T = 1/ 14 C 14 C (1) 14 C

3 (2) 14 C ( t + 6) 14 C SL t 14 C ( t + 1) : t 14 C 14 C GC SL 14 C 14 C GC (2) A 0 ( t) A 0 ( t - 1) m SL m ( 2) SL ( t < 1956) 14 C m GC C m C t ( t - 1) 14 C A S ( t) A S ( t - 1) C (AABS) (2) m ( 2) SL (1) 12 cm GC 12 cm m (1) C A S (1955) SL 0 12 A S (1955) m (2) cm ( T) C A S ( 1998 ) Century [8 9 ] GC 0 12 cm m A S (1998) T Century ( T m m (1) 14 C SL cm GC C 14 C cm T C < 0 ( 2) 14 C m SL ( 2) 14 C 7 0 cm GC 2 0 cm T (1) 14 C : m = C + 1 (3) [10 : = 1/ 8267 ] a - 1 m : a ) m T ( 2) 2. 1 CO SL GC 2 14 C > 0 14 C [7 ] 14 C 14 C 2. 2 CO 2 GC t 14 C CO 2

4 2 : SL GC 14 C CO 2 Table 2 Soil organic matter 14 C values organic carbon contents organic matter turnover rates and CO 2 flux due (cm) to organic matter decomposition of SL profile and GC profile at Dinghushan Mt. (cm) 14 C ( ) m ( %) (a - 1 ) CO 2 gc/ cm 2 a SL SL SL SL SL SL SL SL SL SL SL SL SL GC GC GC GC GC GC GC GC GC GC GC GC a) GC ( gc/ (cm 2 a) 14 SL GC 2 CO 2 CO 2 SL 1 CO 2 ( 2) GC 1 ( 2) CO 2 : SL 1 U = H C m (4) U : CO 2 (gc/ cm 2 a) H : (cm) : (g/ cm 3 ) C : ( %) m : (a - 1 ) ( 2) SL GC CO g/ cm 3 CO 2 [11 ] SL GC CO 2 2 SL CO gc/ (cm 2 GC SL % GC % SL GC SL GC

5 SL GC SL m GC m ( 2) [12 ] [4 ] CO 2 CO 2 SL GC CO 2 98 % 0 10 cm ( 2) CO 2 CO 2 modelling of biomass and soil organic matter dynamics for the grass2 lands biome world2wide[j ]. Global biogeochemical cycles : [10 ]. : 14 C 14 C [J ] (16) : [11 ]. [J ] (2) : : [1 ] Tans P P Fung I Y Takahashi T. Observational constraints on the global atmospheric budget[j ]. Science : [2 ] Jenkinson D S Adams D E Wild A. Model estimates of CO 2 emis2 sions from soil in response to global warming [J ]. Nature : [3 ] Cherkinsky O A Brovkin V A. Dynamics of radiocarbon in soils[j ]. Radiocarbon (3) : C [J ] (5) : [5 ] Nydal R Lovseth. Distribution of radiocarbon from nuclear tests[j ]. Nature : [6 ] Wang Y Amundson R. Radiocarbon dating of soil organic matter [J ]. Quaternary research : [7 ] Burchuladze A Chudy M Eristavi I V et al. Anthropogenic 14 C variations in atmospheric CO 2 and wines[j ]. Radiocarbon (3) : [8 ] Parton W J Schimel D S Cole C V et al. Analysis of factors con2 trolling soil organic matter levels in great plains grasslands[j ]. Soil Sci Soc Am J : [9 ] Parton W J Scurlock J M O Ojima D S et al. Observations and [12 ]. [J ] (1) : Quantitative Study on Organic Matter Turnover Characteristics of Mountainous Soil Profiles in the Subtropical Area South China CHEN Qing2qiang 1 2 SUN Yan2min 1 SHEN Cheng2de 1 PENG Shao2lin 3 YI Wei2xi 1 J IANG Man2tao 1 LI Zhi2an 3 (1. Guangzhou Institute of Geochemistry the Chinese Academy of Sciences Guangzhou Guangdong State Key Laboratory of Estuarine and Coastal Researches East China Normal University Shanghai South China Institute of Botany the Chinese Academy of Sciences Guangzhou Guangdong ) Abstract : Two soil profiles were excavated at the forest vegetation zone and the shrub2meadow transitional zone of Dinghushan Mt. ( N E) and thin2layer sampling were conducted for studies on soil carbon dynamics of mountainous soils in the subtropical area. Based on 14 C radioactivity of soil organic matters (SOM) SOM turnover rate ( m) is calculated with a numerical model for the upper sections with SOM 14 C value

6 2 : 201 greater than zero due to incorporation of 14 C produced by atmospheric nuclear weapon testing (Bomb 14 C) in the 1960s. As for the lower section with SOM 14 C value less than zero the effect of Bomb 14 C may be neglected due to the slow turnover rate of SOM and value m is calculated by one specific equation. Value m decreases downward and is greater than 0. 01a - 1 at the upper 12 cm section of the soil profiles then value m reduces abruptly downward and is about one magnitude less than that of the above specimen. From 12 cm on value m reduces consistently with depth till the minimum at the deepest of the profiles. This suggests that soil organic matters are composed of various compartments with different turnover times ( T). Rapid compartments ( T < 10a) are predominated at the upper 12 cm section slow compartments (100a < T < 1 000a) turn to be the main part of SOM downwards and stable compart2 ments ( T > 1 000a) are predominated at the lower sections of the profiles. CO 2 production resulted from SOM turnover is calculated based on value m organic carbon content soil bulk density and soil section thickness. The results sug2 gest that the CO 2 production from the upper 12 cm section is about 98 percent of the total CO 2 production of one pro2 file. Therefore the upper 12 cm section is the main contributor for CO 2 emission due to SOM decomposition in one soil profile. CO 2 flux of the upper 12 cm section of SL profile is gC/ cm 2 a which is about one magnitude higher than that of the upper 12 cm section of GC profile. This is ascribed to that value m and organic carbon content of the upper 12 cm section of SL profile are greater than those of the upper 12 cm section of GC profile respectively. For ex2 ample value m of the upper 12 cm section of SL profile are greater than 0. 1a - 1 and those of the upper 12 cm section of GC profile are from 0. 01a - 1 to 0. 08a - 1. Value m of the uppermost specimen is a - 1 for SL profile and is a - 1 for GC profile the former is about one magnitude higher than the latter. The aboveground vegetation types contrast obviously between SL profile and GC profile which results in different primary production of aboveground veg2 etation for the two spots. Soil organic carbon content and value m of SOM are controlled directly by primary production of aboveground vegetation. Therefore aboveground vegetation is the key factor controlling SOM turnover and the corre2 sponding CO 2 production of soil profiles within one climatic zone which give scientific supports for increasing soil car2 bon sink through afforestation. The upper soil section has high SOM content and great value m and is apt to be erod2 ed away thus the upper section of one soil profile is prone to be CO 2 source. Plant debris is the main source for SOM of the upper soil section. Therefore to reduce plant debris production and to increase the biomass of deep roots in or2 der to transfer more organic matters into the deep may be one effective measure for reducing and slowing down the e2 mission of CO 2 due to SOM turnover. For this purpose vegetation with high underground biomass should be planted firstly under all possible conditions which needs comprehensive cooperation between soil scientists and botanists. Key words : Soil carbon cycling Soil organic matter turnover rate Terrestrial ecosystem Dinghushan Mt.