南亚热带森林植被恢复演替中土壤有机碳组分及其稳定

以鼎湖山森林植被恢复演替过程中的松林(初期),混交林(中期)和季风林(后期)为研究对象,通过测定其土壤总有机碳(TOC),易氧化有机碳(ROC)和不易氧化有机碳(NROC)及凋落物¹³C-NMR分析,以期阐明森林植被恢复演替过程中土壤有机碳组分变化规律及其原因.结果表明:①3个森林土壤ROC含量差异不显著;由松林向季风林演替过程中,ROC占TOC的比例下降.松林新鲜凋落物层的烷氧基碳含量(57.03%)高于季风林(49.10%)和混交林(54.50%).②3个森林土壤NROC含量差异显著,大小顺序为:季风林>混交林>松林.混交林和季风林凋落物半分解层和已分解层的惰性指数明显高于松林.TOC趋势与NROC一致.南亚热带森林由松林向季风林恢复演替过程中,土壤有机碳的稳定性增加,惰性有机碳的持续积累可能是季风林和混交林土壤TOC积累的一个重要过程.

关键词: 森林恢复演替, 土壤碳积累, 土壤碳固持, 有机碳组分, 南亚热带森林

Soil Organic Carbon (SOC) fractions play a critical role in the stabilization of SOC. It is essential to clarify the variations in SOC fractions along forest succession for predicting soil carbon (C) source/sink capacity as forest develops. In the present study, we collected and analyzed soil samples in Total Organic Carbon (TOC) content and the concentration of its Readily Oxidizable Organic Carbon (ROC) and Non-Readily Oxidizable Organic Carbon (NROC) fractions in a Pine Forest (PF), a pine and broadleaf Mixed Forest (MF), and an old-growth monsoon evergreen Broadleaf Forest (BF) in the subtropical China. The three forests represent different successional stages of forest in southern China, with the PF being at the early, the MF at the middle and the BF at the climax stages, respectively. To clarify the reasons for why SOC fractions changed with forest succession, litterfalls in these forests were also collected to assay C functions by means of ¹³C Nuclear Magnetic Resonance (NMR) analysis. Results showed that although there was no significant difference in the content of ROC among the three forests, the ratio of ROC to TOC in the PF was significantly higher than that in both of the BF and MF. This was likely due to the higher content of O-alkyl C in fresh litter in the PF than in the other two forests. Unlike ROC, however, NROC content was the highest in the BF, followed by the MF and then PF, which could be attributed to the lower recalcitrance index in the partly-decomposed and decomposed litterfall layers in the PF than in the MF and PF. Finally, TOC concentration was significantly the highest in the climax BF, the lowest in the youngest PF, and in between in the MF. Our results suggest that the accumulation of NROC, which is the recalcitrant fraction of SOC, may be the major reason for why forests at the middle and late stages (i.e., the MF and BF, respectively) maintain higher TOC content and Organic Carbon (OC) stabilization in soils.

Key words: Forest succession, Soil C accumulation, Soil C sequestration, SOC fractions, Lower subtropical forest.

中图分类号:

P935

表 1 鼎湖山森林植被恢复演替序列的样地特征

Table 1 Vegetation characteristics and soil properties of three forests at Dinghushan

	松林	混交林	季风林
演替阶段	早期	中期	成熟
林龄(年)	60~70	约110	约400
年凋落物输入量(g/(m²a))	587.6 (115.8)	702.5 (79.3)	891.8 (120)
土壤(0~20 cm)细根生物量(g/m²)	166.08 (35.27)	214.25 (26.92)	226.37 (20.58)
土壤(0~10 cm)pH值	4.06 (0.10)	3.97 ( 0.08)	3.97 ( 0.03)
土壤(0~5 cm)湿度(%)	18.13 (0.94)	28.46 (1.14)	27.40 (1.20)
土壤(0~10 cm)容重(g/cm³)	1.32 (0.04)	1.10 (0.08)	0.86 (0.06)
土壤(0~20 cm)微生物量碳(mg/g)	442.05 (86.99)	526.97 (19.81)	711.46 (88.51)

表 1 鼎湖山森林植被恢复演替序列的样地特征

Table 1 Vegetation characteristics and soil properties of three forests at Dinghushan

	松林	混交林	季风林
演替阶段	早期	中期	成熟
林龄(年)	60~70	约110	约400
年凋落物输入量(g/(m²a))	587.6 (115.8)	702.5 (79.3)	891.8 (120)
土壤(0~20 cm)细根生物量(g/m²)	166.08 (35.27)	214.25 (26.92)	226.37 (20.58)
土壤(0~10 cm)pH值	4.06 (0.10)	3.97 ( 0.08)	3.97 ( 0.03)
土壤(0~5 cm)湿度(%)	18.13 (0.94)	28.46 (1.14)	27.40 (1.20)
土壤(0~10 cm)容重(g/cm³)	1.32 (0.04)	1.10 (0.08)	0.86 (0.06)
土壤(0~20 cm)微生物量碳(mg/g)	442.05 (86.99)	526.97 (19.81)	711.46 (88.51)

图 1 森林植被恢复演替序列的土壤总有机碳,易氧化有机碳和不易氧化有机碳含量
图中误差棒代表标准差,每幅图中不同字母代表在相同土壤层次中不同森林差异显著

Fig. 1 The soil TOC,ROC and NROC in three forests
Bars are means and error bars are standard deviations. Means with different letters are significantly different among the forest types in each soil layer in each panel

表2 森林植被恢复演替序列的土壤易氧化有机碳(ROC)占总有机碳(TOC)比例(单位:%)

Table 2 The percentages of ROC to TOC at three forest types (unit:%)

	松林	混交林	季风林
0~10 cm	41.60 (3.87) ^a	37.12 (1.60) ^ab	32.45 (3.10) ^b
10~20 cm	39.62 ( 6.73) ^a	32.47 (5.76) ^a	34.55 ( 5.34) ^a

表2 森林植被恢复演替序列的土壤易氧化有机碳(ROC)占总有机碳(TOC)比例(单位:%)

Table 2 The percentages of ROC to TOC at three forest types (unit:%)

	松林	混交林	季风林
0~10 cm	41.60 (3.87) ^a	37.12 (1.60) ^ab	32.45 (3.10) ^b
10~20 cm	39.62 ( 6.73) ^a	32.47 (5.76) ^a	34.55 ( 5.34) ^a

图2 森林植被恢复演替序列的凋落物官能团碳相对含量(单位:%)
L: 未分解层, Fresh litter layer;F:半分解层, Fermentation layer;H:已分解层, Humus layer

Fig. 2 Distribution of C functional groups in the forest floor layers among the three forests(unit:%)

表3 鼎湖山森林植被恢复演替序列的凋落物惰性指数(单位:%)

Table 3 The recalcitrance index in the forest floor of three forests(unit:%)

凋落物层次	松林	混交林	季林
未分解层	56.18	51.64	65.56
半分解层	68.88	74.23	80.85
已分解层	80.60	90.29	90.68

表3 鼎湖山森林植被恢复演替序列的凋落物惰性指数(单位:%)

Table 3 The recalcitrance index in the forest floor of three forests(unit:%)

凋落物层次	松林	混交林	季林
未分解层	56.18	51.64	65.56
半分解层	68.88	74.23	80.85
已分解层	80.60	90.29	90.68

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[1]	邓琦,刘世忠,刘菊秀,孟泽,张德强. 南亚热带森林凋落物对土壤呼吸的贡献及其影响因素[J]. 地球科学进展, 2007, 22(9): 976-986.

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摘要

Variations in the Fractions and Stabilization of Soil Organic Carbon with Forest Succession in Southern China