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Cai L, Hou B F, Feng Q H, et al. Composition of soil aggregates and distribution characteristics of organic carbon in different sunccessional stages of subalpine natural secondary forest in western Sichuan[J]. Journal of Sichuan Forestry Science and Technology, 2021, 42(2): 1−7 doi: 10.12172/202009210003
Citation: Cai L, Hou B F, Feng Q H, et al. Composition of soil aggregates and distribution characteristics of organic carbon in different sunccessional stages of subalpine natural secondary forest in western Sichuan[J]. Journal of Sichuan Forestry Science and Technology, 2021, 42(2): 1−7 doi: 10.12172/202009210003

Composition of Soil Aggregates and Distribution Characteristics of Organic Carbon in Different Sunccessional Stages of Subalpine Natural Secondary Forest in Western Sichuan


doi: 10.12172/202009210003
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  • Corresponding author: liuxingliang@126.com
  • Received Date: 2020-09-21
    Available Online: 2021-01-13
  • Publish Date: 2021-04-20
  • The subalpine natural secondary forest in western Sichuan is the main forest type of water conservation forest in alpine forest regions of southwestern China, which plays an important role in the carbon budget of forest ecosystems in this region. In this paper, the soil structure and organic carbon distribution characteristics of secondary forests in different successional stages were studied by dry-sieving method and potassium dichromate oxidation-external heating method. It was found that the soil aggregates of secondary forests in each successional stage in this region was relatively strong. The content of large aggregates was the highest in Abies faxoniana and Betula spp. mixed forest, and the formation of large aggregates was negatively correlated with the content of organic matter. The content of organic carbon mainly existed in large aggregates, and the contribution rate of organic carbon in soil aggregates with particle size >5 mm was the highest, with the order of Abies faxoniana and Betula spp. mixed forest > Abies faxoniana forest > Betula spp. forest. The organic carbon content and soil nitrogen were positively correlated. Although the content of large aggregates in Abies faxoniana forest was lower than that in Abies faxoniana and Betula spp. mixed forest, the content of total organic carbon was the highest. The content of microaggregates increased with the increase of successional stage, and the content of organic carbon basically increased with the decrease of aggregate size. When comparing the organic carbon content and contribution rate of different aggregates, it was found that the organic carbon content of <0.25 mm particle size was high but the contribution rate was low, which indicated that the microaggregates had stronger protection for organic carbon and the ranking order was Abies faxoniana and Betula spp. mixed forest > Betula spp. forests > Abies faxoniana forests.
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Composition of Soil Aggregates and Distribution Characteristics of Organic Carbon in Different Sunccessional Stages of Subalpine Natural Secondary Forest in Western Sichuan

doi: 10.12172/202009210003
  • 1. Ecological Restoration and Conservation on Forest and Wetland Key Laboratory of Sichuan Province, Sichuan Academy of Forestry, Chengdu 610081, China
  • 2. Sichuan Wolong Forest Ecosystem Research Station, Sichuan Academy of Forestry, Chengdu 610081, China
  • 3. Aba Songpan state Foresty Protection Bureau, Aba 623300, China
  • 4. Sichuan Agricultural University, Chengdu 611130, China
  • Corresponding author: liuxingliang@126.com

Abstract: The subalpine natural secondary forest in western Sichuan is the main forest type of water conservation forest in alpine forest regions of southwestern China, which plays an important role in the carbon budget of forest ecosystems in this region. In this paper, the soil structure and organic carbon distribution characteristics of secondary forests in different successional stages were studied by dry-sieving method and potassium dichromate oxidation-external heating method. It was found that the soil aggregates of secondary forests in each successional stage in this region was relatively strong. The content of large aggregates was the highest in Abies faxoniana and Betula spp. mixed forest, and the formation of large aggregates was negatively correlated with the content of organic matter. The content of organic carbon mainly existed in large aggregates, and the contribution rate of organic carbon in soil aggregates with particle size >5 mm was the highest, with the order of Abies faxoniana and Betula spp. mixed forest > Abies faxoniana forest > Betula spp. forest. The organic carbon content and soil nitrogen were positively correlated. Although the content of large aggregates in Abies faxoniana forest was lower than that in Abies faxoniana and Betula spp. mixed forest, the content of total organic carbon was the highest. The content of microaggregates increased with the increase of successional stage, and the content of organic carbon basically increased with the decrease of aggregate size. When comparing the organic carbon content and contribution rate of different aggregates, it was found that the organic carbon content of <0.25 mm particle size was high but the contribution rate was low, which indicated that the microaggregates had stronger protection for organic carbon and the ranking order was Abies faxoniana and Betula spp. mixed forest > Betula spp. forests > Abies faxoniana forests.

  • 土壤是全球陆地生态系统中最大的碳库[1],气候变化和生态系统中植被类型的不同会引起土壤呼吸过程的变化,因此演替进程是影响森林生态系统碳库动态的一个极为重要的影响因素[2]。随着演替阶段的变化,森林生态系统的群落结构、物种组成以及物种丰富度都会产生巨大的变化,生物量的积累以及碳分配也会发生变化,进而影响森林生态系统土壤碳库变化和碳吸存潜力[3-4]

    土壤团聚体作为土壤结构的基本单元,是反映土壤肥力的一项重要指标[5]。不同粒级的团聚体在营养元素的保持、供应及转化能力等方面发挥着不同的作用。对不同演替阶段次生林土壤团聚体的稳定性进行研究可以反映出土壤生态特征以及土壤有机碳的储存能力,揭示土壤特征与演替进程的关系。有机碳在团聚体中的分布形式决定了土壤储存和保留有机碳的能力[6],有机碳水平的提高能促进土壤结构的形成并增强其稳定性。有研究表明,不同粒级团聚体的有机碳含量存在明显差异,一部分认为团聚体有机碳含量随粒级的增加而降低[7-8],另一部分研究则提出了与之相悖的观点,指出大部分土壤有机碳储存在大粒径团聚体中,﹤0.25 mm粒级团聚体有机碳含量相对较低[9-10]

    川西亚高山森林是我国西南亚高山林区水源涵养林的重要组成部分,以冷杉为主的原始暗针叶林在经历大规模采伐利用后,天然次生林已成为该区域的主要森林类型[11-12],因此,研究不同演替阶段的次生林类型的土壤结构及有机碳分布特征,对于准确评估本区森林生态系统的碳收支及大尺度的碳循环模型构建具有非常重要的意义。

1.   材料与方法
  • 研究区位于四川省理县米亚罗林区,地理坐标31º24′—31º55′N,102º35′—103º4′E。该区位于青藏高原东缘褶皱带最外缘部分,具有典型的高山峡谷地貌。气候受太平洋、印度洋及青藏高原三大气团影响,年均温 6 ℃~12 ℃,极端最高气温 32 ℃,极端最低气温−16 ℃。夏季温凉多雨,冬季寒冷干燥,最冷月(1 月)平均气温为−8 ℃,最热月(7 月)均温为 12.6 ℃,≥10 ℃年积温为 1200 ℃~1400 ℃,年蒸发量为 1000~1 900 mm,常年无霜期 200 d,年均降水量为 600~1100 mm,具有降水次数多、强度小的特点。米亚罗林区植被垂直成带明显,其类型和生境随海拔及坡向而分异。原生森林分布于海拔2400~4 200m之间,以亚高山暗针叶林为主,主要优势树种为岷江冷杉(Abies faxoniana),桦木(Betula sp.)、云杉(Picea asperata)、野樱(Pruns tatsienensis)等乔木有分布;灌木主要有臭樱(Maddenia hypoleuca)、红刺悬钩子(Rubus aurantiacus)、红脉忍冬(Lonicera nervosa)、绣线菊(Spiraea salicifolia)等;草本植物主要有野草莓(Fragaria vesca)、婆婆纳(Veronica didyma)、柳叶菜(Epelobium hirsutum)、六叶葎(Galium asperuloides)、橐吾(Ligularia sibirica)等。

    该区成土母岩主要为千枚岩、板岩、白云岩等的残坡积风化物,极易风化,主要土壤类型为山地棕色森林土,土壤养分情况见表1

    森林类型F海拔/m坡向测树因子铵态氮/
    (mg·L−1)
    速效磷/
    (mg·L−1)
    有效钾/
    (mg·L−1)
    有机质/
    (g·kg−1)
    胸径/cm树高/cm林分密度
    桦木林3299西北13.1312.27192519.46.27280.8314.8
    桦木+冷杉混交林3453西北13.4512.69149017.67.43214.179.27
    冷杉林3145东南31.2316.4645937.57.3720010.51

    Table 1.  0−20 cm soil nutrient content of secondary forests in different successional stages

  • 在研究区内依据林分组成,选取桦木纯林、桦木林+冷杉混交林、冷杉原始林作为次生林不同演替阶段的研究对象,分别代表初级演替、中级演替、高级演替三个演替阶段。每个演替阶段设置3~5个20 m×20 m的样方进行植物群落调查并在其中设1 m×1 m的小样方3~5个,采用5点取样法对0~20 cm的表土进行取样,土壤样品用硬质塑料盒盛装,带回实验室,风干、剔除石块和根系后用于分析土壤团聚体结果,并测定土壤碳含量。

  • 有机碳采用重铬酸钾氧化-外加热法测定。

    土壤团聚体分类采用干筛法分离出>5 mm、5~2 mm、2~1 mm、1~0.5 mm、0.5~0.25 mm、0.25~0.053 mm、<0.053 mm共7级土壤团聚体,并计算各粒径土壤团聚体对土壤碳的贡献率(%)[9]。计算公式如下:

  • 所用测定结果用采Microsfot Excel 2012进行整理和初步分析,用SPSS 16.0进行方差分析,多重比较分析采用LSD检验。

2.   结果与分析
  • 3个演替阶段次生林粒径含量与粒径大小基本上呈正相关趋势,含量随粒径减小而降低,且均表现为>5 mm粒径团聚体分布均占主导地位。其中 >5 mm和<0.053 mm粒径的土壤团聚体在中级演替阶段(桦木+冷杉混交林)分布含量最高,2~1 mm粒径的团聚体在高级演替阶段(冷杉原始林)分布大于其他两个演替阶段,而1~0.5 mm、0.5~0.25 mm、0.25~0.053 mm 3个粒径的团聚体含量均是初级演替(桦木林)>高级演替(冷杉原始林)>中级演替(桦木+冷杉混交林)(见表2)。单因素方差分析发现,同一演替阶段内各径级团聚体含量分布存在显著差异;而同一粒径不同演替阶段间除了5~2 mm粒径外,其余6个粒径均存在显著差异(见表3)。

    演替阶段各级团聚体含量(%)
    >5 mm5~2 mm2~1 mm1~0.5 mm0.5~0.25 mm0.25~0.053 mm<0.053 mm
    桦木林23.07±2.79Ba20.20±2.59Aa20.48±2.00Aa17.03±2.53Ab11.27±1.87Ac7.09±1.91Ac0.86±0.21Bd
    桦木+冷杉混交林35.18±3.38Aa18.57±1.32Ab16.55±1.26Bb11.88±1.34Bc7.42±1.43Bd4.07±0.86Be6.33±1.24Ae
    冷杉原始林27.24±1.89Ba19.59±1.03Ac21.10±1.11Ab13.59±0.85Bd9.06±0.61ABe4.22±0.43Bf5.20±0.61Af
      注:同一列中不同大写字母表示不同演替阶段间同一粒径土壤团聚体所占比例差异显著(P<0.05);同一行中不同小写字母表示同一演替阶段不同粒径间团聚体所占比例差异显著(P<0.05)

    Table 2.  Distribution and composition of soil aggregates in secondary forests at different successional stages

    方差结果粒径>5 mm5~2 mm2~1 mm1~0.5 mm0.5~0.25 mm0.25~0.053 mm<0.053 mm
    F11.7750.6323.9216.1155.5214.31016.999
    Sig.0.001**0.5460.044*0.012*0.017*0.035*0.000**
      注:同一粒径在不同演替阶段间团聚体含量P<0.05为显著标记*,P<0.01为极显著标记**

    Table 3.  Single factor variance analysis of soil aggregates content at different successional stages with the same particle size

    对同一演替阶段不同粒径团聚体含量进行多重比较发现初级演替阶段(桦木林)的团聚体在>1 mm粒径含量间不存显著差异,1~0.5 mm与0.5~0.053 mm、0.25~0.053 mm与<0.053 mm 粒径存在显著差异;中级演替阶段(桦木+冷杉混交林)、高级演替阶段(冷杉原始林)>0.25 mm粒径大团聚体与 <0.25 mm 粒径微团聚体间均存在显著差异,其中冷杉林的大团聚体(>0.25 mm)间各粒径均有显著差异,混交林在>5 mm与5~1 mm、2~1 mm与1~0.5 mm、1~0.5 mm与0.5~0.25 mm间存在显著差异,而微团聚体(<0.25 mm)在高级演替阶段(冷杉原始林)和中级演替阶段(桦木+冷杉混交林)均无显著差异。

    虽然单因素方差分析结果显示除了5~2 mm粒径外,其余6个粒径均存在显著差异,但对同一粒径不同演替阶段团聚体含量进行多重比较发现,同一粒径内并不是3个演替阶段均存在显著差异,如>5 mm粒径是桦木+冷杉混交林与桦木林、冷杉原始林存在显著差异,而桦木林与冷杉原始林间无显著差异。

    图1可见,各演替阶段次生林均以土壤大团聚体(>0.25 mm)为主,大团聚体比例皆达90%左右,微团聚体(<0.25 mm)分布较少。各演替阶段次生林土壤大团聚体含量(>0.25 mm)表现为冷杉+桦木混交林最高,微团聚体含量(<0.25 mm)表现为冷杉+桦木混交林>冷杉原始林>桦木林,且桦木林与混交林、冷杉原始林间存在显著差异,这说明土壤团聚性呈“∩型”随着演替阶段上升在中级演替阶段达到最高,随着演替进程的发展到高级阶段又下降。

    Figure 1.  Soil aggregates distribution of secondary

  • 3个演替阶段土壤有机碳总含量介于159.24~561.28 g·kg−1之间,对不同演替阶段有机碳总含量进行比较,冷杉原始林>桦木+冷杉混交林>桦木林,但差异不显著。不同演替阶段各级团聚体的土壤有机碳含量均是冷杉原始林最高,桦木+冷杉混交林次之,桦木林最低,且差异性显著。土壤大团聚体(>0.25 mm)有机碳的含量百分比分别为70.32%、70.21%、68.72%,微团聚体(<0.25 mm)有机碳的含量百分比分别为29.68%、29.79%、31.28%,其中0.053—0.25 mm粒径有机碳含量为14.61%、15.15%、15.05%,<0.053 mm有机碳的含量百分比为15.37%、15.58%、14.60%,微团聚体的两个径级间有机碳含量比例相当,差异不显著(见图2)。

    对同一演替阶段土壤有机碳含量与各团聚体粒径的相关性进行分析,发现其二者相关性不显著,但有机碳的含量随团聚体粒径减小而基本呈增加趋势(见表4),3个演替阶段均是所有<0.25 mm粒径的有机碳含量均值高于其他粒径,所有>2 mm粒径团聚体有机碳含量均值最低,这与刘敏英等[18]的研究结果一致。

    Figure 2.  Percentage of organic carbon in soil aggregates forests at different successional stages of secondary forests at different succession stages

  • 表5所示,3个演替阶段次生林类型的土壤团聚体对有机碳的贡献率均是>5 mm粒径最高,<0.25 mm粒径最低。土壤团聚体对有机碳的贡献率主要集中在大团聚(>0.25 mm),微团聚体(<0.25 mm)占的比重较少。单因素方差分析发现,同一演替阶段内各级团聚体对有机碳贡献率存在显著差异;而同一粒径不同演替阶段间分析结果显示,>5 mm、2~1 mm、1~0.5 mm、0.5~0.25 mm、0.25~0.053 mm这5个粒径对有机碳的贡献率在不同演替阶段间存在显著差异,5~2 mm、<0.053 mm 这2个粒径对土壤的贡献率在不同演替阶段间无显著差异(表6)。其中 >5 mm粒径的土壤团聚体在中级演替阶段(桦木+冷杉混交林)分布含量最高,2~1 mm粒径的团聚体在高级演替阶段(冷杉原始林)分布大于其他两个演替阶段,而1~0.5 mm、0.5~0.25 mm、0.25~0.053 mm 3个粒径的团聚体含量均是初级演替(桦木林)>高级演替(冷杉原始林)>中级演替(桦木+冷杉混交林)(见表6)。

    发育阶段各级团聚体对土壤有机碳的贡献率/%
    >5 mm5~2 mm2~1 mm1~0.5 mm0.5~0.25 mm0.25~0.053 mm<0.053 mm
    桦木林3.01 Ca2.69 Aa2.73 Aa2.43 Aa1.60 Ab1.19 Ab0.15 Bc
    桦木+冷杉混交林4.67 Aa2.49 Ab2.35 Bb1.80 Bc1.12 Bd0.63 Be0.84 Ae
    冷杉原始林3.19 Ba2.19 Ac2.40 Bb1.66 Bd1.09 Be0.53 Bf0.64 Af
      注:同一列中不同大写字母表示不同演替阶段间团聚体有机碳含量差异显著(p<0.05);同一行中不同小写字母表示同一演替阶段不同粒径间团聚体有机碳含量差异显著(p<0.05). The mean difference is significant at the 0.05 level.

    Table 5.  Contribution rate of soil aggregates to organic carbon in secondary forests at different successional stages

    方差结果粒径>5 mm5~2 mm2~1 mm1~0.5 mm0.5~0.25 mm0.25~0.053 mm<0.053 mm
    F11.2830.6964.1654.6425.0844.87715.23
    Sig.0.001**0.5150.038*0.0288*0.022*0.025*0.000**
      注:同一粒径在不同演替阶段间团聚体含量p<0.05为显著标记*,p<0.01为极显著标记**

    Table 6.  Single factor variance analysis of contribution rate of soil aggregates to organic carbon at different successional stages with the same particle size

    对同一演替阶段不同粒径团聚体的有机碳贡献率进行多重比较发现,初级演替阶段(桦木林)在>0.5 mm粒径时,团聚体的大小与有机碳贡献率是无显著差异的,而在0.5~0.053 mm与>0.5 mm粒径间、0.25~0.053 mm与<0.053 mml粒径间团聚体的机碳贡献率存在显著差异;中级演替阶段(桦木+冷杉混交林)除了5~2 mm与2~1 mm粒径间有机碳贡献率无显著差异,其余径级均具有显著差异;高级演替阶段(冷杉原始林)各粒径间团聚体对有机碳的贡献率均有显著差异。这说明随着演替阶段的上升,粒径的大小与土壤有机碳贡献率的联系更加紧密,并基本表现为随粒径增加有机碳贡献率增加。

    对同一粒径不同演替阶段次生林土壤团聚体对有机碳的贡献率进行多重比较发现,>5 mm粒径时3个演替阶段的有机碳贡献率分别存在显著差异,且中级演替(桦木+冷杉混交林)>高级演替(冷杉原始林)>初级演替(桦木林);而在2~1 mm、1~0.5 mm、0.5~0.25 mm、0.25~0.053 mm、<0.053 mm这5个粒径间仅表现为桦木林与混交林、桦木林与冷杉林之间具有显著差异。说明演替阶段不同对>5 mm粒径的团聚体有机碳贡献率具有显著影响。

    比较不同团聚体有机碳含量与贡献率发现,虽然<0.25 mm粒径的有机碳含量高但是贡献率低,说明微团聚体对有机碳的保护力更强,且桦木+冷杉混交林>桦木林>冷杉原始林(见表4表5)。

    发育阶段各级团聚体土壤碳含量/(g·kg−1
    >5 mm5~2 mm2~1 mm1~0.5 mm0.5~0.25 mm0.25~0.053 mm<0.053 mm
    桦木林42.70±8.89Aa42.99±8.59Aa43.41±8.72Aa44.74±8.84Aa45.81±9.19Aa48.03±8.61Aa49.39±7.90Aa
    桦木+冷杉
    混交林
    51.88±3.20Aa51.23±2.42Aa53.69±2.69Aa55.49±2.02Aa55.07±3.18Aa55.76±2.81Aa58.67±2.34Aa
    冷杉原始林60.35±9.70 Aa62.60±4.61Aa62.81±5.02Aa64.55±2.17Aa61.36±8.60Aa66.70±2.57Aa64.70±7.49Aa
      注:同一列中不同大写字母表示不同演替阶段间团聚体有机碳含量差异显著(P<0.05);同一行中不同小写字母表示同一演替阶段不同粒径间团聚体有机碳含量差异显著(P<0.05)

    Table 4.  Percentage of organic carbon in soil aggregates of secondary forests at different successional stages

3.   讨论与结论
  • 有研究认为[13],微团聚体的形成是大团聚体形成的前提条件,空间尺度上土壤团聚体由微团聚体向大团聚体逐级连续层次性形成,而在时间尺度上胶结物质从多糖(暂时稳定)向菌丝根系(短时间稳定)及芳香类物质(持久稳定)层次性变化。李玮[14]等的研究表明,种植年限的增加有利于团聚体胶结物质的积累,从而有利于大团聚体的形成与稳定;Ma[15]等也认为,中龄林和成熟林的土壤团聚性要强于幼龄林。本研究显示,处于中级演替阶段的冷杉+桦木混交林大团聚体含量最高,土壤团聚性呈“∩型”随着演替阶段上升在中级演替阶段达到最高,随着演替进程的发展到高级阶段又下降,这与李玮[14]、Ma[15]、Tisdall[13]的研究结论不一致。这可能是由于大团聚体的稳定性在很大程度上取决于植物根系和菌丝,当根系和菌丝被分解而得不到补给时,稳定性大团聚体的数量随有机质含量的上升而减少,本研究桦木冷杉混交林比冷杉原始林的有机质含量低,可能就是导致混交林大团聚体含量高于冷杉原始林的重要原因。

  • 3个演替阶段土壤有机碳总含量介于159.24~561.28 g·kg−1之间,冷杉原始林>桦木+冷杉混交林>桦木林。不同演替阶段各级团聚体的土壤有机碳含量均是冷杉原始林最高,桦木+冷杉混交林次之,桦木林最低,且土壤大团聚体(>0.25 mm)有机碳的含量百分比远高于微团聚体(<0.25 mm)有机碳的含量百分比。说明各演替阶段土壤有机碳的含量主要是存在于大团聚体中,这与前人的研究结论[16-18]相同。对照土壤养分中铵态氮的含量来看,氮含量和有机碳变化规律趋于一致,这与黄天颖[2]等人对黄浦江上游水源涵养林碳、氮分布特征研究结论相同,原因可能在于土壤碳、氮变化通常相辅相成,团聚体氮元素含量随有机碳含量的变化而变化。

    冷杉原始林的大团聚体分布较其他两个演替阶段稍低,但冷杉原始林有机碳总含量最高,出现这一结果可能是随着演替阶段的前进,干扰因子减少,植物及微生物群落结构趋于稳定,大团聚的更新降低,使得大团体内微团聚体的形成数量增大,而这种从大团聚体中心形成的微团聚体含有很高的且不易分解的有机碳含量,因此出现大团聚体含量低但有机碳总含量高的情况[19-20]

    对同一演替阶段土壤各粒径团聚体中有机碳含量分布的研究表明,有机碳含量与各团聚体粒径的相关性不显著,但有机碳的含量随团聚体粒径减小而基本呈增加趋势。3个演替阶段均是<0.25 mm粒径的有机碳含量高于其他粒径,>2 mm粒径团聚体有机碳含量最低。本研究,<0.25 mm微团聚体有机碳含量最高,究其原因可能是小团聚体的固碳方式决定的。小团聚体主要靠有机和无机胶体紧密结合固持碳,固持的碳不易为微生物分解释放[21],而大团聚体主要靠有机物、多糖等结合,因此大团聚体中的有机碳比微团聚体中的有机碳年轻,有机碳更容易矿化,而微团聚体中的有机碳则大多是高度腐殖化的惰性组[22-23]

  • 3个演替阶段次生林类型的土壤团聚体对有机碳的贡献率均是>5 mm粒径最高,<0.25 mm粒径最低。土壤团聚体对有机碳的贡献率主要集中在大团聚(>0.25 mm),微团聚体(<0.25 mm)占的比重较少。演替阶段不同对>5 mm粒径的团聚体有机碳贡献率具有显著影响。随着演替阶段的上升,粒径的大小与土壤有机碳贡献率的联系更加紧密,并基本表现为随粒径增加有机碳贡献率增加。比较不同团聚体有机碳含量与贡献率发现,虽然<0.25 mm粒径的有机碳含量高但是贡献率低,说明微团聚体对有机碳的保护力更强,且桦木+冷杉混交林>桦木林>冷杉原始林。

    综上所述,对于川西山地天然次生林而言,大团聚体是有机碳的主要来源,而微团聚体能更加持久的稳固碳元素,比较三个演替阶段的次生林发现处于中级演替阶段的桦木+冷杉混交林对该区域森林固碳具有重要作用,而处于高级演替阶段的冷杉林的有机碳含量最高也说明了正向演替对森林固碳是具体促进作用的。

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