浙西北茶园土壤固碳能力及其不同形态有机碳的积累特点

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引用本文0 孔樟良. 浙西北茶园土壤固碳能力及其不同形态有机碳的积累特点[J]. 浙江大学学报(农业与生命科学版), 2016, 42(2): 209-219. DOI:10.3785/j.issn.1008-9209.2015.08.111 KONG Zhangliang. Carbon sequestration potential of tea garden soil in northwest Zhejiang and its accumulation characteristic on different fractions of organic carbon[J]. Journal of Zhejiang University (Agriculture and Life Sciences), 2016, 42(2): 209-219. DOI:10.3785/j.issn.1008-9209.2015.08.111 浙西北茶园土壤固碳能力及其不同形态有机碳的积累特点[PDF全文] 孔樟良浙江省建德市农技推广中心，浙江建德 311600 基金项目: 浙江省建德市耕地地力监测(浙土肥字[2007]35号). 通信作者: 孔樟良(http://orcid.org/0000-0003-1183-3588),E-mail:[email protected] 收稿日期(Received): 2015-08-11; 接受日期(Accepted): 2015-10-10; 网络出版日期(Published online): 2016-03-20 摘要: 为了解茶园土壤的固碳能力及其积累特点，从浙西北茶区采集黄筋泥、黄红泥土和黄泥土等3类土壤上的9个代表性茶园土壤剖面的分层土样，每类土壤包括植茶年龄为5~10、15~20和>30年的3个剖面，分析了有机碳、轻组分有机碳、颗粒态有机碳、微生物生物量碳和水溶性有机碳在土壤剖面中的积累特点，并与利用时间相似的旱地土壤进行比较。结果表明：茶园土壤的各类有机碳具明显的表聚特征，随剖面深度的增加，轻组分有机碳和颗粒态有机碳含量占土壤有机碳总量的比例较有机总碳的下降更为明显；随着植茶年龄的增加，表层土壤中各类有机碳含量及全剖面有机碳贮量明显地增加；表层土壤中>2 mm粒组的水稳定性团聚体明显增加，同时，表层土壤中积累的有机碳(特别是轻组分有机碳)趋向于分布在>2 mm粒组的水稳定性团聚体中；轻组分有机碳和颗粒态有机碳随植茶时间的增加幅度明显大于有机碳总量的增加，表明在植茶过程中有机碳主要以活性较高的轻组分有机碳和颗粒态有机碳的形式积累，且积累的有机碳主要分布在近地表的土层。比较分析表明，茶园土壤有机碳的积累量均高于旱地土壤，说明茶园比一般旱地具有更高的土壤固碳潜力。关键词: 茶园土壤碳库活性有机碳分布特征 Carbon sequestration potential of tea garden soil in northwest Zhejiang and its accumulation characteristic on different fractions of organic carbon KONG Zhangliang Agricultural Technology Extension Center of Jiande City in Zhejiang Province, Jiande 311600, Zhejiang, China Summary: Organic carbon is the basis of soil system, which plays an important role in the soil quality and regulating the supply of nutrients. Physical, chemical and biological properties and productivity of soil were all closely related to the content and character of organic carbon. Therefore, the maintenance of organic carbon in soils is emphasized by various soil researchers and land managers. Appropriate organic carbon contents in soils could increase cation exchange capacity (CEC), moisture storage, mineral nutrients, and food source for soil organisms, and improve soil structure and aggregate stability. As an important component in carbon pool of terrestrial ecosystem, soil organic carbon plays an important role in regulating greenhouse effect and global warming. Organic carbon contents in soils depended on the factors such as climate condition, soil type, mineralization process, and land use type and management. For a given soil, the maximum amount of organic carbon generally accumulated in the topsoil under long-term undisturbed vegetation, typically grassland or forest. Loss of organic carbon is generally regarded as undesirable, though some reports pointed out that low soil carbon contents can reduce application rates of pesticides in soil due to lower sorption. It is well known that various kinds of soil management can cause changes in organic carbon concentrations, and the carbon contents of cropped and tilled soils are usually lower than those of undisturbed grassland or forest. The decline of organic carbon contents was often caused by top soil erosion and breakdown of stabilized soil.

To understand the sequestering carbon potential of tea garden soil and its accumulation characteristic on different fractions of organic carbon, soil profile samples were collected from nine tea gardens and three uplands in northwest Zhejiang. Samples from nine tea gardens were divided into three groups (quaternary red clay, yellow-red soil and yellowish red soil), each group corresponding to three tea plantation ages (5-10 years, 15-20 years, and > 30 years). The contents of total organic carbon, light-fraction organic carbon, particulate organic carbon, microbial biomass carbon and water soluble organic carbon in the soil samples were analyzed, and compared with those local upland soils with similar utilization time.

The results showed that different fractions of organic carbon in the tea garden soils had surface accumulation pattern, and the proportion of the light-fraction and particulate organic carbons in the total organic carbon decreased faster with depth than the content of total organic carbon itself. Furthermore, different fractions of organic carbon in the surface soil and storages of total organic carbon in the whole soil profile increased with the age of tea plantation; the water-stable aggregates with size >2 mm increased obviously in the surface soil. Meanwhile, the organic carbon accumulated in the surface soil tended to distribute in the water-stable aggregates of > 2 mm, especially for the light-fraction organic carbon. Increase rate of the light-fraction and particulate organic carbons was greater than that of the total organic carbon with aging of tea plantation, suggesting that the light-fraction and particulate organic carbons with higher activity were the main forms accumulated, and the organic carbon accumulated in the soils was mainly distributed in the surface layer.

It is concluded that the accumulation rate of organic carbon in the tea garden soil is significantly higher than that in the upland soil. Therefore, the tea garden soil has a greater potential of sequestering carbon than the upland.

Key words: tea garden soil carbon pool active organic carbon distribution characteristic

有机碳是土壤系统的基础物质，是土壤质量的核心，也是控制土壤养分供应能力和碳、氮、磷、硫循环的重要因子[1]，土壤的物理、化学和生物学性质以及土壤的生产力都与土壤有机碳的含量和性状密切相关[2, 3, 4]。作为陆地碳库的重要组成部分，土壤有机碳库对于温室效应和全球变化也具有重要的控制作用[5, 6, 7, 8]。因此，提高土壤有机碳贮量有2方面的意义，一是维持和提高土地质量的需要；二是全球环境固碳的需要。

茶园是我国南方地区重要的土地利用方式，其大多由荒山、荒坡或者林地开垦而成。在荒坡地上种植茶树后，其物质的输入和输出可发生明显的变化，因此种植茶树后土壤质量的演变深受人们的重视[9, 10, 11]。一些研究已表明，长期种植茶树和施肥可导致土壤酸化，促进磷、钾养分的提高[12, 13]；同时，因茶园采用等高种植及每年有大量的落叶返还土壤，与耕地相比，前者水土流失较弱，且有较高的土壤有机质水平。土壤有机质是茶园土壤潜在肥力的重要指标，也是茶园土壤熟化的重要标志；土壤有机质水平对茶树生长、茶叶产量及品质有着极大的影响。土壤碳库成分复杂，不同碳库组分的稳定性变化很大，它们对土壤结构形成、养分供应都存在较大的差异[14]。以往对茶园土壤有机碳的研究主要偏重于表层有机碳总量，对有机碳组分的关注较少[10, 15]。近年来，利用物理、化学分组方法研究有机质组分已成为重要的方法，并提出了轻组分有机碳、微生物生物量碳、颗粒态有机碳和水溶性有机碳等概念[16, 17, 18]，这为深入研究土壤有机碳的稳定性提供了可能[19, 20]。为了深入了解茶园种植过程中有机碳组分的变化特征及其固碳作用，本文以浙西北茶区典型茶园土壤为例，探讨了不同植茶年龄土壤中有机碳积累及其活性组分的变化特点。

1 材料与方法 1.1 供试土壤

在田间调查的基础上，于2013年12月在浙江省西北部选择了9个代表性茶园与3块旱地进行土壤剖面样品的采集，在每一个茶园和旱地中各采集一个代表性土壤剖面。9个代表性茶园土壤剖面按土壤类型可分为3组，分别为发育于第四纪红土母质的黄筋泥、发育于泥页岩的黄红泥土和发育于酸性岩的黄泥土，每组土壤包括植茶年龄分别为5~10年、15~20年和>30年的3个剖面。3个旱地土壤剖面的地理位置与茶园相邻，分别为开垦利用时间为>30年和15~20年的黄筋泥与开垦利用时间为>30年的黄红泥土，主要种植番薯与蔬菜。挖掘的土壤剖面长×宽×深为100 cm×70 cm×100 cm，按15 cm的深度间隔采集分层土壤样品，即每一土壤剖面分别采集0~15、15~30、30~45、45~60、60~75和75~90 cm等6层土样。在采集分层土壤的同时，用环刀法测定每层土壤的体积质量(容重)。本研究的茶园与旱地分布区的地貌类型均为低丘，所采集剖面的基本情况见表 1。

表1(Table 1) 表1 采集的土壤剖面基本情况 Table 1 Basic information of the collected soil profiles 表1 采集的土壤剖面基本情况 Table 1 Basic information of the collected soil profiles 土壤类型Soil type 采样地Location 剖面号Profile No. 利用方式Land use 利用年限Plantation time/a 黄筋泥Quaternary red clay 衢州Quzhou QR 1 茶园Tea garden 5~10 QR 2 茶园Tea garden 15~20 QR 3 茶园Tea garden >30 QR 4 旱地Upland 15~20 QR 5 旱地Upland >30 黄红泥土Yellow-red soil 杭州Hangzhou YR 1 茶园Tea garden 5~10 YR 2 茶园Tea garden 15~20 YR 3 茶园Tea garden >30 YR 4 旱地Upland >30 黄泥土Yellowish red soil 杭州Hangzhou YS 1 茶园Tea garden 5~10 YS 2 茶园Tea garden 15~20 YS 3 茶园Tea garden >30 点击放大 1.2 分析方法

土样经室内风干、混匀后，过2 mm土筛，部分土样进一步研磨过0.125 mm土筛。土壤pH用电位计测定，土水质量比为1∶2.5。土壤有机质用重铬酸钾外加热法测定[21]。土壤轻组分有机碳是指用密度为1.6~2.0 g/cm3重液分离的密度较低的有机碳，本文用密度为1.7 g/cm3的NaI溶液分离，分离获得的轻组分物质中的有机碳用重铬酸钾外加热法测定，然后根据轻组分物质占土壤的比例换算为土壤中轻组分有机碳占土壤的含量。颗粒态有机碳是指粒径大于53 μm的土壤有机碳，主要由与砂粒结合的植物残体半分解产物组成，相对于土壤黏粒和粉砂结合的土壤有机质，被认为是有机碳中的非保护性部分，用5 g/L焦磷酸钠溶液振荡分散土样过53 μm土筛分离获得[22]，其含量用重铬酸钾外加热法测定。微生物生物量碳采用氯仿熏蒸-硫酸钾提取法测定[23]，提取液中可溶性总碳含量用Shimadzu TOC自动分析仪测定。水溶性有机碳用0.5 mol/L K2SO4溶液浸提，用Shimadzu TOC自动分析仪测定。土壤各形态碳的贮量根据各土层中各形态碳的含量与土壤体积质量计算。数据采用Excel 2003处理，统计分析采用DPS 3.0软件实现。

在0~15 cm土层中土壤水稳性团聚体的测定采用CAMBARDELLA等[24]的方法，具体步骤如下：称取60 g风干土，置于套筛(从上到下依次为2、0.25和0.053 mm)顶层上，浸润10 min，上下移动套筛3 cm，2 min内重复50次，然后将土样依次通过土筛，将留在每个土筛上的土壤冲洗至铝盒中，在50 ℃下烘干，称量。各团聚体中的有机碳、轻组分有机碳测定方法同上。根据各粒级水稳定性团聚体的组成及其有机碳与轻组分有机碳含量计算有机碳在各粒级中的分配。

2 结果与分析 2.1 土壤有机碳、轻组分和颗粒态有机碳含量变化

各土层的体积质量和pH值见表 2。随着植茶时间的增加表层土壤pH值呈现下降趋势；土壤体积质量随植茶时间的增加也略有增加。

表2(Table 2) 表2 茶园土壤体积质量、黏粒含量和pH Table 2 Bulk density, clay content and pH of different tea garden soils 表2 茶园土壤体积质量、黏粒含量和pH Table 2 Bulk density, clay content and pH of different tea garden soils 植茶年龄Time of tea plantation/a 土层深度Soil depth/cm 体积质量Bulk density/(g/cm 3) pH w(黏粒) Clay content/(g/kg) 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 5~10 0~15 1.42 1.37 1.35 5.34 5.43 5.13 332 278 218 15~30 1.37 1.34 1.33 5.24 5.54 5.28 354 291 231 30~45 1.36 1.32 1.34 4.89 5.63 5.11 358 301 233 45~60 1.54 1.39 1.42 4.76 5.58 5.37 344 297 227 60~75 1.52 1.42 1.37 4.88 5.64 5.46 352 256 204 75~90 1.49 1.38 1.42 4.78 5.55 5.39 346 223 165 15~20 0~15 1.48 1.41 1.37 5.03 5.32 5.02 324 268 203 15~30 1.39 1.37 1.32 5.12 5.37 5.14 362 285 218 30~45 1.38 1.34 1.35 4.87 5.58 5.13 356 296 225 45~60 1.52 1.38 1.41 4.86 5.47 5.42 352 288 231 60~75 1.56 1.41 1.34 4.79 5.73 5.34 348 263 212 75~90 1.53 1.39 1.39 4.73 5.65 5.37 352 234 187 >30 0~15 1.45 1.42 1.42 4.73 5.14 4.76 319 253 214 15~30 1.42 1.39 1.36 4.89 5.23 4.89 371 279 223 30~45 1.39 1.34 1.37 4.76 5.37 5.03 362 292 214 45~60 1.51 1.36 1.37 4.82 5.48 5.38 341 286 221 60~75 1.54 1.42 1.35 4.83 5.69 5.34 338 272 228 75~90 1.52 1.38 1.37 4.81 5.67 5.41 364 248 199 点击放大

研究区茶园土壤有机碳、轻组分有机碳和颗粒态有机碳含量均以0~15 cm土层最高，随剖面深度的增加而下降(表 3)，这显然与土壤有机碳主要由地表输入有关。相关分析表明，土壤中轻组分有机碳和颗粒态有机碳含量与土壤有机碳含量呈显著的正相关，相关系数分别为0.912**和0.904**(P Vertical profile changes of total, light-fraction and particulate organic carbons (C) in different tea garden soils 表3 茶园土壤中有机碳、轻组分有机碳和颗粒态有机碳的垂直变化 Table 3 Vertical profile changes of total, light-fraction and particulate organic carbons (C) in different tea garden soils g/kg 植茶年龄Time of tea plantation/a 土层深度Soil depth/cm w(有机碳) Organic C content w(轻组分有机碳) Light-fraction organic C content w(颗粒态有机碳) Particulate organic C content 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥 Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 5~10 0~15 5.32 7.36 6.58 0.661 0.833 0.872 1.247 0.998 1.308 15~30 3.18 5.69 5.23 0.131 0.296 0.459 0.257 0.309 0.558 30~45 2.12 3.12 3.69 0.050 0.097 0.157 0.051 0.124 0.126 45~60 1.23 1.27 2.25 0.017 0.029 0.060 0.016 0.066 0.131 60~75 0.48 0.52 0.49 0.008 0.013 0.015 0.007 0.018 0.028 75~90 0.34 0.29 0.31 0.008 0.004 0.004 0.010 0.008 0.013 15~20 0~15 9.31 10.32 11.32 1.840 2.214 2.621 3.104 4.158 4.203 15~30 3.42 6.47 6.89 0.155 0.422 0.680 0.651 0.717 0.956 30~45 2.18 4.23 4.32 0.050 0.163 0.239 0.087 0.227 0.282 45~60 1.13 2.58 2.32 0.017 0.038 0.098 0.022 0.051 0.131 60~75 0.52 0.84 0.47 0.009 0.014 0.020 0.008 0.014 0.041 75~90 0.29 0.45 0.34 0.007 0.009 0.005 0.007 0.014 0.012 >30 0~15 13.25 17.65 19.68 3.517 5.073 6.977 5.780 8.455 11.233 15~30 4.65 8.68 8.98 0.319 0.838 1.186 0.789 1.069 1.692 30~45 2.32 6.49 5.67 0.055 0.302 0.347 0.141 0.330 0.565 45~60 1.07 3.65 3.14 0.015 0.078 0.129 0.019 0.093 0.153 60~75 0.53 1.12 0.51 0.010 0.023 0.020 0.013 0.020 0.038 75~90 0.31 0.49 0.32 0.006 0.010 0.005 0.013 0.016 0.016 点击放大 2.2 土壤微生物生物量碳和水溶性有机碳含量变化

与轻组分有机碳和颗粒态有机碳含量的变化相似，土壤微生物生物量碳和水溶性有机碳含量也随土壤剖面深度的增加明显地下降(表 4)，并随植茶时间的增加而显著地增加。总体上，植茶年龄对土壤微生物生物量碳和水溶性有机碳含量的影响也主要在上层土壤(尤其是0~15 cm土层)，向下的影响明显减弱。土壤中微生物生物量碳和水溶性有机碳含量与土壤有机碳含量间的相关系数分别为0.948**和0.979**(P Vertical profile changes of microbial biomass C and water soluble organic C in different tea garden soils 表4 茶园土壤中微生物生物量碳和水溶性有机碳的垂直变化 Table 4 Vertical profile changes of microbial biomass C and water soluble organic C in different tea garden soils mg/kg 植茶年龄Time of tea plantation/a 土层深度Soil depth/cm w(微生物生物量碳) Microbial biomass C content w(水溶性有机碳) Water soluble organic C content 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 5~10 0~15 87.3 74.3 64.2 13.20 11.87 13.54 15~30 35.4 41.2 34.1 7.54 8.74 10.32 30~45 23.5 25.3 27.4 4.12 5.65 5.43 45~60 18.7 23.1 25.6 2.18 3.54 6.12 60~75 12.3 14.2 18.7 1.24 2.58 3.25 75~90 8.4 9.8 10.3 2.32 1.77 2.26 15~20 0~15 142.3 166.4 159.8 23.50 24.12 25.41 15~30 46.3 54.6 63.5 11.90 13.25 14.62 30~45 24.5 29.8 38.5 6.45 8.58 8.74 45~60 19.8 25.4 31.2 3.21 4.12 6.98 60~75 13.2 15.3 17.6 1.48 2.45 4.23 75~90 7.6 7.6 9.8 1.64 2.63 2.14 >30 0~15 254.6 278.1 312.1 28.70 36.54 39.54 15~30 76.8 87.5 93.6 13.20 16.35 19.56 30~45 35.4 38.7 45.2 8.54 9.56 12.14 45~60 23.5 24.6 33.1 3.28 5.23 7.21 60~75 12.3 14.6 16.5 2.54 2.88 4.32 75~90 8.6 8.7 10.5 3.21 3.56 2.52 点击放大 2.3 植茶后土壤有机碳的积累特征

由表 5可知，随着植茶年龄的增加，0~90 cm土层中有机碳、轻组分有机碳、颗粒态有机碳、微生物生物量碳和水溶性有机碳都呈显著地增加。植茶时间30年以上的黄筋泥在0~90 cm土层中有机碳、轻组分有机碳、颗粒态有机碳、微生物生物量碳和水溶性有机碳总贮量分别为植茶时间5~10年黄筋泥的1.78倍、4.59倍、4.36倍、2.25倍和1.98倍；而在黄红泥土中分别为2.14倍、5.16倍、6.80倍、2.47倍和2.23倍；在黄泥土中分别为2.12倍、5.79倍、6.61倍、2.91倍和2.13倍。轻组分有机碳和颗粒态有机碳随植茶时间的增加明显高于有机碳总量的增加。这表明在植茶过程中有机碳主要以活性较高的轻组分有机碳、颗粒态有机碳形式积累。在黄红泥土和黄泥土中各形态有机碳积累速率总体高于黄筋泥，这可能与黄红泥土和黄泥土土质较为疏松，比较适合茶树根系伸展有关，而黄筋泥黏粒含量较高(表 2)，限制了茶树的生长，导致茶树的生物量较低，进入土壤的枯落物较少有关。表 6和表 7的结果也表明，随着植茶时间的增加,在0~15 cm土层中有机碳、轻组分有机碳、颗粒态有机碳、微生物生物量碳和水溶性有机碳的积累量占全剖面的比例也逐渐增加，轻组分有机碳和颗粒态有机碳尤为明显。这表明在茶树种植过程中积累的土壤有机物质主要集中在近地表的土层，且积累的有机碳主要为活性较高的轻组分有机碳和颗粒态有机碳。

表5(Table 5) 表5 茶园土壤0~90 cm剖面中各类有机碳的总贮量 Table 5 Total storage of different forms of soil organic C in 0-90 cm depth of different tea garden soils 表5 茶园土壤0~90 cm剖面中各类有机碳的总贮量 Table 5 Total storage of different forms of soil organic C in 0-90 cm depth of different tea garden soils 土壤类型Soil type 植茶年龄Time of tea plantation/a w(有机碳) Organic C content/(kg/m 2) w(轻组分有机碳)Light-fraction organic C content/(kg/m 2) w(颗粒态有机碳)Particulate organic C content/(kg/m 2) w(微生物生物量碳) Microbial biomass C content/(g/m 2) w(水溶性有机碳)Water soluble organic C content/(g/m 2) 黄筋泥Quaternary red soil 5~10 2.69 0.19 0.34 39.67 6.51 15~20 3.68 0.46 0.85 55.66 10.49 >30 4.79 0.85 1.46 89.24 12.90 黄红泥土Yellow-red soil 5~10 3.71 0.26 0.31 38.43 6.97 15~20 5.17 0.60 1.09 62.48 11.47 >30 7.96 1.34 2.12 95.19 15.53 黄泥土Yellowish red soil 5~10 3.76 0.32 0.44 36.80 8.34 15~20 5.22 0.75 1.15 65.39 12.66 >30 8.00 1.83 2.90 107.16 17.78 点击放大表6(Table 6) 表6 茶园土壤0~90 cm剖面中各土层有机碳、轻组分有机碳和颗粒态有机碳的构成 Table 6 Proportions of total, light-fraction and particulate organic C of different depths in their total storage of whole 0-90 cm soil profile 表6 茶园土壤0~90 cm剖面中各土层有机碳、轻组分有机碳和颗粒态有机碳的构成 Table 6 Proportions of total, light-fraction and particulate organic C of different depths in their total storage of whole 0-90 cm soil profile % 植茶年龄Time of tea plantation/a 土层深度Soil depth/cm w(有机碳) Organic C percent w(轻组分有机碳) Light-fraction organic C percent w(颗粒态有机碳) Particulate organic C percent 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥 Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 5~10 0~15 42.15 40.77 35.40 75.95 65.97 55.80 78.99 65.94 60.48 15~30 24.31 30.83 27.72 14.52 22.96 28.95 15.71 19.99 25.43 30~45 16.09 16.65 19.71 5.46 7.43 9.96 3.07 7.87 5.78 45~60 10.57 7.14 20.60 2.18 2.33 2.36 1.11 4.44 3.23 60~75 4.07 2.99 2.68 0.99 1.04 0.99 0.45 1.22 1.33 75~90 2.83 1.62 1.75 0.91 0.28 0.28 0.66 0.54 0.62 15~20 0~15 56.21 42.23 44.55 89.07 77.96 72.08 80.95 80.76 75.21 15~30 19.39 25.73 26.13 7.03 14.46 18.02 15.94 13.53 16.49 30~45 12.27 16.45 16.75 2.24 5.45 6.47 2.12 4.20 4.98 45~60 7.01 10.33 9.40 0.87 1.32 2.76 0.59 0.96 2.40 60~75 3.31 3.44 1.81 0.46 0.49 0.53 0.21 0.28 0.71 75~90 1.81 1.82 1.36 0.33 0.32 0.13 0.18 0.27 0.21 >30 0~15 60.15 47.24 52.38 89.84 80.69 81.16 85.82 85.08 82.61 15~30 20.67 22.74 22.89 7.99 13.04 13.22 11.48 10.53 11.92 30~45 10.10 16.39 14.56 1.34 4.54 3.89 2.01 3.13 4.01 45~60 5.06 9.36 8.06 0.39 1.19 1.45 0.29 0.90 1.08 60~75 2.56 3.00 1.29 0.26 0.37 0.22 0.20 0.20 0.27 75~90 1.48 1.27 0.82 0.17 0.16 0.05 0.19 0.16 0.11 点击放大表7(Table 7) 表7 茶园土壤0~90 cm剖面中各土层微生物生物量碳和水溶性有机碳的构成 Table 7 Proportions of microbial biomass C and water soluble organic C of different depths in their total storage of whole 0-90 cm soil profile 表7 茶园土壤0~90 cm剖面中各土层微生物生物量碳和水溶性有机碳的构成 Table 7 Proportions of microbial biomass C and water soluble organic C of different depths in their total storage of whole 0-90 cm soil profile % 植茶年龄Time of tea plantation/a 土层深度Soil depth/cm w(微生物生物量碳) Microbial biomass C percent w(水溶性有机碳) Water soluble organic C percent 黄筋泥Quaternary red soil 黄红泥土Yellow-red soil 黄泥土Yellowish red soil 黄筋泥 Quaternary red soil 黄红泥土 Yellow-red soil 黄泥土Yellowish red soil 5~10 0~15 46.88 39.73 35.33 43.21 35.00 32.86 15~30 18.34 21.55 18.49 23.81 25.21 24.67 30~45 12.09 13.04 14.97 12.92 16.05 13.08 45~60 10.89 12.53 16.60 7.74 10.59 24.96 60~75 7.07 7.87 10.44 4.35 7.89 8.00 75~90 4.73 5.28 5.96 7.97 5.26 5.77 15~20 0~15 56.75 56.33 50.22 49.74 44.48 41.25 15~30 17.34 17.96 19.23 23.66 23.74 22.87 30~45 9.11 9.59 11.92 12.73 15.04 13.98 45~60 8.11 8.41 10.09 6.98 7.44 11.66 60~75 5.55 5.18 5.41 3.30 4.52 6.72 75~90 3.13 2.54 3.12 3.59 4.78 3.52 >30 0~15 62.05 62.23 62.03 48.40 50.11 47.36 15~30 18.33 19.17 17.82 21.80 21.95 22.44 30~45 8.27 8.17 8.67 13.81 12.37 14.03 45~60 5.96 5.27 6.35 5.76 6.87 8.33 60~75 3.18 3.27 3.12 4.55 3.95 4.92 75~90 2.20 1.89 2.01 5.68 4.74 2.91 点击放大 2.4 表层土壤中有机碳和轻组分有机碳在不同团聚体中的分布

由表 8可见：各表层土壤水稳定性团聚体以粒径为>2 mm和0.25~2 mm的为主，2 mm的团聚体比例增加，而相应的0.25~2 mm和 2 mm和0.25~2 mm的团聚体中，与水稳定性团聚体的分布相似，随着植茶年龄的增加,>2 mm的团聚体中有机碳和轻组分有机碳分配的比例也增加，而相应地0.25~2 mm和 2 mm的团聚体中。

表8(Table 8) 表8 茶园土壤0~15 cm土层中有机碳和轻组分有机碳在不同团聚体中的分布 Table 8 Distribution of organic C and light-fraction organic C in different sizes of aggregates in 0-15 cm surface soil 表8 茶园土壤0~15 cm土层中有机碳和轻组分有机碳在不同团聚体中的分布 Table 8 Distribution of organic C and light-fraction organic C in different sizes of aggregates in 0-15 cm surface soil % 植茶年龄Time of tea plantation/a 土层深度Soil depth/cm 水稳定性团聚体分布Distribution of water-stable aggregates 有机碳分布Distribution of organic C 轻组分有机碳分布Distribution of light-fraction organic C >2 mm 0.25~2 mm 2 mm 0.25~2 mm 2 mm 0.25~2 mm 30 55.8 41.5 2.7 64.7 32.5 2.8 79.3 18.9 1.8 黄红泥土Yellow-red soil 5~10 27.5 61.2 11.3 31.4 53.4 15.2 41.6 51.0 7.4 15~20 39.8 52.5 7.7 45.6 44.6 9.8 56.7 39.5 3.8 >30 47.6 46.6 5.8 53.7 38.7 7.6 80.4 18.1 1.5 黄泥土Yellowish red soil 5~10 30.3 61.1 8.6 28.4 59.2 12.4 39.2 55.6 5.2 15~20 45.6 50.2 4.2 49.6 43.2 7.2 62.8 34.5 2.7 >30 50.7 45.5 3.8 58.2 36.0 5.8 78.4 20.7 0.9 点击放大 2.5 茶园与旱地土壤有机质积累的差异

与相同利用年限的旱地相比，茶园土壤的有机碳和轻组分有机碳含量均较高，这在离地表较近的土层中尤为明显(图 1)。利用年限>30年的黄筋泥茶园土壤的0~15 cm土层有机碳和轻组分有机碳含量分别为相同利用年限旱地土壤的1.76倍和5.39倍；利用年限15~20年的黄筋泥茶园0~15 cm土层有机碳和轻组分有机碳含量分别为相同利用年限旱地土壤的1.19倍和2.44倍；利用年限>30年的黄红泥土茶园0~15 cm土层有机碳和轻组分有机碳含量分别为相同利用年限旱地土壤的1.54倍和2.34倍。与茶园土壤随利用时间增加土壤有机碳积累明显增加不同，旱地土壤有机碳随时间增加积累并不明显。对0~90 cm全剖面土壤有机碳贮量计算表明，茶园土壤明显高于旱地，其中，利用年限>30年的黄筋泥茶园有机碳贮量(4.79 kg/m2)和轻组分有机碳贮量(0.85 kg/m2)分别为相同利用年限旱地土壤的1.60倍和5.00倍；利用年限15~20年的黄筋泥茶园土壤有机碳贮量(3.68 kg/m2)和轻组分有机碳贮量(0.46 kg/m2)分别为相同利用年限旱地土壤的1.10倍和2.42倍；利用年限>30年的黄红泥土茶园土壤有机碳贮量(7.96 kg/m2)和轻组分有机碳贮量(1.34 kg/m2)分别为相同利用年限旱地土壤的1.73倍和2.48倍。由此可见，茶园土壤比旱地土壤具有更高的固碳潜力。

图1(Figure 1) 各剖面号表示的含义详见表 1. Please see Table 1 for details of each profile number. 图1 茶园与旱地土壤有机碳和轻组分有机碳剖面分布的比较 Fig. 1 Comparison of organic C and light-fraction organic C distribution in soil profiles between tea garden and upland 3 讨论

土壤固碳潜力主要由生物潜力、物理化学潜力和社会经济潜力等构成[5, 25, 26, 27]，不同土壤之间的固碳潜力有很大的差异。生物潜力与进入土壤的不同有机碳源的数量有关，并与气候条件有关，它是土壤固碳的主要动力；物理化学潜力与土壤中有机碳的稳定机制有关，主要与粉砂黏粒结合的化学稳定性、与微团聚体结合的物理稳定性和与有机质本身性质成分有关的生物学稳定性等有关；社会经济潜力与土壤管理措施有关。在本研究中相同土壤类型的茶园与旱地，由于分布区域相同、土壤质地等性状基本一致，它们对土壤中有机碳的保护能力较为接近。因此，茶园与旱地土壤之间有机碳固定能力的差异可能与外源有机物质投入量差异及土壤管理措施对土壤中有机碳分解的影响不同有关。在研究区的旱地农业系统中，由于不推行秸秆还田和缺乏有机肥的施用，每年进入土壤的有机物质非常有限，这在很大程度上影响了土壤中有机碳的积累；同时，旱地土壤耕作频繁，加剧了土壤有机碳的分解速率[28, 29]，从而导致土壤有机碳的积累普遍偏低。而在茶园中，由于每年有一定数量的枯叶或修剪物进入土壤[30]，大大促进了茶园土壤中有机碳的积累；另外，茶树是多年生植物，不用耕作，对土壤扰动较弱，有利于土壤有机碳的保护。另外，茶园由于植被覆盖度较高，在降雨季节有较多的降水进入土壤，这在一定程度上增加了土壤的湿度，也可在一定程度上降低土壤有机碳的分解速率[31, 32]。

本研究还表明，在植茶过程中有机碳主要以活性较高的轻组分有机碳和颗粒态有机碳的形式积累，而且增加的有机碳主要积累在近地表的土层中，这种积累方式显然与进入茶园的有机碳主要来自地表，即通过枯枝落叶的方式进入茶园土壤有关。积累在茶园土壤中的有机碳主要为活性较高的轻组分有机碳，表明植茶有利于土壤有机碳更新，同时也表明积累在茶园土壤中的有机碳稳定性相对较低，容易发生降解。在茶园土壤中有机碳主要分布于>2 mm和0.25~2 mm的水稳定性团聚体的结果也表明，这些积累在茶园土壤中的有机碳容易随环境变化发生改变，特别是当茶园土壤受人为扰动时其有机碳可能会明显的下降。

4 结论

对从浙西北茶区采集的黄筋泥、黄红泥土和黄泥土等3个土壤类型上植茶年限分别为5~10、15~20和>30年的9个代表性茶园土壤剖面的有机碳、轻组分有机碳、颗粒态有机碳、微生物生物量碳和水溶性有机碳分析表明：茶园土壤的有机碳随土壤深度的增加而下降，表层土壤的有机碳含量及全剖面有机碳贮量随植茶年龄的增加呈明显的增加；轻组分有机碳含量和颗粒态有机碳含量占土壤有机碳总量的比例在土壤剖面中的分布变化比有机碳总量的变化更为明显；在植茶过程中有机碳主要以活性较高的轻组分有机碳和颗粒态有机碳的形式积累，主要分布在近地表的土层；轻组分有机碳和颗粒态有机碳随植茶时间的增加幅度明显大于有机碳总量的增加；茶园土壤有机碳的积累量显著高于旱地土壤。

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