植物营养与肥料学报   2018, Vol. 24  Issue (6): 1508-1519 
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不同土地利用方式对土壤有机无机碳比例的影响
李雄1, 张旭博2 , 孙楠3 , 张崇玉1, 徐明岗3, 冯龙4    
1. 贵州大学农学院,贵阳 550025;
2. 中国科学院地理科学与资源研究所/生态网络观测与模拟重点实验室,北京 100101;
3. 中国农业科学院农业资源与农业区划研究所/耕地培育技术国家工程实验室,北京 100081;
4. 贵州工程职业学院,德江 565200
摘要: 【目的】 土壤有机碳 (SOC) 和无机碳 (SIC) 对全球碳循环和减缓气候变化具有重要作用,进一步明确二者之间相互转化关系,对准确估算土壤碳储量具有重要意义。现有研究对SOC和SIC相互关系缺乏系统量化,研究结果不一。因此,明确SOC和SIC之间相互关系,可为准确估算和模拟土壤碳的转化过程提供理论基础。【方法】 本研究搜集了我国1990—2018年已发表的文献共41篇,从不同气候区、不同土地利用方式、不同土层深度探究了SOC和SIC比例的变化,进一步量化了二者之间的相互关系。【结果】 不同气候区、不同土地利用方式下土壤SOC/SIC值在0—20 cm土层均大于20—100 cm土层。具体来说,在温带大陆性气候区,草地0—20 cm土壤SOC/SIC值最小 (0.53),林地 (0.90) 和农田 (0.80) 土壤较高,且三种土地利用方式下SOC和SIC呈极显著正相关关系;而在温带季风性气候区,0—20 cm土壤SOC/SIC值表现为草地 (0.82) ≈ 农田 (1.05) > 林地 (0.29),且SOC和SIC在林地、农田土壤中呈正相关关系,但在草地土壤中二者为负相关关系。另外,温带大陆性气候区20—100 cm以林地土壤SOC/SIC值最高,草地和农田次之,而在温带季风性气候区三种土地利用方式下无显著差异;SOC和SIC在林地和农田土壤中呈正相关关系,然而在草地土壤中为负相关关系。温带大陆性气候区SOC/SIC值总体以林地较大,农田、草地次之。温带季风性气候区,0—20 cm土层SOC/SIC值以草地较大,农田和林地分别次之。这可能是因为植被覆盖不同,导致了作物碳的归还量不一。同时,不同的植被覆盖还影响了土壤中的各种生物化学进程,改变了碳在土壤中的循环转化过程,进而影响了SOC和SIC含量,使得SOC/SIC值产生较大差异。【结论】 SOC和SIC之间存在循环转化关系,且不同气候条件、不同土地利用方式、不同土壤类型对SOC和SIC循环转化存在显著影响。不同条件下SOC/SIC值存在显著差异,且二者呈现不同的相关性。本研究结果可为明确土壤碳的循环积累机制,准确估算土壤有机和无机碳库提供理论依据。
关键词: 土壤有机碳     土壤无机碳     气候类型     土地利用方式     SOC/SIC    
Impact of land uses on the ratio of soil organic and inorganic carbon
LI Xiong1, ZHANG Xu-bo2 , SUN Nan3 , ZHANG Chong-yu1, XU Ming-gang3, FENG Long4    
1. College of Agriculture, Guizhou University, Guiyang 550025, China;
2. Institute of Geographic Sciences and Natural Resources Research/Key Lab of Ecosystem Network Observation and Modeling, Chinese Academy of Sciences, Beijing 100101, China;
3. Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences/National Engineering Laboratory for Improving Quality of Arable Land, Beijing 100081, China;
4. Guizhou Engineering Vocational College, Dejiang 565200, China
Abstract: 【Objectives】 Soil organic carbon (SOC) and inorganic carbon (SIC) play an important role in the global carbon cycle and the mitigation of climate change. Better understanding of transformations between them has important implications for reliable estimation of soil carbon stocks. However, there are few studies on it, and the research results are discrepant. 【Methods】 This study collected 41 literatures published from 1990 to 2018 in China, on the effect of different climatic zones, different land uses and different soil layers on the relationship of soil organic and inorganic carbon. 【Results】 SOC/SIC values were higher in 0−20 cm soil layer than those in 20−100 cm soil layer in all climatic zones and land uses. Specifically, in the temperate continental climate zone the SOC/SIC value in the 0−20 cm soil layer was the lower (0.53) in the grassland, and higher in forestland (0.90) and the cropland (0.80). There was a significant positive correlation between SOC and SIC under all three types of land uses. However, the SOC/SIC value of the 0−20 cm layer in the temperate monsoon climate zone was in the order of grassland (0.82) ≈ cropland (1.05) > forest (0.29). SOC and SIC had a positive correlation in forest and cropland, but a negative correlation in grassland. In addition, the SOC/SIC value of the 20−100 cm soil layer was the highest in the forest, followed by grassland and cropland in the temperate continental climate zone. In contrast, there was no significant difference in the SOC/SIC value among the three land uses in the temperate monsoon climate zone. The relationship between SOC and SIC was positive in forest and cropland, but negative in grassland. The climate type and land use affected not only the content of SOC and SIC, but their relationship. In the temperate continental climate zone, the SOC/SIC value of the forest was higher than cropland and grassland. In the temperate monsoon climate zone, however, the SOC/SIC value was higher in grassland than those in forest and cropland. This may be due to 1) the different vegetation coverage, resulting in different amounts of crop carbon, and 2) the different vegetation cover also affects the various biochemical processes in the soil, leading to different transformation process of carbon, the content of SOC and SIC. 【Conclusions】 There is a cyclic transformation between SOC and SIC, and climatic condition, land use and soil type have significant effects on SOC and SIC cycling and conversion. SOC and SIC show different correlations under different conditions. The results of this study can provide a theoretical basis for estimating soil organic and inorganic carbon pools accurately.
Key words: soil organic carbon     soil inorganic carbon     climatic regions     land use     SOC/SIC    

土壤碳库是陆地生态系统中最大且周转周期最慢的碳库,主要由土壤有机碳 (Soil organic carbon,SOC) 和无机碳 (soil inorganic carbon,SIC) 两部分组成,是继海洋碳库和地质碳库之后的第三大碳库[1]。全球0—100 cm土壤剖面SOC的储量约为1220~1576 Pg,SIC的储量约为700~1700 Pg[2]。SOC和SIC的巨大库容决定了二者在碳循环和减缓气候变化方面具有重大作用[3]

有学者对我国SOC和SIC储量的研究发现,0—100 cm土壤剖面SOC储量为83.8 Pg,SIC储量为77.9 Pg,且该研究结果表明我国的SOC储量高于美国的SOC储量 (65.5 Pg)[4]。Wu等[5]对我国SIC储量的估计值为55.3 Pg,且该研究发现SIC主要分布在我国的华北、西北地区,土地利用方式对SIC的储量影响显著。Wang等[6]在新疆地区的研究发现,农田土壤中SOC和SIC的含量高于撂荒地。也有学者通过在甘肃河西走廊、宁夏云雾山等地区的研究发现,农田土壤中SIC的含量高于草地[78]。这些研究结果均表明,在干旱半干旱地区将土地转化为农田有利于SIC的积累。

陆地生态系统中存在着“SOC—CO2—SIC”的微碳循环系统,SOC以CO2为媒介转化为SIC[9],当前对SOC和SIC相互关系的研究极其缺乏,且研究结果不一。潘根兴等[10]研究发现,在干旱地区,由石灰性母质发育的均腐土、淋溶土、干旱土和雏形土的SOC和SIC呈现负相关关系。然而,在我国新疆焉耆盆地,SOC和SIC呈现显著的正相关关系[11]。同时有学者在加拿大以及美国部分地区的研究结果也表明SOC和SIC为显著的正相关关系[1213]。因此,急需系统量化不同条件下SOC和SIC之间的相互关系,进一步明确碳在土壤中的转化过程。

本研究旨在总结现有关于SOC和SIC研究的结果,通过数据的收集、整理、分析,量化SOC和SIC之间的相互转化关系,以期为更好地理解碳循环、更准确地模拟碳在土壤中的转化过程、更精准地估计碳储量奠定理论基础。

1 材料与方法 1.1 文献搜集

为了系统地揭示SOC和SIC的相互关系,本研究从Web of Science、中国知网和百度学术等文献库对1990—2018年期间发表的文献进行检索。选取土壤碳库 (soil carbon pool,soil carbon stock),土壤有机碳 (soil organic carbon) 和土壤无机碳 (soil inorganic carbon) 等关键词进行文献搜集。筛选文献采用以下标准:1) 文献中数据至少含有均值、标准差SD (或标准误差SE) 和重复数 3个要素,其中重复数至少为3次;2) 文献中必须包含SOC和SIC含量或其中一个数据以及总碳 (soil total carbon, STC) 含量 (STC = SOC + SIC);3) 文献中包含明确的土地利用方式 (草地、林地、农田等)。同时,还获取了每个独立试验站点的基本信息,包括气候类型、地理位置 (经度、纬度和海拔)、土壤类型、年降雨量、年蒸发量和年均温等。

1.2 数据分析

本研究选用GetData Graph Digitizer 2.24软件进行数据提取,Excel2007统计整理数据,SPSS进行数据分析及Origin9.2进行作图,采用LSD法进行多重比较分析 (显著性水平P = 0.05)。

为了进一步探讨不同气候区、不同土地利用方式及不同土壤类型SOC和SIC的比例 (相互关系),对搜集整理后的数据按照气候区、土地利用方式、土壤类型进行分类。按照各试验站点的降雨量大小,将气候区划分为温带大陆性气候区和温带季风性气候区,青海、新疆、内蒙、陕西、甘肃气候区属于温带大陆性气候区,吉林、山东、河北、宁夏为温带季风性气候区;土地利用方式包括草地、林地和农田;土壤类型包括棕壤、荒漠土和黑垆土。按照数据在土壤剖面的分布,将所得数据分为0—20 cm和20—100 cm两个土壤剖面层次。提取文献基本信息如表1所示。

表1 文献信息 Table 1 Information of literature
2 结果与分析 2.1 不同气候区SOC和SIC含量变化

温带大陆性气候区,0—20 cm土层草地、林地和农田三种土地利用方式下,SOC含量无显著差异 (P > 0.05),20—100 cm土层SOC含量草地 > 农田 > 林地,且差异显著 ( P < 0.05);0—20 cm、20—100 cm土层SIC含量草地 > 农田 > 林地,且差异显著 ( P < 0.05)。温带季风性气候区0—20 cm土层土壤中SOC含量农田显著高于其他两种土地利用方式 ( P < 0.05),林地土壤中SOC含量最低;20—100 cm土层SOC含量无显著差异,草地和林地土壤中SIC含量无显著差异,但都显著高于农田土壤的SIC含量 ( P < 0.05, 表2)。

表2 不同气候区SOC和SIC含量 Table 2 SOC and SIC contents in different climate zones
2.2 不同气候区SOC和SIC比例分布

温带大陆性气候区,0—20 cm、20—100 cm土层SOC/SIC均值 (标准差) 分别为0.70 (0.34)、0.50 (0.24)(图1a图1c)。温带季风性气候区0—20 cm、20—100 cm土层SOC/SIC值分别为1.06 ± 0.05、0.31 ± 0.08 (图1b图1d)。且两个气候区SOC/SIC符合正态分布 (P < 0.05)。

图1 温带大陆性气候区、温带季风性气候区0—20 cm、20—100 cm SOC/SIC频率分布 Fig. 1 Distribution frequency of SOC/SIC in the 0−20 and 20−100 cm soil layers of the temperate continental climate zone and the temperate monsoon climate zone [注(Note):M、SD、SE分别代表平均值、标准差、标准误;曲线代表数据的高斯分布;P为SOC/SIC正态分布显著性检验。M, SD and SE represent mean value, standard deviation and standard error, respectively. The curve represents the Gauss distribution of the data. P is the significant test for the SOC/SIC.]
2.3 不同土地利用方式下SOC和SIC比例特征

温带大陆性气候区0—20 cm土层,草地、林地和农田土壤中SOC/SIC值变化范围 (均值) 分别为0.10~1.54 (0.53)、0.15~1.95 (0.90)、0.32~1.46 (0.80),林地和农田土壤中SOC/SIC值无明显差异,但都显著高于草地 (P < 0.05)。20—100 cm土层,SOC/SIC值变化范围 (均值)0.10~0.86 (0.38)、0.12~1.07 (0.68)、0.13~1.04 (0.49),林地土壤中SOC/SIC值显著高于草地 ( P < 0.05),农田和其他两种土地利用方式无显著差异 ( P > 0.05)。相同土地利用方式下,林地、农田土壤0—20 cm土层中SOC/SIC值显著高于20—100 cm土层 ( P < 0.05,图2a)。

图2 不同气候区三种土地利用方式下0—20 cm、20—100 cm土层SOC/SIC值 Fig. 2 SOC/SIC value in the 0−20 cm and 20−100 cm soil layers of grassland, forest and cropland in different climate zones [注(Note):n—数据量;柱上不同小写字母表示不同分组间差异显著 (P < 0.05);箱体中黑线为中位数,正方形代表平均数,上下圆圈分别代表 95% 和 5% 置信区间。n—The number of data; Different lowercases above the box indicate significantly different among different classification conditions (P < 0.05); Black line in the box represents the median value,the square represents the average value,the upper and lower circles represent 95% and 5% confidence intervals,respectively.]

温带季风性气候区0—20 cm土层,草地、林地和农田三种土地利用方式下SOC/SIC值变化范围 (均值) 分别为0.18~2.23 (0.82)、0.22~0.36 (0.29)、0.55~1.4 (1.05),农田土壤中SOC/SIC值显著高于其他两种土地利用方式,且草地显著高于林地 (P < 0.05)。20—100 cm土层SOC/SIC值变化范围 (均值) 分别为0.14~0.46 (0.27)、0.13~0.44 (0.18)、0.17~0.59 (0.31),三种土地利用方式下SOC/SIC值无显著差异 ( P > 0.05)。同一土地利用方式下,草地和农田土壤0—20 cm土层显著高于 20—100 cm土层 ( P < 0.05,图2b)。

2.4 不同土地利用方式下SOC和SIC的相互关系

温带大陆性气候区,草地、林地和农田三种土地利用方式下总的SOC和SIC在0—20 cm、20—100 cm两个土层呈极显著正相关关系 (图3a)。温带季风性气候区,0—20 cm土层二者呈显著负相关关系,20—100 cm土层则呈显著正相关关系 (图3b)。

温带大陆性气候区,草地、林地和农田0—20 cm土层中SOC和SIC均呈现极显著正相关关系 (图3c);林地和农田20—100 cm土层中,SOC和SIC呈极显著正相关关系。然而,草地土壤20—100 cm土层二者则呈现显著负相关关系 (图3e)。温带季风性气候区,林地和农田0—20 cm、20—100 cm土层中SOC和SIC均为显著的正相关关系,而在草地中则为显著的负相关关系 (图3d图3f)。

2.5 土壤类型对SOC和SIC比例特征的影响

农田土地利用方式下,0—20 cm土层,棕壤土、荒漠土和黑垆土三种土壤类型中SOC/SIC值变化范围 (均值) 分别为0.84~1.27 (1.10)、0.33~1.96 (1.00)、0.17~0.72 (0.45),棕壤土和荒漠土SOC/SIC无显著差异 (P > 0.05),但均显著高于黑垆土 ( P < 0.05)。20—100 cm土层,三种土壤类型二者比例 (均值) 分别为0.18~0.53 (0.35)、0.19~1.15 (0.58),0.13~0.59 (0.28),荒漠土显著高于其他两种土壤 ( P < 0.05),其他两种土壤类型间无显著差异 ( P > 0.05)。同一土壤类型,0—20 cm土层SOC/SIC值均显著高于20—100 cm土层 ( P < 0.05,图4)。

图4 棕壤土、荒漠土、黑垆土农田0—20 cm、20—100 cm土层SOC/SIC值 Fig. 4 SOC/SIC value in 0−20 cm and 20−100 cm of brown loamy soil, desert soil and dark loessial soil in cropland [注(Note):n—数据量;柱上不同小写字母表示不同分组间差异显著 (P < 0.05);箱体中黑线为中位数,正方形代表平均数,上下圆圈分别代表 95% 和 5% 置信区间 n—The number of data; Different lowercases above the box indicate significantly different among different classification conditions (P < 0.05); Black line in the box represents the median value,the square represents the average value,the upper and lower circles represent 95% and 5% confidence intervals,respectively.]

三种土壤类型中SOC和SIC在0—20 cm、20—100 cm土层均呈现正相关关系,且棕壤土和荒漠土中二者极显著正相关 (P < 0.01,图5)。

图5 棕壤土、荒漠土、黑垆土农田0—20 cm、20—100 cm SOC和SIC的相互关系 Fig. 5 Relationship between SOC and SIC in the 0−20 cm and 20−100 cm of brown loamy soil, desert soil and dark loessial soil in cropland [注(Note):阴影部分表示 95% 置信区间 The shaded region is the 95% confidence interval.]
3 讨论 3.1 不同气候区SOC和SIC含量变化

温带大陆性气候区,0—20 cm土层草地、林地、农田土壤中SOC含量无显著差异。其原因可能是本研究搜集的数据中,草地和林地部分的数据为人工管理措施下的植被恢复,植被地上、地下生物量较丰富,作物碳回归量大,SOC含量无显著差异[4748]。SIC含量为草地 > 农田 > 林地,草地土壤中植物根系较浅,根系分泌物对SIC的影响较小,而林地土壤中植物根系发达,根呼吸、根系分泌物会形成酸性环境,易造成SIC的溶解 [49]。因此,在林地土壤中SIC含量最低 (表2)。

温带季风性气候区,0—20 cm土层农田土壤中SOC含量最高,其原因可能是施肥、灌溉等农田管理措施促进了作物的生长,作物碳归还量较高,且秸秆还田、有机无机配施等管理措施进一步提高了SOC的含量[5051]。草地、林地土壤中SIC含量显著高于农田土壤中SIC含量。该气候区降雨量丰富,土壤水分含量较高,不利于SIC的形成,农田土壤中集中式的灌溉措施会引起SIC的溶解,易淋失至更深层土壤[5253],导致SIC含量低于其他两种土地利用方式 (表2)。

3.2 不同土地利用方式对SOC/SIC的影响

温带大陆性气候区,SOC/SIC为林地 > 农田 > 草地。一方面,林地土壤中植物根系发达,分泌物较多,土壤腐殖层较厚,腐殖质含量高,且微生物活动旺盛,促进了有机质的分解,提高了SOC的累积 [5457]。农田土壤中施肥和灌溉等农田管理措施促进了作物的生长,作物根系发达,有益于SOC的累积,但对土壤的翻耕等会加速SOC的矿化,且作物成熟后被收割,减少了碳素向土壤的输入,一定程度上降低了SOC的含量[5859]。该气候区草地多为荒漠草原,地上生物量相对少,投入土壤中的碳素较少,所以草地SOC相对最低[6061]。另一方面,SOC分解会释放更多的CO2,与土壤水作用后形成酸性环境,而且根系分泌物产生有机酸,导致土壤pH降低,促进了SIC的溶解[60, 62],因此,根系相对发达的林地土壤中SIC含量较低,SOC/SIC值较大 (图2a)。

相同土地利用方式,草地土壤不同土层中SOC/SIC无显著差异,因为该气候区草地土壤中SOC含量较低,导致在两个土层其比例较低。林地和农田土壤中0—20 cm土层SOC和SIC比例显著高于20—100 cm (图2a)。这与SOC、SIC含量随土壤深度的变化有关:SOC含量随土壤深度的增加而降低,SIC含量则随土壤深度的增加而增加[6, 63],因此,SOC/SIC值随之降低。

温带季风性气候区0—20 cm土层中,SOC/SIC表现为草地 > 农田 > 林地 ( 图2b)。该气候区草地土壤中常伴生灌木,植物种类复杂多样,回归土壤枯枝落叶量大,微生物活动频繁,促进了SOC的累积[6465];农田管理措施促进了作物的生长,作物根系发达,分泌物增多,但作物成熟后地上部分被移除,降低了SOC含量[58]。本研究搜集的文献中林地大多为乔木林,群落结构较简单,且植物自身消耗也多,土壤碳归还较少,导致SOC含量低,SOC/SIC值较低。

3.3 SOC和SIC相互关系及其影响因素

SIC主要为碳酸盐类,包括岩生性碳酸盐、发生性碳酸盐。岩生性碳酸盐主要由母岩发育形成,在较短时期内不会发生改变。发生性碳酸盐在风化成土过程中形成,以碳酸钙为例,其形成过程包括以下两个化学过程[41, 54, 66]

${\rm{C}}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{O}} \leftrightarrow {\rm{HCO}}_3^ - + {{\rm{H}}^ + }$ (1)
${\rm{C}}{{\rm{a}}^{2 + }} + 2{\rm{HCO}}_3^ - \leftrightarrow {\rm{CaC}}{{\rm{O}}_3} + {\rm{C}}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{O}}$ (2)

通常情况下,SOC含量增加能提高土壤中CO2的浓度,此时,反应 (1) 向右移动,HCO3和H+含量提高,在土壤中形成酸性环境,易造成碳酸钙的溶解,即SIC的含量下降,SOC、SIC呈现负相关关系[6768]。当土壤中钙镁离子含量较高时,高的HCO3则使反应 (2) 向右移动,利于碳酸钙的形成,即SIC含量增加,二者呈现正相关关系[11, 69]

本研究结果表明在温带大陆性气候区,林地和农田0—20 cm、20—100 cm土层SOC和SIC皆为正相关关系,和前人研究结果一致[2, 70]。该气候区土壤类型大多为碱性土,土壤pH > 7.5,具备一定的酸碱缓冲能力,而额外的钙镁离子则促进了碳酸盐类物质的形成,SOC含量越高,分解产生的CO 2越多,更有利于碳酸盐的形成。因此,SOC、SIC呈现正相关关系 (图3a图3c图3e)。然而,草地0—20 cm土层中二者呈正相关关系,20—200 cm土层呈负相关关系 (图3c图3e),0—20 cm土层,植物枯枝落叶较多,SOC含量较高,分解产生CO2,有利于SIC的形成,20—100 cm土层SIC含量明显增加,而SOC含量由于受到作物碳归还的限制,其含量急剧减少[54, 66],二者呈负相关关系。

温带季风性气候区0—20 cm、20—100 cm土层草地中SOC和SIC呈现负相关关系,与Li等[60]和Zhao等[71]研究结果一致。该气候区气候湿润,植被覆盖较好,植被根系和凋落物丰富,产生了大量的有机酸,降低了土壤pH[63, 71],且SOC分解产生CO2,土壤中CO2分压增强,促使反应 (1) 向右移动,产生更多的H+,易造成碳酸盐的溶解。因此,SOC和SIC呈显著的负相关关系。农田土壤中施肥、灌溉等农田管理措施促进了作物生长,提高了生物量的投入,增加了作物碳的归还,SOC含量提高[7273],同时施肥、灌溉等农田管理措施向土壤提供额外的钙镁离子,促使反应 (2) 向右移动,促进SIC的形成[7475],田土壤中二者为正相关关系。林地土壤中二者相互关系与Zhao等[71]的研究结果不一致,其机制需要进一步探究明确 (图3b图3d图3f)。

图3 不同气候区、土地利用方式及土层SOC和SIC相互关系 Fig. 3 Relationship between SOC and SIC affected by climatic regions, land use and soil layers [注(Note):阴影部分表示 95% 置信区间 The shaded region is the 95% confidence interval.]
3.4 不同土壤类型对SOC/SIC的影响

农田土地利用方式下,20—100 cm土层荒漠土SOC/SIC高于棕壤土和黑垆土 (P < 0.05,图4)。荒漠土未开垦为农田时,植物类型大多为荒漠草原,有机质和养分含量极低,且植物残渣年归还量低,SOC含量低。开垦为农田后,灌溉和施肥等增加了有机胶结物质的输入,持续的农业利用提高了作物地上、地下部生物量,增加了土壤碳的输入,SOC含量提高[72]。因此,荒漠土开垦为农田提高了SOC含量,SOC和SIC比例随之提高。同时农田管理措施还提供了额外的钙镁离子[74],所以在提高SOC含量的同时,存在SOC向SIC的转化,三种土壤类型中SOC和SIC均呈现正相关关系 (图5)。

4 结论

不同土地利用方式、不同土壤剖面深度对SOC和SIC比例影响显著,SOC和SIC在温带大陆性气候区0—20 cm土层为显著的正相关关系,20—100土层林地和农田中SOC、SIC呈正相关关系,但草地呈负相关关系。温带季风性气候区0—20 cm、20—100 cm土层林地和农田中SOC、SIC呈正相关关系,但在草地中呈负相关关系。这表明碳在土壤中存在着显著的转化循环,SOC可能最终转化为SIC储存,也可能溶解SIC,导致土壤碳的流失,这种相关性与土地利用方式密切相关。就目前的研究现状来看,我国对土壤碳库的大部分研究只关注SOC,忽略了对SIC的研究,对土壤碳储量估计值偏低,未来的研究应该侧重于不同气候条件、不同土地利用类型、不同土壤类型及农田管理措施下SOC和SIC的相互关系,明确土壤碳的循环积累机制,精确地估算土壤碳储量。

参考文献
[1] Lal R, Kimble J M, Stewart B A, et al. Global climate change and pedogenic carbonate[J]. Geoderma, 1999, 104(1): 135–141.
[2] Shi H J, Wang X J, Zhao Y J, et al. Relationship between soil inorganic carbon and organic carbon in the wheat-maize cropland of the North China Plain[J]. Plant & Soil, 2017, 418(1-2): 1–14.
[3] Lal R. Soil carbon sequestration impacts on global climate change and food security[J]. Science, 2004, 304(5677): 1623–1627. DOI:10.1126/science.1097396
[4] Li Z P, Han F X, Su Y, et al. Assessment of soil organic and carbonate carbon storage in China[J]. Geoderma, 2007, 138(1): 119–126.
[5] Wu H B, Guo Z T, Gao Q O, et al. Distribution of soil inorganic carbon storage and its changes due to agricultural land use activity in China[J]. Agriculture Ecosystems & Environment, 2009, 129(4): 413–421.
[6] Wang J P, Wang X J, Zhang J, et al. Soil organic and inorganic carbon and stable carbon isotopes in the Yanqi Basin of Northwestern China[J]. European Journal of Soil Science, 2015, 66(1): 95–103. DOI:10.1111/ejss.2015.66.issue-1
[7] Su Y Z, Wang X F, Yang R, et al. Effects of sandy desertified land rehabilitation on soil carbon sequestration and aggregation in an arid region in China[J]. Journal of Environmental Management, 2010, 91(11): 2109. DOI:10.1016/j.jenvman.2009.12.014
[8] Liu W, Wei J, Cheng J, et al. Profile distribution of soil inorganic carbon along a chronosequence of grassland restoration on a 22-year scale in the Chinese Loess Plateau[J]. Catena, 2014, 121(7): 321–329.
[9] 张林, 孙向阳, 曹吉鑫, 等. 西北干旱区森林和草原SOC向SIC转移的研究进展[J]. 西北林学院学报, 2010, 25(2): 40–44.
Zhang L, Sun X Y, Cao J X, et al. Research progress on the transfer of SOC to SIC in forest and grassland in arid area of northwestern China[J]. Journal of Northwest Forestry University, 2010, 25(2): 40–44.
[10] 潘根兴. 中国干旱性地区土壤发生性碳酸盐及其在陆地系统碳转移上的意义[J]. 南京农业大学学报, 1999, 22(1): 51–57.
Pan G X. Significance of soil occurring carbonates in the arid region of China and their role in carbon transfer of terrestrial system[J]. Journal of Nanjing Agricultural University, 1999, 22(1): 51–57.
[11] Wang X, Wang J, Xu M, et al. Carbon accumulation in arid croplands of northwest China: pedogenic carbonate exceeding organic carbon[J]. Scientific Reports, 2015, 5: 11439. DOI:10.1038/srep11439
[12] Landi A, Mermut A R, Anderson D W. Origin and rate of pedogenic carbonate accumulation in Saskatchewan soils, Canada[J]. Geoderma, 2003, 117(1-2): 143–156. DOI:10.1016/S0016-7061(03)00161-7
[13] Stevenson B A, Kelly E F, Mcdonald E V, et al. The stable carbon isotope composition of soil organic carbon and pedogenic carbonates along a bioclimatic gradient in the Palouse region, Washington State, USA[J]. Geoderma, 2005, 124(1): 37–47.
[14] Wang Z P, Han X G, Chang S X, et al. Soil organic and inorganic carbon contents under various land uses across a transect of continental steppes in Inner Mongolia[J]. Catena, 2013, 109(10): 110–117.
[15] 张煜, 张琳, 吴文良, 等. 内蒙农牧交错带地区土地利用方式和施肥对土壤碳库的影响[J]. 土壤学报, 2016, 53(4): 930–941.
Zhang Y, Zhang L, Wu W L, et al. Impact of land use and fertilization measures on soil C stock in farming-grazing interlacing zone of inner mongolia, China[J]. Acta Pedologica Sinica, 2016, 53(4): 930–941.
[16] 杨黎芳, 李贵桐, 赵小蓉. 栗钙土不同土地利用方式下有机碳和无机碳剖面分布特征[J]. 生态环境, 2007, 16(1): 158–162.
Yang L F, L G T, Zhao X R. Profile distribution of soil organic and inorganic carbon in chestnut soils of Inner Mongolia[J]. Ecology and Environment, 2007, 16(1): 158–162. DOI:10.3969/j.issn.1674-5906.2007.01.029
[17] 耿元波, 罗光强, 袁国富, 等. 农垦及放牧对温带半干旱草原土壤碳素的影响[J]. 农业环境科学学报, 2008, 27(6): 2518–2523.
Geng Y B, Luo G Q, Yuan G F, et al. Effects of cultivating and grazing on soil organic carbon and soil inorganic carbon in temperate semiarid grassland[J]. Journal of Argo-Environment Science, 2008, 27(6): 2518–2523. DOI:10.3321/j.issn:1672-2043.2008.06.072
[18] 陈永乐, 张志山, 赵洋. 人工固沙区土壤碳分布及其与土壤属性的关系[J]. 中国沙漠, 2017, 37(2): 296–304.
Chen Y L, Zhang Z S, Zhao Y. Distribution of soil carbon in sand-binding area and its relation with soil properties[J]. Journal of Desert Research, 2017, 37(2): 296–304.
[19] Zhang Y, Hao H M, Wang D, et al. Revegetation of artificial grassland improve soil organic and inorganic carbon and water of abandoned mine[J]. Journal of Soil Science & Plant Nutrition, 2015, 15(3): 629–638.
[20] Tang J, Liang S, Li Z, et al. Effect of freeze-thaw cycles on carbon stocks of saline-alkali paddy soil[J]. Archives of Agronomy & Soil Science, 2016, 62(12): 1640–1653.
[21] 牛子儒, 王玉刚, 邓彩云, 等. 耕作对干旱区表层土壤无机碳的影响[J]. 生态学杂志, 2016, 35(10): 2714–2721.
Niu Z R, Wang Y G, Deng C Y, et al. Effects of tillage on inorganic carbon in upper soil profiles in arid zone[J]. Chinese Journal of Ecology, 2016, 35(10): 2714–2721.
[22] 颜安, 王泽, 李周晶. 绿洲盐渍土不同开垦期土壤有机碳和无机碳剖面分布特征[J]. 新疆农业大学学报, 2016, 39(3): 246–252.
Yan A, Wang Z, Li Z J. Profile distribution of soil organic carbon and inorganic carbon in oasissaline during different reclaimed period[J]. Journal of Xinjiang Agricultural University, 2016, 39(3): 246–252. DOI:10.3969/j.issn.1007-8614.2016.03.013
[23] 雒琼, 王玉刚, 邓彩云, 等. 不同农业土地利用年限干旱区土壤剖面碳存储动态变化[J]. 农业工程学报, 2017, 33(19): 287–294.
Luo Q, W Y G, D C Y, et al. Dynamics of soil carbon storage under different land use years in arid agriculture[J]. Transactions of the Chinese Society of Agricultural Engineering, 2017, 33(19): 287–294. DOI:10.11975/j.issn.1002-6819.2017.19.037
[24] 赵晶晶, 贡璐, 安申群, 等. 塔里木盆地北缘绿洲不同连作年限棉田土壤有机碳、无机碳含量与环境因子的相关性[J]. 环境科学, 2018, 39(7): 3373–3381.
Zhao J J, Gong L, An S Q, et al. Correlation between soil organic and inorganic carbon and environmental factors in cotton fields in different continuous cropping years in the oasis of the Northern Tarim Basin[J]. Environmental Science, 2018, 39(7): 3373–3381.
[25] Li Z G, Tian C Y, Zhang R H, et al. Plastic mulching with drip irrigation increases soil carbon stocks of natrargid soils in arid areas of northwestern China[J]. Catena, 2015, 133: 179–185. DOI:10.1016/j.catena.2015.05.012
[26] 党珍珍, 王凯博, 周正朝, 等. 黄土丘陵区人工刺槐林恢复对土壤碳库动态的影响[J]. 干旱区研究, 2015, 32(6): 1082–1087.
Dang Z Z, Wang K B, Zhou Z C, et al. Effects of artificial acacia forest restoration on soil carbon pool dynamics in Loess hilly region[J]. Arid Zone Research, 2015, 32(6): 1082–1087.
[27] 李旭东. 黄土高原草地与农田系统土壤呼吸及碳平衡[D]. 甘肃兰州: 兰州大学博士学位论文, 2011.
Li X D. Soil respiration and carbon balance in grassland and cropland system on the loess plateau[D]. Lanzhou, Gansu: PhD Dissertation of Lanzhou university, 2011.
[28] Li D, Gao G, Lü Y, et al. Multi-scale variability of soil carbon and nitrogen in the middle reaches of the Heihe River basin, northwestern China[J]. Catena, 2016, 137: 328–339. DOI:10.1016/j.catena.2015.10.013
[29] Zhao J, Dong Y, Wang Y, et al. Natural vegetation restoration is more beneficial to soil surface organic and inorganic carbon sequestration than tree plantation on the Loess Plateau of China[J]. Science of the Total Environment, 2014, 485-486: 615–623. DOI:10.1016/j.scitotenv.2014.03.105
[30] Niu R, Liu J, Zhao X, et al. Ecological benefit of different revegetated covers in the middle of Hexi corridor, northwestern China[J]. Environmental Earth Sciences, 2015, 74(7): 1–12.
[31] 姚小萌, 牛桠枫, 党珍珍, 等. 黄土高原自然植被恢复对土壤质量的影响[J]. 地球环境学报, 2015, 6(4): 238–247.
Yao X M, Niu Y F, Dang Z Z, et al. Effects of natural vegetation restoration on soil quality on the Loess Plateau[J]. Journal of Earth Environment, 2015, 6(4): 238–247.
[32] Liu Y, Dang Z Q, Tian F P, et al. Soil organic carbon and inorganic carbon accumulation along a 30-year grassland restoration Chronosequence in semi-arid regions (China)[J]. Land Degradation & Development, 2017, 28(1): 189–198.
[33] 王莲莲, 张树兰, 杨学云. 长期不同施肥和土地利用方式对 娄土耕层碳储量的影响[J]. 植物营养与肥料学报, 2013, 19(2): 404–412.
Wang L L, Zhang S L, Yang X Y. Soil carbon storage affected by long-term land use regimes and fertilization in manural loess soil[J]. Plant Nutrition and Fertilizer Science, 2013, 19(2): 404–412.
[34] 焦瑞. 陕北黄土丘陵区土地利用方式对土壤水碳垂直分布的影响[D]. 陕西杨凌: 西北农林科技大学硕士学位论文, 2017.
Jiao R. Effects of Different Land Use Types On Distributions of Soil Moisture and Carbon in Loess Plateau of Northern Shanxi Province[D]. Yangling Shaanxi: MS Thesis of Northwest A&F University, 2017.
[35] 曹华. 黄土高原土壤有机碳与无机碳耦合关系的初步探讨[D]. 湖北武汉: 华中农业大学硕士学位论文, 2012.
Cao H. Initial Study on the Coupling Correlations Between Soil Organic Carbon and Inorganic Carbon on the Loess Plateau[D]. Wuhan, Hubei: MS Thesis of Huazhong Agricultural University, 2012.
[36] 张瑞, 曹华, 黄传琴, 等. 地形和土地利用对黄土丘陵沟壑区小流域土壤无机碳分布的影响[J]. 水土保持学报, 2012, 26(4): 143–147.
Zhang R, Cao H, Huang C Q, et al. Effects of topography and land use on spatial distribution of soil inorganic carbon in a small watershed of the loess Hilly-gully Region[J]. Journal of Soil Water Conservation, 2012, 26(4): 143–147.
[37] 李小涵, 王朝辉, 郝明德, 等. 黄土高原旱地不同种植模式土壤碳特征评价[J]. 农业工程学报, 2010, 26(增刊2): 325–330.
Li X H, Wang Z H, Hao M D, et al. Evaluation on soil carbon contents under different cropping systems on dryland in Loess Plateau[J]. Transactions of the CSAE, 2010, 26(Suppl.2): 325–330.
[38] Song B L, Yan M J, Hou H, et al. Distribution of soil carbon and nitrogen in two typical forests in the semiarid region of the Loess Plateau, China[J]. Catena, 2016, 143: 159–166. DOI:10.1016/j.catena.2016.04.004
[39] 兰志龙, 赵英, 张建国, 等. 陕北黄土丘陵区不同土地利用方式下土壤碳剖面分布特征[J]. 环境科学, 2018, (1): 339–347.
Lan Z L, Zhao Y, Zhang J G, et al. Profile distribution of soil organic and inorganic carbon under different land use types in the loess plateau of Northern Shaanxi[J]. Environmental Sciences, 2018, (1): 339–347.
[40] 李利利, 王朝辉, 王西娜, 等. 不同地表覆盖栽培对旱地土壤有机碳、无机碳和轻质有机碳的影响[J]. 植物营养与肥料学报, 2009, 15(2): 478–483.
Li L L, Wang Z H, Wang X N, et al. Effects of soil-surface mulching on organic carbon , inorganic carbon and light fraction organic carbon in dryland soil[J]. Plant Nutrition and Fertilizer Science, 2009, 15(2): 478–483. DOI:10.3321/j.issn:1008-505X.2009.02.034
[41] 刘梦云, 常庆瑞, 杨香云. 黄土台塬不同土地利用方式下土壤碳组分的差异[J]. 植物营养与肥料学报, 2010, 16(6): 1418–1425.
Liu M Y, Chang Q R, Yang X Y. Differences in soil carbon composition under different land use patterns in Loess Tableland[J]. Plant Nutrition and Fertilizer Science, 2010, 16(6): 1418–1425.
[42] 韩可欣, 禹朴家, 韩东亮, 等. 开垦年限对松嫩碱化草地土壤碳库的影响[J]. 土壤通报, 2017, (1): 127–133.
Han K X, Yu P J, Han D L, et al. Effect of cultivation chronosequence on the dynamics of soil carbon pool in songnen alkaline grassland[J]. Chinese Journal of Soil Science, 2017, (1): 127–133.
[43] 张华杰. 黄河三角洲不同形成时期盐渍土碳氮分布特征研究[D]. 山东济南: 山东农业大学硕士学位论文, 2016.
Zhang H j. Distribution characteristics of saline soil carbon and nitrogen of different formation period in the Yellow River Delta[D]. Jinan, Shandong: MS Thesis of Shandong Agricultural University, 2016.
[44] Guo Y, Wang X, Li X, et al. Dynamics of soil organic and inorganic carbon in the cropland of upper Yellow River Delta, China[J]. Scientific Reports, 2016, 6: 36105. DOI:10.1038/srep36105
[45] 吴利晓, 柳伟祥, 何进勤, 等. 不同种植年限下玉米田淡灰钙土有机碳组分变化特征研究[J]. 玉米科学, 2016, (1): 137–141.
Wu L L, Liu W X, He J Q, et al. Changes in Ningxia maize field light sierozems soil organic carbon fractions with of different cultivating years[J]. Journal of Maize Sciences, 2016, (1): 137–141.
[46] 石小霞, 赵诣, 张琳, 等. 华北平原不同农田管理措施对土壤碳库的影响[J]. 环境科学, 2017, 38(1): 301–308.
Shi X X, Zhao Y, Zhang L, et al. Effects of different agricultural practices on soil carbon pool in North China Plain[J]. Environmental Sciences, 2017, 38(1): 301–308.
[47] 党珍珍, 周正朝, 王凯博, 等. 黄土丘陵区不同恢复年限对天然草地土壤碳库动态的影响[J]. 水土保持通报, 2015, 35(5): 49–54.
Dang Z Z, Zhou Z C, Wang K B, et al. Effects of vegetation restoration ages on carbon pool of natural grassland in loess hilly region[J]. Bulletin of Soil and Water Conservation, 2015, 35(5): 49–54.
[48] Deng L, Shangguan Z P, Sweeney S. Correction: Changes in soil carbon and nitrogen following land abandonment of farmland on the Loess Plateau, China[J]. PLoS One, 2013, 8(8): 71923. DOI:10.1371/journal.pone.0071923
[49] He S, Liang Z, Han R, et al. Soil carbon dynamics during grass restoration on abandoned sloping cropland in the hilly area of the Loess Plateau, China[J]. Catena, 2015, 137: 679–685.
[50] Dong L, Yu D, Zhang H, et al. Long-term effect of sediment laden Yellow River irrigation water on soil organic carbon stocks in Ningxia, China[J]. Soil & Tillage Research, 2015, 145: 148–156.
[51] He Y T, Zhang W J, Xu M G, et al. Long-term combined chemical and manure fertilizations increase soil organic carbon and total nitrogen in aggregate fractions at three typical cropland soils in China[J]. Science of the Total Environment, 2015, 532(1): 635–644.
[52] Monger H C, Kraimer R A, Khresat S, et al. Sequestration of inorganic carbon in soil and groundwater[J]. Geology, 2015, 43(5): 375–378. DOI:10.1130/G36449.1
[53] Wu L, Wood Y, Jiang P, et al. Carbon sequestration and dynamics of two irrigated agricultural soils in California[J]. Soil Science Society of America Journal, 2008, 72(3): 808–814. DOI:10.2136/sssaj2007.0074
[54] Chang R, Fu B, Liu G, et al. The effects of afforestation on soil organic and inorganic carbon: A case study of the Loess Plateau of China[J]. Catena, 2012, 95(3): 145–152.
[55] Hooker T D, Compton J E. Forest ecosystem carbon and nitrogen accumulation during the first century after agricultural abandonment[J]. Ecological Applications, 2003, 13(2): 299–313. DOI:10.1890/1051-0761(2003)013[0299:FECANA]2.0.CO;2
[56] Liu S, Bliss N, Sundquist E, et al. Modeling carbon dynamics in vegetation and soil under the impact of soil erosion and deposition[J]. Global Biogeochemical Cycles, 2003, 2: 1074.
[57] 王渊刚, 罗格平. 天山北麓不同土地覆被下土壤有机碳垂直分布特征[J]. 干旱区研究, 2013, 30(5): 913–918.
Wang Y G, Luo G P. Vertical distribution characteristics of soil organic carbon under different land cover in the northern slope of the Tianshan Mountains[J]. Journal of Arid Land Research, 2013, 30(5): 913–918.
[58] Yu P, Li Q, Jia H, et al. Effect of cultivation on dynamics of organic and inorganic carbon stocks in Songnen Plain[J]. Agronomy Journal, 2014, 106(5): 1574–1582. DOI:10.2134/agronj14.0113
[59] Wang Q, Zhang L, Li L, et al. Changes in carbon and nitrogen of chernozem soil along a cultivation chronosequence in a semi-arid grassland[J]. European Journal of Soil Science, 2010, 60(6): 916–923.
[60] Li C, Li Q, Zhao L, et al. Land-use effects on organic and inorganic carbon patterns in the topsoil around Qinghai Lake basin, Qinghai-Tibetan Plateau[J]. Catena, 2016, 147: 345–355. DOI:10.1016/j.catena.2016.07.040
[61] Wu H, Guo Z, Peng C. Land use induced changes of organic carbon storage in soils of China[J]. Global Change Biology, 2010, 9(3): 305–315.
[62] Wu H, Guo Z, Gao Q, et al. Distribution of soil inorganic carbon storage and its changes due to agricultural land use activity in China[J]. Agriculture Ecosystems & Environment, 2009, 129(4): 413–421.
[63] 荣井荣, 李晨华, 王玉刚, 等. 长期施肥对绿洲农田土壤有机碳和无机碳的影响[J]. 干旱区研究, 2012, 29(4): 592–597.
Rong J R, Li C H, Wang Y G, et al. Effect of long-term fertilization on soil organic carbon and inorganic carbon in oasis farmland[J]. Journal of Arid Land Research, 2012, 29(4): 592–597.
[64] Wang K B, Ren Z P, Deng L, et al. Profile distributions and controls of soil inorganic carbon along a 150-year natural vegetation restoration chronosequence[J]. Soil Science Society of America Journal, 2016, 80(1): 193–202. DOI:10.2136/sssaj2015.08.0296
[65] Jing L I, Yu X Y, Tang M. Effects of different plants on soil microbial biomass and enzyme activities in Zhifanggou watershed of Loess Plateau[J]. Acta Botanica Boreali-Occidentalia Sinica, 2013, 33(2): 387–393.
[66] Monger H C, Martinez-Rios J J. Inorganic carbon sequestration in grazing lands [A]. The potential of U. S. grazing lands to sequester carbon and mitigate the greenhouse effect [M]. Boca Raton, FL: CRC Press, 2001. 87–118.
[67] Manning D A C. Biological enhancement of soil carbonate precipitation: passive removal of atmospheric CO2[J]. Mineralogical Magazine, 2008, 72(2): 639–649. DOI:10.1180/minmag.2008.072.2.639
[68] Shi Y, Baumann F, Ma Y, et al. Organic and inorganic carbon in the topsoil of the Mongolian and Tibetan grasslands: pattern, control and implications[J]. Biogeosciences, 2012, 9(6): 2287–2299. DOI:10.5194/bg-9-2287-2012
[69] Sartori F, Lal R, Ebinger M H, et al. Changes in soil carbon and nutrient pools along a chronosequence of poplar plantations in the Columbia Plateau, Oregon, USA[J]. Agriculture Ecosystems & Environment, 2007, 122(3): 325–339.
[70] Gao Y, Tian J, Pang Y, et al. Soil inorganic carbon sequestration following afforestation is probably induced by pedogenic carbonate formation in northwest China[J]. Frontiers in Plant Science, 2017, 8: 1282. DOI:10.3389/fpls.2017.01282
[71] Zhao W, Zhang R, Huang C, et al. Effect of different vegetation cover on the vertical distribution of soil organic and inorganic carbon in the Zhifanggou Watershed on the Loess Plateau[J]. Catena, 2016, 139(3): 191–198.
[72] Jelinski N A, Kucharik C J. Land-use effects on soil carbon and nitrogen on a U. S. Midwestern floodplain[J]. Soil Science Society of America Journal, 2009, 73(1): 217–225. DOI:10.2136/sssaj2007.0424
[73] Kessler T J, Harvey C F. The global flux of carbon dioxide into groundwater[J]. Geophysical Research Letters, 2001, 28(2): 279–282. DOI:10.1029/2000GL011505
[74] Li Z, Xu X, Pan G, et al. Irrigation regime affected SOC content rather than plow layer thickness of rice paddies: A county level survey from a river basin in lower Yangtze valley, China[J]. Agricultural Water Management, 2016, 172: 31–39. DOI:10.1016/j.agwat.2016.04.009
[75] Stewart C E, Halvorson A D, Delgado J A. Long-term N fertilization and conservation tillage practices conserve surface but not profile SOC stocks under semi-arid irrigated corn[J]. Soil & Tillage Research, 2017, 171: 9–18.