川西贡嘎山不同森林生态系统土壤有机碳垂直分布与组成特征

通过野外采样与室内实验相结合的方法,对川西典型亚高山不同海拔处暗针叶林、针阔混交林和常绿-落叶阔叶林3种森林类型表层土壤总有机碳（SOC）和活性有机碳的含量特征进行分析,旨在为亚高山生态系统土壤碳循环研究提供理论和数据支撑。结果表明：3种森林类型土壤中总有机碳含量（SOC）在44.21～179.98g·kg-1,表层（0-15cm）SOC含量大小顺序为针阔混交林＞常绿-落叶阔叶林＞暗针叶林,0-5cm土层SOC含量与活性有机碳含量均高于5-15cm土层,说明土壤有机碳具有土壤表聚现象。3种森林类型间SOC密度差异不显著,但不同森林类型土壤SOC密度沿土层的分布具有差别：与常绿-落叶阔叶林和暗针叶林相比,针阔混交林5-15cm土层SOC密度较高。土壤溶解性有机碳（DOC）、轻组分有机碳（LFOC）和微生物（MBC）含量均以针阔混交林最高,但其相对于SOC的比例则以暗针叶林最高,说明高海拔生态系统土壤活性有机碳有更大的累积,同时也暗示在气候变化背景下,高海拔生态系统可能具有更大的CO2排放风险。     

不同植被下中国土壤有机碳的储量与影响因子

基于第二次土壤普查和新疆土壤调查等 2 4 4 0个典型土壤剖面数据和 1∶4 0 0万中国植被图 ,对中国不同植被类型下的 1 0 0cm和 2 0cm厚度土壤有机碳密度和储量进行估算 ,绘制了土壤有机碳储量的地理分布图 ,并且对土壤有机碳储量与生境条件之间的关系进行统计分析。结果表明 :不同植被类型下的土壤有机碳密度存在显著差异 ,草甸和森林最高 ,灌木和农田次之 ,再其次是草原 ,最低的是荒漠 ;基于植被分类计算的我国 1 0 0cm和 2 0cm厚度土壤有机碳总储量分别为 6 9.38Gt和 2 3.81Gt。 1 0 0cm深度土壤碳储量在森林、农田、灌丛、草甸、草原、荒漠植被下分别为 1 7.39Gt、1 4 .6 9Gt、1 3.6 2Gt、1 2 .2 2Gt、7.4 6Gt、3.93Gt;土壤有机碳储量的空间分布差异明显 ,具有明显地域性 ,青藏高原东南地区、阿尔泰山和天山山地等高寒草甸、灌丛草甸区是土壤有机碳储量最高的地区 ,其次是东北地区北部的针叶林、草甸区和我国南方的亚热带阔叶林区 ,土壤有机碳储量最低的地区是西北地区和藏北高原的荒漠、草原干旱区 ;在不同生态系统中环境变量对土壤有机碳储量的影响是不同的 ,在温带草原年平均温度是土壤有机碳储量主要控制因素 ,而对于针叶林海拔是导致土壤有机碳储量变异的主导因子 ;随着研究尺度的细化 ,环境变     

川西亚高山次生林恢复过程中土壤物理性质及水源涵养效应

川西亚高山原始针叶林遭受大规模采伐后自然恢复形成的次生林已成为该区域的主要森林类型之一,也是我国西南林区水源涵养林的重要组成部分。现有亚高山森林水源涵养功能研究主要集中在暗针叶林,对天然次生林关注较少。选择川西米亚罗林区亚高山次生林自然恢复演替序列上高山柳灌丛、次生桦木阔叶林、岷江冷杉桦木针阔混交林,以相邻岷江冷杉成熟林为对照,采用空间代替时间的方法,基于土壤容重、孔隙度、持水性能等测定,分析了次生林恢复过程中土壤物理性质变化及土壤水源涵养效应动态,结果表明:(1)次生林恢复过程中,土壤容重总体呈下降趋势,除灌丛与阔叶林、针阔混交林、暗针叶林间具有显著差异外,其余植被类型间无显著差异,随着土层的加深,土壤容重呈增加趋势;(2)不同恢复阶段土壤孔隙度具有显著差异,以针阔混交林0—30 cm土层总孔隙度(64.39%)和毛管孔隙度(50.49%)为最高,灌丛总孔隙度(41.25%)和毛管孔隙度(33.70%)为最低;而土壤非毛管孔隙度以暗针叶林(14.27%)为最高;随着土层的加深,土壤孔隙度大致呈现出递减的趋势;(3)随着林龄增加,次生林土壤0—30 cm土层最大持水量呈波动性增加趋势,在针阔叶混交林阶段达到最大(1 815.02 t/hm~2),到暗针叶林阶段有所下降(1 659.88 t/hm~2);土壤毛管持水量以针阔混交林(1 369.72 t/hm~2)为最高,而非毛管持水量以暗针叶林(534.95 t/hm~2)为最高,暗示针阔混交林树木生长所需有效水贮存量较大,亚高山暗针叶林具有较强的土壤水分调节能力和土壤渗透能力。从水源涵养功能角度,川西亚高山森林植被恢复应注重构建针阔叶混交林结构。     

涪江流域丘陵区不同植被类型水源涵养功能

采用野外调查和水浸法,研究涪江流域丘陵地区5种典型植被系统的雨水截留能力、凋落物蓄积量和持水能力、土壤物理特性、蓄水能力和渗透性能,并基于坐标综合评定法对不同植被类型的水源涵养和保土功能进行综合评价。各植被类型降雨截留量、凋落物蓄积量和持水量均以阔叶灌丛最高,草地最低,阔叶灌丛的平均截留量、凋落物蓄积量和持水量分别为草地的4.9,2.9,1.8倍。不同植被类型的土壤容重和孔隙度差异较大,容重表现为草地>针叶林>针阔混交林>常绿阔叶林>阔叶灌丛;总孔隙度为阔叶灌丛>常绿阔叶林>针阔混交林>针叶林>草地。土壤渗透速率和贮水能力随土壤深度增加而降低,以阔叶灌丛最高,其次为常绿阔叶林、针阔混交林、针叶林,草地贮水能力最弱。5种植被类型水源涵养能力依次为阔叶灌丛>常绿阔叶林>针阔混交林>针叶林>草地,阔叶灌丛明显优于其他植被类型。     

辽东山地古石河冰缘地貌不同植被类型表层土壤特性

[目的]对辽东山地古石河冰缘地貌不同植被类型下表层土壤特性进行研究,为辽东山区冰缘地貌土壤生态环境的管理和保护提供基础数据和科学依据。[方法]以老秃顶子古石河冰缘地貌发育的落叶阔叶林、针阔混交林、暗针叶林、灌草丛4种植被类型表层土壤为研究对象,采用野外定点取样及实验室分析相结合的方法,研究不同植被类型下的土壤特性。[结果]土壤属于酸性淋溶土,含有多种氧化物,各植被类型间土壤特性存在明显差异,相对而言,灌草丛表土温度较高,毛管孔隙所占比例大,保水蓄水能力较强;针阔混交林土壤比重小,疏松程度好,有机质含量较高;暗针叶林土壤酸性较强;落叶阔叶林和针阔混交林土壤水分更有利于植物生长,枯落物现存量较多,涵养水源和保持水土功能较好。[结论]海拔高度对土壤特性影响显著,枯落物现存量及养分储量与土壤特性有明显定量关系。保护区可通过改善土壤养分含量维持生境稳定性。     

缙云山5种植被下土壤活性有机碳及碳库变化特征

为揭示重庆市缙云山不同植被下土壤活性有机碳及碳库分配特征，以该地区5种植被类型：阔叶林、针叶林、混交林、竹林和荒草地为研究对象，分析不同植被类型下各土壤层次中有机碳（Soil organic carbon, SOC）、微生物量碳(Microbial biomass carbon，MBC)、可溶性有机碳(Dissolved organic carbon，DOC)、易氧化有机碳(Readily oxidized organic carbon，ROC)含量及其土壤碳库的变化特征。结果表明：土壤有机碳和各活性有机碳组分含量及分配比例受到植被类型和土层深度的明显影响。土壤有机碳的平均含量在0~100 cm土层表现为竹林（16.74 g/kg）>阔叶林（12.62 g/kg）>草地(11.14 g/kg)>混交林（8.16 g/kg）>针叶林（5.98 g/kg），并随土层深度的增加而减小。竹林和阔叶林的微生物量碳和易氧化有机碳含量均明显高于混交林和针叶林，各植被在剖面上均表现出垂直递减规律，表现出明显的表聚效应。除草地，4种植被的土壤碳库管理指数随土层深度的加深而减小，均表现为表层(0~20 cm土层)最高。不同植被类型间，竹林的可溶性有机碳分配比例在各土壤层次均最小，整个土壤剖面均值仅为0.1%。由相关性分析可知，微生物量碳、易氧化有机碳、土壤总有机碳含量和土壤有机碳储量有着极其显著的相关性。因此，土壤微生物量碳和易氧化有机碳可以作为衡量亚缙云山森林不同植被土壤有机碳库变化的敏感性指标。     

高寒草甸典型小流域土壤水分空间变异对比研究

以寒区两个典型小流域为例,根据理论变异函数,通过Krige空间内插法对比研究小流域0～30cm层土壤水分空间变异性及其特征。结果表明：（1）受植被类型、覆盖度影响,水平方向上,同一流域不同植被类型土壤含水量分布为：高寒灌丛草甸〉高寒嵩草草甸〉退化草地;相同草甸类型条件下,纳通河流域平均土壤水分含量均小于跨热洼尔玛流域;各坡位、坡向草甸植被严重退化区域土壤水分含量均略小于高寒草甸草地区域。（2）从剖面分析,跨热洼尔玛流域各层土壤含水量均大于纳通河流域;剖面变异性、土壤水分下渗速度纳通河流域总体均大于跨热洼尔玛流域;土壤水分变化剧烈程度高寒草甸草地区域在20～30 cm层、植被退化区域10～20 cm层;土壤水分下渗速度草甸植被严重退化区域大于高寒草甸草地;高寒草甸草地区域在10～20 cm层土壤水分在下渗过程中有一定的滞后作用;而草甸植被严重退化区域则无此类情况。     

东祁连山高寒草甸土壤“固-液-气”三相组成对海拔和坡向的响应

为探究不同海拔和坡向下高寒草甸土壤"固—液—气"三相组成变化特征,以东祁连山高寒草甸为研究对象,分析了不同海拔(2 800,3 000,3 200,3 400,3 600,3 800,4 000 m)、坡向(阳坡、阴坡)高寒草甸的植被特征和土壤物理特征,结合植被指标拟合探讨高寒草甸"固—液—气"三相的最佳组成比例。结果表明:植被盖度、草层高度和地上生物量均随海拔升高呈先升高后降低,在海拔3 200 m处达最大值,同一海拔的阴坡植被盖度、草层高度、地上生物量均高于阳坡;土壤容重随海拔和坡向的变化规律与植被盖度相反,而土壤含水量、孔隙度和持水性变化规律与植被盖度类似;经方程拟合发现,土壤"固—液—气"三相比例为31∶33∶36时,高寒草甸生产力最优。综上所述,在海拔3 200 m处是东祁连山高寒草甸分布的中心典型区域,海拔和坡向是影响高寒草甸土壤物理质量和"固—液—气"三相组成的重要环境因子,且该区域高寒草甸土壤"固—液—气"最佳比例为31∶33∶36。     

吉林省辽河流域不同植被类型土壤水源涵养能力分析

选取吉林省辽河流域6种样地类型(阔叶林、针叶林、针叶混交林、灌木林、草地、农田),研究不同植被类型土壤在0～60 cm深度的结构特征、持水能力和渗透能力，并综合评价不同植被类型土壤的水源涵养能力，为营建水源涵养林提供支撑。结果表明：(1)除农田外其他样地类型土壤的容重随着土层深度的增加而变大，土壤总孔隙度和毛管孔隙度随着土层深度的增加而减小；(2)不同植被类型土壤的持水能力表现为阔叶林>针阔混交林>针叶林>灌木林>草地>农田，土壤渗透能力表现为针阔混交林>针叶林>灌木林>阔叶林>草地>农田；(3)不同植被类型土壤的水源涵养能力为阔叶林>针阔混交林>针叶林>灌木林>草地>农田，吉林省辽河流域内阔叶林的水源涵养能力最优，农田的水源涵养能力最差，退耕还林工程可以提高土壤的水源涵养能力。     

红壤丘陵区不同植被类型土壤颗粒分形与水分物理特征

为探明红壤丘陵区不同植被对土壤分形结构及水分物理特征的改良作用与机制,运用土壤分形学和水文物理学原理与方法,以南方红壤丘陵区福建省长汀县为例,研究经济林、针阔混交林、乔灌混交林及针叶林4种植被类型土壤颗粒组成、分形维数、水分物理参数及其相关性。结果表明:1)红壤丘陵区不同植被类型土壤中以粗砂粒质量含量最高,细砂粒和石砾质量含量次之,粉黏粒质量含量较低,与裸地相比,不同植被类型具有显著提高土壤细砂砾和粉黏粒质量含量的作用,并且混交林作用程度高于纯林;2)红壤丘陵区不同植被类型具有降低土壤密度、增加土壤孔隙度的功能,针阔混交林、乔灌混交林、针叶林、经济林土壤的饱和蓄水量分别是裸地的1.20、1.16、1.14和1.10倍,表土层(0～20 cm)贮水能力好于表下土层(20～40 cm);3)土壤颗粒分形维数与土壤粉黏粒、总孔隙度、饱和蓄水量、孔隙比呈极显著正相关,与石砾质量含量、土壤密度呈极显著负相关,红壤丘陵区4种植被类型土壤均为不均匀性良好的土壤,以混交林土壤粒径分布结构较好,尤其是以针阔混交林的最好,其次是纯林的,针叶林好于经济林,表土层(0～20 cm)大于20～40 cm土层。     

太白山不同海拔土壤碳、氮、磷含量及生态化学计量特征

为探究太白山土壤碳(C)、氮(N)、磷(P)含量垂直分布特征,阐明土壤C、N、P生态化学计量学特征对海拔梯度的响应规律,在秦岭太白山1 700~3 500 m区域以100 m海拔间隔进行研究。结果表明:(1)不同海拔高度下土壤有机碳、全氮、全磷变化范围分别是23.56~83.59g kg-1、2.00~5.77 g kg-1、0.32~0.47 g kg-1。土壤有机碳与全氮含量随海拔梯度升高先增后降,土壤全磷含量空间变异较小;(2)土壤C∶N、C∶P、N∶P范围分别为7.17~18.41、60.61~190.4、5.81~12.26。随海拔增加,土壤C∶N在阔叶林带呈降低趋势,针叶林带时转变为增加趋势。土壤C∶P随海拔梯度的变化趋势与土壤C∶N类似,N∶P随海拔梯度增加先升后降,至3 200 m有所升高;(3)两个阔叶林带(辽东栎林带和桦木林带)与高山草甸的土壤C、N含量及生态化学计量比高。冷杉林带C、N含量及其生态化学计量比最小;(4)温度、含水量、海拔和植被对土壤C、N、P化学计量特征具有重要影响,通过冗余分析揭示每个因素分别可解释系统变异信息的25.0%、24.3%、11.1%和6.9%,合计为67.3%。可见这些环境因素直接决定了土壤养分及生态化学计量特征。结果可为探明森林土壤养分供应状况和限制因素及太白山生态系统的保护、森林土壤质量评价等提供基础。     

长期秸秆还田显著降低褐土底层有机碳储量

  【目的】  秸秆还田作为一种有效的培肥方式,对土壤固碳效果显著,但对于深层土壤有机碳的影响还存在不确定性。分析不同秸秆还田方式下褐土剖面土壤有机碳(SOC)储量变化,为褐土区秸秆还田措施优化和固碳减排等提供科学依据。  【方法】  长期秸秆还田试验开始于1992年,采用裂区设计,主区为化肥春季和秋季施用,副区为4个秸秆还田处理:秸秆不还田 (CK)、秸秆覆盖还田 (SM)、秸秆粉碎后直接还田 (SC) 和秸秆过腹还田 (CM)。在2013年春玉米收获后采集0—100 cm土层土壤样品,分析不同秸秆还田方式下SOC和土壤养分含量。  【结果】  在春季和秋季施肥下,与CK相比,CM、SM和SC处理表层 (0—20 cm) SOC含量显著提高,而SM和SC处理40—60和80—100 cm SOC含量显著降低。同时,与CK处理相比各处理SOC储量变化量在处理间存在显著差异。在春季和秋季施肥下,与CK相比,SM、SC和CM处理表层SOC储量平均分别增加2.32、5.42和12.60 t/hm2,且CM处理显著高于SM和SC处理;而在底层 (40—100 cm) 平均分别降低3.98、6.99和3.76 t/hm2;0—100 cm,CM处理SOC储量增加9.62 t/hm2,而SM和SC处理平均分别降低1.81和5.36 t/hm2。冗余分析结果表明,有机碳输入和土壤养分对表层碳储量变化的总解释率为90.10%,而对下层 (20—100 cm) 的总解释率仅为31.80%。其中,影响表层碳储量变化的主要因子是有效磷 (解释率为80.10%),而下层则是全氮 (25.28%)。  【结论】  在施用化肥基础上,长期秸秆还田促进表层碳累积,但底层氮素供应不足引起碳耗竭。总体上,秸秆过腹还田是褐土区农田培肥和增产的最优秸秆还田方式。     

Storage and controlling factors of soil organic carbon in alpine wetlands and meadow across the Tibetan Plateau

Alpine wetlands and meadows across the Three Rivers Source Region (TRSR) store high soil organic carbon (SOC). However, information on factors affecting SOC storage is scanty. Herein, we investigated SOC storage and explored factors affecting SOC storage, including climate, soil properties and above- and belowground biomass, using 50 soil profiles across the TRSR on the Tibetan Plateau. The SOC storage was 491.9 ± 158.5 Tg C and 545.2 ± 160.8 Tg C in the TRSR alpine wetlands and meadow, respectively. The SOC stock was positively correlated with the mean annual precipitation. However, no significant correlation between SOC stock and mean annual temperature was observed, as opposed to the global trend. In addition, SOC stock was positively correlated with both the aboveground biomass (AGB) and belowground biomass (BGB). Soil pH indirectly affected SOC stock, while SOC stock positively correlated with Al and Fe oxyhydroxides. Compared with vegetation biomass and climatic factors, soil properties, including soil pH and Al and Fe oxyhydroxides (Al_o and Fe_o), affected not only SOC stock variation but also affected the impact of vegetation and climatic factors on SOC stock. Climate factors, AGB, BGB, soil pH, Al_o and Fe_o jointly accounted for 59% of SOC stock variation in alpine wetlands and 64% of SOC stock variation in alpine meadow. This study suggests that soil properties are the dominant factors affecting SOC variation in alpine wetlands and meadow on the Tibetan Plateau.     

Soil organic carbon in semiarid alpine regions: the spatial distribution,stock estimation,and environmental controls

Purpose

Soil organic carbon (SOC) in alpine regions is characterized by a strong local heterogeneity, which may contribute to relatively large uncertainties in regional SOC stock estimation. However, the patterns, stock, and environmental controls of SOC in semiarid alpine regions are still less understood. Therefore, the purpose of this study is to comprehensively quantify the stock and controls of SOC in semiarid alpine regions.

Materials and methods

Soils from 138 study sites across a typical semiarid alpine basin (1755–5051 m, ~1?×?10⁴ km²) are sampled at 0–10, 10–20, 20–40, and 40–60 cm. SOC content, bulk density, soil texture, and soil pH are determined. Both a classical statistical model (i.e., a multiple linear regression, MLR) and a machine learning technique (i.e., a random forest, RF) are applied to estimate the SOC stock at a basin scale. The study further quantifies the environmental controls of SOC based on a general linear model (GLM) coupled with the structural equation modeling (SEM).

Results and discussion

SOC density varies significantly with topographic factors, with the highest values occurring at an elevation zone of ~3400 m. The results show that the SOC is more accurately estimated by the RF compared to the MLR model, with a total stock of 219.33 Tg C and an average density of 21.25 kg C m^?2 at 0–60 cm across the study basin. The GLM approach reveals that the topography is seen to explain about 58.11% of the total variation in SOC density at 0–10 cm, of which the largest two proportions are attributable to the elevation (44.32%) and the aspect factor (11.25%). The SEM approach further indicates that, of the climatic, vegetative, and edaphic factors examined, the mean annual temperature, which is mainly shaped by topography, exerts the most significant control on SOC, mainly through its direct effect, and also, through indirect effect as delivered by vegetation type.

Conclusions

The results of this study highlight the presence of high stocks of organic carbon in soils of semiarid alpine regions, indicating a fundamental role played by topography in affecting the overall SOC, which is mainly attained through its effects on the mean annual temperature.

     

长白山东部4种林分类型土壤有机碳及养分特征研究

以长白山东部长白落叶松天然林、长白落叶松人工林、天然阔叶混交林、天然针阔混交林4种林分类型为研究对象,对比分析了土壤有机碳(SOC)的垂直分布特征,以及与土壤理化性质的相关性.结果表明,4种林分下土壤有机碳含量及其差异程度随土壤深度增加均呈现逐渐减小的趋势.0-60 cm土层土壤有机碳含量大小依次为天然针阔混交林(33.64士17.48 g/kg)＞长白落叶松天然林(25.30±15.09 g/kg)＞天然阔叶混交林(22.13±13.74 g/kg)＞长白落叶松人工林(19.23±12.35 g/kg);天然针阔混交林0-60 cm土壤有机碳密度为21.44±8.31 kg/m2,显著高于其他3种林分类型,长白落叶松人工林最小,为14.29±1.59 kg/m2.对不同土层土壤有机碳和土壤理化性质进行相关分析,结果表明,整个土壤剖面有机碳含量与自然含水率、全N、全P、全K、速效K均呈极显著或显著正相关,与土壤密度呈极显著负相关;不同林分类型土壤有机碳含量和碳密度与全N均呈显著或极显著正相关,与土壤理化性质相关性存在较大差异.     

The elevational patterns and key drivers of soil microbial communities strongly depend on soil layer and season

Knowledge about the elevational patterns of soil microbial biomass and communities can facilitate accurate prediction of the responses of soil biogeochemical processes to climate change. However, previous studies that have considered intra- and inter-annual variations have reported inconsistent results on the one hand, and they have paid little attention to the effect of soil layer on the other hand. We, therefore, conducted a 4-year in situ soil core incubation experiment along a 2431-m elevational gradient across the dry valley shrubland, valley-montane ecotone forest, subalpine coniferous forest, alpine coniferous forest, and alpine meadow in an ecologically fragile alpine-gorge region on the eastern edge of the Qinghai-Tibetan Plateau. Soil microbial biomass and community composition in the organic and mineral layers were measured using the phospholipid fatty acids (PLFA) method at five critical periods each year. Our results indicated that soil microbial biomass in the organic layer was the highest in the subalpine coniferous forest, followed by the alpine meadow, alpine coniferous forest, and valley-montane ecotone forest. In contrast, soil microbial biomass in the mineral layer was significantly higher in the alpine meadow than in the other sites. Soil microbial biomass exhibited differential seasonal fluctuations at different elevations, resulting in their elevational patterns being strongly intra-annual and inter-annual dependent. Our results revealed that elevation and seasonality significantly affected soil microbial communities. Seasonality had a more substantial effect than elevation on soil microbial communities during the first 3 years of incubation, whereas the relative importance of seasonal and elevational effects on microbial communities was reversed in the organic layer with incubation time. These results are mainly attributed to the magnitude and direction of effect of environmental variables on soil microbial biomass and communities vary with elevation, soil layer, and sampling time. Briefly, the elevational patterns and dominant factors of soil microbial biomass and communities have intense soil layer and temporal specificity, implying that differential responses of soil biochemical processes to climate change might be observed at different elevations.     

Effects of topography on soil organic carbon stocks in grasslands of a semiarid alpine region,northwestern China

Purpose

Soil organic carbon (SOC) in mountainous regions is characterized by strong topography-induced heterogeneity, which may contribute to large uncertainties in regional SOC stock estimation. However, the quantitative effects of topography on SOC stocks in semiarid alpine grasslands are currently not well understood. Therefore, the purpose of this research study is to determine the role of topography in shaping the spatial patterns of SOC stocks.

Materials and methods

Soils from the summit, shoulder, backslope, footslope, and toeslope positions along nine toposequences within three elevation-dependent grassland types (i.e., montane desert steppe at ~?2450 m, montane steppe at ~?2900 m, and subalpine meadow at ~?3350 m) are sampled at four depths (0–10, 10–20, 20–40, and 40–60 cm). SOC content, bulk density, soil texture, soil water content, and grassland biomass are determined. The general linear model (GLM) is employed to quantify the effects of topography on the SOC stocks. Ordinary least squares regressions are performed to explore the underlying relationships between SOC stocks and the other edaphic factors.

Results and discussion

In accordance with the present results, the SOC stocks at 0–60 cm show an increasing trend in respect to the elevation zone, with the highest stock being approximately 37.70 g m^?2 in the subalpine meadow, about 2.07 and 3.41 times larger than that in the montane steppe and montane desert steppe, respectively. Along the toposequences, it is revealed the SOC stocks are maximal at toeslope, reaching to 14.98, 31.76, and 49.52 kg m^?2, which are also significantly larger than those at the shoulder by a factor of 1.38, 2.31, and 1.44, in montane desert steppe, montane steppe, and subalpine meadow, respectively. Topography totally is seen to explain about 84% of the overall variation in SOC stocks, of which 70.61 and 9.74% are attributed to elevation zone and slope position, while the slope aspect and slope gradient are seen to plausibly explain only about 1.84 and 0.01%, respectively.

Conclusions

The elevation zone and the slope position are seen to markedly shape the spatial patterns of the SOC stocks, and thus, they may be considered as key indicating factors in constructing the optimal SOC estimation model in such semiarid alpine grasslands.

     

黄土高原草地土壤有机碳分布及其影响因素

以黄土高原水平方向的4种主要草地类型为研究对象,分析了不同草地类型土壤有机碳(SOC)的分布特征及其影响因素。结果表明:土壤有机碳含量随土壤深度的增加而降低,其中0～20 cm土壤有机碳含量与20～40、40～60、60～80、80～100 cm有机碳含量差异显著。4种草地类型土壤有机碳含量分布规律:0～40 cm为高山草甸草原>典型草原>森林草原>荒漠草原,40～100 cm为高山草甸草原>森林草原>典型草原>荒漠草原;4种草地类型中各土层土壤有机碳含量最高的是高寒草甸,其空间变异最大,最小的是荒漠草原,其变异最小。黄土高原上高寒草甸草原、森林草原、典型草原土壤有机碳均集中分布在浅表层0～40 cm,分别占0～100 cm的71%、50%、46%,而荒漠草原各层分布较均匀;黄土高原土壤有机碳含量与海拔高度呈显著正相关(p<0.01);0～40 cm土壤有机碳含量与土壤含水量呈显著正相关(p<0.01);与全氮有极显著的正相关性,相关系数达0.984 3;与年均温呈极显著负相关(p<0.01),几种草地类型100 cm深土壤有机碳含量与年降水量无明显相关。     

不同土地利用方式对土壤有机无机碳比例的影响

【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。