长期施肥对绿洲农田土壤有机碳和无机碳的影响

以中国科学院阜康荒漠生态站的绿洲农田养分循环长期定位试验（始于1990年）为研究平台,研究了无施肥处理（CK）、单施化肥处理（NPK）、有机/无机配施处理（NPKM）和秸秆还田处理（NPKS）下,土壤无机碳(SIC)和有机碳(SOC)在剖面和各施肥年限的含量变化特征及其影响。结果表明：施肥、剖面层次和施肥年限对SOC与SIC含量变化影响显著(P<0.01)。在各施肥处理中,与CK相比,NPK、NPKM和NPKS的SOC与SIC含量明显增加(P<0.05）,并且有机/无机肥配施模式下的SIC含量显著高于单施化肥模式;在剖面层次间,SIC含量从0～20 cm 的9.12 g/kg 增加到40～60 cm 的9.94 g/kg,而SOC变化趋势与之相反。表明合理施肥能够增加土壤表层有机碳含量,有机/无机配施会使耕层以下土壤无机碳增加。     

Effects of long-term cultivation practices and nitrogen fertilization rates on carbon stock in a calcareous soil on the Chinese Loess Plateau

Soil organic carbon(SOC) and soil inorganic carbon(SIC) are important C pools in the Loess Plateau of Northwest China, however, variations of SOC and SIC stocks under different cultivation practices and nitrogen(N) fertilization rates are not clear in this area. A long-term field experiment started in June 2003 was conducted to investigate the SOC and SIC stocks in a calcareous soil of the Chinese Loess Plateau under four cultivation practices, i.e., fallow(FA), conventional cultivation(CC), straw mulch(SM), and plastic film-mulched ridge and straw-mulched furrow(RF), in combination with three N fertilization rates, i.e., 0(N0), 120(N120), and 240(N240) kg N/hm~2. Results indicate that the crop straw addition treatments(SM and RF) increased the contents of soil microbial biomass C(SMBC) and SOC, and the SOC stock increased by 10.1%–13.3% at the upper 20 cm soil depth in comparison to the 8-year fallow(FA) treatment. Meanwhile, SIC stock significantly increased by 19% at the entire tested soil depth range(0–100 cm) under all crop cultivation practices in comparison to that of soil exposed to the long-term fallow treatment, particularly at the upper 60 cm soil depth. Furthermore, moderate N fertilizer application(120 kg N/hm~2) increased SOC stock at the upper 40 cm soil depth, whereas SIC stock decreased as the N fertilization rate increased. We conclude that the combined application of crop organic residues and moderate N fertilization rate could facilitate the sequestrations of SOC and SIC in the calcareous soil.     

土壤盐分对干旱区盐渍土壤碳垂直分布的影响

以新疆玛纳斯县盐渍土壤盐分和碳为研究对象,通过野外实地采样调查,分析干旱区盐渍土条件下的土壤盐分、有机碳、无机碳的垂直分布(0~300 cm)特征,探究土壤盐分对土壤碳垂直分布的影响。结果表明:土壤盐分含量随剖面深度增加呈"先增后降"的趋势,有机碳(SOC)含量随剖面深度增加呈下降趋势,无机碳(SIC)含量随剖面深度增加无明显变化规律。土壤剖面中,盐分与有机碳(SOC)含量及密度呈显著正相关(P0.05),在0~100cm土体中相关性最高(r=0.53);盐分与无机碳(SIC)含量及密度在整个土体中呈负相关关系,相关性不显著。     

不同荒漠生态系统下有机碳和微生物碳的分布特征

基于新疆古尔班通古特沙漠南缘原始盐生旱生荒漠的3种建群灌木琵琶柴(Reaumuria soongori-ca)、多枝柽柳(Tamarix ramosissima)和梭梭(Haloxylon ammodendron)生态系统下土壤剖面实测数据,分析了土壤有机碳(SOC)和土壤微生物量碳(Mc)的垂直分布特征及其与土壤理化因子的关系。结果表明:3个生态系统类型之间土壤剖面SOC分布状况和含量不存在显著差别,但每个生态系统土壤剖面土层之间存在显著差别。各生态系统土壤上层均存在着一定厚度的SOC富集层,中部(10～30cm)SOC含量迅速下降,下部有机碳含量低而稳定。Mc分布与含量与SOC存在相似的规律。Mc对90cm以上的土壤碳循环起着重要的作用,而对深层次的碳库影响不大,不会对全球变化做出响应,但意义更重要,它们可以更长期保留于土壤中而不释放回大气圈。     

Distribution of soil aggregates and organic carbon in deep soil under long-term conservation tillage with residual retention in dryland

To ascertain the effects of long-term conservation tillage and residue retention on soil organic carbon(SOC) content and aggregate distribution in a deep soil(>20-cm depth) in a dryland environment,this paper analyzed the SOC and aggregate distribution in soil, and the aggregate-associated organic carbon(OC) and SOC physical fractions. Conservation tillage(reduced tillage with residue incorporated(RT) and no-tillage with residue mulch(NT)) significantly increased SOC sequestration and soil aggregation in deep soil compared with conventional tillage with residue removal(CT). Compared with CT, RT significantly increased the proportion of small macroaggregates by 23%–81% in the 10–80 cm layer, and the OC content in small macroaggregates by 1%–58% in the 0–80 cm layer. RT significantly increased(by 24%–90%) the OC content in mineral-SOC within small macroaggregates in the 0–60 cm layer, while there was a 23%–80% increase in the 0–40 cm layer with NT. These results indicated that:(1) conservation tillage treatments are beneficial for soil aggregation and SOC sequestration in a deep soil in a dryland environment; and(2)the SOC in mineral-associated OC plays important roles in soil aggregation and SOC sequestration. In conclusion, RT with NT is recommended as an agricultural management tool in dryland soils because of its role in improving soil aggregation and SOC sequestration.     

Natural vegetation restoration of Liaodong oak (Quercus liaotungensis Koidz.) forests rapidly increased the content and ratio of inert carbon in soil macroaggregates

The lack of clarity of how natural vegetation restoration influences soil organic carbon (SOC) content and SOC components in soil aggregate fractions limits the understanding of SOC sequestration and turnover in forest ecosystems. The aim of this study was to explore how natural vegetation restoration affects the SOC content and ratio of SOC components in soil macroaggregates (>250 μm), microaggregates (53-250 μm), and silt and clay (<53 μm) fractions in 30-, 60-, 90- and 120-year-old Liaodong oak (Quercus liaotungensis Koidz.) forests, Shaanxi, China in 2015. And the associated effects of biomasses of leaf litter and different sizes of roots (0-0.5, 0.5-1.0, 1.0-2.0 and >2.0 mm diameter) on SOC components were studied too. Results showed that the contents of high activated carbon (HAC), activated carbon (AC) and inert carbon (IC) in the macroaggregates, microaggregates and silt and clay fractions increased with restoration ages. Moreover, IC content in the microaggregates in topsoil (0-20 cm) rapidly increased; peaking in the 90-year-old restored forest, and was 5.74 times higher than AC content. In deep soil (20-80 cm), IC content was 3.58 times that of AC content. Biomasses of 0.5-1.0 mm diameter roots and leaf litter affected the content of aggregate fractions in topsoil, while the biomass of >2.0 mm diameter roots affected the content of aggregate fractions in deep soil. Across the soil profiles, macroaggregates had the highest capacity for HAC sequestration. The effects of restoration ages on soil aggregate fractions and SOC content were less in deep soil than in topsoil. In conclusion, natural vegetation restoration of Liaodong oak forests improved the contents of SOC, especially IC within topsoil and deep soil. The influence of IC on aggregate stability was greater than the other SOC components, and the aggregate stability was significantly affected by the biomasses of litter, 0.5-1.0 mm diameter roots in topsoil and >2.0 mm diameter roots in deep soil. Natural vegetation restoration of Liaodong oak forests promoted SOC sequestration by soil macroaggregates.     

密度调控对华北落叶松人工林土壤有机碳及养分特征的影响

以华北落叶松人工林为对象,研究不同林分密度下(分别为740、1480、2000和2170株.hm-2)各土层的土壤有机碳含量、有机碳密度、养分特征以及它们之间的相关关系。结果表明:土壤有机碳含量及碳密度随着土壤深度增加而减少,呈明显的垂直分布特征;当林分密度增大到2170株.hm-2时,土壤有机碳含量及碳密度显著增加至最大,分别为25.45g.kg-1和15.68kg.m-2,并与740株.hm-2林地土壤有机碳含量及碳密度差异显著。当林分密度由740株.hm-2增加到2170株.hm-2时,各种养分变化规律不尽一致,但当林分密度为2170株.hm-2时,0-60cm深度的土壤全氮、全磷及速效钾含量均保持在一个相对较高的水平,而土壤全钾和有效磷含量仅在0-20cm土层较高。对于落叶松人工林地整个土壤剖面,土壤有机碳含量及碳密度与土壤全氮、全磷、速效钾含量均呈显著或极显著正相关。从林地土壤固碳的角度,建议将华北落叶松人工林的林分密度控制在2170株.hm-2。     

Changes in soil organic carbon and nitrogen after 26 years of farmland management on the Loess Plateau of China

Soil carbon(C) and nitrogen(N) play a crucial role in determining the soil and environmental quality. In this study, we investigated the effects of 26 years(from 1984 to 2010) of farmland management on soil organic carbon(SOC) and soil N in abandoned, wheat(Triticum aestivum L.) non-fertilized, wheat fertilized(mineral fertilizer and organic manure) and alfalfa(Medicago Sativa L.) non-fertilized treatments in a semi-arid region of the Loess Plateau, China. Our results showed that SOC and soil total N contents in the 0–20 cm soil layer increased by 4.29(24.4%) and 1.39 Mg/hm2(100%), respectively, after the conversion of farmland to alfalfa land. Compared to the wheat non-fertilized treatment, SOC and soil total N contents in the 0–20 cm soil layer increased by 4.64(26.4%) and 1.18 Mg/hm2(85.5%), respectively, in the wheat fertilized treatment. In addition, we found that the extents of changes in SOC, soil total N and mineral N depended on soil depth were greater in the upper soil layer(0–30 cm) than in the deeper soil layer(30–100 cm) in the alfalfa land or fertilizer-applied wheat land. Fertilizer applied to winter wheat could increase the accumulation rates of SOC and soil total N. SOC concentration had a significant positive correlation with soil total N concentration. Therefore, this study suggested that farmland management, e.g. the conversion of farmland to alfalfa forage land and fertilizer application, could promote the sequestrations of C and N in soils in semi-arid regions.     

川西北高寒沙地红柳灌丛内外有机碳及腐殖质碳组分变化特征

为了解川西北高寒沙地红柳对土壤有机碳及腐殖质碳组分的影响,选取了沙地上修复24 a的红柳灌丛作为研究对象,通过野外调查并结合土壤样品采集和室内分析,研究了川西北沙地红柳灌丛根区(SR)、灌丛中部(SM)、灌丛边缘(SE)、灌丛外部(SO)的0~20,20~40 cm和40~60 cm土层土壤有机碳及腐殖质碳组分变化特征。结果表明:随着距灌丛植株水平距离的增加,土壤有机碳(SOC)、胡敏酸碳(HAC)、富里酸碳(FAC)和胡敏素碳(HMC)含量均呈现下降的特征;0~20 cm表层土壤,灌丛根区、灌丛中部和灌丛边缘土壤有机碳含量分别为灌丛外部的1.86倍、2.35倍和1.63倍,灌丛根区、灌丛中部和灌丛边缘土壤腐殖质碳含量分别为灌丛外部的1.96倍、0.68倍和1.22倍;在距灌丛植株水平距离相同条件下,随土层深度增加,土壤有机碳及腐殖质碳各组分含量呈降低趋势;在灌丛根区,20~40 cm和40~60 cm土层土壤有机碳相对于0~20 cm土层分别降低了32.31%和38.38%,20~40 cm和40~60 cm土层土壤腐殖质碳相对于0~20 cm土层分别降低了49.34%和53.40%。研究得出,红柳灌丛内外土壤有机碳及腐殖质碳组分存在空间异质性分布。     

Vertical distribution and storage of soil organic and inorganic carbon in a typical inland river basin,Northwest China

Knowledge of soil carbon(C) distribution and its relationship with the environment can improve our understanding of its biogeochemical cycling and help to establish sound regional models of C cycling. However, such knowledge is limited in environments with complex landscape configurations. In this study, we investigated the vertical distribution and storage of soil organic carbon(SOC) and soil inorganic carbon(SIC) in the 10 representative landscapes(alpine meadow, subalpine shrub and meadow, mountain grassland, mountain forest, typical steppe, desert steppe, Hexi Corridor oases cropland, Ruoshui River delta desert, Alxa Gobi desert, and sandy desert) with contrasting bioclimatic regimes in the Heihe River Basin, Northwest China. We also measured the 87 Sr/86 Sr ratio in soil carbonate to understand the sources of SIC because the ratio can be used as a proxy in calculating the contribution of pedogenic inorganic carbon(PIC) to total SIC. Our results showed that SOC contents generally decreased with increasing soil depth in all landscapes, while SIC contents exhibited more complicated variations along soil profiles in relation to pedogenic processes and parent materials at the various landscapes. There were significant differences of C stocks in the top meter among different landscapes, with SOC storage ranging from 0.82 kg C/m~2 in sandy desert to 50.48 kg C/m~2 in mountain forest and SIC storage ranging from 0.19 kg C/m~2 in alpine meadow to 21.91 kg C/m~2 in desert steppe. SIC contributed more than 75% of total C pool when SOC storage was lower than 10 kg C/m~2, and the proportion of PIC to SIC was greater than 70% as calculated from Sr isotopic ratio, suggesting the critical role of PIC in the C budget of this region. The considerable variations of SOC and SIC in different landscapes were attributed to different pedogenic environments resulted from contrasting climatic regimes, parent materials and vegetation types. This study provides an evidence for a general trade-off pattern between SOC and SIC, showing the compensatory effects of environmental conditions(especially climate) on SOC and SIC formation in these landscapes. This is largely attributed to the fact that the overall decrease in temperature and increase in precipitation from arid deserts to alpine mountains simultaneously facilitate the accumulation of SOC and depletion of SIC.     

不同覆盖方式对旱作农田土壤碳氮含量及玉米产量的影响

设置垄膜沟播(R)、平作全覆膜(P)和平作秸秆覆盖(S)3种不同覆盖栽培模式,以传统平作(CK)为对照,通过3 a大田定位试验,研究不同覆盖方式对农田土壤碳氮及其组分变化、玉米干物质积累和籽粒产量的影响。结果表明:连续覆盖3 a后,R和P处理土壤有机碳和全氮含量及储量均呈逐渐下降趋势,而S处理则呈上升趋势且每年的增幅逐渐增大;各处理0～40 cm土层土壤有机碳储量均表现为S>R>P>CK,全氮储量表现为S>CK>R>P,S处理有机碳和全氮储量分别较CK提高3.4%和7.5%;与CK相比,R和P处理可提高土壤碳氮比,在0～20 cm土层平均分别提高7.9%和9.6%(P<0.05),而S处理0～20 cm土层土壤碳氮比平均降低了9.9%(P<0.05);各覆膜处理(R和P)均较CK显著降低了0～40 cm土层土壤可溶性有机碳(DOC)和土壤可溶性有机氮(DON)含量,而S处理较CK处理0～60 cm土层DOC和DON含量2 a平均均提高6.2%;各处理收获期硝态氮含量在0～100 cm剖面中的垂直分布与CK无明显差异;各处理土壤铵态氮含量均...     

Characteristics of soil organic carbon and total nitrogen under various grassland types along a transect in a mountain-basin system in Xinjiang,China

Soil organic carbon(SOC) and soil total nitrogen(STN) in arid regions are important components of global C and the N cycles, and their response to climate change will have important implications for both ecosystem processes and global climate feedbacks. Grassland ecosystems of Funyun County in the southern foot of the Altay Mountains are characterized by complex topography, suggesting large variability in the spatial distribution of SOC and STN. However, there has been little investigation of SOC and STN on grasslands in arid regions with a mountain-basin structure. Therefore, we investigated the characteristics of SOC and STN in different grassland types in a mountain-basin system at the southern foot of the Altai Mountains, north of the Junggar Basin in China, and explored their potential influencing factors and relationships with meteorological factors and soil properties. We found that the concentrations and storages of SOC and STN varied significantly with grassland type, and showed a decreasing trend along a decreasing elevation gradient in alpine meadow, mountain meadow, temperate typical steppe, temperate steppe desert, and temperate steppe desert. In addition, the SOC and STN concentrations decreased with depth, except in the temperate desert steppe. According to Pearson's correlation values and redundancy analysis, the mean annual precipitation, soil moisture content and soil available N concentration were significantly positively correlated with the SOC and STN concentrations. In contrast, the mean annual temperature, p H, and soil bulk density were significantly and negatively correlated with the SOC and STN concentrations. The mean annual precipitation and mean annual temperature were the primary factors related to the SOC and STN concentrations. The distributions of the SOC and STN concentrations were highly regulated by the elevation-induced differences in meteorological factors. Mean annual precipitation and mean annual temperature together explained 97.85% and 98.38% of the overall variations in the SOC and STN concentrations, respectively, at soil depth of 0–40 cm, with precipitation making the greatest contribution. Our results provide a basis for estimating and predicting SOC and STN concentrations in grasslands in arid regions with a mountain-basin structure.     

外源铅在土壤中的年际变化及对土壤有机碳矿化和速效养分的影响

以关中土为供试土样进行田间试验,向耕层土壤中添加不同浓度外源铅(Pb0:背景值,CK;Pb1:175 mg·kg~(-1)+背景值;Pb2:350 mg·kg~(-1)+背景值),进行小麦—玉米轮作试验。分别于2011—2013年小麦收获季采集耕层(0~20 cm)土壤,分析土壤中铅全量及有效态铅含量的年际变化,以及铅对小麦-玉米轮作模式下土壤有机碳(SOC)、溶解性有机碳(DOC)、微生物量碳(MBC)、碱解氮、速效磷、速效钾含量的影响。结果表明,三年中,施铅处理下土壤中铅全量及有效态铅含量分别下降13.22%和30.65%,总体呈现逐年下降趋势。与对照(CK)相比,Pb1、Pb2处理下SOC平均含量分别下降了16.30%和11.86%;DOC平均含量分别下降了4.05%和7.34%,与土壤铅含量呈现显著负相关关系;低浓度铅污染下土壤微生物商(q M)显著高于对照土壤,微生物量碳含量变化不显著。此外,土壤速效养分的分析显示,土壤碱解氮含量在外源铅加入初期下降明显,且在Pb1处理下碱解氮减少量最大;土壤速效磷含量随土壤铅含量增加而呈现下降趋势;土壤速效钾含量则随土壤铅含量的增加而增加。试验表明,外源铅的加入影响了土壤有机碳的稳定性,对土壤碳、氮循环产生了一定的影响;能够与土壤溶液中的磷酸根生成难溶性盐,与土壤胶体或土壤矿物晶格中的K+发生置换,加大土壤速效养分的流失风险。     

The impact of land use change on soil organic carbon and labile organic carbon stocks in the Longzhong region of Loess Plateau

Land use change (LUC) is widely recognized as one of the most important driving forces of global carbon cycles. The soil organic carbon (SOC) and labile organic carbon (LOC) stores were investigated at arable land (AL), artificial grassland (AG), artificial woodland (AW), abandoned arable land (AAL) and desert steppe (DS) in the Longzhong region of the Loess Plateau in Northwest China. The results showed that conversions from DS to AL, AL to AG and AL to AAL led to an increase in SOC content, while the conversion from DS to AW led to a decline. The differences in SOC content were significant between DS and AW at the 20-40 cm depth and between AL and AG at the 0-10 cm depth. The SOC stock in DS at the 0-100 cm depth was 39.4 t/hm 2 , increased by 28.48% after cultivation and decreased by 19.12% after conversion to AW. The SOC stocks increased by 2.11% from AL to AG and 5.10% from AL to AAL. The LOC stocks changed by a larger magnitude than the SOC stocks, which suggests that it is a more sensitive index of carbon dynamics under a short-term LUC. The LOC stocks increased at 0-20 cm and 0-100 cm depths from DS to AW, which is opposite to that observed for SOC. The proportion of LOC to SOC ranged from 0.14 to 0.20 at the 0-20 cm depth for all the five land use types, indicating low SOC dynamics. The allocation proportion of LOC increased for four types of LUC conversion, and the change in magnitude was largest for DS to AW (40.91%). The afforestation, abandonment and forage planting on arable land led to sequestration of SOC; the carbon was lost initially after afforestation. However, the carbon sink effect after abandonment may not be sustainable in the study area.     

耕作方式对旱地麦田土壤团聚体及其碳氮组分分布的影响

为明确蓄水保墒耕作方式下旱地麦田土壤团聚体稳定性、有机碳及碳组分和全氮及氮组分在不同粒径团聚体组分中的分布特征,深入了解不同耕作方式下土壤碳氮固持机制,以连续3 a(2017—2020年)实施不同耕作方式(免耕、深松、深翻)后冬小麦收获期0～20 cm土壤为研究对象,采用湿筛法测算土壤团聚体的构成与稳定性(R_0.25,>0.25 mm团聚体含量;MWD,平均重量直径;GMD,几何平均直径),并测定各粒径团聚体有机碳(SOC)和碳组分(重组有机碳,HFOC;轻组有机碳,LFOC;易氧化有机碳,EOC;可溶性有机碳,DOC;颗粒有机碳,POC)含量、全氮(TN)和氮组分(硝态氮,NO^-₃-N;铵态氮,NH⁺₄-N;可溶性有机氮,SON)含量,分析了碳氮组分的相关关系。结果显示：(1)免耕和深松处理>2 mm团聚体土壤比例较深翻处理分别提高8.8%和22.1%,免耕有利于增加<0.053 mm粉黏粒比例,较深松和深翻处理分别提高46.4%和27.7%。深松处理较深翻...     

Crop yields and soil organic carbon dynamics in a long-term fertilization experiment in an extremely arid region of northern Xinjiang,China

A long-term fertilization experiment was set up in northern Xinjiang, China to evaluate the dynamics of crop production and soil organic carbon(SOC) from 1990 to 2012 with seven fertilization treatments. The seven treatments included an unfertilized control(CK) and six different combinations of phosphorus(P), potassium(K), nitrogen(N), straw(S) and animal manure(M). The balanced fertilization treatments had significantly(P0.05) higher average yields than the unbalanced ones. The treatment with 2/3 N from potassium sulfate(NPK) and 1/3 N from farmyard manure(NPKM) had a higher average yield than the other treatments. The average yields(over the 23 years) in the treatments of NPK, and urea, calcium superphosphate(NP) did not differ significantly(P0.05) but were higher than that in the treatment with urea and potassium sulfate(NK; P0.05). The results also show that the highest increases in SOC(P0.05) occurred in NPKM with a potential increase of 1.2 t C/(hm~2·a). The increase in SOC was only 0.31, 0.30 and 0.12 t C/(hm~2·a) for NPKS(9/10 N from NPK and 1/10 N from straw), NPK and NP, respectively; and the SOC in the NP, NK and CK treatments were approaching equilibrium and so did not rise or fall significantly over the 23-year experiment. A complete NPK plus manure fertilization program is recommended for this extremely arid region to maximize both yields and carbon sequestration.     

黄土丘陵区不同土地利用方式土壤碳氮磷及其生态化学计量特征

以陕北米脂谷子、苜蓿、柠条和枣树4种不同土地利用方式土壤为研究对象，采集0~100 cm土层土壤样品，采样数共288个，分别对样品土壤的C、N、P及其生态化学计量比C/N、C/P和N/P进行了研究。结果表明：黄土丘陵区土壤C、N、P含量均值分别为2.12、0.21 g·kg^-1和0.43 g·kg^-1;C/N、C/P和N/P均值分别为10.83、5.0和0.48;土壤C、N、P及C/N、C/P和N/P的变异系数均大于10%且小于100%，属于中等变异。土地利用方式对土壤C、N、P含量及其生态化学计量特征有显著影响，其中谷子地0~20 cm土层土壤C含量显著高于柠条地和枣树林（P<0.05），谷子地20~40 cm土层的C含量显著高于苜蓿地（P<0.05）;0~20、20~40 cm和60~80 cm土层谷子地N含量显著高于柠条地（P<0.05）;苜蓿地P含量在0~20、60~80 cm和80~100 cm土层显著高于柠条地（P<0.05）。谷子地、苜蓿地和枣树林土壤C、N呈表聚性分布，而柠条地随深度增加无明显降低，表明柠条有较好的固碳能力。各土层C/N在不同土地利用方式间存在显著差异（P<0.05），其中柠条地最高，谷子地最低;80~100 cm土层土壤C/P在柠条地和苜蓿地间具有显著差异（P<0.05）。0~20 cm和20~40 cm土层深度下，土壤N/P在不同土地利用方式之间具有显著差异（P<0.05），其中谷子地最高，柠条地最低。通过典型相关分析得出，土壤C、N、C/P和N/P与环境因子中的土层深度、粘粒含量和土壤pH值的累积关系较大。     

Revegetation with artificial plants improves topsoil hydrological properties but intensifies deep-soil drying in northern Loess Plateau,China

Knowledge about the effects of vegetation types on soil properties and on water dynamics in the soil profile is critical for revegetation strategies in water-scarce regions, especially the choice of vegetation type and human management measures. We focused on the analysis of the effects of vegetation type on soil hydrological properties and soil moisture variation in the 0–400 cm soil layer based on a long-term(2004―2016) experimental data in the northern Loess Plateau region, China. Soil bulk density(BD), saturated soil hydraulic conductivity(Ks), field capacity(FC) and soil organic carbon(SOC) in 2016, as well as the volumetric soil moisture content during 2004–2016, were measured in four vegetation types, i.e., shrubland(korshinsk peashrub), artificial grassland(alfalfa), fallow land and cropland(millet or potato). Compared with cropland, revegetation with peashrub and alfalfa significantly decreased BD and increased Ks, FC, and SOC in the 0–40 cm soil layer, and fallow land significantly increased FC and SOC in the 0–10 cm soil layer. Soil water storage(SWS) significantly declined in shrubland and grassland in the 40–400 cm soil layer, causing severe soil drought in the deep soil layers. The study suggested that converting cropland to grassland(alfalfa) and shrubland(peashrub) improved soil-hydrological properties, but worsened water conditions in the deep soil profile. However, natural restoration did not intensify deep-soil drying. The results imply that natural restoration could be better than revegetation with peashrub and alfalfa in terms of good soil hydrological processes in the semi-arid Loess Plateau region.     

巴音布鲁克主要草地类型表层土壤有机碳特征及其影响因素的研究

以新疆天山中段巴音布鲁克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)的分布特征及其与气候因子、植被特征和土壤特性的关系。结果表明:分布在盆地海拔最低处的高山沼泽化草甸的土壤有机碳含量最高,而分布在盆地中间海拔的高山草原最低,分布在较高海拔的高寒草甸和高山草原化草甸处于高山沼泽化草甸和高山草原之间。0-30cm土壤有机碳含量与空气相对湿度、草地生产力、植被盖度、土壤含水量呈显著正相关(P<0.05),与土壤容重、土壤紧实度、土壤pH呈显著负相关(P<0.05),土壤有机碳与温度存在一定负相关,但未达到显著水平。偏相关分析显示,影响表层土壤有机碳含量最主要的因素是土壤含水量、土壤紧实度、草地生产力、空气相对湿度。     

Soil exchangeable base cations along a chronosequence of Caragana microphylla plantation in a semi-arid sandy land,China

As a pioneer leguminous shrub species for vegetation re-establishment,Caragana microphylla is widely distributed in the semi-fixed and fixed sandy lands of the Horqin region,North China.C.microphylla plantations modify organic carbon(SOC),nitrogen(N) and phosphorus dynamics,bulk density and water-holding capacity,and biological activities in soils,but little is known with regard to soil exchange properties.Variation in soil exchangeable base cations was examined under C.microphylla plantations with an age sequence of 0,5,10,and 22 years in the Horqin Sandy Land,and at the depth of 0-10,10-20,and 20-30 cm,respectively.C.microphylla has been planted on the non-vegetated sand dunes with similar physical-chemical soil properties.The results showed that exchangeable calcium(Ca),magnesium(Mg),and potassium(K),and cation exchange capacity(CEC) were significantly increased,and Ca saturation tended to decrease,while Mg and K saturations were increased with the plantation years.No difference was observed for exchangeable sodium(Na) neither with plantation years nor at soil depths.Of all the base cations and soil layers,exchangeable K at the depth of 0-10 cm accumulated most quickly,and it increased by 1.76,3.16,and 4.25 times,respectively after C.microphylla was planted for 5,10,and 22 years.Exchangeable Ca,Mg,and K,and CEC were significantly(P<0.001) and positively correlated with SOC,total N,pH,and electrical conductivity(EC).Soil pH and SOC are regarded as the main factors influencing the variation in exchangeable cations,and the preferential absorption of cations by plants and different leaching rates of base cations that modify cation saturations under C.microphylla plantation.It is concluded that as a nitrogen-fixation species,C.microphylla plantation is beneficial to increasing exchangeable base cations and CEC in soils,and therefore can improve soil fertility and create favorable microenvironments for plants and creatures in the semi-arid sandy land ecosystems.