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土地利用变化对伊犁河谷典型农牧交错区土壤碳氮磷的影响
刘翔
Subtype博士
Thesis Advisor李兰海
2018-06-05
Degree Grantor中国科学院大学
Place of Conferral新疆乌鲁木齐
Degree Discipline理学博士
Keyword土地利用变化 农牧交错区 土壤有机碳 化学计量比 土壤质量 Land-Use Change Agro-Pastoral Ecotone Soil Organic Carbon Stoichiometric Ratio Soil Quality
Abstract草地生态系统约占陆地总面积的 20%,其土壤碳、氮、磷动态在全球生物地球化学循环中扮演着重要的角色。我国拥有丰富的草地资源,草地面积位居全球第二位。然而在开垦等人类活动的影响下,我国草地面积呈缩减趋势,并形成了大面积的农牧交错区。尽管种植业和畜牧业共存的生产模式使得该区域蕴含着巨大的粮食生产潜力,但在全球气候变化和人类活动的影响下,该区域同时也成为了典型的生态脆弱区。因此,评估土地利用变化对农牧交错区土壤碳、氮、磷的影响对于保障区域可持续发展和国家粮食安全具有重要的科学意义。本研究以西北内陆干旱区的新疆伊犁河谷典型农牧交错区为研究区,采用相邻样地比较法,选取了草地、耕地、林地和园地 4 种该区域主要的土地利用方式,研究了草地开垦以及耕地退耕还林对土壤垂直方向上(0~60 cm)碳、氮、磷储量、化学计量比、有机碳组分以及 Hedley 磷形态的影响,对比了表层土(0~30 cm)和下层土(30~60 cm)碳、氮、磷对土地利用变化的响应特征,同时以碳、氮、磷等土壤性质作为评价指标,分析了土地利用变化对土壤质量的影响,主要研究结论如下:(1)研究区不同土地利用方式下的土壤呈碱性(pH > 8.00),属粉质壤土,缺乏碱解氮和速效磷,但富含速效钾。草地开垦为耕地不仅导致了土壤盐碱化,还降低了表层土的微生物量。相比之下,耕地退耕还林则有助于土壤盐碱化的缓解和微生物量的提升,但耕地转化为林地使得部分土层的容重增大了10.4~24.6%,将土体变得过于紧实。(2)草地开垦为耕地引起了土壤碳、氮、磷的损耗,而耕地退耕还林则促进了土壤碳、氮、磷的累积。在草地开垦为耕地后,下层土碳、氮、磷储量的降幅(-8.1~-24.1%)要大于表层土(-5.9~-17.9%),表明在评估土地利用变化的环境效应时,不应忽视下层土碳、氮、磷的动态。土壤碳、氮、磷含量与 pH(R2 =0.24~0.80,P < 0.05)和电导率(R2 = 0.16~0.63,P < 0.01)的负相关关系预示着土壤盐碱化可能会引起土壤碳、氮、磷的损耗。(3)不 同土 地利 用方 式下 的土 壤碳 氮比 、 碳磷 比和 氮磷 比分 别在14.4~19.0、34.3~60.1 和 1.9~3.6 之间变化。在草地开垦为耕地以及耕地退耕还林后,土壤碳氮比分别增大和减小了 5.1~6.7%和 7.8~13.5%,而土壤氮磷比则分别减小和增大了 8.2~12.3%和 14.1~31.7%,表明土地利用变化会对土壤碳氮比和氮磷比产生截然相反的影响。尽管表层土和下层土的碳磷比在草地开垦为耕地后均有所减小(-3.1~-6.1%),但二者在退耕还林后表现出了相反的变化趋势,表明退耕还林对土壤碳磷比的影响在不同土层有所差异。(4)土地利用方式发生转变后,表层土和下层土活性碳组分Ⅰ的储量分别作出了相反的响应,而两个土层活性碳组分Ⅱ和惰性碳组分的储量则表现为同增同减的变化趋势,表明土地利用变化不仅会改变土壤活性碳库的大小,也会对土壤惰性碳库造成一定的影响,且该影响不仅仅局限于表层土。土壤有机碳惰性指数在草地开垦为耕地后减小了 3.3~7.9%,在耕地转化为林地后增大了 6.9~8.2%,表明农业活动降低了土壤有机碳的稳定性,而耕地转化为林地有助于土壤有机碳稳定性的提升。(5)与土壤活性磷(H2O-Pi、NaHCO3-Pi 和 NaHCO3-Po)和中等活性磷(NaOH-Pi 和 NaOH-Po)相比,研究区土壤稳定性磷(HCl-Pi 和残留-P)在全磷中的比例较高,且更容易受到土地利用变化的影响。相关分析的结果表明,稳定性磷主要决定土壤磷库的大小,而 NaHCO3-Pi 则影响着土壤磷库对植物的有效性。(6)不同土地利用方式下表层土和下层土的土壤质量综合指数(SQI)分别在0.372~0.586和0.228~0.314之间变化,表明研究区土壤质量处于中等偏差水平。SQI 在土地利用变化后的变化特征预示着草地开垦为耕地会引起土壤的退化,而退耕还林则有助于土壤质量的恢复。土壤氮磷比与 SQI 较高的相关性(R2 = 0.71,P < 0.001)预示着土壤氮磷比是反映研究区土壤质量的潜在指标。综上所述,草地开垦为耕地和耕地退耕还林会对伊犁河谷农牧交错区土壤碳、氮、磷储量、碳氮比、氮磷比和有机碳稳定性带来截然不同的影响,其中前者会导致土壤盐碱化,引起土壤碳、氮、磷的损耗,降低土壤有机碳的稳定性,使土壤发生退化,后者则有助于土壤盐碱化的缓解,促进土壤碳、氮、磷的累积,提升土壤有机碳的稳定性,对土壤肥力的恢复具有重要的意义。然而土地利用变化对土壤磷的有效性影响较小。本研究的结果还表明,下层土的碳、氮、磷也会受到土地利用变化的影响,且在部分情况下其受影响的程度要大于表层土,表明在评估土地利用变化的环境效应时,下层土土壤性质的变化情况不容忽视。本研究不仅有助于了解西北内陆干旱区土地利用变化带来的环境效应,也为该区域农牧交错区土地资源的科学管理和可持续利用提供理论依据。
Other AbstractGrassland ecosystems cover approximately 20% of the total land area. Therefore, dynamics of soil carbon (C), nitrogen (N) and phosphorus (P) in grassland may playimportant roles in the global biogeochemical cycles. The grassland area in China isthe second largest in the world, making an abundant grassland resource. However, grassland area in China showed a decreasing trend under the disturbance of humanactivities (e.g. reclamation) in recent decades. As a consequence, a large area ofagro-pastoral ecotone has been established. Although such ecotones have tremendouspotential for food production due to the coexistence of planting industry and animalhusbandry, these regions are fragile to global climate change and human activities. Hence, evaluating the effects of land-use change on soil C, N and P in agro-pastoralecotone has vital scientific significance to guarantee the national food security and theregional sustainable development. In this study, a typical agro-pastoral ecotone in theIli River Valley in Xinjiang, Northwest inland arid China, was selected to: (1) studythe effects of grassland reclamation and cropland afforestation on stocks andstoichiometric ratios of soil C, N and P, soil organic C (SOC) fractions as well asHedley P forms along the 0~60 cm soil profile; (2) compare the responses of C, N andP in topsoil (0~30 cm) and subsoil (30~60 cm) to land-use change; (3) investigate theeffect of land-use change on soil quality based on several soil properties such as C, Nand P. Considering the main land-use types in the study area, four land-use types wereselected using adjacent comparison method including a grassland (GL), a cropland(CL), a woodland (WL) and an orchard (OC). The main conclusions of this study canbe drawn as the follows:(1) Soils in the study area were alkaline (pH > 8.00) with silt loamy texture. Thesoils were lack of alkali-hydrolyzable N and available P but were rich in availablepotassium. GL reclamation not only induced soil salinization, but also decreasedtopsoil microbial biomass. By contrast, CL afforestation contributed to suppress soil salinization and increase soil microbial biomass. However, soil compaction might beinduced by converting CL into WL because bulk density in some soil layers increasedby 10.4~24.6%. (2) Depletion of SOC, total N (TN) and total P (TP) pools were observed afterGL reclamation, whereas CL afforestation contributed to SOC, TN and TPaccumulation. The responses of SOC, TN and TP stocks in subsoil (-8.1~-24.1%) toland-use change were stronger than those in topsoil (-5.9~-17.9%), indicating that thedynamics of subsoil properties should not be ignored when evaluating theenvironmental effects induced by land-use change. The negative relationshipsbetween SOC, TN and TP concentrations as well as pH (R2 = 0.24~0.80, P < 0.05)and electrical conductivity (R2 = 0.16~0.63, P < 0.01) suggested that soil salinizationwas a potential reason that caused the depletion of C, N and P. (3) Soil C to N ratio (RCN), C to P ratio (RCP) and N to P ratio (RNP) of differentland-use types varied in range of 14.4~19.0, 4.3~60.1 and 1.9~3.6, respectively. AfterGL reclamation and CL afforestation, soil RCN increased by 5.1~6.7% and decreasedby 7.8~13.5%, respectively, while soil RNP decreased by 8.2~12.3% and increased by14.1~31.7%, respectively, indicating that land-use change had opposite impacts onsoil RCN and RNP. Although RCP in both topsoil and subsoil decreased by 3.1~6.1%after GL reclamation, they showed opposite responses to CL afforestation. (4) Labile C pool Ⅰ in topsoil and subsoil showed opposite responses to land-usechange, whereas labile C pool Ⅱ and recalcitrant C pool in both soil layers showedsimilar trends after land-use change, indicating that land-use change not only changedsoil labile C pool, but also influenced soil recalcitrant C pool, and such influence wasnot restricted to topsoil. Recalcitrance index of SOC decreased by 3.3~7.9% after GLreclamation, whereas increased by 6.9~8.2% after CL conversion into WL, implyingthat agricultural activities decreased the stability of SOC, while converting CL intoWL contributed to increase the stability of SOC. (5) Compared with soil labile P (H2O-Pi, NaHCO3-Pi and NaHCO3-Po) andmoderately labile P (NaOH-Pi and NaOH-Po), soil stable P (HCl-Pi and residual-P)took larger proportions in TP and were more sensitive to land-use change. The results of correlation analysis suggested that stable P determined the level of P stock, whileNaHCO3-Pi influenced the availability of soil P to plant. (6) Soil quality indexes (SQI) of different land-use types in topsoil and subsoilvaried in range of 0.372~0.586 and 0.228~0.314, respectively, implying that soilquality in the study area was in a low middle level. The variation characteristics ofSQI after land-use change demonstrated that GL reclamation induced soil degradation, whereas CL afforestation contributed to soil restoration. The significant relationshipbetween soil RNP and SQI (R2 = 0.71, P < 0.001) suggested that soil RNP was apotential indicator to predict soil quality in the study area. In summary, GL reclamation and CL afforestation had opposite impacts on SOC, TN and TP stocks, RCN, RNP as well as SOC stability. GL reclamation led to soildegradation because it induced soil salinization, depleted soil C, N and P pools anddecreased the stability of SOC. In contrast, CL afforestation contributed to therestoration of soil fertility because it suppressed soil salinization, accumulated C, Nand P and increased the stability of SOC. However, land-use change had little impacton soil P availability. The results also showed that in some cases, the responses of C, N and P in subsoil to land-use change were stronger than those in topsoil, indicatingthat it is necessary to investigate the variation characteristics of subsoil propertieswhen evaluating the environmental effects induced by land-use change. The presentstudy not only contributes to better understand the environmental effects induced byland-use change in arid inland area of northwest China, but also provides theoreticalbasis for scientific management and sustainable utilization of land resources inagro-pastoral ecotones in this area.
Subject Area自然地理学
Language中文
Document Type学位论文
Identifierhttp://ir.xjlas.org/handle/365004/14929
Collection研究系统_荒漠环境研究室
Affiliation中国科学院新疆生态与地理研究所
First Author Affilication中国科学院新疆生态与地理研究所
Recommended Citation
GB/T 7714
刘翔. 土地利用变化对伊犁河谷典型农牧交错区土壤碳氮磷的影响[D]. 新疆乌鲁木齐. 中国科学院大学,2018.
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