Acidity controls on dissolved organic carbon mobility in organic soils

Dissolved organic carbon (DOC) concentrations in surface waters have increased across much of Europe and North America, with implications for the terrestrial carbon balance, aquatic ecosystem functioning, water treatment costs and human health. Over the past decade, many hypotheses have been put forward to explain this phenomenon, from changing climate and land management to eutrophication and acid deposition. Resolution of this debate has been hindered by a reliance on correlative analyses of time series data, and a lack of robust experimental testing of proposed mechanisms. In a 4 year, four‐site replicated field experiment involving both acidifying and deacidifying treatments, we tested the hypothesis that DOC leaching was previously suppressed by high levels of soil acidity in peat and organo‐mineral soils, and therefore that observed DOC increases a consequence of decreasing soil acidity. We observed a consistent, positive relationship between DOC and acidity change at all sites. Responses were described by similar hyperbolic relationships between standardized changes in DOC and hydrogen ion concentrations at all sites, suggesting potentially general applicability. These relationships explained a substantial proportion of observed changes in peak DOC concentrations in nearby monitoring streams, and application to a UK‐wide upland soil pH dataset suggests that recovery from acidification alone could have led to soil solution DOC increases in the range 46–126% by habitat type since 1978. Our findings raise the possibility that changing soil acidity may have wider impacts on ecosystem carbon balances. Decreasing sulphur deposition may be accelerating terrestrial carbon loss, and returning surface waters to a natural, high‐DOC condition.     

江淮丘陵地区油-稻轮作条件下土壤硫库变化研究

江淮丘陵地区下蜀系黄土母质发育的水稻土油2稻轮作试验表明, 油菜种植期间, 耕层土壤硫主要来源于耕层以下土层的补给, 其次是大气干湿沉降;该时期耕层土壤硫输出主要是油菜吸收, 其次是淋失.油菜种植期间耕层土壤硫输入量小于输出, 导致耕层土壤硫库下降8.76kg·hm^-2, 22%来自无机硫库的下降.水稻种植期间, 耕层土壤硫输入主要来自灌溉水, 其次是底土层的补给和大气干湿沉降;而硫输出主要是淋失, 其次是水稻吸收.耕层土壤硫输入量大于输出, 导致耕层土壤硫库增加18.69kg·hm^-2, 18%来自无机硫库的增加.全年油2稻轮作期间耕层土壤硫输入量大于输出, 导致耕层土壤硫库增加9.93kg·hm^-2, 13%来自无机硫库的增加.     

不同植被类型下红壤pH和交换性酸的剖面特征

研究湘南红壤丘陵区11种植被类型下施肥区域和未施肥区域红壤剖面(0～100 cm)pH及交换性酸的变化特征.结果表明: 施肥区域0～60 cm土层土壤的pH大小顺序为茶园<花生地<柑橘园,交换性酸含量大小为花生地≤柑橘园<茶园;种植茶树和花生后,表层(0～40 cm)相对底层(60～100 cm)均产生酸化,pH分别降低0.55和0.17,而种植柑橘后,土层间无显著差异.未施肥区域中,植被恢复区0～40 cm土层pH大小为白檵木林≤湿地松林<板栗园<白茅草地,交换性酸含量大小为白茅草地<板栗园<白檵木林≤湿地松林;天然林区0～20 cm土层中次生林和油茶林的pH均显著低于马尾松林0.34和0.20个单位,马尾松林和次生林交换性酸含量显著低于油茶林.与裸地相比,未施肥区域除白茅草地外,其他植被类型均加速了表层土壤酸化,其中天然次生林酸化最严重,pH降低0.52;未施肥区域除天然次生林外,其他植被类型均提高了深层土壤pH,其中白茅草地提升效果最显著,pH升高0.43.无论施肥区域还是未施肥区域,整体上随着土层深度的增加,植被类型或施肥对土壤酸度的影响越来越小.     

Changes in species richness and composition in European acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen deposition

Our study investigates the negative impact of nitrogen (N) deposition on species richness in acidic grasslands, based on a temporal comparison of vegetation data spanning a period of almost 70 years. We compiled a large data base of plots assigned to the Violion caninae grassland type, composed of managed, but unfertilized semi-natural grasslands on nutrient-poor, acidic soils. In total 1114 plots, mainly from Great Britain, the Netherlands and Germany, were compiled, dating back to 1939. Environmental site information included geographical and soil (mean Ellenberg values) variables as well as estimates of cumulative N and sulphur (S) deposition since 1939. Statistical analyses were carried out separately for the data subsets from the three regions. In all regions, the vegetation differentiation was mainly related to soil acidity and nutrient availability, as well as to the year of sampling and the cumulative amounts of N and S deposition. Plot-species richness of vascular plants and bryophytes (analysed for Great Britain only) decreased with time and analyses suggest these are affected by various factors, notably soil pH, but also latitude and cumulative N deposition. The latter explained more of the variation in species number than the year of sampling and cumulative S deposition, which supports the interpretation that the decline in species richness is mainly caused by increasing N availability and less by altered management and soil acidification. For Great Britain and Germany, cumulative N deposition showed a strong negative relationship with several biodiversity measures, especially the proportion of dicots, whereas it was positively related to the proportion of grass species. In general, our results give temporal evidence for the negative effect of N deposition on species richness in semi-natural vegetation.     

Temporal changes and fluxes of sulphur and calcium in wet and dry deposition, internal circulation as well as in run-off and soil in a forest at Gårdsjön, Sweden

Sulphur dioxide in air as well as dry deposition of sulphur dioxide to a forest has decreased by a factor of 20 during the last two decades. It was earlier found that the internal circulation of calcium in Norway spruce follows the dry deposition of sulphur dioxide. The sulphur and calcium fluxes from 1992 were calculated from wet deposition, throughfall and a surrogate surface. Earlier fluxes from 1981 to 1991 were calculated using assumptions of the dry deposition of non-marine sulphate and calcium. The new estimates confirm the earlier studies that the internal circulation of calcium in a coniferous forest is directly related to the dry deposition of sulphur dioxide to the canopies and that the internal circulation of calcium decreases at the same rate as the deposition of sulphur decreased during the last two decades. The deposition fluxes were also compared to run-off and uptake of calcium in the forest as well as on modelled weathering rates from severely acidified forested catchments near the coast and inland and the soil pool. A reconstruction of changes in the soil pool of calcium over the last 100 years indicate that the soil pool has decreased by ca. 70% in catchments with complete harvest of the forest and ca. 40% if branches and needles are left on the ground. In a natural forest without acid deposition the soil pool of calcium would have increased by 6%. Estimates for the 21st century show that harvesting of stems+branches and needles may almost empty the soil pool of calcium in the next 100 years. Increased nitrogen deposition has increased forest growth, which indirectly increased uptake of calcium by the trees and indirectly caused a further decrease of the soil pool of calcium.     

土地整理对土壤微生物群落多样性的影响

土地整理保证了我国耕地总量的动态平衡和占补平衡,已成为实现国土资源集约利用的主要手段,但整治过程中的强度扰动会对土壤质量产生一定的影响.为了解土地整理对土壤微生物多样性的影响,采用PLFA法研究了土地整理1年(Z1a)、4年(Z4a)后土壤微生物群落多样性的变化.结果表明: 与未整理(Z0)相比,土地整理1年后,土壤pH值提高了14.6%,土壤有机碳质量分数降低了65.4%;各菌群磷脂脂肪酸PLFAs含量和相对丰度均显著下降(P<0.05),下降幅度达43.4%～63.7%和25.2%～53.9%;真菌/细菌(F/B)显著下降(P<0.05),降低了35.9%,而革兰氏阳性菌/革兰氏阴性菌(G⁺/G^-)升高明显,增加了56.1%,均与有机碳的降低和pH值的升高有显著相关关系;土壤微生物多样性Shannon指数和均匀度指数(E)均显著下降,Z0与Z1a、Z4a之间的差异达显著水平;土地整理4年后,表征土壤微生物群落多样性的各指标相比整理1年的样地有所提升,但与未整理样地仍有显著差异.综上,土地整理显著影响着土壤微生物群落的组成,降低了土壤生态系统的稳定性.     

Long-term changes in soils of second-growth forest following abandonment from agriculture

Aim The assembly of a forest flora on sites abandoned from agriculture is potentially limited by the physical and chemical suitability of soils. This paper describes the post‐agricultural development of soil in deciduous forest sites to gauge its importance in limiting a second‐growth forest flora. Location Northern Delaware and south‐eastern Pennsylvania, USA. Methods A chronosequence of 99 second‐growth forest sites was assembled in the Piedmont region. Stand age ranged from 0–20 to > 100 years since canopy closure, as determined from historical aerial photographs. Seventy‐four sites are likely to have experienced cultivation before regeneration of forest. The presence of large rocks or pit‐and‐mound microtopography suggests that the remaining 25 sites were not cultivated, although they were probably used as pasture and/or woodlot. Soil organic content, moisture, pH, and concentrations of extractable potassium, phosphorous, calcium, magnesium and sulphur were measured in samples from each site. Coarse woody debris, size of the largest tree, canopy openness and several microtopographic features were also recorded. Results Most soil variables fell into two separate but internally correlated groups: the first group including organic matter, moisture and sulphur; the second including pH, calcium, potassium and magnesium. In formerly cultivated sites, organic matter, moisture and sulphur increased gradually through the chronosequence, approaching values recorded in uncultivated sites at 81–100 years. Calcium, potassium, magnesium and pH declined sharply between the 21–40‐ and 41–60‐year classes – probably an indirect effect related to geographic location and selective abandonment. Phosphorous also declined with time, but the decline was not as clearly defined. Main conclusions The progress of soil recovery observed here is faster than rates implied in other studies, possibly because these sites experienced a period as pasture before reversion to forest. Sites appear to have returned to undisturbed‐forest levels as fast as or faster than the predicted accumulation of a forest flora, suggesting that assembly of second‐growth forest communities is not limited by the rate of soil development in this region.     

不同土地利用类型下氮、磷在土壤剖面中的分布特征

在北京市东南郊大兴区采取了44处0～20cm,20～40cm,40～60cm,60～80cm,80～100cm5个不同深度的土壤剖面样品。按土地利用类型,采样点可分为农田、菜地、果园、林地、草地。土壤剖面中,由表层向深层,pH值升高,有机质、速效磷、全磷、硝态氮、全氮降低,且在20～40cm处有较大变化。表层土壤受土地利用影响,不同土地利用类型的土壤性质差别较大,尤以菜地土壤,pH为8.01低于其他类型土壤的平均值8.27,有机质、速效磷、全磷、硝态氮、全氮都高于其他类型的土壤,分别是其他类型土壤的110%～198%,355%～1629%,162%～224%,724%～1540%,130%～248%,速效磷和硝态氮远高于其他土壤。深层土壤性质差异不大,各项土壤性质差异随深度而变小,但菜地80～100cm处,硝态氮含量为18.8mgkg-1,是同深度其他类型土壤的175%～389%。土壤中硝态氮的积累情况,菜地>农田、果园、林地>草地。磷的积累与氮不同,速效磷在0～20cm大量积累,不同类型的土壤,速效磷积累差异显著,在40～60cm处,菜地速效磷含量是其他利用类型土壤的161%～602%;在80～100cm处,不同利用类型的土壤中速效磷无显著性差异。这一情况表明,菜地的过量施用氮、磷肥导致了土壤中的磷和氮大量积累,并以速效磷、硝态氮的形态向下淋溶并在深层土壤中积累。硝态氮在80～100cm的积累仍相当严重,有继续向下淋溶的可能,速效磷的淋溶在80～100cm处已较为微弱,其淋溶过程主要在0～60cm处。对速效磷和硝态氮的累积进行多元线性回归分析,发现速效磷与全磷含量有着良好的线性相关性,而与有机质和全氮含量关系不大。硝态氮则受土壤中pH、有机质和全氮3因素的共同影响。     

Mapping global soil acidification under N deposition

Soil pH is critically important in regulating soil nutrients and thus influencing the biodiversity and ecosystem functions of terrestrial ecosystems. Despite the ongoing threat of nitrogen (N) pollution especially in the fast-developing regions, it remains unclear how increasing N deposition affects soil pH across global terrestrial ecosystems. By conducting a global meta-analysis with paired observations of soil pH under N addition and control from 634 studies spanning major types of terrestrial ecosystems, we show that soil acidification increases rapidly with N addition amount and is most severe in neutral-pH soils. Grassland soil pH decreases most strongly under high N addition while wetlands are the least acidified. By extrapolating these relationships to global mapping, we reveal that atmospheric N deposition leads to a global average soil pH decline of −0.16 in the past 40 years and regions encompassing Eastern United States, Southern Brazil, Europe, and South and East Asia are the hotspots of soil acidification under N deposition. Our results highlight that anthropogenically amplified atmospheric N deposition has profoundly altered global soil pH and chemistry. They suggest that atmospheric N deposition is a major threat to global terrestrial biodiversity and ecosystem functions.     

施肥和增水对弃耕草地土壤酸中和容量的影响

大气氮沉降增加是草地土壤酸化的主要原因。土壤酸缓冲性能作为评估土壤酸化的重要指标,对氮输入的响应受到降水与其他限制养分含量的影响。本研究以我国北方温带弃耕草地氮、磷、水添加试验13年后的土壤为对象,利用二次多项式模型拟合酸滴定曲线,计算了土壤酸缓冲容量(ABC)以及以pH 5.0和4.0为参比的土壤酸中和容量(ANC)。结果表明: 不增水处理下,单独加氮和同时添加氮磷均显著降低土壤pH,降低以pH 5.0和4.0为参比时的酸中和容量(ANC_pH5.0和ANC_pH4.0);单独加磷对土壤pH、ANC_pH5.0和ANC_pH4.0均无显著影响。增水处理下,加氮及加氮磷显著降低土壤pH、ANC_pH5.0和ANC_pH4.0;加磷显著降低土壤pH,但增加了ANC_pH4.0,而对ANC_pH5.0无显著影响。与不增水处理相比,增水处理对土壤pH、酸中和容量均具有显著的正效应。对于初始pH值不同的土壤,采用土壤酸中和容量比酸缓冲容量能更好地指示土壤抗酸化能力。     

新疆玛纳斯流域非农业种植地盐碱性空间变异特征

土壤盐渍化是导致干旱区土地退化的主要原因之一,也是影响干旱区可持续发展和环境改善的基本问题。充分挖掘不同分类体系下盐渍土空间变异性可以为实施开垦或恢复生态措施提供科学依据。以干旱区开垦近50a的玛纳斯流域为研究区,在不同分类体系下,以土壤盐度,p H值,离子类型为指标,分析该区域非农业种植地(弃耕地,盐碱地,裸地,沙地)盐渍土类型的空间分布特征。结果表明:(1)研究区68%的样本属于非盐渍化,不同类型的盐渍土主要以链状分布于泉水溢出带-冲积平原-干三角洲地带,由南向北,区域整体盐分大致遵循先升高后降低再升高趋势,半方差函数分析土壤盐分呈现弱变异,说明这种分布情况是受随机(人为)因素的影响;而p H整体由南向北递增,传统统计学和地统计学的分析结果都表明土壤碱化呈现中等变异,受结构(自然)因素和随机(人为)因素的共同影响。表层土壤除在溢出带为氯化物型盐渍土外,其他地区自南向北由硫酸-氯化物型逐渐变为氯化-硫酸盐型和硫酸盐土、苏打盐土,离子的半方差函数拟合模型结果均是弱变异和中等变异,与美国盐度实验室分类体系的变异性结果相同,此类分布特征也是结构因素和随机因素共同作用的结果。(2)分析五种典型地貌的盐渍土分布,方差分析结果表明,5种地貌类型均呈现盐分表聚特征,碱化度则由南向北递增;其中盐碱特征最为显著的是泉水溢出带。泉水溢出带的盐土垂直方向的变化趋势为由表层至深层,盐土类型由硫酸-氯化物盐土变为氯化盐土;冲积平原和干三角洲样点处全剖面为氯化物-硫酸盐土,冲积洪积扇和沙漠地区则包含所有阴离子盐土类型。对玛纳斯流域盐渍土特性的空间异质性进行分析,可以为下一步有针对性地治理与改善土壤盐渍化提供科学依据。     

施氮频率和强度对内蒙古温带草原土壤pH及碳、氮、磷含量的影响

以内蒙古温带典型草原为研究对象,通过 9 个氮沉降梯度以及一年 12 次和一年 2 次的施氮频率比对,经过4年的氮沉降模拟,研究不同氮沉降强度和频率对不同土层土壤 pH 及碳、氮、磷含量的影响.结果表明: 随着施氮强度的增加,土壤 pH 及全磷含量逐渐降低,但土壤有效氮和有效磷的含量呈增加趋势,可溶性有机碳(DOC)含量无明显变化规律,而土壤全碳、全氮含量基本保持不变.与更接近于自然氮沉降状况的一年 12 次施氮相比,一年 2 次施氮明显高估了氮沉降在降低土壤 pH和增加有效磷含量上的作用,低估了氮沉降在增加土壤有效氮含量上的作用,其中0～5 cm土层差异显著.     

黑河中游荒漠绿洲区土地利用的土壤养分效应

土地利用影响地表覆被状况和生态过程,关系到土壤肥力与土壤碳库功能"源-汇"关系的改变。黑河中游甘州区和临泽县是我国西北干旱区典型的荒漠绿洲区,以土壤表层(0-20 cm)养分变化为对象,利用2011-2012年甘州区和临泽县的土壤野外调查数据和该区全国第二次土壤普查数据,对两时期土壤表层养分(土壤有机质、全氮、全磷、全钾及pH值)的变化特征进行比较研究。结果表明:研究区土壤有机质、全磷含量分别降低了3.54%和12.5%;而全氮、全钾和pH值分别增加了74.4%、98.2%和4.9%。全国第二次土壤普查时期,荒漠、耕地与草地三者在各土壤养分上没有显著差异,但林地在土壤有机质、全氮、全钾上显著高于前三者。2011-2012年,耕地土壤的全磷、全氮与其它土地利用存在显著差异。土地利用的保持和改变对土壤养分变化有着重要影响,耕地的长期耕作使得土壤有机质含量降低4.94%,全氮增加86.93%,全磷减少5.02%,土壤碱性增强;荒漠植被的自然演替使土壤有机质含量增加66.21%,全氮增加71.70%,全磷含量减少37.33%,土壤碱性变弱。所以,耕地扩张及其长期耕作活动将导致地力退化并有盐碱化风险,而荒漠等自然生态系统保护有利于土壤肥力的改善和土壤固碳功能的发挥。     

封育对黄土高原草地深层土壤pH的影响

土壤酸碱度变化, 直接影响植被类型及植物对土壤养分的吸收效率, 同时在土壤有机碳和无机碳相互转化过程中起重要作用, 为明确草地封育过程中土壤酸碱度的变化特征。以黄土高原云雾山自然保护区放牧草地(封育0年)、封育15年草地、封育30年草地为研究对象, 采用空间代替时间方法, 研究封育过程中深层(0-500 cm)土壤酸碱度变化特征。结果表明: (1)3个封育年限草地土壤pH随着土层深度的增加而增加, 放牧草地土壤pH变化范围为8.54-9.26、封育15年草地土壤pH变化范围为8.56-8.97、封育30年草地土壤pH变化范围为8.12-8.74。(2)不同封育年限0-500cm土壤各粒级差异较大, 放牧草地在40-60 cm土层, 3-2 mm土壤团粒结构的土壤pH最低为8.38, 显著低于其它粒级(P˂0.05); 封育15年草地土壤pH各粒级差异较小; 封育30年草地土壤pH整体呈上升趋势, 0-20 cm各粒级土壤pH差异显著。(3) 在0-500 cm, 封育30年草地土壤pH显著低于放牧草地和封育15年草地(P˂0.05), 其平均值分别为8.50、8.94和8.87。因此, 长期封育显著降低土壤pH值。     

宁夏银北盐碱地油葵田土壤动物多样性及群落结构

【目的】调查宁夏银北盐碱地油葵田的土壤动物多样性及群落结构,探讨不同改良时间盐碱地土壤动物多样性及群落结构与环境因子之间的相关性。【方法】生物与环境因子之间的关系研究一直是生态学研究的热点,尤其是恢复生态学中如何设计环境因子来恢复生物群落的结构和功能最近引起了国内外学者的关注。以宁夏银北盐碱地油葵田为对象,研究了不同改良时间盐碱地中油葵田土壤动物与环境因子的相互关系,采用野外调查和室内试验相结合。【结果】共采集12个土壤动物类群,优势类群为弹尾目(60.67%)、蜱螨亚纲(23.24%)和鞘翅目(6.45%);土壤动物物种多样性、丰富度指数和均匀度在未改良盐碱地中较高。【结论】土壤pH值、碱化度和全盐质量分数是土壤动物分布的限制因素,土壤动物的数量随土壤pH值、碱化度和全盐质量分数的降低而增加。这些结果为盐碱地改良的恢复与评价提供了重要的数据支持和基础资料。     

黄土高原小流域土壤pH、阳离子交换量和有机质分布特征

通过野外调查采样和室内分析,研究了黄土高原小流域土壤pH、阳离子交换量（cation exchange capacity,CEC）和有机质的分布特征及其与土地利用方式、地形条件和土壤类型的关系.结果表明：黄土高原小流域土壤pH、CEC和有机质分别介于7.7～8.6、11.9～28.7 cmol·kg^-1和3.0～27.9 g·kg^-1,分别服从正态分布、对数正态分布和负二项分布.3种土壤性质随地形、土地利用方式和土壤类型的不同差异很大.不同土地利用方式下,土壤有机质和CEC以林地、草地和农田较高,果园较低;pH则以林地较低,其他利用方式较高;不同地形条件下,3种土壤性质均呈塬面和坡地大于沟道和梯田的趋势;不同类型土壤中,有机质和CEC以黑垆土和红土较高,pH则以黄绵土较高.整体上,土壤有机质和CEC呈现出相似的变化趋势,而pH的分布特征则与之相反.     

人参种植对林地土壤细菌群落结构和代谢功能的影响

揭示人参种植对土壤微生物群落结构和代谢功能的影响,对防治人参连作障碍具有重要的理论意义。利用高通量测序技术研究了林地和由林地开垦耕种人参3a和4a后土壤微生物群落结构和代谢功能的变化。结果表明,变形菌门(Proteobacteria)、放线菌门(Actinobacteria)、酸杆菌门(Acidobacteria)、疣微菌门(Verrucomicrobia)、绿弯菌门(Chloroflexi)是林地和人参种植土壤微生物的主要优势类群。林地开垦种植人参后,土壤放线菌门和疣微菌门的相对丰度显著增加,土壤酸杆菌门的相对丰度显著降低;而土壤微生物多样性指数明显降低。除趋势对应分析(DCA)显示不同种植a限人参的土壤微生物群落结构存在明显差异。Tax4Fun功能预测表明,人参种植后土壤微生物的萜类化合物和聚酮类化合物代谢与信号转导功能的相对丰度显著降低,而膜转运功能的相对丰度增加。典范对应分析(CCA)和Partial Mantel Test分析表明,土壤速效钾、全钾含量和土壤pH值是影响土壤微生物群落结构的重要因子。因此,林地开垦种植人参对土壤微生物群落结构、多样性以及代谢功能产生了显著影响,土壤速效钾、全钾含量和pH值是影响土壤微生物群落结构的重要因素。     

Fine-scale temporal characterization of trends in soil water dissolved organic carbon and potential drivers

Long-term monitoring of surface water quality has shown increasing concentrations of dissolved organic carbon (DOC) across a large part of the Northern Hemisphere. Several drivers have been implicated including climate change, land management change, nitrogen and sulphur deposition and CO₂ enrichment. Analysis of stream water data, supported by evidence from laboratory studies, indicates that an effect of declining sulphur deposition on catchment soil chemistry is likely to be the primary mechanism, but there are relatively few long term soil water chemistry records in the UK with which to investigate this, and other, hypotheses directly. In this paper, we assess temporal relationships between soil solution chemistry and parameters that have been argued to regulate DOC production and, using a unique set of co-located measurements of weather and bulk deposition and soil solution chemistry provided by the UK Environmental Change Network and the Intensive Forest Monitoring Level II Network. We used statistical non-linear trend analysis to investigate these relationships at 5 forested and 4 non-forested sites from 1993 to 2011. Most trends in soil solution DOC concentration were found to be non-linear. Significant increases in DOC occurred mostly prior to 2005. The magnitude and sign of the trends was associated qualitatively with changes in acid deposition, the presence/absence of a forest canopy, soil depth and soil properties. The strongest increases in DOC were seen in acidic forest soils and were most clearly linked to declining anthropogenic acid deposition, while DOC trends at some sites with westerly locations appeared to have been influenced by shorter-term hydrological variation. The results indicate that widespread DOC increases in surface waters observed elsewhere, are most likely dominated by enhanced mobilization of DOC in surficial organic horizons, rather than changes in the soil water chemistry of deeper horizons. While trends in DOC concentrations in surface horizons have flattened out in recent years, further increases may be expected as soil chemistry continues to adjust to declining inputs of acidity.     

广东省不同区域农田土壤酸化时空变化及其影响因素

基于广东省1980s、2010年以及2015年3期土壤数据,对全省不同区域农田耕作层土壤pH值的时空变异特征进行分析,并初步探讨了可能导致土壤pH变化的因素.结果表明: 不同时期广东全省土壤pH值空间分布格局变化显著. 全省农田土壤在1980s—2010年间,pH整体下降了0.3,呈酸化趋势,2010—2015年,土壤pH上升了0.09,但不均匀势态有所增强,酸碱分化趋势较明显. 从各区域看,1980s—2010年,各区域土壤均呈现酸化趋势;2010—2015年,珠三角地区农田土壤pH均值上升了0.27,而东、西两翼土壤pH均值分别下降了0.05、0.15,山区土壤pH变化不明显. 分析表明:广东省各地区土壤酸化除受土壤自身及降水等自然因素影响外,酸雨、不合理施肥以及高产作物高复种的种植结构等人为因素也是导致土壤酸化的主要原因;工业化、城市化、矿山开发和测土配方施肥的推广导致局部地区土壤pH值有所上升. 研究结果可为不同区域控制缓解土壤酸化、提高耕地质量提供理论指导.     

Effect of available burrow densities of plateau pika (Ochotona curzoniae) on soil physicochemical property of the bare land and vegetation land in the Qinghai-Tibetan Plateau

The available burrow densities of plateau pika (Ochotona curzoniae) regulate the soil physicochemical property in alpine meadow. A field survey was conducted to investigate the effect of available burrow densities of plateau pika on soil physicochemical property of bare land (bare patch produced by burrowing behavior of plateau pika) and vegetation land (land covered with vegetation). This study indicated that the increase in available burrow of plateau pika caused the soil water content at 0–10 cm layer of bare land and that at 10–20 cm of vegetation land to reduce, and caused the soil water content at 10– 20 cm layer of bare land and that at 0–10 cm layer of vegetation land to firstly increase and then decline. In the increasing process of available burrow of plateau pika, the soil silt content firstly increased and then decreased, and soil sand content firstly decreased and then increased. With the increase of available burrow of plateau pika, the soil porosity at 0–10 cm layer of bare land and that at 10–20 cm layer of vegetation land decreased, while the soil porosity at 10–20 cm layer of bare land and that at 0–10 cm of vegetation land firstly increased and then decreased. Soil pH value, soil organic matter, total nitrogen and total phosphorus content firstly increased and then decreased, peaking at 14 available burrows per 625 m², while total soil potassium content did not respond to available burrow densities of plateau pika. This study suggested that the proper available burrows existing in the alpine meadow increased soil permeability, accelerated soil moisture to penetrate deeply, increased the proportion of soil silt, and improved the soil nutrient; however, this beneficial effect was strongly influenced by the available burrow density of plateau pika, implying that plateau pika did not benefit soil structure when its available burrow was over 34 number/625 m².