子午岭植被恢复对土壤饱和导水率的影响

通过对子午岭林区不同植被的土壤性质进行实验室测定和野外调查,对饱和土壤水分运动的重要参数之一土壤饱和导水率(Ks)及其相关因子进行了多元分析和通径分析,揭示了植被恢复提高土壤水分传输性能的机理,主要结论如下:土壤有机质是子午岭林区九种植被下土壤饱和导水率提高的主要驱动因子.不同植被下的土壤饱和导水率均随深度的增加而迅速降低,尽管草地和先锋草地在5～10cm深度有一强透水层.土壤饱和导水率在剖面上的平均值,从辽东栎、早期森林、灌丛、先锋草地、弃耕地到草地依次降低.灌丛与草地、弃耕地的差异达到显著水平,辽东栎顶级群落的饱和导水率最高,植被的恢复明显提高了土壤饱和导水率.土壤容重、毛管孔隙度、>0.25mm团聚体含量及粘粒含量直接影响土壤饱和导水率.土壤有机质含量的提高能够改善容重、毛管孔隙度、团聚体含量等物理性质.     

黄土高寒区典型植被类型土壤入渗特征及其影响因素

为了研究黄土高寒区典型植被在不同坡位下土壤入渗性能差异及其影响因素,采用恒定水头法测定了不同植被类型的土壤入渗过程,并分析了土壤孔隙状况、机械组成、水稳性团聚体等与渗透速率的相关性。结果表明:(1)初渗速率和稳渗速率均表现为青海云杉祁连圆柏华北落叶松荒草地,且差异性显著;同一植被类型的土壤入渗速率沿坡面向下逐渐增大,但差异性不显著;(2)对不同植被类型的土壤入渗过程模拟发现Horton模型拟合效果最好,决定系数均在0.8以上,通用经验模型拟合精度较差,决定系数在0.614—0.982之间;(3)土壤入渗性能与孔隙状况、水稳性团聚体质量分数、有机质含量均有极显著相关性;0.25 mm团聚体质量分数是影响稳渗速率的主要决策因素;总孔隙度是影响初渗速率的最主要的决策因素,而毛管孔隙度是主要的限制因子。为高寒地区土壤入渗模拟以及植被配置等提供了科学依据。     

甘肃兴隆山森林演替过程中的土壤理化性质

在森林群落恢复演替过程中,由于森林类型及其所处立地环境不同,森林与土壤相互作用过程具有复杂性。以甘肃兴隆山6种森林类型(青杄林、青杄-白桦林、山杨-白桦林、灌丛林、落叶松林和油松林)0—60 cm土壤层为研究对象,探讨森林恢复演替过程中土壤理化性质的变化规律,旨在为该区域退化森林生态系统恢复与重建提供依据。结果表明:1)在土壤剖面上,兴隆山森林土壤容重随深度的增加而逐渐增大,总孔隙度、毛管孔隙度、自然含水量、最大持水量、毛管持水量、田间持水量均随深度的增加而减小;pH值差异不显著,无明显变化规律;土壤有机质、全N、水解N、有效P、速效K均随深度的增加而变小,表聚效应明显;全P差异不显著,呈"圆柱体"分布模式;2)在森林恢复演替过程中,天然林容重、孔隙度、持水能力、渗透性明显好于人工林,随森林正向演替的进行,天然林容重不断减少,孔隙度明显改善,通透性能不断增强,而人工林土壤物理性质出现明显退化现象;天然林pH值在演替方向上并未表现出酸化现象;天然林土壤有机质、全N、水解N、有效P和速效K变化规律不明显,但总的变化趋势为先增加后减小;3)有机质与全N、水解N、最大持水量、毛管持水量、田间持水量呈显著正相关,而与容重呈显著负相关;全N与水解N呈显著正相关;土壤有机质在改善土壤理化性质和促进养分循环方面具有重要作用,已成为植被恢复过程中土壤变化的一个重要标志。     

岩溶坡地不同植被类型土壤水分入渗特征及其影响因素

通过野外调查与室内分析,研究了广西平果果化典型岩溶坡地荒地、草地、灌丛、林灌4种不同植被覆盖下土壤水分入渗特征及其影响因素。结果表明:荒地、草地和灌丛土壤的平均初渗速率差异不显著,但均明显低于林灌;土壤初渗速率和稳渗速率均较低,均1 mm·min~(-1);随土层深度的增加,土壤初渗速率和稳渗速率均逐渐降低;荒地、草地和灌丛土壤的渗透系数、累积渗水量差异均不显著,但均明显低于林灌,且随土层深度的增加而降低;稳渗速率、渗透系数与土层深度、土壤容重、粘粒含量、初始含水量呈显著负相关,而与土壤有机碳、非毛管孔隙度、粉(砂)粒、水温呈显著正相关;影响土壤水分入渗性能的主要因素为土壤非毛管孔隙度和土壤中粘粒(0.002 mm)含量。     

不同初始含水率下粘质土壤的入渗过程

土壤入渗是降雨渗入土体形成土壤水的基本水文过程,土壤渗透能力影响着地表径流和土壤侵蚀强度。土壤初始含水量决定了入渗初期的土水势,是影响土壤入渗过程的重要因素。利用环刀法,观测了三峡库区林地和草地的土壤入渗过程,对比分析了不同初始含水率下土壤入渗率和常用入渗模型的适宜性。结果表明,随土壤初始含水率的增大,林地和草地下土壤初始入渗率减小,入渗趋于稳定所需时间缩短,累积入渗量和稳定入渗率增大。土壤含水率为12%的林地初始入渗率为8.95 mm/min,是含水率40%林地初始入渗率的4倍,但1h累积入渗量仅是含水率40%林地的2/3。有机质含量丰富的草地土壤入渗过程对初始含水率的敏感性较弱,干湿草地相比较入渗参数的差异不如林地明显。随时间的延长,土壤入渗率逐渐降低,入渗曲线渐趋平缓,最小二乘法拟合结果显示Horton模型对林地和草地下土壤入渗过程的拟合效果较好,且模型参数具有物理意义,是分析和预测三峡库区林草覆盖下土壤入渗过程的适宜模型。     

紫色土区坡耕地不同种植模式对土壤渗透性的影响

以裸地为对照,研究紫色土区坡耕地不同种植模式对土壤渗透性的影响.结果表明:6种种植模式土壤渗透性表现为枇杷＞柠檬＞香根草植物篱+玉米＞新银合欢植物篱+玉米＞黄花＞玉米＞裸地;各种植模式土壤渗透性均随土壤深度的增加而降低,土壤入渗特征值均表现为初始入渗率＞平均渗透率＞稳定入渗率;土壤渗透性与土壤非毛管孔隙、总孔隙度、初始含水率、有机质含量和土壤持水量呈显著正相关,与土壤容重呈显著负相关;通用经验模型对各种植模式土壤入渗过程的拟合效果最好,而Kostiakov方程不适于描述该流域土壤水分的入渗过程.     

天山林区土壤总氮矿化过程对季节性冻融的响应

森林土壤总氮矿化对冻融过程的响应机制尚不明确,氮矿化速率和转化情况尚缺乏定量刻画。通过土壤原位法与室内培养分析相结合,利用~(15)N同位素稀释技术,研究冻融期间天山林区乔木林地、灌丛、草地3种群落类型土壤总氮矿化及转化累积量的动态,分析土壤总氮矿化速率与土壤温度、含水率及微生物量氮(MBN)的相互关系。结果表明:(1)冻融过程及群落类型对总氮矿化速率和MBN含量有极显著的影响(P0.01),秋、春季冻融期的总氮矿化速率相比冻结期更高;(2)季节性冻融期间,乔木林地土壤总氨化累积量在3种群落类型中最高(163.9 kg N hm~(-2) a~(-1)),秋、春冻融期占整个时期的比值约为66%;而总硝化累积量在3种群落类型中相差较小,秋、春冻融期占比均约为77.4%;(3)土壤温度和含水率显著影响总氮矿化速率、净氮矿化速率和MBN速率,随土壤温度增加,总氨化速率(林地和灌丛)显著升高(P0.05);随土壤含水率增加,净氨化速率(灌丛)和净硝化速率(灌丛)显著降低(P0.05)。通过揭示天山林区土壤总氮矿化速率(总氨化速率和总硝化速率)及转化累积量对冻融过程的响应情况,本研究为天山森林土壤中氮的生物地球化学过程提供了有价值的基础数据。     

长白山北坡阔叶红松林和暗针叶林的土壤水分物理性质

对长白山北坡阔叶红松林和暗针叶林的土壤水分物理性质进行了观测和对比分析.结果表明:两种森林类型的土壤容重和各种孔隙度随土壤深度的变化趋势相同,即随着土壤深度的增加,容重和毛管孔隙度逐渐增加,总孔隙度和非毛管孔隙度逐渐降低;两种森林类型土壤物理性质的差异比较明显,阔叶红松林0～100 cm土层的平均土壤容重、总孔隙度、毛管孔隙度和非毛管孔隙度分别为1.41 g·cm^-3、52.31%、46.11%和6.20%,暗针叶林地土壤分别为0.98 g·cm^-3、50.65%、40.32%和10.33%;阔叶红松林和暗针叶林地土壤100 cm土层贮水能力相差较大,分别为619.89和1 033.05 t·hm^-2.两种森林类型的土壤水分特征曲线与一般土壤水分特征曲线相一致.     

天山林区不同类型群落土壤氮素对冻融过程的动态响应

季节性冻融过程对北方温带森林土壤氮素的转化与流失具有重要影响,但不同类型群落对冻融过程响应的差异尚不明确。通过在林地、草地、灌丛上设置系列监测样地,采用原位培养的方法,利用林冠遮挡形成的自然雪被厚度差异,监测分析了冻融期天山林区不同群落表层土壤(0—15 cm)的氮素动态及净氮矿化速率间的差异。结果表明:(1)不同类型群落土壤的铵态氮(NH+4-N)含量、微生物量氮(MBN)含量基本与土壤(5 cm)温度呈正相关,深冻期林地土壤铵态氮含量低于其他群落类型而硝态氮含量高于其他群落类型;(2)硝态氮(NO-3-N)为天山林区季节性冻融期间土壤矿质氮的主体,占比达78.4%。灌丛土壤硝态氮流失风险较大,融化末期较融化初期灌丛土壤硝态氮含量下降了64.6%;(3)冻融时期对整体氮素矿化速率影响显著,群落类型对氨化速率影响显著;(4)天山林区土壤氮素在冻结期主要以氮固持为主。通过揭示不同类型群落土壤氮素对冻融格局的响应,能够助益于对北方林区冬季土壤氮素循环的认识。     

油松人工林火烧迹地早期土壤入渗动态

土壤入渗是决定雨水或融水通过地表再分配给土壤的关键, 影响着森林生态水文过程。为研究北京油松(Pinus tabulaeformis)人工林火烧迹地早期土壤入渗特征及其结构性控制因素, 在火灾发生(2019年3月)的当年对火烧和对照样地的0-20 cm土壤进行为期8个月(5-12月)的采集, 测定分析土壤结构和入渗对火烧干扰的响应及随土壤深度和时间的变化, 并通过路径分析探讨火烧和土壤结构性质对土壤入渗的作用机制。结果表明: 1)土壤各结构指标(除小团聚体外)随土壤深度和时间变化总体具有浅层>深层和6-8月>其他月份的趋势。火烧改变了土壤结构原有的垂直分布特征和季节动态规律, 火烧后2个月土壤>5、2-5和1-2 mm团聚体含量和容重显著增加, 其余指标均显著减少。随土层加深和时间推移, 火烧的作用减弱, 但与土壤深度和时间变化具有明显的交互效应。2)土壤入渗特征随土壤深度变化缓慢, 但随时间变化显著, 表现为雨水较多且出现强降雨事件的8月土壤初渗速率、稳渗速率、入渗总量和饱和导水率最大。火烧后0-5 cm和6-9月的土壤入渗过程与对照相比差异较大, 各月土壤入渗特征均下降, 出现峰值时间提前1-2个月。3)火烧显著影响土壤结构性质, 而土壤入渗性主要受土壤结构性质的直接影响。在未受火烧干扰的情况下, 土壤的入渗性受到土壤团聚体、容重和持水量的正效应以及孔隙度的负效应, 有机质含量和初始含水率对入渗性的直接影响均不显著, 但有机质含量可以通过影响孔隙度或持水量间接影响入渗性。火烧后土壤初始含水率是唯一显著且直接影响入渗性的因素, 且初始含水率越高, 土壤入渗越慢。综上所述, 火烧会改变或解耦火烧迹地早期土壤结构对土壤入渗及其内部的作用程度及途径而间接影响土壤入渗。     

Shrub-encroachment induced alterations in input chemistry and soil microbial community affect topsoil organic carbon in an Inner Mongolian grassland

Shrub encroachment frequently occurs in arid and semi-arid grasslands worldwide and affects the regional carbon balance. Many previous studies have revealed the effects of shrub encroachment on bulk carbon content of grasslands, but molecular evidence is surprisingly lacking. In this study, we examined the chemical composition of plant tissues and soil organic carbon (SOC), and soil microbial communities to identify the effects of shrub (Caragana microphylla) encroachment on SOC storage in the top layer (0–10 cm) along a gradient of natural shrub cover in the grasslands of Inner Mongolia. We found that SOC in the shrub patches was derived mainly from leaves, whereas SOC in the grassy matrix was composed of a mixture of fresh root- and leaf-derived compounds. Compared with pure grassland, the SOC decreased by 29% in the shrub-encroached grasslands (SEGs), and this decrease was enhanced by increasing shrub cover. We also found that free lipids and lignin-derived phenols increased while the ratios of ω-C₁₈/∑C₁₈ and suberin/cutin decreased with increasing shrub cover. In addition, the ratios of fungal to bacterial phospholipid fatty acids (PLFAs) and gram-negative to gram-positive bacterial PLFAs decreased with increasing shrub cover. These results indicate that the encroachment of nitrogen-rich legume shrubs can lead to carbon loss by altering the chemical composition of plant inputs as well as the soil microbial community in grassland ecosystems.     

Plant–community responses to shrub cover in a páramo grassland released from grazing and burning

Shrub encroachment can follow grazing or burning release in páramo grasslands. While encroachment decreases herbaceous species richness in some grassland systems, the effects of this process on the herbaceous community in páramo grasslands are currently unknown. We collected data on shrub cover, herbaceous‐species cover and species composition in a páramo grassland 12 years after release from burning and cattle grazing near Zuleta, Ecuador. Topographic and soil measures were also included as predictor variables of differences in community composition. Contrary to studies in other systems, shrub cover did not have a significant effect on herbaceous‐species richness, whereas shrub‐species richness significantly increased with shrub cover. However, shrub cover was associated with significant shifts in herbaceous–community composition. Most notably, there was an increase in some shade‐tolerant forbs and tall‐statured wetland grasses with increasing shrub cover, and a corresponding decrease in some short‐statured grasses and early successional forbs. These results could indicate that the ameliorative effects of shrubs (e.g. frost and wind protection) in harsh alpine environments may partially compensate for the expected competitive effect of shrubs due to shading.     

Influence of Shrub Encroachment on the Soil Microbial Community Composition of Remnant Hill Prairies

Hill prairies are remnant grasslands perched on the bluffs of major river valleys, and because their steep slopes make them unsuitable for traditional row crop agriculture, they have some of the lowest levels of anthropogenic disturbance of any prairie ecosystems in the Midwestern USA. However, many decades of fire suppression have allowed for shrub encroachment from the surrounding forests. While shrub encroachment of grasslands can modify soil respiration rates and nutrient storage, it is not known whether shrubs also alter the community composition of soil microorganisms. We conducted transect sampling of nine different hill prairie remnants showing varying degrees of shrub encroachment, and we used DNA-based community profiling (automated ribosomal intergenic spacer analysis) to characterize the composition of bacterial and fungal communities in the open prairie habitat, the shrub-encroached border, and the surrounding forest. While both bacterial and fungal communities showed statistically significant variation across these habitats, their predominant patterns were different. Bacterial communities of forest soils were distinct from those of the open prairie and the shrub-encroached areas, while fungal communities of the open prairie were distinct from those of the forest and the shrub-encroached border. Shrub encroachment significantly altered the community composition of soil fungal communities. Furthermore, fungal communities of heavily encroached prairie remnants more closely resembled those of the surrounding forest than those of lightly encroached prairies. Thus, shrub encroachment can cause soil fungi to shift from a “grassland” community to a “woody” community, with potential consequences for soil processes and plant-microbe interactions.     

A functional analysis of vegetation dynamics in abandoned and restored limestone grasslands

Question: How do various plant functional groups and types are related to regeneration of limestone grasslands and to temporal changes in cover of trees and shrubs? Which mechanisms are responsible for changes in differently treated grasslands? Location: Southern Poland, 50° 01'N, 19° 50'E. Methods: A 12‐year restoration experiment after the clearing of a 35‐yr‐old secondary pine wood developed on limestone grassland, and a parallel observation of succession in neighbouring abandoned grassland were carried out. Changes in cover of species with different functional traits and established strategies in relation to time and cover of shrub layer were analysed using multiple linear regression. Results: Over 12 years the composition and cover of species changed in the studied grasslands, but significant differences still occurred between the old grassland and the grassland restored in former wood gaps and that developed in former closed wood. Despite the very close proximity of the old grassland, the composition of restored grasslands was still much determined by initial conditions. In these grasslands, the cover of Festuco‐Brometea species was significantly lower than in the old grassland. In all sites, the cover of species with large leaves and with leaves distributed regularly along the stem, and the cover of CS strategists increased. With increasing shrub cover in restored grasslands, the cover of annuals and biennials, tall species, and R and CS strategists decreased. Conclusions: Limited availability of seeds seems the principal reason for the weak regeneration of xerothermic limestone grasslands. Trees and shrubs inhibit the developed of both early successional species and perennials occurring in established communities. They significantly hinder regeneration of grasslands and should be cut every five or six years.     

天山林区土壤真菌多样性及其群落结构

土壤真菌群落结构对森林生态系统功能的维持具有重要作用,目前对天山林区土壤微生物的种类和群落结构了解甚少。为了解天山不同植被类型下土壤真菌的群落动态及优势菌属,使用Illumina MiSeq高通量测序技术,研究天山林区根际土与非根际土中真菌群落组成及多样性。结果表明:(1)对有效序列进行OTU聚类(operational taxonomic unit)后共得到14121个OTUs,经注释划分为7个门、33个纲、109个目、255个科、444个属、677个种;(2)子囊菌门(Ascomycota)和担子囊菌门(Basidiomycota)是天山植物的优势菌门,灌丛中相对丰度较高的有帚枝霉属(Sarocladium)、鬼笔属(Lysurus)、Microidium;云杉林中相对丰度较高的属有镰刀属(Fusarium)、赤霉属(Gibberella)、丝盖伞属(Inocybe);(3)灌丛与云杉林土壤真菌的群落结构和丰富度有显著差异,灌丛土壤真菌的多样性和丰富度更高,云杉林中阴坡的土壤真菌丰富度较高而阳坡和林窗较低;(4)丝盖伞属(Inocybe)、被孢霉属(Mortierella)、赤霉属(Gibberella)、镰刀属(Fusarium)与云杉的生长可能具有密切的关系。本文推测,根际土壤真菌的多样性和丰富度较低可能是导致云杉幼苗成活率低等更新障碍的问题。     

浙江天童地区常绿阔叶林退化对土壤养分库和碳库的影响

为了解常绿阔叶林退化对土壤碳库和养分库的影响,采用空间代替时间的研究方法,以常绿阔叶林顶级群落为参照,选择了次生常绿阔叶幼年林、次生针阔混交林、次生针叶林、灌丛和灌草丛代表不同的退化类型,分别对其土壤氮磷养分库、碳库进行了调查和分析。结果表明：土壤氮库贮量从大到小依次为,成熟常绿阔叶林、次生常绿阔叶幼年林、灌丛、次生针叶林、灌草丛和次生针阔混交林;土壤总磷含量也是在成熟林最高,次生针阔混交林和次生针叶林的总磷含量显著高于次生常绿阔叶幼年林和灌丛;土壤有机碳含量从高到低依次为：成熟常绿阔叶林,次生针叶林、次生常绿阔叶幼年林、灌丛、灌草丛和次生针阔混交林;土壤铵态氮在成熟林、灌丛和灌草丛的库容量最大,其次分别为次生幼年常绿阔叶林、次生针阔混交林,最小的为次生针叶林;硝态氮则在灌草丛的库容量最大,其次分别为次生针叶林、次生针阔混交林和成熟林针叶林,最小的为次生常绿阔叶幼年林和灌丛。统计显示,常绿阔叶林退化不仅导致土壤有机碳库含量的显著下降,也使得土壤氮磷养分库含量显著下降。可以认为,砍伐导致的大量生物量输出和森林管理措施的影响,植物种类组成的改变,土壤物理性质的改变以及养分和有机碳的主要生物化学转化环节发生改变是导致此类变化的主要因素,常绿阔叶林顶极群落土壤是该地区土壤的最大养分库和碳库。     

宁夏大罗山4种主要植被类型的细根生物量

采用根钻法,分析了宁夏大罗山4种主要植被类型(青海云杉纯林、油松纯林、落叶灌木和荒漠草原)0～40 cm土层的细根生物量、土壤含水量和土壤容重,并对50 a、70 a和100 a 3种树龄的青海云杉纯林细根生物量进行了研究.结果表明: 4种植被类型的细根生物量集中分布在0～20 cm土层,大小顺序为油松纯林>青海云杉纯林>落叶灌木>荒漠草原,其中油松纯林显著高于其他3种植被类型;不同树龄青海云杉纯林细根生物量表现为70 a > 100 a > 50 a,且其活细根和死细根生物量分配比例无显著性差异;4种植被类型下0～40 cm土壤含水量的大小表现为:青海云杉纯林>油松纯林>落叶灌木>荒漠草原;土壤容重则呈相反的规律,并与细根生物量呈极显著负相关.