近30年来土壤种子库研究的回顾与展望

土壤种子库(Soil Seed Bank)是指单位面积的土壤及土壤表面的落叶层中所有具有生命力的种子的总和.由于土壤种子库在植被的更新和恢复、生物多样性的维护、植被的演替过程和扩散过程等方面都具有重要作用,近年来成为生态学和土壤学等学科的研究热点.文章查阅了近30年来发表的关于土壤种子库研究的代表性SCI论文,首次运用文献分析与管理软件Endnote X1和Refviz对该研究领域的相关文献进行了系统的分析,结果发现:有关土壤种子库论文发表数量逐年增长的同时,每个年代末会呈现一个明显的峰值.在此基础上,根据不同年代研究的内容和特点,初步将土壤种子库的研究划分为三个主要阶段:(1)土壤种子库研究的探索阶段(1978-1989年);(2)土壤种子库研究方法与内容的成熟阶段(1990-1999年);(3)土壤种子库理论体系与研究内容扩展阶段(2000年至现在),并对各个阶段的研究重点和主要研究成果进行了详细的综述.最后就长久土壤种子库调查、种子库年际变化、干扰影响机制等研究热点做了展望,为今后土壤种子库的研究工作提供了参考策略.     

火烧和植造桉林对南亚热带退化草坡土壤种子库的影响

对南亚热带典型火烧草坡迹地和人工造桉林后的退化草坡土壤种子库进行了取样调查,采用种子萌发试验研究了这些不同处理的土壤种子库特征,结果表明:(1)火烧处理对土壤种子库有显著影响,具体表现为种子库储量减小、物种种类减少、优势种组成单一、物种多样性指数和地上植被相似性系数低、土壤种子库物种组成与地上植被物种组成差异显著;(2)种植桉树对土壤种子库储量、物种生活型分布、土壤种子库物种组成与地上植被物种组成差异均没有影响,但能增加草本物种种类;(3)火烧并种植桉树对土壤种子库的影响与火烧处理结果一致,能使土壤种子库中优势物种种子密度增加,但不能增加草本种类在种子库中的密度.该研究表明采用火烧处理有利于南亚热带退化草坡植被恢复;采用种桉树的方法短期内植被恢复的效果不明显;退化草坡的植被恢复需要适度的人为干预与调控.     

盐池封育草场土壤种子库特征及其与植被的关系

封育是退化草场恢复的重要措施之一,封育的效果在一定程度上取决于土壤中种子库的状况。以毛乌素沙地西南缘宁夏盐池县的退化草场为研究对象,采用相似性分析和排序方法对封育和未封育草场土壤种子库的特征及其与地上植被间关系进行了研究,结果表明无论封育区还是未封育区,土壤种子库中的种子主要分布于0～5cm的土层,6～15cm土层的种子数很少;封育区土壤种子库的物种丰富度大于未封育区,物种多样性则表现为H值较大,而D值较小,总体上看封育措施可以提高地上植被和土壤中种子的种类和数量,一些一年生植物、中生植物和盐生植物开始出现在地面或土壤种子库中。地上植被和土壤种子库间的相似性分析结果则表明相同措施同一土层间种子库中等相似,而不同土层间还是存在着一些差异。由于封育措施导致了植被样方的相似性较低,然而土壤种子库间的相似性仍然较高,两者间是否存在着一定程度的滞后效应有待于进一步研究。     

土壤种子库植物种类组成与土壤采集地植被的关系

土壤种子库作为区域自然植被恢复的途径之一,在实际应用之前有许多课题需要研究,土壤种子库出芽植物组成与土壤采集地自然植被的关系就是一个需要弄清的问题。文章从土壤种子库的生态学意义出发,首次对森林表土作为城市自然植被恢复绿化手段的可能性进行了探讨。试验材料取自日本大阪府箕面市大阪国际文化公园都市建设地,选取面积为20m×20m的栓皮栎Quercusvariabilis群落,采集林下5cm厚森林表土;试验场地设在大阪府枚方市山田池公园的一隅荒地,共设置4个试验区,每个试验区7个试验处理,计28个试验小区。研究结果表明:土壤种子库植物种类组成与表土采集地的植被关联性较低,但与种子散布型关系密切;表土的不同铺撒厚度在木本植物出现的种类、出芽个体数、生存个体数等方面都表现出明显的差异性。     

天津市“城-郊-乡”样带土壤种子库特征分析

为了解天津市不同地理位置土壤种子库物种组成和群落结构的变化,沿天津市设置＂城区—城郊—远郊＂的生态样带,在6个典型样地选取20个样方进行土壤种子库的采样工作并进行萌发试验。结果表明：土壤种子库的密度、物种组成及群落结构差异性明显,除趋势对应分析后分异出典型的城市土壤种子库、城郊土壤种子库、远郊土壤种子库3种类型。从远郊到城区,土壤种子库的密度递增,相似性指数也递增,而物种丰富度却递减。相比远郊地区,城区、城郊区土壤种子库物种丰富度损失率分别为66.67%、45.23%。城区因城市化水平较高及频繁的人为干扰致使土壤种子库物种呈现匀质化特点,物种多为一年生的耐踩踏草本。城郊区的多样性指数、生态优势度指数、均匀度指数最低,但是种子库密度较大,物种丰富,萌发种子中木本植物可观,适合用于进行植被恢复的试验研究。     

重庆喀斯特山地土壤种子分布特征

土壤种子库对岩溶山地退化植被恢复具有重要意义。采用萌发法,比较了重庆典型岩溶山地处于不同生态演替序列的自然林地、次生林地、灌草坡、坡耕地、人工林、弃耕撂荒地等土地利用系统的土壤种子库分布特点。喀斯特山地各植被类型的土壤中贮藏着丰富的种子,每个40cm×25cm×15cm土柱内储藏有227.4~454.8粒种子,土壤种子集中分布在土壤表层(0~5cm),乔灌种子主要分布于0~5cm土壤层。土地利用强度越大,木本植物种子越少,草本植物种子越多,且以农田杂草为主,土地利用方式的变化(如陡坡开垦)是对次生植被及其种子库的主要威胁;坡度、溶沟、溶隙等土壤分布环境和土壤水分等也对喀斯特山地的种子密度产生影响,这就使得种子密度在不同地点及植被类型间相差很大,生境异质性是种子库分布模式的决定因子。     

科尔沁沙地恢复过程中地上定植群落与土壤种子库特征及其关系研究

选择科尔沁沙地固定沙地、半流动沙地和流动沙地样地,研究沙地恢复过程中土壤种子库密度、组成及其与地上植被的关系。结果表明,(1)退化沙地恢复过程中,流动沙地、半流动沙地、固定沙地的土壤种子库平均密度(以单位面积有效种子数量表示,ind·m~(-2))分别为814、3 125和16 294 ind·m~(-2)。土壤种子库物种组成以一年生草本为主,多年生植物和灌木类所占的比例小。(2)地上定植群落与土壤种子库的变化趋势一致,地上定植群落的平均密度分别为68、242和673 plant·m~(-2)。地上定植群落物种组成也以一年生植物为主,但所占比例较土壤种子库有所下降。(3)不管是土壤种子库还是地上定植群落,Shannon-Wiener指数、Simpson指数、均匀度指数和丰富度指数大小顺序均为:固定沙地半固定沙地流动沙地,土壤种子库物种多样性指数均大于地上植被。(4)地上植被与土壤种子库组成上的相似性系数在0.333~0.739之间,相似性系数较高。地上定植群落与土壤种子库密度存在显著的正相关关系。流动沙地、半流动沙地、固定沙地地上植被密度分别有36%、52%、60%的变异可归结为土壤种子库密度的变异。科尔沁沙地土壤种子库是地上植被自然恢复的重要物质基础,土壤种子库中的大量种子,在植被自然恢复中将发挥积极的作用。     

土壤种子库研究方法评述

土壤种子库（soil seed bank,SSB）是指存在于土壤表面和土壤中的全部存活种子的总和。开展对土壤种子库的研究,对于分析了解过去地上植被植物群落和预示未来植被发展方向具有重要的指导意义,而对于土壤种子库研究方法的探讨则是开展土壤种子库基础实验研究的基础和支撑。本文从土壤种子库的取样时间、取样方法、取样大小和数量、鉴定方法四个方面归纳了土壤种子库的研究方法,理论分析了同位素应用于土壤种子库中种子年龄结构测定的可行性,以及植冠种子库的研究方法,并探讨了提高土壤种子库中种子萌发率的新方法。综合分析来看：（1）土壤种子库的取样时间、取样方法、取样大小和数量、鉴定方法是土壤种子库研究方法需要关注的四大关键问题,对土壤种子库的实验结果具有显著的直接影响。不同的取样时间代表的土壤种子库的内容和意义不同,取样方法、大小和数量则应根据研究区和研究内容来确定,鉴定方法也应根据具体实验区研究的物种数来考量;（2）理论上在利用同位素来测定土壤种子库中种子年龄结构是可行的,但若想广泛应用于实验中仍需进一步的深入研究;（3）目前对植冠种子库的研究方法也仅仅局限于直接计数法和间接计数法,对植冠种子库的研究方法的探讨则急需加强;（4）同时总结和提出了4种提高土壤种子库中种子萌发率的方法,未来在利用种子萌发法时,应加强注意和应用这4种方法来测定土壤种子库。     

岷江干旱河谷不同植物斑块的土壤种子库特征

岷江干旱河谷生境恶劣,植物种群呈斑块状单物种聚集分布,研究植物斑块及斑块下土壤种子库的特征,有利于指导植被的自然恢复更新工作。选择岷江干旱河谷广泛存在的10种植物斑块,进行植物斑块特征的调查及斑块内土壤种子库的采样分析,结果表明:白刺花(Sophora davidii)、刺旋花(Convolvulus tragacanthoides)、金花蚤草(Pulicaria chrysantha)、矮探春(Jasminum humile)、川甘亚菊(Ajania potaninii)、小叶杭子梢(Campylotropis wilsonii)斑块有一定的土壤种子库库容量,土壤种子库种子密度在(890.0±282.233)/m2以上,而马鞍羊蹄甲(Bauhinia faberi)、芦苇(Phragmites australis)、竹叶草(Oplismenus compositus)斑块和裸斑的种子库库容量较小,土壤种子库种子密度分别为(437.5±260.615)/m2、(145.0±45.917)/m2、(172.5±69.567)/m2和(105.0±40.104)/m2;各植物斑块及土壤种子库中地面芽和高位芽生活型的植物占的比例较大,以禾本科(Poaceae)、豆科(Leguminosae)、菊科(Compositae)植物较多;各植物斑块瞬时种子库物种比例较大,在干旱河谷的大环境下,各植物斑块内的种子在土壤种子库中留存的时间可能均较短;马鞍羊蹄甲、芦苇和竹叶草斑块土壤种子库与相应地上植被物种组成的较低相似性(Sorensen相似性指数低于0.369)、极显著负相关性,以及较低的密度和物种丰富度,意味着这3种植物斑块依靠土壤种子库进行自然恢复更新的潜力可能比其他植物斑块更低。此外,裸斑的土壤种子库中存在一定量的种子且长期持续种子库的比例较大(占56%),裸斑具有一定的依靠土壤种子库进行植被恢复的潜力。针对具体的斑块特征,充分利用土壤种子库作为种源,促进现有种子的萌发,改善幼苗的定居环境是今后该区域植被恢复更新工作应更多关注的一种途径。另外,对马鞍羊蹄甲、芦苇、竹叶草斑块辅以适当的人为补充种源等措施也是值得考虑的植被恢复更新途径。     

森林土壤种子库研究进展

土壤种子库与物种多样性存在密切相关性,森林土壤种子库是植被天然更新的物质基础。文章阐述了森林土壤种子库的内涵、森林生态系统土壤种子库的基本特征及其主要研究方法,探讨了影响种子库的基本因素及当前极为关注的热点问题。在受损森林生态系统目标树种培养、植被群落快速恢复和生态系统科学管理等领域仍存在一些理论和实践急待解决的问题,如随着群落进展演替土壤种子库种子数量在增加而质量却在逐渐下降,面临如何解决生态系统健康稳定发育和物种多样性长期维持问题。文章认为今后应加强土壤种子库与生物多样性保护、防止外来物种入侵乡土物种利用及对全球变化的响应等领域的研究工作,以期为从事森林土壤种子库研究和退化森林植被群落恢复实践提供理论指导。     

植被恢复的生态效应研究进展

植被在水土保持、水源涵养及生态系统的固碳过程中起着重要的作用。植被恢复是指运用生态学原理,通过保护现有植被、封山育林或营造人工林、灌、草植被,修复或重建被毁坏或被破坏的森林和其他自然生态系统,恢复其生物多样性及其生态系统功能。目前,植被的自然及人工恢复是改善脆弱生态系统及退化生态系统生态环境现状最有效的措施。植被在恢复过程中对地上植被生态系统,物种多样性的恢复有着重要影响,同时通过凋落物及根系的输入,可以有效改善地下生态系统,增加土壤的养分含量、改善土壤的物理结构、增加土壤生物的生物量及活性。文章以地上及地下生态系统为出发点,综述了植被恢复过程中自然及人工恢复过程中不同的植被类型、不同的恢复时间下植物物种组成和多样性、土壤理化性质及土壤微生物群落的变化。植被的自然及人工恢复在一定程度上均能增加植物物种的多样性,随着恢复年限的增加物种的组成发生改变且多样性呈增加趋势,但一些特殊环境下不当的人工恢复可造成植被演替向退化方向发展,降低生物多样性。不同的植被类型由于其生长方式的不同对土壤理化性质和土壤微生物的影响存在差异,随着恢复年限的增长,土壤理化指标及微生物学指标呈现先增加而后趋于平稳的状态。针对已有的研究进展,提出在未来的研究过程中,一方面应该增加更多的对比研究,对不同环境下,不同的恢复物种,不同的恢复方式进行更深入地探讨;另外一方面应增加不同尺度的研究,现有的研究多集中在样地尺度,未来应在更大尺度上进行分析;再者,地上及地下生态系统之间的相互关系及影响机理一直是土壤学科研究的热点,植被恢复过程中应增加更多该方面的机理研究。     

Are trade-offs in plant resprouting manifested in community seed banks?

Trade-offs in allocation to resprouting vs. seedling regeneration in plants are predicted to occur along fire disturbance gradients. Increased resprouting ability should be generally favored in plant communities with a high probability of crown fire return. Hence, communities dominated by resprouters are predicted to have smaller seed banks than those dominated by species killed by fire. We tested whether there were trait shifts in resprouting ability among growth forms (short-lived herbaceous vs. ground-dwelling perennials vs. shrubs) and among communities (rocky outcrop vs. sclerophyll forest) with contrasting probabilities of crown fire return. Resprouting was more common in ground-dwelling perennials and in the sclerophyll forest community with a high probability of crown fire. Soil seed banks were sampled in rocky outcrop and sclerophyll forest communities in recently burned (18 months) and long-since-burned (12 years) locations at interspersed replicated sites. Collected seed banks were treated with orthogonal treatments of fire stimuli or no stimuli, and seedling emergence was measured in controlled conditions. Seed bank composition reflected the pattern of extant vegetation, with resprouting species being more common in the community with a higher probability of crown fire. Overall, however, resprouting species were poorly represented in the seed bank compared to those species killed by fire. Predicted shifts in allocation to seed production were strongly manifested in community seed banks across the disturbance gradient. Fewer species, seedlings, and seedlings per adult emerged from seed banks in the sclerophyll forest. This suggests that the dominance of resprouting species influences recruitment at the community scale. Community patterns in the seed bank also reflected predicted trade-offs with plant size and growth rate. Short-lived species that are killed by fire dominated the seed bank on rocky outcrops, while longer-lived resprouting species were found in low abundance. Life history trade-offs in persistence and regeneration strongly contribute to coexistence patterns between and within communities with contrasting probabilities of fire return.     

Ecological effects of cultivation on the machair sand dune systems of the Outer Hebrides, Scotland

The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability. Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important factor. The implications of these findings for the long-term management of machair plant communities are discussed and in particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into both seed banks and seed rain and into processes of vegetative reproduction is stressed.     

植被根系及其土壤理化特征在高寒小嵩草草甸退化演替过程中的变化

以野外样地调查和室内分析法研究了不同退化演替阶段高寒小嵩草草甸的植被根系空间变化和土壤环境因子间的关系。结果表明,不同退化演替阶段高寒小嵩草草甸群落植被根系和蕴育植被根系的土壤量发生了明显的变化。特别是0~10 cm土层的植被根系在重度退化阶段显著高于其它退化演替阶段（P〈0.05）,而蕴育植被根系的＂载体＂量在重度退化阶段显著低于其它退化演替阶段（P〈0.05）,根土比（根和土的重量比）明显高于其它退化演替阶段（P〈0.05）;随着退化演替阶段的进行,高寒小嵩草草甸群落物种数、地上部分、植被根系锐减,群落结构和功能明显发生变化;不同退化演替阶段,植被根系（0~40 cm）的垂直分布、根土比与土壤容重、土壤含水量以及土壤中N、P含量存在一定的相关性;不同退化演替阶段高寒小嵩草草甸土壤理化特性的变化影响草地群落地上部分和植被根系;土壤的稳定性是草地生产稳定和恢复的重要因素,在评价与改良退化草地时,要充分了解土壤的退化程度。在高寒草甸地下根系取样方法难以统一,而且土壤表层根系和土壤很难难以分离,加之根系采样破坏性大、工作量大,根土比可能是指示高寒草甸退化程度相对可靠的量化指标。     

Ecological effects of cultivation on the machair sand dune systems of the Outer Hebrides, Scotland

The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability. Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important factor. The implications of these findings for the long-term management of machair plant communities are discussed and in particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into both seed banks and seed rain and into processes of vegetative reproduction is stressed. Nomenclature: Clapham et al. (1981) and Stace (1991, 1997) for vascular plants; Hubbard (1984) for grasses; Pankhurst & Mullin (1991) for the regional flora; Dobson (1992) for lichens; Watson (1981) for mosses and liverworts.     

Effectiveness of vegetation‐based biodiversity offset metrics as surrogates for ants

Biodiversity offset schemes are globally popular policy tools for balancing the competing demands of conservation and development. Trading currencies for losses and gains in biodiversity value at development and credit sites are usually based on several vegetation attributes combined to yield a simple score (multimetric), but the score is rarely validated prior to implementation. Inaccurate biodiversity trading currencies are likely to accelerate global biodiversity loss through unrepresentative trades of losses and gains. We tested a model vegetation multimetric (i.e., vegetation structural and compositional attributes) typical of offset trading currencies to determine whether it represented measurable components of compositional and functional biodiversity. Study sites were located in remnant patches of a critically endangered ecological community in western Sydney, Australia, an area representative of global conflicts between conservation and expanding urban development. We sampled ant fauna composition with pitfall traps and enumerated removal by ants of native plant seeds from artificial seed containers (seed depots). Ants are an excellent model taxon because they are strongly associated with habitat complexity, respond rapidly to environmental change, and are functionally important at many trophic levels. The vegetation multimetric did not predict differences in ant community composition or seed removal, despite underlying assumptions that biodiversity trading currencies used in offset schemes represent all components of a site's biodiversity value. This suggests that vegetation multimetrics are inadequate surrogates for total biodiversity value. These findings highlight the urgent need to refine existing offsetting multimetrics to ensure they meet underlying assumptions of surrogacy. Despite the best intentions, offset schemes will never achieve their goal of no net loss of biodiversity values if trades are based on metrics unrepresentative of total biodiversity.     

Short reviews by the Editor

Soil desiccation is a major issue limiting development and sustainability of forest vegetation in the Loess Plateau of China. Better understanding of the mechanisms of soil desiccation in the Loess Plateau can help scientists and forest managers improve vegetation management practices. The arid soil layer is the ecological aftermath of intense soil desiccation due to disturbed plant succession and soil water reduction. The formation and types of arid soil layer in the Loess Plateau were investigated to determine major causes of soil desiccation and its impact on forest vegetation. The negative effects of soil desiccation on the ecological environment and forest vegetation mainly include drying microclimate, degrading soil quality, poor vegetation growth, difficult forest renewal from natural seed banks, making it even more difficult to reforest forest lands and grasslands following plant senescence. Low precipitation, high evaporation, soil and water losses, improper selection of vegetation types, and too high population density of trees are probably the major reasons for the arid soil layer. Proper selection of vegetation types, adjusting tree density and other management practices can reduce the negative effects of the arid soil layer on forest vegetation.     

三江源区不同建植年代人工草地群落演替与土壤养分变化

研究了了三源区不同建植期人工修复草地在不同演替阶段毒杂草[主要是甘肃马先蒿(Pedicularis kansuensis)]的入侵规律、数量特征,植物群落物种组成、生物苗和草地质最以及土壤养分、微生物活性的变化规律.结果表明,不同建植期人工修复草地植物群落的种类组成、植物功能群组成和群落数量特征存在显著差异.随着演替时间的推移,人工草地群落盖度、高度、物种数、生物最和多样性指数均表现出"V"字型变化规律,杂类草--甘肃马先蒿的数量特征变化尤为明显,在4 a的人工草地群落中开始局部入侵,在5～6 a的人工草地群落中大面积入侵,其入侵速度、入侵面积达到高峰期.土壤的含水量、容重、土壤中有机质、氮素和磷素在演替过程(7 a、9 a草地)中逐渐降低,到一定时期又逐步增加;随着演替的进行,不同建植期人工草地的土壤微牛物生物量碳和酶活性均呈"V"字型,变化.对于退化生态系统的恢复首先是植被恢复,其次是土壤肥力的恢复.土壤有机质等养分的积累、微生物活性的改善不仅能使土壤-植物复合系统的功能得以恢复,同时也能促进物种多样性的形成,有利于人工草地群落稳定性的提高.在试验区尽管植被恢复演替进行得比较缓慢,但从土壤发展的角度看,仍属进展演替.所以,在退化高寒草甸的恢复过程中,若降低和有效控制外界的干扰(如围栏封育),可为退化草地恢复提供繁殖体与土壤环境,实现人工草地逐步向恢复(正向)演替进行.图3表6参34