放牧和围封条件下克氏针茅草原土壤种子库的比较

应用幼苗萌发法对比研究了我国北方农牧交错区克氏针茅(Stipa krylovii)草原在放牧和围封条件下土壤种子库的差异。围封样地的土壤种子库中记录有16个物种,其中禾草类6种,非禾草类10种;若以生活型划分,则全部为多年生植物;若以单子叶或双子叶植物划分,则单子叶植物9种,双子叶植物7种。放牧样地的土壤种子库中记录有13个物种,其中禾草类4种,非禾草类9种;多年生植物12种,一二年生植物1种;单子叶植物5种,双子叶植物8种。放牧样地土壤种子库的密度为(3 664±1 087)粒·m^-2,围封样地土壤种子库的密度是(5 139±1 848)粒·m^-2,差异显著。采用Sorensen指数计算土壤种子库与地上植被的物种相似性,围封样地和放牧样地分别是0.711 1和0.611 1。两个地点的全部种子中, 81.0%属于冷蒿(Artemisia frigida)、克氏针茅、星毛委陵菜(Potentilla acaulis)、糙隐子草(Cleistogenes squarrosa)和砂韭(Allium bidentatum)5种优势植物,16.2% 属于二裂委陵菜(P. bifurca)、菊叶委陵菜(P. tanacetifolia)、猪毛蒿(A. scoparia)、冰草(Agropyron cristatum)和羊草(Leymus chinensis)5种常见植物,而其余9种植物的种子数只占2.8%。此外,通常作为优良牧草的豆科植物的种子数仅占0.6%。上述结果表明,在放牧条件下由于土壤种子库中一些重要物种的缺失或数量很少以及极不均匀的分布,可能会降低退化克氏针茅草原的自然恢复速度。我们建议采取补播这些重要物种并结合其它恢复措施来加快退化克氏针茅草原的恢复进程。     

荒漠草原土壤种子库对草地管理方式的响应

以宁夏中部不同封育年限(封育1a、3a、5a和7a)、不同放牧方式(中等强度自由放牧、中等强度4区轮牧)、补播改良(2006年补播沙打旺Astragalus adsurgens和紫花苜蓿Alfalfa stiva)及未封育等管理方式下的荒漠草原为研究对象,采用空间梯度代替时间梯度法,于2012年3月下旬用样线法采集土壤样品,采用温室萌发法,统计土壤种子库物种组成和种子数,研究了不同草地管理方式下的种子库与地上植被相似性、多样性等特征。结果表明:1)宁夏荒漠草原土壤种子库中共出现14种植物,分属6科14属,除牛枝子(Lespedeza potanimii)为半灌木外其余均为草本植物。多年生植物占土壤种子库植物总数的65.3%,一年生植物占土壤种子库植物总数的35.7%;多年生植物种子数量随封育年限增加而表现为下降趋势,封育1a和未封育草地最多;2)不同管理方式下土壤种子库和地上植被的共有物种数为2—6种,封育时间延长导致土壤种子库物种与地上植被相似性下降,土壤种子库和地上植被共有物种数有减少趋势,自由放牧降低了土壤种子库和地上植被的共有物种数,补播恢复的草地土壤种子库中未出现补播物种;3)种子库物种多样性与管理方式无明显的相关性;种子库物种多样性指数4区轮牧草地最高,封育7a草地最低,物种丰富度指数封育1a草地最高,均匀度指数自由放牧草地最高,补播草地最低。若荒漠草原仅依靠土壤种子库恢复自然植被,则不建议封育时间过久,需间以适当的干扰(放牧);补播外来种未对荒漠草原土壤种子库产生贡献,反而对乡土种产生了一定限制。     

科尔沁沙地围封沙质草甸土壤种子库特征的研究

科尔沁沙地沙质草甸围封 5年后土壤种子库中植物种类有 38种 ,其中一、二年生草本植物 2 4种 ,多年生草本植物 9种 ,灌木 5种。土壤种子库密度为 (1385 5± 16 5 1)粒·m-2 ,其中 ,一、二年生草本植物所占的比例最大为 96 5 8% ,前 5种一、二年生草本植物黄蒿、灰绿藜、猪毛菜、狗尾草和画眉草占总数的 87 2 0 % ,而多年生草本植物和灌木类种子库密度分别占0 94 %和 2 4 8%。若以单子叶和双子叶植物统计 ,单子叶植物种子数占 13 13% ,双子叶植物的种子数占 86 87% ,其中豆科植物仅占 2 83%。土壤种子库中所有植物种的密度与其相对应的地面植物种的密度呈显著非完全相关性 ,其关系可用三次曲线来表示。从种子库组成分析 ,已围封 5年的沙质草甸植被仍处在黄蒿 -杂类草混合植被阶段。     

南洞庭湖杨树清理迹地恢复初期土壤种子库特征及其与土壤因子的关系

本文研究了杨树清理1、2年后迹地的土壤种子库结构、多样性及其与地上植被和土壤因子的关系,并以未清理杨树洲滩为对照,探讨洞庭湖杨树清理迹地土壤种子库在植被自然恢复中的潜力。结果表明: 研究样地土壤种子库萌发出的植物种子分属23科59属65种,各样地土壤种子库密度和物种数大小为:1年迹地(11810粒·m^-2,49种)＞2年迹地(9686粒·m^-2,44种)＞对照(6735粒·m^-2,29种)。与未清理洲滩相比,清理迹地土壤种子库与地上植被多年生中生和湿生植物物种多样性和相似性系数增加,土壤含水率和养分含量升高,pH值降低。土壤含水率和有机质与水蓼等湿生植物分布的关系密切,全钾和全磷对虉草等多年生植物分布的影响较大。在杨树清理迹地自然恢复过程中,随着土壤理化性质的变化,土壤种子库的物种数目和密度显著增加,以致地上植被物种多样性升高,因此,土壤种子库成为迹地湿地植被恢复的重要繁殖体来源。     

围封沙质草甸土壤种子库与幼苗库的特征

采用野外定点取样和萌发实验相结合的方法,研究了科尔沁沙地围封沙质草甸土壤种子库和幼苗库的特征.结果表明:土壤种子库总密度为13854±1651有效种子数/m2,而幼苗库的总密度为808±164株/m2,仅为土壤种子库总密度的6%,土壤种子库与幼苗库总密度之间存在显著的差异 F=36.0,n=219,P<0.001 .土壤种子库与幼苗库的植物种数分别为37和44,其中一、二年生草本植物分别占种子库与幼苗库植物种数的62%和50%,而多年生草本植物所占的比例分别为24%和41%,灌木所占的比例很小,分别为14%和9%.土壤种子库与幼苗库种类组成上的相似性系数为0.667,表现出较小的异质性.土壤种子库密度与幼苗库密度之间存在显著的相关性,其间关系可用三次曲线来描述.     

草地沙化过程地上植被与土壤种子库变化特征

研究了草地沙漠化过程地上植被与土壤种子库的变化特征。获如下结论：(1)草地沙漠化过程地上植被与土壤种子库物种多样性的衰减模式不同,土壤种子库植物种数从潜在沙漠化阶段(固定沙地)到中度沙漠化阶段(半流动沙地)变化很小,而从中度沙漠化到严重沙漠化阶段(流动沙地)衰减速度明显加快;地上植被种数随着沙漠化程度增加而下降,其中从中度沙漠化到严重沙漠化发展阶段衰减幅度最大。(2)地上植被与土壤种子库密度随着沙漠化程度增加而下降,但下降速率因沙漠化发展阶段不同而异,从固定到半固定沙地是地上植被与土壤种子库密度下降最快的时期。(3)地上植被与土壤种子库共有种数随着沙漠化程度的增加而减少,从而导致了地上与土壤种子库群落组成的相异性增大。(4)4种退化沙地土壤种子库组成的相似性要高于地上植被,表明在沙漠化过程中土壤种子库群落组成的稳定性要高于地上植被。(5)地上植被密度与土壤种子库密度存在显著相关性,其关系可用二次曲线来描述。     

围封对内蒙古典型草原与荒漠草原植被-土壤系统碳密度的影响

草地生态系统是巨大的碳库, 在全球碳循环中起着重要的作用。该研究以内蒙古中温带草地区典型草原和荒漠草原为研究对象, 测定了两种草原类型围封与放牧后地上生物量碳密度、地下生物量碳密度和土壤碳密度, 探讨围封对两种草原类型植被-土壤系统碳密度的影响。结果表明: (1)围封显著地增加了典型草原地上和地下生物量的碳密度, 对荒漠草原地上生物量碳密度增加影响显著, 对地下生物量碳密度增加影响不显著; (2)围封显著地增加了典型草原土壤碳密度, 使荒漠草原土壤碳密度有增加的趋势, 但影响不显著; (3)典型草原围封样地地下生物量和土壤碳密度的垂直分布显著高于放牧样地, 而荒漠草原围封样地地下生物量和土壤碳密度的垂直分布与放牧样地的差异不显著; (4)围封分别提高了典型草原和荒漠草原植被-土壤系统碳密度的2.2倍和1.6倍, 典型草原和荒漠草原分别有超过65%和89%的碳储存在土壤中, 两种草原类型的地下生物量碳库均占总生物量碳库的90%以上。研究结果表明围封能够有效地增加草原生态系统的碳储量。     

基于地统计学的退化草地狼毒种群土壤种子库空间异质性

土壤种子库作为植被天然更新的物质基础,其空间异质性对于认识种群繁殖更新机制具有重要意义。利用野外调查和地统计学方法,设置4个草地退化梯度,研究了祁连山北坡狼毒种群土壤种子库空间异质性及其与地上植被的关系。结果表明:4个退化梯度草地土壤种子库的半变异函数模型均为非线性模型,表现为聚集分布;随着天然草地退化程度加剧,狼毒种群土壤种子库的密度与变程不断增大、基台值与结构比呈"U"型变化趋势,其中76.88%~93.75%的空间异质性是由空间自相关引起;在未退化和重度退化草地地上植被密度与土壤种子库密度呈正相关,在轻度和中度退化草地中地上植被密度与土壤种子库密度之间未呈现相关性。在草地退化演替过程中,土壤种子库空间分布主要受地上植被等结构性因素影响,而放牧等干扰因素也在一定程度上降低了空间自相关性。     

Effects of enclosure on carbon density of plant-soil system in typical steppe and desert steppe in Nei Mongol,China

草地生态系统是巨大的碳库, 在全球碳循环中起着重要的作用。该研究以内蒙古中温带草地区典型草原和荒漠草原为研究对象, 测定了两种草原类型围封与放牧后地上生物量碳密度、地下生物量碳密度和土壤碳密度, 探讨围封对两种草原类型植被-土壤系统碳密度的影响。结果表明: (1)围封显著地增加了典型草原地上和地下生物量的碳密度, 对荒漠草原地上生物量碳密度增加影响显著, 对地下生物量碳密度增加影响不显著; (2)围封显著地增加了典型草原土壤碳密度, 使荒漠草原土壤碳密度有增加的趋势, 但影响不显著; (3)典型草原围封样地地下生物量和土壤碳密度的垂直分布显著高于放牧样地, 而荒漠草原围封样地地下生物量和土壤碳密度的垂直分布与放牧样地的差异不显著; (4)围封分别提高了典型草原和荒漠草原植被-土壤系统碳密度的2.2倍和1.6倍, 典型草原和荒漠草原分别有超过65%和89%的碳储存在土壤中, 两种草原类型的地下生物量碳库均占总生物量碳库的90%以上。研究结果表明围封能够有效地增加草原生态系统的碳储量。     

放牧对鄂尔多斯高原油蒿草场生物量及植被-土壤碳密度的影响

以围封保护和自由放牧油蒿草场为研究对象,通过野外调查与室内分析,研究了围封和放牧条件下沙地草场生物量和植被-土壤碳密度。结果表明:(1)自由放牧使油蒿群落中植物种类增加,但降低了植物群落盖度。自由放牧不仅导致油蒿草场地上、地下总生物量降低,也使得油蒿地上、地下生物量占群落地上、地下总生物量的比例减小。生长季自由放牧样地凋落物生物量显著大于围封保护样地(P0.05);(2)围封保护样地植被碳密度大于自由放牧样地,土壤碳密度却小于自由放牧样地,但两个样地间差异不显著(P0.05);(3)油蒿草场90%以上的碳储存于土壤中,围封保护样地和自由放牧样地油蒿草场土壤碳密度占植被-土壤系统碳密度的91%、93%;(4)围封保护油蒿草场碳密度为2.29 kg/m2,自由放牧油蒿草场碳密度为2.68 kg/m2,两个样地间差异不显著,自由放牧对油蒿草场碳密度影响不大。     

Influence of Grazing on Soil Seed Banks Determines the Restoration Potential of Aboveground Vegetation in a Semi‐arid Savanna of Ethiopia

Species composition, number of emerging seedlings, species diversity and functional group of the soil seed banks, and the influence of grazing on the similarity between the soil seed banks and aboveground vegetation, were studied in 2008 and 2009 in a semi‐arid savanna of Ethiopia. We tested whether the availability of persistent seeds in the soil could drive the transition from a degraded system under heavy grazing to healthy vegetation with ample perennial grasses. A total of 77 species emerged from the soil seed bank samples: 21 annual grasses, 12 perennial grasses, 4 herbaceous legumes, 39 forbs, and 1 woody species. Perennial grass species dominated the lightly grazed sites, whereas the heavily grazed sites were dominated by annual forbs. Heavy grazing reduced the number of seeds that can germinate in the seed bank. Species richness in the seed bank was, however, not affected by grazing. With increasing soil depth, the seed density and its species richness declined. There was a higher similarity in species composition between the soil seed bank and aboveground vegetation at the lightly grazed sites compared with the heavily grazed sites. The mean similarity between the seed banks and aboveground vegetation was relatively low, indicating the effect of heavy grazing. Moreover, seeds of perennial grasses were less abundant in the soil seed banks under heavy grazing. We concluded that restoration of grass and woody species from the soil seed banks in the heavily grazed areas could not be successful in semi‐arid savannas of Ethiopia.     

Vegetation and soil seed bank in a 23-year grazing exclusion chronosequence in a Mediterranean dry grassland

Long-term grazing shaped plant diversity in dry Mediterranean grasslands. Abandonment of grazing affects plant diversity especially in the northern Mediterranean. Considerable efforts are, therefore, under way for grassland conservation and restoration. Yet, we do not know at which temporal scales impacts of grazing abandonment appear and in particular how soil seed banks evolve after longer grazing abandonment. Here, we provide detailed data from one of the very few long-term experiments available. These experiments provide data for up to 23 years (1982–2005) of grazing exclusion built in 1982, 1989, 2000 and 2001. Grazing exclusion decreased species richness, modified vegetation structure and changed soil parameters. Decline in species richness appears in communities that experienced 16 and 23 years of grazing exclusion. Only four to nine plant species of this Mediterranean grassland built persistent soil seed banks appearing after grazing exclusion, compared to 40–50 species in the established vegetation of grazed plots. Hence, similarity between vegetation and soil seed bank decreased with time of grazing exclusion. Even 23 years after abandonment, no woody plants colonised the experiments. We conclude that vegetation will recover fast from grazing abandonment in the short-term. Nevertheless, longer abandonment will impact diversity due to reduced soil seed banks.     

Soil seed bank dynamics of fire-prone wooded grassland, woodland and dry forest ecosystems in Ethiopia

In order to reveal the role of soil seed banks in vegetation recovery after fire in savanna, the spatial distribution and temporal changes in the soil seed banks of regularly burning savanna in Gambella, western Ethiopia, was studied. The seedling emergence technique was employed to determine the species composition and density of the soil seed bank of six sites ranging in fire severity from wooded grassland with frequent fires over woodland with intermediate fire frequency to forest with absence of fires. Species composition and density of seeds in the soil were compared between seasons, depths and sites with different types of standing vegetation. Fourteen plant species were recorded in the soil seed bank from the grassland and woodland sites and 6 from the dry forests; 60 % of the taxa in the soil seed bank were annuals and 40 % were perennials. The soil seed banks were largely dominated by graminoids and 48–97 % of the soil seed bank in the grasslands and woodlands was of a single grass species, Hyparrhenia confinis , which was absent from the dry forests. The soil seed pools ranged from less than 100 to 4700 seeds per m² depending upon the season. The soil seed bank of graminoids was nearly empty after the onset of the rainy season whereas seeds of broadleaved herbs and woody species able to germinate were still found after this time. Floristic composition, representation of life forms and density of seeds in soil did not correspond closely with that of the standing vegetation, but within graminoids there was a strong similarity between the soil seed bank and the standing vegetation. The current fire regime of Ethiopian savanna woodlands appears to maintain the dominance of graminoids over broadleaved herbs and woody plants both as seeds in the soil and in the standing vegetation.     

The role of the soil seed bank in vegetation recovery on an oceanic island severely damaged by introduced goats

Question: Are the seed banks of an isolated subtropical oceanic island capable of naturally regenerating vegetation either with species of the historical forest community or with the existing grassland community after severe damage to the vegetation by goats? Location: Nakoudojima Island, Bonin Archipelago (Ogasawara Shoto), Japan. Methods: Soil samples were collected at 0–5 cm and 5–10 cm depths from seven plots in forests, grasslands, artificially matted areas and bare land. Soil seed banks were assessed using the seedling emergence method followed by the hand‐sorting of ungerminated seeds. We determined the size and composition of the seed banks in upper soil layers of plots and compared the seed banks to the standing vegetation. Results: A total of 12 220 seedlings belonging to 42 species from 20 families germinated. Total mean seed density (0–5 cm depth) was low in all plots within forest, grassland, and heavily degraded vegetation types (34.7 ± 8.6 to 693.5 ± 123.6, 58.6 ± 7.8 to 107.1 ± 10.0, and 1.1 ± 0.5 to 7.2 ± 2.3 seeds/m², respectively). Forbs and graminoids dominated the seed banks of grassland and forest plots including Cyperus brevifolius, Gnaphalium pensylvanicum, Oxalis corniculata and Solanum nigrum, and these alien species comprised 90% of the density of the seed bank. There was little correlation between seed banks and standing vegetation of the island (Sørensen similarity coefficient values 0.26 to 0.45). Conclusions: If natural regeneration occurs from the seed bank of the island, future vegetation will not move toward the original forest community, because the seed bank is dominated by non‐native herbaceous grassland species. Though isolated, a few forest remnants with low species richness could be an important source for the natural re‐establishment of forest on the island; however, seed availability may be limited by either poor dispersal or pollination so that woody species will probably recover very slowly on this goat‐impacted island.     

Effects of grazing on soil seed bank dynamics: An approach with functional groups

Abstract. The relationship between intensity and timing of cattle grazing on changes in the size and composition of the soil seed bank were investigated in a 3‐yr study in a Mediterranean grassland in northeastern Israel. Treatments included manipulations of stocking rates and of grazing regimes, in a factorial design. The retrieved soil seed bank community was rich in species, with 133 species accounting for 80% of the 166 species recorded at the site. Within the seed bank, 89% of the species were annuals. Seed bank dynamics was analysed in terms of plant functional groups and germination strategies. In terms of total seed bank density and including all functional groups, 42% of the seeds present in the soil did not germinate under watering conditions. The dormancy level differed greatly among functional groups. The seed bank of annual legumes, crucifers, annual thistles and annual forbs had a large fraction of non‐germinated seeds and characterized areas grazed early in the growing season under high and very high grazing intensity. These functional groups were considered to have a higher potential for persistent seed banks production. In contrast, short and tall annual grasses and tall perennial grasses, that were dominant in ungrazed or moderately grazed paddocks, generally had seed banks with a very small fraction of non‐germinated seeds. Seed bank densities varied widely between grazing treatments and years. Under continuous grazing, heavy grazing pressure reduced seed bank densities of grasses and crucifers in comparison to moderate grazing. The greatest reduction on the seed bank densities resulted from heavy grazing concentrated during the seed‐set stages.     

滇东南岩溶山地退化植被土壤种子库的储量与组成

 在云南省东南部3个典型岩溶地点的土壤种子库储量与组成的研究表明,不同地点代表不同退化与恢复阶段的次生林、灌丛与退化草地的土壤内均储藏有丰富的植物种子,其密度值变动于4 090～14 930粒·m－2之间;物种数23～45种,其中草本物种及其种子储量最丰, 灌木次之,乔木和藤本及其种子稀少。在0～10 cm土层内,随着深度的加深,种子密度由0～2 cm,2～5 cm,5～10 cm逐渐减少,次生林的降低幅度相对较小。相对而言,种子密度值、物种数都以次生林为高,灌丛与退化草地之间的差异较小。同时次生林种子库中的乔、灌木的种子数量相对较多,而草本相对较少。从物种组成来看,少数物种的种子在库中的储量十分丰富,且各种子库间在物种组成上有很大的相似性,同一地点的3种植被类型间的两两相似性系数在0.6～0.7之间,不同地点的任一两类型间的相似性系数在0.4～0.6之间。9.3%的物种在所有样地内都出现。每一种子库中储量最丰的前3位都来自菊科的胜红蓟（Ageratum conyzoides）、劲直白酒草(Conyza stricta)、紫茎泽兰(Eupatorium adenophorum)、一点红（Emilia sonchifolia）,唇形科的鸡骨柴（Elsholtzia fruticosa）,蔷薇科的长毛绣线菊(Spiraea martinii var. pubescens)。     

Similarity between seed bank and vegetation in Mediterranean grassland: a predictive model

Abstract. The similarity in species composition between seed bank and vegetation was analysed in Mediterranean grasslands in relation to altitude, topography and grazing. Soil samples were collected in permanent plots in autumn at the end of the summer drought period and in spring, before the new seed fall and after the natural winter seed stratification. The seed bank composition was determined by greenhouse germination over a nine-month period. Presence/absence of species in the standing vegetation throughout the complete annual cycle, and the percentage area of bare ground in October, were recorded in the same plots. The species composition of the standing vegetation is clearly determined by altitude, topography and grazing, while the floristic composition of the seed banks is only related to altitude and topography in the case of autumn seed bank and with any of the three factors in the spring seed bank. Relative abundances of grasses, legumes and forbs also show different patterns in vegetation and seed bank data. Sørensen similarity between the autumn seed bank and the vegetation declines as altitude rises, but there are no significant differences for topography and grazing. This similarity decreases in the case of the spring seed bank and does not show any significant relationship with any of the factors. The perennial/ annual ratio and the proportion of bare soil in October are proposed as explanatory variables in a predictive model of similarity between the seed composition of the seed bank and vegetation.     

Edaphic patchiness influences grassland regeneration from the soil seed‐bank in mountain grasslands of central Argentina

The soil seed‐banks in the main natural vegetation patches that make up mountain grasslands on granite substrates in central Argentina were studied. The main natural vegetation types are moist swards, tall‐tussock grasslands and stony grasslands. Ten compound soil samples from each community at two soil depths (0–5 and 5–10 cm) were taken. The density of soil seed‐banks was highest in moist swards, intermediate in stony grasslands and lowest in tall‐tussock grasslands. Low levels of similarity were found between the established vegetation and total soil seed‐bank in tall‐tussock grasslands and stony grasslands, but the similarity was higher in swards. In all three communities the seed‐bank was most frequently transient in nature. Short‐term persistent and long‐term persistent seed‐banks were less frequent. Regeneration from the seed‐banks after disturbance is expected to differ among communities on different edaphic patches. On the basis of the density and longevity of the soil seed‐banks and the similarity to the established vegetation, potential for in situ regeneration should be lower in tall‐tussock grasslands, intermediate in stony grasslands and higher in moist swards.     

Soil seed bank in different vegetation types in the Loess Plateau region and its role in vegetation restoration

In the Loess Plateau region, soil erosion is a serious problem. Vegetation restoration is an effective approach to control soil erosion and improve ecosystems. The soil seed bank generally plays an important role in vegetation restoration after disturbance. Thus, we reviewed soil seed bank studies to reveal the soil seed bank characteristics and its role in vegetation restoration in three vegetation types (forest, forest‐steppe, and steppe). We selected 38 seed bank studies and analyzed several seed bank characteristics, such as seed density, species composition, and the relationship between seed size and seed bank. We also assessed the role of the soil seed bank in vegetation restoration. The soil seed bank density ranged from 2,331 ± 1,993 to 6,985 ± 4,047 seeds/m² among the different vegetation types. In the soil seed bank, perennial herbs and grasses accounted for 51.5% of the total species. Native species that were dominant or common in the standing vegetation usually had relatively high seed bank densities. Moreover, species with smaller seeds generally had higher soil seed bank densities. The present study indicates that the soil seed bank plays a significant role in spontaneous vegetation restoration, especially during the early successional stages in abandoned slope farmlands and grazing‐excluded grasslands. However, species with large seeds or transient soil seed banks should be reintroduced through seeding to accelerate target species restoration. More studies on soil seed banks need to be conducted to comprehensively reveal their characteristics.