Size Of Seed Bank Research Articles

Modeling the Simultaneous Evolution of Resistance to ALS- and ACCase-Inhibiting Herbicides in Barnyardgrass (Echinochloa crus-galli) in Clearfield®Rice

Herbicide-resistant barnyardgrass has become widespread in the rice production systems of the midsouthern United States, leaving few effective herbicide options for controlling this weed. The acetolactate synthase (ALS)- and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides remain largely effective in Clearfield®rice production, but strategies need to be developed to protect the long-term utility of these options. A two-trait model was developed to understand simultaneous evolution of resistance in barnyardgrass to the ALS- and ACCase-inhibiting herbicides in Clearfield rice. The model was used to predict resistance under a number of common weed management scenarios across 1,000 hypothetical rice fields in the Mississippi Delta region and answer some key management questions. Under an ALS inhibitor–only program consisting of three annual applications of imidazolinone herbicides (imazethapyr or imazamox) in continuous Clearfield rice, resistance was predicted within 4 yr with 80% risk by year 30. Weed management programs that consisted of ALS- and ACCase-inhibiting herbicides such as fenoxaprop and cyhalofop greatly reduced the risk of ALS-inhibiting herbicide resistance (12% risk by year 30), but there was a considerable risk for ACCase resistance (evolving by year 14 with 13% risk by year 30) and multiple resistance (evolving by year 16 with 11% risk by year 30) to both of these mechanisms of action. A unique insight was that failure to stop using a herbicide soon after resistance evolution can accelerate resistance to the subsequent herbicide option. Further, a strong emphasis on minimizing seedbank size is vital for any successful weed management strategy. Results also demonstrated that diversifying management options is not just adequate, but diversity combined with timely herbicide applications aimed at achieving high efficacy levels possible is imperative.

Soil seed bank in a patchy vegetation of coastal sandy plains in southeastern Brazil

AbstractLarge seed banks have been found in tropical dry forests and also in habitats with high seasonality in rainfall. However, patchily structured vegetation could induce great spatial variation in the seed bank. We characterized the seed bank in a patchy vegetation of restinga, a common type of coastal vegetation found in the Atlantic forest biome. We also evaluated whether there is any spatial variation between the litter and soil layer, bare sand, and the edge and center of vegetation patches with distinct species dominance. We found 104 seeds/m2 in the seed bank using a 5‐cm‐depth sampling. Seven out of 16 species found in the restinga seed bank germinated; two of these were found in the early stages of vegetation patches. We found a higher number of seeds at the edge than in the center of vegetation patches. However, there were no significant differences in the number of seeds in the seed bank between the litter and soil layer, and between vegetation patches with distinct species dominance. Bare sandy soils had lower seed bank densities than vegetation patches. A small seed bank size might be explained by the low proportion of seeds from herbaceous and woody species, which are pioneers in the Atlantic forest. However, seed bank might play an important role in the early stages of the successional process, due to the occurrence of the few species that are able to colonize new young vegetation patches.

Development of a thermal-time model for combinational dormancy release of hairy vetch (Vicia villosa ssp. villosa)

Seed dormancy could be a factor related to natural reseeding of hairy vetch (Vicia villosa ssp. villosa Roth.), a winter annual species cultivated for seed, pasture, hay, green manure and cover crop. The presence of combinational dormancy (physical dormancy + physiological dormancy, PY + PD) in hairy vetch was explored by a model using laboratory and field measures. At the stage of natural dispersal, dry seeds of hairy vetch were stored under laboratory conditions at 5, 10, 20 and 30°C (±2°C) or buried at 5 cm depth in an experimental field. Germination at 5, 8, 10, 15, 20 and 25°C was assessed at regular intervals up to 295 days after harvest. Following the hypothesis of the existence of a combinational dormancy mechanism, model development was based on the estimation of: (i) the fraction of non-PY seed as a function of after-ripening thermal-time accumulation, and (ii) seed population thermal parameters associated with a given level of PD. The developed model adequately described the after-ripening thermal-time requirements for PY + PD release of V. villosa. Based on model predictions, under a semi-arid thermal regime, >45% of vetch seeds shed during the summer season would be able to germinate during early autumn. Thus, the seed-bank size threshold at the end of the first growing season should be >65 seeds m–2 in order to reach a minimum stand of 30 plants m–2 necessary for a productive pasture.

Diversity in weed seed production and the soil seed bank: Contrasting responses between two agroecosystems

This study was carried out to compare the diversity in seed production and the soil seed bank in a dryland and an irrigated agroecosystem in the dry tropics. Both agroecosystems showed a comparable number of species, but only 25% and 38% similarity during the winter and rainy cropping seasons, respectively. In the irrigated agroecosystem, the amount of seed production diversity was almost double in the winter season, compared to the rainy season. The weed seedbank diversity was low but was sensitive to cropping practices and seasons in both agroecosystems. A considerably smaller soil seedbank size in the irrigated agroecosystem (cf. dryland) was related to lowered weed seed production. The dryland agroecosystem showed a greater accumulation of the seeds of broad‐leaved weeds, whereas the irrigated agroecosystem accumulated more seeds of the grasses or sedges. About three‐fourths of the seeds during the winter season were accounted for by Anagallis arvensis and Chenopodium album in the dryland agroecosystem and by C. album and Melilotus indica in the irrigated agroecosystem. However, during the rainy season, Ammannia baccifera, Echinochloa colona and Cyperus rotundus dominated in both agroecosystems. The changes in the weed seed bank and its diversity are mainly attributed to differences in water management, which tends to reduce species diversity, especially at a lower depth, but leads to the dominance of some potentially noxious weeds (e.g. Phalaris minor and M. indica). Approximately double the soil seedbank size and a greater diversity at a lower depth might indicate an adaptive mechanism in the storage of weed seeds in the dryland agroecosystem.

Grazing impact on desert plants and soil seed banks: Implications for seed-eating animals

We assess whether the knowledge of livestock diet helps to link grazing effects with changes in plant cover and soil seed bank size, aiming at inferring the consequences of grazing on seed-eating animals. Specifically, we test whether continuous and heavy grazing reduce the cover, number of reproductive structures and seed reserves of the same grass species whose seeds are selected and preferred by granivorous animals in the central Monte desert, Argentina. Grass cover and the number of grass spikes usually diminished under grazing conditions in the two localities studied (Telteca and Ñacuñán), and soil seed bank was consistently reduced in all three years evaluated owing to a decline of perennial grass and forb seeds. In particular, the abundance of those seeds selected and preferred by birds and ants (in all cases grass species) declined 70–92% in Ñacuñán, and 52–72% in Telteca. Reduction of perennial grass cover and spike number in grazed sites reinforced the causal link between livestock grazing and the decline of grass soil seed reserves throughout failed plant reproduction. Grass seed bank depletion suggests that grazing may trigger a “cascade” of mechanisms that affect the abundance and persistence of valuable fodder species as well as the availability of seed resources for granivorous animals.

Soil seedbanks in slash‐and‐burn rice fields of northern Laos

SummaryCrops in shifting cultivation fields often suffer from severe weed infestation when long fallow periods are replaced by short fallow periods. The soil seedbank as a source of weed infestation was studied in four fields that differed in their last fallow duration. The effect of burning was analysed by comparing adjacent pre‐burn and post‐burn samples (two sites). Surface vegetation was monitored from burning to harvest in the plots from which soil samples were taken to determine the fraction of the seedbank germinating (three sites). Seedbank size (1700–4000 seedlings m−2) varied depending on a single species, Mimosa diplotricha. Burning reduced emergence of most species, but stimulated emergence in others. Densities in the seedbank were not correlated with above‐ground abundances in the field, except for some species. Most species emerging after 50 days from the soil samples (40% of seedlings) were absent from the field after 190 days. Whilst the data from this study are derived from only four fields, the weed problems after short‐term fallowing appeared to be due to a larger fraction of the seedbank emerging, possibly due to shallow burial, and to a floristic shift towards adaption to burning, rather than the size of the seedbank per se.

Soil seed bank in selected patches of vegetation in the beech forest of Beskid Śląski (Southern Poland)

The aim of this study was to examine the size and composition of soil seed bank in the beech forest of Beskid Śląski (southern Poland). The study was conducted in autumn 2009 on two patches of vegetation. The applied method of research was seedling germination from the soil samples. The soil was sampled to the depth of 10 cm using a 5 cm diameter cylinder. The observation of the seedling's growth was conducted in laboratory conditions for 5 months. The size of the soil seed bank was estimated at 592 seeds/m (16 species) for Dentario glandulosae-Fagetum community and 2030 seeds/m (9 species) for Luzulo nemorosae-Fagetum comunnity. Dominant species in the seed bank was Juncus sp. and Luzula luzuloides. In addition, the composition of the seed bank and the above-ground vegetation did not show any significant similarities and a greater number of seeds were located in the upper 5cm layer of soil.

Effects of fuel reduction treatments on a gorse shrubland soil seed bank in the north of Spain: Comparing mastication and prescribed burning

Fuel reduction treatments are commonly used to decrease the risk of severe wildfire in shrubland areas in the North of Spain. Information about the associated environmental effects is required to help forest managers select the most appropriate treatment. Although the soil seed bank plays an important role in post-disturbance recovery and resilience of frequently disturbed shrubland communities, little is known about how it is affected by fuel reduction treatments. We carried out a combined greenhouse and field study to evaluate the effects of two fuel reduction methods (prescribed burning and mastication) on the size and composition of the soil seed bank in a fire-prone gorse shrubland area in northern Spain. Total seedling density, species richness and similarity index were the variables analyzed. We also determine the effect of the depth of the soil organic cover remaining after mastication on the soil seed bank composition.In the greenhouse experiment, significantly more seedlings emerged from the samples of the soil seed bank obtained after burning (810.6seedlingsm−2) than in those obtained before burning (608.3seedlingsm−2) and after mastication (610.1seedlingsm−2). This contrasted with the lack of differences observed before and after mastication. Species richness in the soil seed bank was not altered by either prescribed burning or mastication. The observed high degree of similarity between soil seed bank and above-ground vegetation in both pre and post-treated soils was attributed to the dominance of resprouting species.Post-burning seedling density was not significantly related to any of the soil thermal regime parameters during burning. The depth of the soil organic cover after mastication apparently did not affect the composition of the soil seed bank.The field study revealed a low rate of seed germination of all species, which along with the rapid recovery of cover by the resprouting woody species in the community, suggests that the soil seed bank makes little contribution to the recovery of shrubland communities after fuel reduction treatments.There was little opportunity to enhance vegetation recovery through the soil seed bank after prescribed burning and mastication. Mastication seems to be a more conservative technique although low intensity burnings as those conducted in the present study did not stimulate seed germination nor reduce seed bank size. In summary, prescribed burning and mastication can be considered feasible techniques for fuel management in these shubland areas.

Efectos de dos sistemas de labranza sobre poblaciones de arroz rojo (Oryza sativa L.) en un agroecosistema arrocero inundado.

Effects of two tillage systems on red rice (Oryza sativa L.) populations in a flooded rice agroecosystem. The influence of two tillage systems was evaluated on red rice (Oryza sativa L.) populations and other frequent weeds in rice agroecosystems throughout four consecutive cycles of commercial flooded rice. In order to estimate the seed bank size, soil samples from three depths (0 to 5, 5 to 20 and 20 to 40 cm) were taken at the beginning of each crop cycle. The density of the most abundant weeds in the crop area was also measured. In both tillage systems there were significant differences in emerged weeds and seed banks. While the red rice seed bank and its emerged populations on the field presented incremental trends in conventional mechanized sowing (CMS), a progressive decrease in bank size and a lower density was observed in direct seeding into stubble (DSS), during cycles in which no tillage was used. Populations of annual sedges like Cyperus spp. and Fimbristylis milliaceae increased in both tillage systems, with greater intensity in CMS. The vertical distribution of the weed seed bank in the soil was also different for both tillage systems. In DSS more than 66% of the red rice seed bank and 82% of the germinated seeds were found within the first five cm of the soil profile. It is concluded that the DDS system promotes favorable conditions to maintain control over red rice populations and other weeds in flooded rice.

Seeds of EndangeredHarrisia fragransform Persistent Soil Seed Banks and Withstand Orthodox Storage Conditions

Understanding soil seed-bank dynamics of endangered species is crucial for their effective management and conservation. Whether or not seeds of Harrisia fragrans Small, a U.S. endangered cactus endemic to Florida (USA) form persistent soil seed-banks or withstand drying and/or freezing under storage conditions was unknown. We conducted a seed burial experiment with seeds collected from three sites (North, Middle, and South) within the Savannas Preserve State Park, FL, USA. We buried the seeds in plots with three light conditions (sun, partial sun, and shade) at each of the three sites and tested their viability in germination trials after 3.5, 8, 11, 16, 19 and 23 months of burial in soil. Buried seeds remained alive throughout the 23 months of the study period with germination ranging from 64 to 100%, which suggests that this species forms a persistent soil seed-bank. Microhabitat conditions markedly affected seed-bank size and subsequent seed viability. Seeds from the South site exhibited higher and faster germination than seeds from the Middle or North sites. We also evaluated if H. fragrans seeds could withstand dry storage under low relative humidity (RH) and low temperature. In the laboratory 76% of seeds stored under 12% RH and -20°C for 1 and 24 weeks germinated faster than seeds stored under 21–23°C and 50% RH. Thus, the capacity of Harrisia fragrans to form a persistent soil seed bank influences population persistence. Its ability to be stored in orthodox ex-situ conditions offers viable options for its future conservation and regeneration.

Advances, trends and challenges in seed bank research for sand dune ecosystems

Sand dunes, characterized by wind erosion and sand burial, are a unique habitat with particular physical and biological processes. The study of sand dune seed banks is vital to biodiversity conservation and vegetation restoration. However, spatial-temporal patterns, mechanism of formation and ecological function of seed banks in the dune habitat are not fully understood. In recent years, much attention has been paid to these seed banks. Seed bank size and composition are dependent on dune type, position and soil depth. Seasonal and annual patterns of the seed bank are regulated by wind and the rainy season. The seed bank is shaped by diverse disturbances and habitat types. The structure and composition of the seed bank are highly related to plant reproductive strategies of colonizers. Contribution of the seed bank to vegetation restoration varies with dune type. Further studies are needed on 1) regional differences in seed banks, 2) relationship to stages of plant life history, 3) consequences of various disturbances, 4) contribution to vegetation restoration and 5) linkages to sand burial and erosion.

Effects of repeated clover undersowing, green manure ley and weed harrowing on weeds and yields in organic cereals

Cover crops can be used to reduce leaching and erosion, introduce variability into crop rotation and fix nitrogen (N) for use by the main crops, less is however known about effects on weeds. The effects on weed seed bank, weed growth and grain yield of 4 years of annual undersown clover and ryegrass alone and in combination, and one of the 4 years with clover or clover + grass as green manure, were studied in oat and spring wheat at two experimental sites in south-eastern Norway. These treatments were compared with no undersown crop (control) and with weed harrowing. In contrast to many results in the literature, the undersown clover in this study did not suppress annual weeds, but fertilized the weeds as well as the cereals. Undersown clover resulted in a statistically significant increase of grain yield at the two sites to 116% and 121% of control. During the 4-year period relative seed bank and density of emerged weed (dominated by Spergula arvensis) increased significantly about 4.5 and 10 times respectively in the undersown clover plots at Apelsvoll. At Kise both ryegrass alone and ryegrass mixed with clover significantly suppressed the weed biomass to 70% and 74% of control respectively. It is concluded that fertilization effects of undersown clover may have dominated and overriden the competitive effects. One whole-season clover green manure did not increase the mean yield, but resulted in a significant drop in seed bank size the following year, because of limited weed establishment in an established ley. Only a slight increase in average weed biomass was observed at one of the two experimental sites. The weed seed bank and the weed biomass were essentially kept at steady state during the experimental period in harrowed plots, but harrowing decreased grain yield significantly at both sites.

Size and composition of weed seedbank in long-term organic and conventional low-input cropping systems

Long-term effects of organic (ORG) and conventional low-input (CONV) farming systems on size and composition of weed seedbank were assessed in 2007 in central Italy, in an on-farm experiment set up in 1996. In this experiment, six rotations (R1–R6) were considered, basically consisting on the same crop sequence with different starting points, i.e. (1) legume crop (soybean/field bean/common pea), (2) vegetable crop (pepper/melon), (3) winter cereal (soft/durum wheat), (4) summer cereal (maize) (5) industrial vegetable (processing tomato), (6) winter cereal (soft/durum wheat). All rotations were established both in ORG and in CONV, in strict adherence to EU regulations (ORG: EU reg. 2092/91; CONV: EU reg. 2078/92). Intercrops with green manuring purposes were included in ORG, while weed control was performed mechanically in ORG and chemically/mechanically in CONV. Weed seedbank was determined on 10 soil samples (0–0.30m depth) in each plot and seeds were directly extracted, identified and counted. In all rotations, the adoption of ORG resulted in a significant increase in weed seedbank density, particularly in the case of summer weed species (Portulaca oleracea L., Amaranthus retroflexus L. and Chenopodium album L.), which are more competitive and difficult to control in summer crops under organic farming systems in the Mediterranean climates. Small differences between ORG and CONV were found in terms of number of weed species (23 in ORG and 20 in CONV, on average), but the index of diversity in CONV was on average higher than in ORG. Furthermore, the most dominant weeds in CONV represented a lower percentage of total seedbank (40%, 23% and 5%, respectively, for P. oleracea, A. retroflexus and C. album in CONV and 56%, 32% and 4% for the same three weeds in ORG). These results confirm that the wider availability of effective weed control methods in integrated low-input farming systems (CONV) is helpful to maintain a low seedbank size, with a lower dominance structure. However, the adoption of ORG systems based on long rotation cycles, very competitive crops and accurate weed control, especially at the beginning of the ORG management, may be sustainable in the long run, in terms of potential weed infestation levels.

Response of Biomass and Seedbanks of Rangeland Functional Groups to Mechanical Control of Yellow Starthistle

Abstract Yellow starthistle ( Centaurea solstitialis L.) is a nonnative pest of rangelands that decreases forage quality and yield. Mowing may control starthistle effectively and complement herbicide use in an integrated pest management strategy, but little research has investigated its effects on nontarget vegetation. We monitored biomass and seedbank size of annual and perennial species, in addition to starthistle, in response to 3 yr of mowing treatments, either mowing alone or in combination with solarization tarps or thatch removal. All mowing treatments were very effective at reducing starthistle biomass and seedbank: mowing alone reduced biomass 92 ± 2%, mowing with thatch removal 91 ± 1%, and mowing with solarization 95 ± 1%. Compared to seedbank sizes in the control plots, yellow starthistle seedbank decreased by 100% (mowing alone), 92% (mowing + thatch removal), and 100% (mowing with solarization) after 3 yr of treatment. Mowing also significantly improved perennial species' biomass. Annual species' biomass varied on a year-to-year basis but was not significantly affected by any treatment. Seedbank sizes of annuals and perennials also did not differ according to mowing treatment. This research indicates that late-season mowing can effectively reduce starthistle biomass without adverse effects on other vegetation and that mowing alone is sufficient to reduce starthistle seedbank size without additional methods of decreasing seed rain.

Seed-bank and seedling dynamics in Hyparrhenia hirta are influenced by herbicide application and mowing management

Hyparrhenia hirta (L.) Stapf (Coolatai grass) is a summer-active, C4 perennial tussock grass, native to southern Africa and the Mediterranean region, which has invaded areas of native flora in Australia in recent decades. Understanding its seed and seedling dynamics and how various management treatments (e.g. mowing, herbicide and no management) affect these may assist in identifying the conditions and management strategies required to limit its invasion. The population dynamics of H. hirta have not been comprehensively studied previously. A 2-year field experiment (December 2005–December 2007) was conducted to determine the seed-bank size, pattern of seedling emergence and survival of H. hirta seedlings at three sites in northern New South Wales, Australia, under three treatments: unmanaged (control), mowing and herbicide treatments. The density of H. hirta seeds in the soil at each experimental site under different treatments was measured in December 2005 at the start of the experiment, in December 2006 before the application of the second round of treatments and again at the end of the experiment in December 2007. Hyparrhenia hirta seedlings were assessed at monthly intervals in permanent quadrats (0.5 × 0.5 m) to determine seedling emergence and survival. Seedling emergence occurred on many occasions during the 2-year period of the experiment in each treatment and at all sites but the main seedling flushes were observed from mid summer to early autumn. In 2007, at all sites, seedling emergence declined by more than 90% on the mowing and herbicide treatments compared with the control treatment. Seedling survival was greater in the mowing and herbicide treatments than in the control treatment. The seedling cohorts emerging in winter had a lower survival. This study showed that H. hirta infestations have a large viable seed-bank (~3000 m–2), dependent on the level of infestation and climatic conditions, but that the seed-bank declines rapidly when seed addition is prevented. Some form of direct control of established H. hirta plants in combination with providing appropriate grazing management to encourage competition between grasses will assist in the control of H. hirta.

Acacia saligna seed banks: Sampling methods and dynamics, Western Cape, South Africa

Acacia saligna is potentially the most damaging invasive species in the coastal lowlands of the south-western Cape. The gall rust fungus, Uromycladium tepperianum, has been highly successful as a biological control agent for A. saligna populations in South Africa and has effectively reduced density, canopy cover and seed production of the tree. However, concerns still remain about the soil-stored seed bank and knowledge of seed bank status and dynamics is crucial for effective management. This study evaluated the effectiveness of two different sampling methods in assessing the status of the seed bank, how the seed bank of A. saligna at two different sites varies over time and how these findings compare to findings of other seed bank studies of A. saligna across southern Africa. Even with the reduction in seed production caused by biological control, numbers of seed in the soil seed bank are high enough to maintain high levels of recruitment after management or natural disturbances. Both sampling methods (grid and random sampling) attempted were effective in assessing the vertical distribution of the seed bank and estimated the size of the seed bank to be within the same order of magnitude. However, random sampling is more effective in assessing seed bank size as it was found that the seed has a clumped horizontal distribution. The vertical distribution of seed in the seed bank was found to be influenced by soil properties. The largest portion of the seed bank is situated in the upper 10cm of the soil profile and declines in size with depth.

Seedbank Size and Emergence Pattern of Barnyardgrass (Echinochloa crus-galli) in Arkansas

Barnyardgrass is one of the most problematic weeds in Arkansas, and with the documentation of herbicide-resistant biotypes, there is a need to gain a detailed understanding of its ecology. In particular, knowledge on barnyardgrass seedbank size and emergence pattern is vital. An extensive seedbank survey was carried out in 2008 in 12 counties in eastern Arkansas to determine barnyardgrass seedbank size across the region. There was a great variability in seedbank size with a maximum of 215,000 seeds m−2. Among the fields surveyed, barnyardgrass seedbank was found only in 7% of the cotton fields, while it was 22 and 20%, respectively, for rice and soybean. To examine the emergence pattern of barnyardgrass, experiments were conducted in Rohwer (two sites), Stuttgart (one site), and Fayetteville (one site), Arkansas in 2008 and 2009. In each site, barnyardgrass emergence was quantified from naturally occurring seedbanks. Barnyardgrass exhibited an extended period of emergence with days to 100% emergence ranging from 99 to 165 across sites and years. Nevertheless, effective management may be achieved by targeting the peak emergence periods, which range from mid-April to mid-June in Arkansas. The four-parameter Weibull model provided a better fit to the cumulative emergence data. However, the thermal time (growing degree days, GDDs) or hydrothermal time (HTT) models did not predict barnyardgrass emergence any better than calendar days, perhaps because of the inherent variations associated with natural seedbanks. This study establishes seedbank size and general emergence pattern for barnyardgrass in Arkansas. Additionally, these results will be useful for parameterizing herbicide-resistance simulation models for barnyardgrass.

Weed seedbanks in arable fields: effects of management practices and surrounding landscape

José‐María L & Sans FX (2011). Weed seedbanks in arable fields: effects of management practices and surrounding landscape. Weed Research51, 631–640.SummaryWeed seedbanks are a reserve of weed diversity and can contribute to the prediction of future weed problems in arable fields. Managing seedbanks should therefore help in optimising biodiversity and controlling weed infestations. This study assessed the effects of management system (organic vs. conventional) and landscape complexity on seedbank size and species richness at the edges and centres of Mediterranean dryland cereal fields and examines the relationship between specific management practices and seedbanks. Field edges and organic fields had more species‐rich, denser seedbanks than field centres and conventional fields, and landscape complexity had a limited effect on arable seedbanks. Accordingly, the promotion of low‐intensity farming practices regardless of landscape complexity, especially at field edges, would be an effective measure for conservation purposes in Mediterranean agroecosystems. Nevertheless, the high seed density of organic seedbanks reveals the need for more effective seedbank management. The analysis of the effects of specific management practices highlights the importance of cleaning crop seeds properly to reduce seedbank size and using complex rotations, especially as this tends to conserve species richness while reducing seed abundance.

Bacterial Communities Associated with Chenopodium album and Stellaria media Seeds from Arable Soils

The bacterial community compositions in Chenopodium album and Stellaria media seeds recovered from soil (soil weed seedbank), from bulk soil, and from seeds harvested from plants grown in the same soils were compared. It was hypothesized that bacterial communities in soil weed seedbanks are distinct from the ones present in bulk soils. For that purpose, bacterial polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints, made from DNA extracts of different soils and seed fractions, were analyzed by principal component analysis. Bacterial fingerprints from C. album and S. media seeds differed from each other and from soil. Further, it revealed that bacterial fingerprints from soil-recovered and plant-harvested seeds from the same species clustered together. Hence, it was concluded that microbial communities associated with seeds in soil mostly originated from the mother plant and not from soil. In addition, the results indicated that the presence of a weed seedbank in arable soils can increase soil microbial diversity. Thus, a change in species composition or size of the soil weed seedbank, for instance, as a result of a change in crop management, could affect soil microbial diversity. The consequence of increased diversity is yet unknown, but by virtue of identification of dominant bands in PCR-DGGE fingerprints as Lysobacter oryzae (among four other species), it became clear that bacteria potentially antagonizing phytopathogens dominate in C. album seeds in soil. The role of these potential antagonists on weed and crop plant growth was discussed.

Similarity between seed bank and herb layer in a natural deciduous temperate lowland forest

Forest seed banks mostly studied in managed forests proved to be small, species poor and not reflecting aboveground species composition. Yet studies conducted in undisturbed communities indicate a different seed bank characteristic. Therefore we aimed at describing soil seed bank in an undisturbed forest in a remnant of European lowland temperate forests, the Białowieża Forest. We compared similarity between the herb layer and seed bank, similarity of seed bank between different patches, and dominance structure of species in the herb layer and in the seed bank of two related oak-hornbeam communities. We report relatively high values of Sorensen species similarity index between herb layer and seed bank of both patches. This suggests higher species similarity of the herb layer and soil seed bank in natural, unmanaged forests represented by both plots than in fragmented communities influenced by man. Although there was a set of core seed bank species present at both plots, yielding high Sorensen species similarity index values, considerable differences between plots in seed bank size and dominance structure of species were found, indicating spatial variability of studied seed bank generated by edaphic conditions. Dominance structure of species in the herb layer was not reflected in the underlying seed bank. This stresses, that natural forest regeneration cannot rely only on the seed bank, although some forest species are capable of forming soil seed banks. While forest seed banks may not reflect vegetation composition of past successional stages, they may inform on history and land use of a specific plot.