Soil Seed Bank Community Research Articles

Effects of Acmella radicans Invasion on Soil Seed Bank Community Characteristics in Different Habitats.

To examine the effects of the recent Acmella radicans invasion on plant community and diversity in invaded habitats, the composition, density, species richness, diversity indices, and evenness index of the soil seed bank community of two different habitats (wasteland and cultivated land) in Yunnan Province, China, were analyzed through field sampling and greenhouse germination tests. A total of 28 species of plants belonging to 15 families and 28 genera, all annual herbs, were found in the soil seed bank. Seed densities and species number in the seed bank tended to be greater in April than in October; cultivated land also featured higher seed densities and species numbers compared to wasteland. With increased A. radicans cover, the seed bank population of A. radicans also significantly increased, but the seed bank populations of many other dominant species (e.g., Ageratum conyzoides and Gamochaeta pensylvanica) and native species (e.g., Laggera crispata and Poa annua) clearly declined. The germination of A. radicans seeds was concentrated during the period from the 4th to the 5th weeks. Vertically, the seed number of A. radicans was significantly different among the 0-5 cm, 5-10 cm and 10-20 cm layers that accounted for 80.7-90.6%, 9.4-16.1% and 0.0-3.2% of the total seed density in wasteland, respectively; and in cultivated land, A. radicans accounted for 56.8-64.9%, 26.7-31.8% and 8.1-13.5% of the total seed density, respectively. With reduced A. radicans cover, the species richness, Simpson index, Shannon-Wiener index, and Pielou indices of the weed community generally increased, and most diversity indices of weed communities in cultivated land were lower than in wasteland under the same cover of A. radicans. The results indicate that the invasion of A. radicans has negatively affected local weed community composition and reduced weed community diversity, and that these negative impacts in cultivated land may be enhanced by human disturbance. Our study was the first to elucidate the influence of A. radicans invasion on soil seed bank community characteristics in invaded habitats, providing a better understanding of its invasion and spread mechanisms in order to aid in developing a scientific basis for the prevention and control of this invader.

Homogenization of soil seed bank communities by fire and invasive species in the Mojave Desert

Soil seed banks help maintain species diversity through temporal storage effects and function as germination pools that can optimize fitness across varying environmental conditions. These characteristics promote the persistence of native plant communities, yet disturbances such as fire and associated invasions by non-native species can disrupt these reserves, fundamentally altering successional trajectories. This may be particularly true in deserts, where native plant communities are less adapted to fire. While studies of fire effects on desert plant communities are not uncommon, information regarding the short- and long-term effects of fire on seed banks is less available. To better understand the influence of fire and invasive species on desert seed banks, we investigated soil seed bank biodiversity from 30 wildfires that burned between 1972 and 2010 across the Mojave Desert ecoregion of North America. We assessed how characteristics of fire regimes (frequency, time since fire, and burn severity) interacted with climate and invasive plants on measures of α-, β-, and γ-diversities. Because β-diversity is a direct measure of community variability and reveals important information about biodiversity loss, we further examined the nestedness and turnover components of β-diversity. Mean α- and γ-diversities were generally higher for burned locations than in unburned reference sites, however individual fire variables had little influence on patterns of seed bank diversity. Burned area seed banks tended to be dominated by non-native invasive species, primarily two grasses, (Bromus rubens, Bromus tectorum), as well as an invasive forb (Erodium cicutarium). The most striking pattern we observed was a collective sharp decline in α-, β-, and γ-diversities with increased invasive species dominance, indicating the homogenization of seed bank communities with the colonization of invasive species after fire. Evidence of homogenization was further supported by reduced turnover and increased nestedness in burn areas compared to reference areas indicating potential biodiversity loss. Our findings highlight how biological processes such as plant invasions can combine with disturbance from fire to alter patterns of seed bank composition and diversity in desert ecosystems.

Long‐term relationships between seed bank communities and wildfire across four North American desert sites

AbstractIt is well documented that the recovery of dryland plant communities following wildfire can be variable, and that legacies of fire can have long‐lasting effects on aboveground plant communities. However, our understanding of the degree to which dryland soil seed banks, or the viable seeds in situ, are impacted by fire and their subsequent postfire succession remains extremely poor. To address this important knowledge gap, we used a time‐since‐fire approach to investigate soil seed bank community changes approximately 15 and 30 years after wildfire and to determine the influence of microsites (e.g., shrub vs. interspace) on seed bank composition. We assessed soil seed bank metrics across four North American deserts, including two cold desert sites (Colorado Plateau and Great Basin) and two warm desert sites (Chihuahuan and Sonoran). In greenhouse emergence trials, we found that seed bank characteristics diverged between warm and cold desert sites, such that warm desert sites had seed banks dominated by annual plants while our cold desert sites had seed banks with greater proportions of perennial species, regardless of fire history. In cold desert sites, fire significantly altered seed bank species composition even 30 years after fire. Shrub versus interspace microsites had no observed influence on seed bank composition in any desert. However, seed bank species richness was greater under shrubs in both warm deserts. Non‐native species were present in the seed banks of all deserts and some were particularly abundant in the burned sites. Despite the presence of native species in both burned and unburned seed banks, the presence of non‐native species suggests some degree of vulnerability to future disturbances because fire can create amplifying feedback with many non‐native plants. Our results highlight strong differences in fires' relationship with seed banks for warm and cold desert sites and lend insight into how fire relates to the composition and diversity of the seeds that play a fundamental role in future plant communities.

Changes in the composition of the soil seed bank of grassland after giant ragweed (Ambrosia trifida L.) invasion.

Giant ragweed (Ambrosia trifida L.), an invasive weed, has an expanding distribution area and has recently started to spread in grasslands. This unusual event threatens grasslands worldwide. In this study, we aimed to evaluate the changes in the grassland soil seed banks caused by the giant ragweed invasion in Yili Valley, Xinjiang, China. Using the space-for-time substitution approach, we compared and quantified the soil seed bank communities in a grassland over eight years following giant ragweed invasion and after its removal. The results showed that the duration of invasion determined whether giant ragweed might pose a significant threat to the native seed bank community. Four years after the invasion, the in-site seed bank density of native community significantly decreased (30.44%), while the relative coverage of giant ragweed aboveground reached 83.75%. Furthermore, the species richness in the seed bank decreased significantly (12.36%), while the relative coverage of giant ragweed reached 100% six years after the invasion. Eight years after the invasion, the seed bank density and species richness of the native community decreased by 83.28% and 39.33%, respectively, whereby the seed banks tended to be homogeneous. After the removal of giant ragweed, the potential for regeneration was limited by the residual seed bank densities of the native community. Although the native seed bank density had increased significantly after three years of restoration, new growth was dominated by weedy species, rather than by the distinctive components of the grassland habitat. Our study clarifies the process by which giant ragweed causes damage to grasslands and serves as a reference for grassland restoration and management efforts.

A global meta‐analysis of grazing effects on soil seed banks

AbstractLivestock grazing is a major disturbance affecting plant diversity and abundance in terrestrial ecosystems. The intermediate disturbance hypothesis (IDH) predicts that moderate‐intensity grazing should produce the highest species diversity, while the Milchunas‐Sala‐Lauenroth (MSL) model posits that the IDH is valid only for mesic areas. However, it remains unclear how grazing affects soil seed bank and whether or not the IDH or MSL models are valid for soil seed bank communities. Here, we presented a global meta‐analysis synthesizing 483 observations: we found that grazing had a negative effect on soil seed bank abundance, but did not alter seed bank richness or the compositional similarity between the soil seed bank and the aboveground vegetation. Further refining the analysis, light‐intensity grazing was found to increase seed bank richness, while moderate‐intensity grazing had no effect, and heavy‐intensity grazing had a negative effect. Additionally, for both arid and mesic areas, soil seed bank richness declined with grazing intensity increased. Overall, grazing effects on soil seed banks differed from expectations set by studies of aboveground vegetation. Our study provides key insights for policy‐makers managing livestock grazing and grassland conservation.

The feasibility of using soil seed bank for natural regeneration of degraded sandy grasslands

Desertification in degraded grasslands is manifested through the development of bare sandy patches, which eventually lead to habitat fragmentation. The ability of these bare sandy patches to regenerate naturally through in-situ soil seed banks is not well understood. To fill this knowledge gap, we randomly selected 24 bare sandy patches with areas ranging from 19 to 898 m2 in a desertified grassland of the Horqin sandy land, Northern China to determine whether soil seed bank can be used for natural regeneration of bare sandy patches. Species composition and density of soil seed bank as well as aboveground vegetation composition, abundance and coverage were investigated. We then determined their relationships with in-situ habitat characteristics. Our observations showed that the studied area had low soil seed bank density and species richness, as well as depauperate soil seed bank communities. Consequently, local soil seed bank was not able to provide sufficient seed source for natural regeneration. This was indicated by the relationships between aboveground vegetation, soil seed bank and the in-situ habitat characteristics. For bare patches with an area between 300 m2 and 900 m2, increase the soil seed bank density and species richness should be the main restoration measures. For bare patches with a small area of less than 50 m2, restoration of vegetation density should be the main measure. Our data highlighted that different extents of desertification, indicated by different bare patches, are requiring distinct restoration measures.

Species richness, diversity, density and spatial distribution of soil seed banks in the riparian woodland along the Thamalakane River of the Okavango Delta, northern Botswana

Soil seed banks serve as reservoirs of seeds for subsequent regeneration of plants. Soil seed banks were investigated along the Thamalakane Riparian Woodlands (hereafter referred to as TRWs) of the Okavango Delta, northern Botswana, from January-July 2015 and January-July 2016. The study aimed at examining species richness and diversity, determining densities, assessing the spatial distribution of seeds in the soil and comparing the similarity in species composition between the standing vegetation and soil seed bank flora. The vegetation was sampled in 71 plots (20 × 50 m) and soil samples were collected from 568 subplots. Agglomerative hierarchical cluster analysis was used to determine soil seed bank communities. Indicator species analysis was used to calculate indicator values for species in each community of germinated seeds and across different soil layers. Multi-response permutation procedures (MRPP) were used to compare similarity in soil seed bank composition. Bray-Curtis ordination was used to infer spatial relationships of soil layers in terms of soil seed bank composition. A total of 109 plant species were identified in the litter and top 9 cm soil layers with a mean density of 2101 seeds m−2. Herbs, grasses, sedges and woody plants were represented by 68, 19, 9 and 13 species, respectively, in 30 families and 87 genera. The overall total diversity and evenness of the soil seed bank in the TRWs was 3.25 and 0.69, respectively. Four plant communities were identified from the soil seed bank, namely Setaria verticilata-Amaranthus hybridus, Acanthospermum hispidum-Setaria sagittifolia, Digitaria eriantha-Eclipta prostrata and Cyperus longus-Fimbristylis dichotoma. Bray-Curtis ordination showed that there was overlap between these communities in terms of seed bank composition. However, MRPP analysis showed that there was significant (P < 0.05) separation between germinated soil seed bank communities. The overall horizontal distribution of seeds varied among sampling quadrats while the vertical distribution of seeds exhibited the highest densities occurring in the upper 3 cm of the soil and gradually decreasing densities with increasing depth. Relatively high densities also occurred in the litter layer. There were large differences in depth distribution between species, suggesting differences in seed longevity. The similarity in species composition between the soil seed flora and standing vegetation was low (27%). The results demonstrated that many species in TRWs store quantities of seeds in the soil. The fact that most of the woody species do not accumulate more seeds in the soil suggests that their regeneration from seeds would be unlikely if mature individuals disappeared (die or are harvested). Because of its diverse seed banks, the herbaceous flora would have a better chance of re-establishing in the event of anthropogenic or natural disturbances. Therefore, the future of the TRW woody flora seems to depend on the successful conservation of the standing vegetation.

Seasonal fires shape the germinable soil seed bank community in eastern Mediterranean woodlands

AbstractWe explored if and how seasonal fires interact with microhabitat type (i.e. under Pistacia shrub, under Cistus shrub or a canopy gap) to influence the composition of the germinable soil seed bank (GSSB) community in a typical eastern Mediterranean woodland. We conducted a field experiment, involving prescribed spring and autumn burns, and thereafter quantified the seed germination patterns using soil samples collected from both burned and adjacent unburned control plots. Soil temperature was significantly higher during autumn burns, while being more variable during spring burns. Fire caused overall reductions in GSSB density, richness and diversity. The reductions in GSSB richness and diversity were significantly stronger under Pistacia and Cistus shrubs located within plots subjected to autumn burns, and these patterns were mainly evident among annuals. GSSB density of dwarf shrubs was higher in samples collected from burned plots, and this pattern was more pronounced in samples collected under Pistacia and Cistus shrubs. Together with the appearance of unique species, seasonal fires led to significant changes in the composition of the GSSB community. Our results illustrate that seasonal fires interact with spatial heterogeneity to influence the composition of the GSSB community mostly via differential effects on the germination densities of annuals and dwarf shrubs. These findings imply that the increase in the frequency of seasonal fires, which has occurred in the eastern Mediterranean basin during the last few decades, may translate into a shift in eco-evolutionary selection pressures, operating on plants inhabiting this unique ecosystem.

Elevation and micro environmental conditions directly and indirectly influence forests’ soil seed bank communities

The soil seed bank (SSB) plays an important role in determining future community composition and health of forests. The extent to which abiotic conditions alter the abundance and diversity of the future forest composition via modulating the regenerative capacity of the SSB and their relationship with each other is not fully understood. We studied how elevation and abiotic conditions (canopy openness, slope, aspect, soil pH, and a natural gradient of these soil nutrients: total nitrogen [N], total carbon [C], C:N ratio, available phosphorus [P], available potassium [K], calcium [Ca], iron [Fe], magnesium [Mg], manganese [Mn], and sulfur [S]) affect community characteristics, calculated as: (1) seedling abundance, (2) species richness, (3) Shannon-Weiner diversity index, (4) Simpson index, (5) Chao 2 richness estimator, (6) number of species represented by only one individual, and (7) number of species that occur only in one plot. We used soils sampled in 13 1-ha plots along an altitudinal gradient from 400 to 1850 m above sea level. We determined both direct and indirect causal relationships between abiotic factors and SSB community characteristics using linear mixed models and structural equation modeling. Increased elevation and canopy openness resulted in lower species richness and diversity as well as fewer rare species. However, greater canopy openness resulted in higher abundance. Abundance and richness of the SSB were lower in steeper slopes, but this negative effect appeared to be along an indirect pathway through soil pH and nutrients such as soil Mn and S. Soil P had a significant negative relationship with SSB characteristics for all indices evaluated here, except for SSB abundance, which was positively affected by increased soil pH. Our results highlight the role of abiotic factors in forest regeneration and resilience through their influence on the soil seed bank community. This study is one of the very first to provide data on the SSB along a wide elevational range in subtropical forests, and can be the basis to assess the regeneration potential and health of the study region.

Direct and indirect effects of temperature and precipitation on alpine seed banks in the Tibetan Plateau.

Plant community responses to global environmental change focus primarily on aboveground vegetation; however, the important role of the seed bank is frequently neglected. Specifically, the direct and indirect effects of changes in temperature and precipitation on seed banks remain poorly understood, yet seed banks provide a vital source of ecosystem resilience to global environmental change. We used a structural equation model to explore the direct and indirect effects of temperature, precipitation, and other biotic and abiotic factors on soil seed bank community composition using 1,026 soil seed bank samples from 57 sites along an elevation gradient that served as a space-for-time substitution for changing climate in the Tibetan Plateau. Seed bank richness was negatively correlated with both precipitation and temperature, but neither climate factor affected seed bank density. Temperature was also negatively correlated with vegetation species richness, which was positively correlated with seed bank richness and density. Both precipitation and temperature were positively correlated with soil total N, and total N was negatively correlated with vegetation richness. Both precipitation and temperature were negatively correlated with soil pH, and soil pH was negatively correlated with vegetation richness, but positively correlated with seed bank richness and density. Increasing precipitation and temperature would decrease seed bank diversity through direct effects as well as indirectly by decreasing vegetation diversity. Soil pH and total N emerged as the most important soil abiotic factors for seed bank diversity. Increasing precipitation and temperature under climate change may increase the extinction risk of some species in the seed bank by altering bet-hedging and risk-spreading strategies, which will degrade natural restoration ability and ultimately ecosystem resilience. This research is important because it identifies the potential underlying mechanistic basis of climate change impacts on seed banks through effects of aboveground vegetation and belowground biotic and abiotic factors.

Seeds of change: characterizing the soil seed bank of a migrating salt marsh.

The capacity for dispersal to promote or hinder species' responses to global change remains a major question in ecology. One ecosystem experiencing rapid change is the tidal marsh, which is migrating inland in response to accelerated sea level rise. Few studies to date have investigated the ecological dynamics that impact this large-scale migration. Seed dispersal and persistence in the soil seed bank is a component that can be strongly indicative of community trajectories. With this in mind, the aim of our study was to characterize the germinable seed bank across a marsh-forest ecotone in the Chesapeake Bay. Soil samples were collected across transects that ran from the high marsh to the coastal loblolly pine forest in a brackish marsh in Blackwater National Wildlife Refuge, MD, USA. Samples were grown in a greenhouse and watered with either freshwater or 3 ppt seawater solution. We compared community composition across transects and between salinity treatments. Additionally, we compared the seed bank with standing vegetation and used seed trait data from the TRY Database to investigate changes in functional traits along this ecotone. We found halophytic species dispersing up to 15 m into the forest and a general lack of obligate upland species, including near absence of Pinus taeda, the dominant species in the forest canopy. A majority of species detected in the seed bank were wetland species of various types, with species with wide salinity tolerance arising most frequently. Salinity addition had a significant negative influence on seed bank diversity. Overall, our seed bank results suggest that dispersal and germination under the conditions of saltwater intrusion will limit forest regeneration and favour marsh plant dispersal. This indicates that the ecological processes that determine the soil seed bank community will support continued migration of marsh species into uplands.

Seed bank community and soil texture relationships in a cold desert

Sustainable dryland management depends on understanding environmental factors driving the composition of current and future ecological communities. While there has been extensive research on aboveground plant communities, less is known about belowground soil seed bank communities. In the Colorado Plateau of the western United States, we simultaneously explored aboveground and belowground plant communities and how they varied across sites with similar climate but contrasting soil textures. We found that aboveground vegetation and belowground seed bank community composition each varied significantly among sites. We also observed marked aboveground-belowground compositional dissimilarity across sites, suggesting that the two spatially-associated communities may respond differently to the same environmental gradient. Lastly, we found that abundances of cheatgrass (Bromus tectorum) – one of the region's major exotic invasive plants – varied strongly with soil texture, a finding with implications for invasive species management. From our results, we highlight two general patterns for dryland managers. First, we show that aboveground and belowground plant communities can respond to the same environmental variation in a strongly divergent manner. Second, the data underscore a large potential role for soil texture and its associated factors in mediating plant community responses to a range of environmental conditions.

Dynamic Analysis of Arbor Species Germinated from Soil Seed Bank under Watering Strategies Driving

The watering gradient is an important factor affecting the composition and structure of the soil seed bank community. The germplasm resources in the soil seed bank have their corresponding water germination intervals. The soil seed bank of Tianjin Guangang Forest Park was selected as the research object and different watering gradients were set to test. Through statistical analysis and regression equation model, we could analyse and evaluate the morphological features of arbor species in soil seed bank under different watering gradients and find out the soil moisture interval which was most suitable for the restoration effect of soil seed bank in Tianjin. The study results showed that: (1) the watering gradient was set to 1000 mL, the arbor population in the experimental dish had the highest plant height, the largest canopy cover and the best arbor community; when the water content was less than 1000 mL, it couldn’t meet the water demand of plant growth and the number of seed germination was greatly reduced; while above 1000mL, the soil was in flooded state, inhibited the germination of some seeds; (2) under the same watering gradients, the average height and canopy cover of Fraxinus chinensis species showed great advantages compared with Robinia pseudoacacia L. and Koelreuteria paniculate species; (3) the average height and canopy cover of three arbor species were positively correlated by regression analysis, and when the watering gradient was set to 1000mL, its correlation was best.

Factors affecting soil seed banks of riparian communities in an agricultural ecosystem: potential for conservation of native plant diversity

AbstractQuestionsDo agricultural land use and nitrogen (N) enrichment have negative effects on riparian soil seed banks? What is the potential of the soil seed bank for the conservation and restoration of native riparian plant diversity? Are non‐native dominant grass species affected by agriculture and do they affect species richness?LocationSouth Nation River watershed (an agricultural watershed), Ontario, Canada.MethodsWe examined the riparian above‐ground vegetation at 24 sites located across a large (~4000 km2) North American watershed and identified the corresponding soil seed bank composition from soil cores using the seedling emergence method. The above‐ground vegetation and soil seed bank species compositions were compared in terms of species richness, percentage of non‐native species and a floristic quality index. Factors affecting these descriptors of plants communities (concentration of in‐stream nitrate and percentages of surrounding natural habitat and annual crop land) were assessed. The effects of agriculture on two dominant non‐native grasses species and their effects on species richness were also assessed.ResultsIn total, 274 plant taxa were identified, including 181 taxa in the soil seed bank and 231 taxa in the vegetation. Overall species richness was high in both the soil seed bank and above‐ground vegetation and was unaffected by measures of agricultural intensity (surrounding annual crop land and N enrichment). Above‐ground vegetation species richness was strongly negatively affected by the widespread and dominant non‐native grasses, Phalaris arundinacea and Bromus inermis, whereas soil seed bank species richness was unaffected. The community compositions of both the soil seed bank and vegetation were negatively affected by the loss of natural habitat and by N enrichment. In fact, an increase in the percentage of non‐native species and a decrease in floristic quality were observed along a gradient of agricultural intensity.ConclusionsSpecies richness of the soil seed bank demonstrated resilience to invasions by P. arundinacea and B. inermis, and the soil seed bank showed good potential for conservation of taxonomic diversity. However, the loss of natural habitat and N enrichment had negative effects on the soil seed bank community composition that may lead to an eventual decline in above‐ground species richness.

Soil seed bank depletion as a mechanism of Lantana camara L. invasion

Lantana camara is an invasive plant in South Africa with a wide range of impacts. This study assessed the impact of L. camara invasion on the soil seed bank. The study asked the question, does species density and diversity of soil seed banks differ between L. camara invaded and uninvaded sites? The study was conducted over a 10-month period under greenhouse conditions using soils collected from five L. camara invaded and uninvaded sites that were located between Port Alfred and East London in the Eastern Cape province of South Africa. The study measured species density, diversity and identified seedlings that germinated in trays containing soils from invaded and uninvaded sites. Species density and diversity were lower in L. camara invaded sites compared with uninvaded sites, an indication that L. camara invasion has the potential to deplete the soil seed bank of other species. The study concluded that L. camara invasion reduces the soil seed bank community composition and structure.

Invasion by Solidago species has limited impacts on soil seed bank communities

Increasing attention in invasion biology is being paid to measuring and understanding the impacts of invasive species. For plant invasions, however, the impact of invasion on soil seed bank communities has been under-studied. At six sites in southern Germany, we investigated whether areas invaded by Solidago gigantea and Solidago canadensis experienced a reduction in seed bank species richness, size and diversity, and a change in species composition compared to adjacent uninvaded areas. We found no overall effect of invasion on seed bank size, or on species richness and diversity. Seed bank size significantly decreased from 0–5cm to 5–10cm depth in both invaded and uninvaded areas. A significant amount of variation in species composition was explained by invasion, but it was only one-tenth of that explained solely by site effects. Our study suggests that invasion by Solidago species may not have the same impacts on the soil seed banks of native species as other invasive perennial forbs that have so far been studied.

Soil seed bank community structure of pastures and hayfields on an organic farm

Sanderson, M. A., Stout, R., Goslee, S., Gonet, J. and Smith, R. G. 2014. Soil seed bank community structure of pastures and hayfields on an organic farm. Can. J. Plant Sci. 94: 621–631. Understanding the composition of seed banks in pasture soils would help farmers anticipate and manage for weed problems. We characterized the soil seed bank in eight pastures and hayfields [two alfalfa (Medicago sativa L.) and two predominantly grass hayfields; two recently established and two permanent pastures] within an organic dairy farm in southeastern New Hampshire. Seed banks were sampled in the upper 5 cm of soil in each field at a point scale in 2007 and 2010. In 2010, the seed bank was characterized at the field scale by taking soil samples on six 52-m transects in each field. Seed banks sampled at the field scale in 2010 contained 66 plant species. The total number of seeds in the seed bank ranged from 1560 m−2 in grass hayfields in autumn to more than 20 000 m−2 in alfalfa hayfields in summer. Annual forbs dominated the seed bank of alfalfa fields and recently established pastures, whereas perennial graminoids dominated in one grass hayfield and the permanent pastures. These results suggest that management history affects soil seed bank composition and abundance, and these effects should be considered before implementing management practices that could stimulate recruitment from the seed bank.

Impact of invasions by alien plants on soil seed bank communities: Emerging patterns

Much of our current understanding of the impact of invasive species on plant communities is based on patterns occurring in the above-ground vegetation, while only few studies have examined changes in soil seed banks associated with plant invasions, despite their important role as determinants of vegetation dynamics. Here, we reviewed the literature on the impact of plant invasions on the seed bank and we provide a quantitative synthesis using a meta-analysis approach. Specifically, (1) we quantified the impact of 18 invasive alien plants on (i) species richness and (ii) density of the seed banks of invaded communities, based on 58 pair-wise invaded-uninvaded comparisons (cases); we identified (2) the invasive taxa that are responsible for the largest changes in the seed bank; and (3) the habitats where substantial changes occur. Our study showed three major findings: (1) species richness (68% of cases) and density (58% of cases) were significantly lower in native seed banks invaded by alien plants; (2) species richness and density of native and alien species were remarkably lower in seed banks invaded by large, perennial herbs compared to uninvaded sites; and (3) invaded seed banks were often associated with a larger richness and/or abundance of alien species. This study indicates a need for additional seed bank data in invasion ecology to characterize species-specific and habitat-specific impacts of plant invasions, and to determine whether changes in the seed banks of native and alien species are a symptom of environmental degradation prior to a plant invasion or whether they are its direct result. The findings of this study help improve our capacity to predict the long-term implications of plant invasions, including limitations in the recruitment of native species from the seed bank and the potential for secondary invasions by seeds of other alien species.

Warming increases plant biomass and reduces diversity across continents, latitudes, and species migration scenarios in experimental wetland communities

Atmospheric warming may influence plant productivity and diversity and induce poleward migration of species, altering communities across latitudes. Complicating the picture is that communities from different continents deviate in evolutionary histories, which may modify responses to warming and migration. We used experimental wetland plant communities grown from seed banks as model systems to determine whether effects of warming on biomass production and species richness are consistent across continents, latitudes, and migration scenarios. We collected soil samples from each of three tidal freshwater marshes in estuaries at three latitudes (north, middle, south) on the Atlantic coasts of Europe and North America. In one experiment, we exposed soil seed bank communities from each latitude and continent to ambient and elevated (+2.8°C) temperatures in the greenhouse. In a second experiment, soil samples were mixed either within each estuary (limited migration) or among estuaries from different latitudes in each continent (complete migration). Seed bank communities of these migration scenarios were also exposed to ambient and elevated temperatures and contrasted with a no-migration treatment. In the first experiment, warming overall increased biomass (+16%) and decreased species richness (-14%) across latitudes in Europe and North America. Species richness and evenness of south-latitude communities were less affected by warming than those of middle and north latitudes. In the second experiment, warming also stimulated biomass and lowered species richness. In addition, complete migration led to increased species richness (+60% in North America,+100% in Europe), but this higher diversity did not translate into increased biomass. Species responded idiosyncratically to warming, but Lythrum salicaria and Bidens sp. increased significantly in response to warming in both continents. These results reveal for the first time consistent impacts of warming on biomass and species richness for temperate wetland plant communities across continents, latitudes, and migration scenarios.

Soil Seed Bank Responses to Postfire Herbicide and Native Seeding Treatments Designed to Control Bromus tectorum in a Pinyon–Juniper Woodland at Zion National Park, USA

AbstractThe continued threat of an invasive, annual brome (Bromus) species in the western United States has created the need for integrated approaches to postfire restoration. Additionally, the high germination rate, high seed production, and seed bank carryover of annual bromes points to the need to assay soil seed banks as part of monitoring programs. We sampled the soil seed bank to help assess the effectiveness of treatments utilizing the herbicide Plateau® (imazapic) and a perennial native seed mix to control annual Bromus species and enhance perennial native plant establishment following a wildfire in Zion National Park, Utah. This study is one of few that have monitored the effects of imazapic and native seeding on a soil seed bank community and the only one that we know of that has done so in a pinyon–juniper woodland. The study made use of untreated, replicated controls, which is not common for seed bank studies. One year posttreatment, Bromus was significantly reduced in plots sprayed with herbicide. By the second year posttreatment, the effects of imazapic were less evident and convergence with the controls was evident. Emergence of seeded species was low for the duration of the study. Dry conditions and possible interactions with imazapic probably contributed to the lack of emergence of seeded native species. The perennial grass sand dropseed outperformed the other species included in the seed mix. We also examined how the treatments affected the soil seed bank community as a whole. We found evidence that the herbicide was reducing several native annual forbs and one nonnative annual forb. However, overall effects on the community were not significant. The results of our study were similar to what others have found in that imazapic is effective in providing a short-term reduction in Bromus density, although it can impact emergence of nontarget species.