Soil Seed Bank Research Articles

May the Inclusion of a Legume Crop Change Weed Composition in Cereal Fields? Example of Sainfoin in Aragon (Spain)

Onobrychis viciifolia (Scop.) (sainfoin) is promoted in the Spanish Aragón region through the Agro-Environmental Schemes (AES) since 2007 with the aim of enhancing biodiversity. Also, in other countries, the interest in this legume crop is growing due to its rusticity and beneficial effects on the soil and livestock. However, the effect of the crop on weed flora in the subsequent cereal crops has hardly been investigated yet. With this aim, weed flora has been characterised in 2011–2014 in sainfoin fields in the second and third year of establishment (S2 and S3), in cereal monocrop (CM), in cereal after sainfoin (CS) and in organic cereal fields (OC). Additionally, the soil seedbank was determined in two years in CM and S3 fields. Weed species richness of emerged flora and of the soil seedbank was highest for sainfoin and lowest for CM, being intermediate for OC and CS regardless of the sampling year. The most feared weed species in winter cereal did not increase by growing sainfoin or in CS compared to CM. Curiously, summer annuals dominated in the soil seedbank. Sainfoin fields cause thus a shift in the weed flora, which does not seem to damage subsequent cereal crops provided fields are mouldboard ploughed after sainfoin.

Physical environmental conditions determine ubiquitous spatial differentiation of standing plants and seedbanks in Neotropical riparian dry forests.

Mexican tropical dry forests are remarkably extensive and floristically diverse despite manifesting alarming rates of deforestation. Riparian habitats within dry forests provide critical ecological benefits that may mitigate negative impacts, but processes underlying riparian functions are still not well understood. We identified physical environmental conditions affecting the composition and abundance of standing vegetation assemblages and woody and herbaceous components in soil seedbank assemblages of riparian corridors in central Mexico using mainly NMDS ordination techniques, permuted analysis of variance (PERMANOVA), permuted analysis of multivariate dispersions and constrained ordination (CAP). We then determined representative species associated with particular environmental conditions using an indicator species analysis and assessed the effects of physical environmental variables/factors on total seed abundances by fitting a mixed-effect model. For the standing vegetation study, we assessed the effects of the type of the river condition (differing in surface flow permanence), location, and height above river level on the community composition based on three species importance criteria (abundance, coverage and DBH). For the soil seedbank study, we assessed the effects of these variables/factors plus season and land use. Spatial heterogeneity was a prevailing feature in riparian vegetation, in the standing vegetation and soil seedbank of both woody and herbaceous components. Height above river level had a significant effect on the three species importance criteria of standing vegetation and so did the interaction between surface flow permanence and height on coverage. The soil seedbank of woody and herbaceous plants showed significant differences between seasons; Taxodium mucronatum was an indicator tree species in dry seasons. Land use, height, surface flow permanence and the interaction between land use and surface flow permanence had significant effects on the soil seedbank of herbaceous plants. Total seed abundances in the soil varied between years and were higher at lower height values, during the dry seasons, and when rivers were permanent. Tree communities, commonly the most important elements in riparian ecosystems, were preserved in the soil seedbank of cultivated areas for >30 years. Seeds of herbaceous communities were predominant and ecologically relevant as indicator species because of their high sensitivity to several key environmental factors, constituting a critical component of Mexican tropical dry forests riparian corridors.

Microsite conditions in retrogressive thaw slumps may facilitate increased seedling recruitment in the Alaskan Low Arctic.

In Low Arctic tundra, thermal erosion of ice‐rich permafrost soils (thermokarst) has increased in frequency since the 1980s. Retrogressive thaw slumps (RTS) are thermokarst disturbances forming large open depressions on hillslopes through soil wasting and vegetation displacement. Tall (>0.5 m) deciduous shrubs have been observed in RTS a decade after disturbance. RTS may provide conditions suitable for seedling recruitment, which may contribute to Arctic shrub expansion. We quantified in situ seedling abundance, and size and viability of soil seedbanks in greenhouse trials for two RTS chronosequences near lakes on Alaska's North Slope. We hypothesized recent RTS provide microsites for greater recruitment than mature RTS or undisturbed tundra. We also hypothesized soil seedbanks demonstrate quantity–quality trade‐offs; younger seedbanks contain smaller numbers of mostly viable seed that decrease in viability as seed accumulates over time. We found five times as many seedlings in younger RTS as in older RTS, including birch and willow, and no seedlings in undisturbed tundra. Higher seedling counts were associated with bare soil, warmer soils, higher soil available nitrogen, and less plant cover. Seedbank viability was unrelated to size. Older seedbanks were larger at one chronosequence, with no difference in percent germination. At the other chronosequence, germination was lower from older seedbanks but seedbank size was not different. Seedbank germination was positively associated with in situ seedling abundance at one RTS chronosequence, suggesting postdisturbance revegetation from seedbanks. Thermal erosion may be important for recruitment in tundra by providing bare microsites that are warmer, more nutrient‐rich, and less vegetated than in undisturbed ground. Differences between two chronosequences in seedbank size, viability, and species composition suggest disturbance interacts with local conditions to form seedbanks. RTS may act as seedling nurseries to benefit many Arctic species as climate changes, particularly those that do not produce persistent seed.

Effects of Reduced and Conventional Tillage on Weed Communities: Results of a Long-Term Experiment in Southwestern Spain

ABSTRACT: An important drawback in adopting minimum tillage (MT) and no-tillage (NT) techniques is the frequently observed weed shift promoting adapted species and achieving poorer weed control. These changes can be detected best with long-term experiments, and results might differ depending on soil characteristics and the local flora. The objectives of this work were to evaluate the effect of reduced tillage on weed seed distribution in the soil profile and to identify possible consequences on weed diversity on a long-term experiment maintained during 24 years in Seville (Spain) with three tillage systems: NT, MT and conventional tillage (CT) including moldboard plow on a vertisol. For this purpose, soil seedbanks at 0-8 cm and 8-16 cm depths were enumerated in autumn 2005 and in-field emerged plants in autumn 2005 and winter 2006. Shannon diversity index (H) and evenness (J’) were calculated for seedbank and aboveground weed communities. Total weed seed density was highest for NT and lowest for CT. Some big-seeded species, such as Chrozophora tinctorea L., showed highest seed density in CT. NT increased the relative density of Amaranthus blitoides S. Watson seeds in the seedbank and the abundance of emerged plants of Malva parviflora L., Anagallis arvensis L. and Picris echioides L. Overall, MT led to a less diverse seedbank in the 0-8 cm depth of soil than CT. The frequent drought-induced deep fractures in the expandable clay soil caused natural tillage, which probably resulted in fewer differences in weed seed and seedling densities among tillage treatments compared to what might be expected in other soil types.

Combining optimization and simulation modelling to measure the cumulative impacts of prescribed fire and wildfire on vegetation species diversity

Abstract Growth‐stage optimization (GSO) offers a new approach to biodiversity conservation in fire‐prone regions by estimating the optimal distribution of vegetation growth stages that maximize a species diversity index. This optimal growth‐stage structure provides managers an operational goal explicitly linked to a positive conservation outcome but does not define the fire regime needed to achieve it. We paired GSO with LANDIS II, a landscape succession and disturbance simulation model, to (a) estimate the optimal growth‐stage structure that maximized vegetation diversity in a south‐east Australian heathy woodland, (b) define the fire regime needed to achieve it, and (c) determine the cumulative effects of different fire‐regime scenarios on vegetation diversity over a 60‐year period. Scenarios included 0%, 2%, 5%, and 10% of the landscape burnt per year by prescribed fire only, or in combination with three alternative wildfire regimes. Furthermore, we investigated the differences in the optimal growth‐stage structure relating to above‐ground, soil seedbank, and total (above and soil seedbank) diversity datasets. The growth‐stage structure that maximized total vegetation diversity comprised approximately even proportions of all stages. In contrast, separately analysed above‐ground and soil seedbank data resulted in a greater proportion of younger and older growth‐stages, respectively. Scenarios including 5% prescribed burning per year (with and without wildfire) resulted in diversity values within 1.5% of the theoretical maximum value. Scenarios including 2% and 10% prescribed fire resulted in diversity values 8%–12% and 1.5%–5% lower than the maximum, respectively. Scenarios without prescribed fire caused diversity to fall 30%–70%. Trends across the 60 years showed that wildfire depressed diversity and subsequent prescribed fire drove recovery within 15 years. The largest threat to vegetation diversity was the absence of fire. Synthesis and applications. Combining growth‐stage optimization and simulation modelling is a powerful way of defining a conservation‐based fire management goal and identifying the prescribed fire regime needed to achieve it. We demonstrated that vegetation diversity in heathy woodland was increased by prescribed fire, with and without the cumulative effect of wildfire, and declined sharply when fire was excluded. Our method provides a flexible platform for developing long‐term fire management strategies that seek to balance human safety and biodiversity conservation. Including both plants and animals in GSO will help land managers meet the needs of multiple taxa.

Real-time PCR quantification of Fusarium avenaceum in soil and seeds

The pathogenic fungus Fusarium avenaceum infects a broad range of plant hosts across the globe. While primarily soilborne, F. avenaceum can colonize all plant tissues, including buds, seeds, fruits, stems, crowns, and roots, resulting in significant crop yield reductions and economic losses for growers. In addition to its impact on crop productivity, F. avenaceum produces toxic metabolites that can be transferred to humans and livestock through consumption of infected foods. The ability of F. avenaceum to cause seed decay may be utilized to deplete the weed seedbank in soil, an important integrated weed management strategy. We developed a SYBR Green I-based real-time polymerase chain reaction (qPCR) assay to efficiently detect and quantify F. avenaceum in soil, wild oat (Avena fatua L.) seed caryopses, and wild oat seed hulls. The primer pair was designed from the translation elongation factor 1-alpha (TEF1) gene. In silico and wet lab testing were done to assess the ability of the primers to bind TEF1 sequences from Fusarium spp. and common soil fungi. The findings indicated that the primers were specific to F. avenaceum, and also recognized GenBank TEF1 accessions annotated as F. arthrosporioides, which has been listed as a foliar pathogen of wheat in Oregon, and conspecific with F. avenaceum. Standard curves of F. avenaceum DNA diluted with soil, caryopsis, or hull extracts indicated primer amplification efficiency was not significantly affected by PCR inhibitors. This real-time PCR assay effectively assesses the presence and abundance of F. avenaceum and its close relative F. arthrosporioides, if present, in soil and seed tissues. The assay can be used for endpoint PCR as well.

Contrasting land use systems influence soil seed bank composition and density in a rural landscape mosaic in West Africa

Soil seed banks (SSBs) play a key role in the post-disturbance recruitment of many plant species. Seed bank diversity can be influenced by spatial and environmental variability and disturbance heterogeneity across the landscape. Understanding the recovery potential of native vegetation from SSBs is important for restoration and biodiversity conservation. Yet, in savanna-woodland, little is known about how SSBs vary in their germination, composition and density under different land uses, and how SSBs relate to aboveground vegetation (AGV). Using a sampling design based on the Land Degradation Surveillance Framework, we assessed the SSB and AGV in twelve 0.25 ha plots among sixteen in four contrasting land use systems of savanna-woodland in Burkina Faso: bushland, cultivated farmland, fallow and wetland. A total of 720 soil samples were taken from four stratified depths of 0–5 cm, >5–10 cm, >10–15 cm, and >15–20 cm. The SSB composition and richness was determined by the seedling emergence technique. Results showed that the SSB in all land uses was largely dominated by annual grasses with few perennial herbaceous and woody species. Seed density was highest in the fallow soil and highest in the upper soil layers for all land uses. A non-metric multidimensional scaling ordination of the SSB and AGV indicated that the SSBs were a poor reflection of the AGV. Based on these findings, spatial variations in landscape characteristics not only influence seed distribution and viability but also have the potential to influence population persistence. These results imply that successful restoration of fragmented ecosystems requires the addition of seeds and seedlings of target species.

The composition of the soil seedbank and its role in ecosystem dynamics and rehabilitation potential in the arid Tankwa Karoo Region, South Africa

Very few soil seedbank studies have been conducted in South Africa, especially in arid rangelands. Insight into the soil seedbank could therefore improve assessment of rangeland dynamics and enhance rehabilitation efforts. This study aimed to characterise the soil seedbanks in various vegetation types of the Tankwa Karoo National Park, an arid environment in South Africa. At 43 sites soil was sampled twice at the end of spring and the end of autumn, and the composition and structure of aboveground vegetation were described at the peak growth period in spring. Seeds were isolated from the soil samples by means of flotation in a salt solution, seedbank species composition was obtained by seedling germination, and the vegetation was investigated using a line-point survey method. Overall seed density was 8 034 seeds m−2 of which 55% was viable, and the common life-forms were therophytes and chamaephytes. Species richness and diversity were lower in the seedbank compared with those of the vegetation, and the two vegetation spheres were 25% similar. While seedbank composition suggested poor veld condition, there was enough seed density and viability for future regeneration and rehabilitation initiatives. However, this may be impeded by the absence of many perennial species in the soil seedbank.

Seed Fecundity, Persistence, and Germination Biology of Prairie Groundcherry (Physalis hederifolia) in Australia

AbstractPrairie groundcherry [Physalis hederifolia(A. Gray) var.fendleri(A. Gray) Cronquist] is an invasive perennial weed with the potential to become a significant summer weed across 409 million hectares in Australia. Current management practices do not provide effective control of established populations. A better understanding of the seed biology is needed to effectively manage this weed. A series of field and laboratory studies were conducted to determine plant fecundity, soil seedbank longevity, and the factors that affect seed germination.Physalis hederifoliahas the capacity to produce 66 to 86 berries plant−1, 51 to 74 seeds berry−1, and approximately 4,500 seeds plant−1, with the seeds potentially able to persist in the soil seedbank for 20 yr if buried in an intact dry berry pod. The bare-seed component of the soil seedbank can be virtually exhausted within 3 yr if cultivation is minimized to avoid burial of seed. Optimal temperature for germination is diurnal fluctuations of 15 C within the temperature range of 10 and 30 C. Increasing osmotic stress levels reduced the germination under all temperature regimes, with less than 6% germination occurring at −0.96 MPa.Physalis hederifoliaseed germination was not significantly affected by substrate pH 4 to 10 or salt levels less than 160 mM, while the germination was significantly reduced at NaCl concentrations above 160 mM. These results suggest thatP. hederifoliacan adapt to a range of substrate conditions. Stopping seed set, avoiding grazing plants with viable seeds, and minimizing seed burial in the soil are some effective strategies to control this weed.

Survivorship of plant species from soil seedbank after translocation from subtropical natural forests to plantation forests

The enhancement of biodiversity is an important strategy to improve the structure and functioning of monoculture plantations. However, compared with seedling transplanting, there is limited information about the utilization of soil seedbanks in regenerating plantation forests. In the present study, to investigate the potential application of soil seedbanks in plantation forest regeneration, the topsoil (0–10 cm) of natural forests was translocated to different monoculture plantations, namely, Acacia crassicarpa, Castanopsis hystrix and Eucalyptus urophylla monocultures. Seed germination, seedling growth and related environmental conditions of the plantation forests were monitored in the experiment. Although, at the very start, large numbers of seedlings emerged from the soil seedbank, only nine species survived after 2.5 years, including seven tree species and two shrub species. Notably, Machilus chekiangensis, a tree species with high economic value, was established in the plantation forests. Except for the common species that emerged in the three plantations, there were some special species that were only associated with a specific plantation. Redundancy analysis revealed that nitrogen from both the natural forest and plantation forest soil had significant effects on seedlings growth. However, environmental conditions such as light (reflected by leaf area index), soil temperature, moisture and pH showed no obvious influence on seedling growth. Our study suggests that soil seedbank translocation from a natural forest to a plantation forest can be a useful approach for plantation forest regeneration because it could introduce valuable plant species and improve the plant biodiversity.

The Relationship between the Soil Seed Bank and Above-ground Vegetation in a Sandy Floodplain, South Korea

The Relationship between the Soil Seed Bank and Above-ground Vegetation in a Sandy Floodplain, South Korea

Estimating the abundance and composition of soil seed bank at Bekol Savanna in Baluran National Park, West Java

The composition of soil-seed bank reflects the condition of vegetation in the past and could be used for predicting the composition of plants that will grow in the future. This study aims to determine the amount and composition of soil-seed bank in Bekol savanna, Baluran National Park. Soil samples were taken using a combination method of quadrat-transect on the invaded and not invaded areas by Acacia nilotica. Soil samples were extracted using wet-sieving method. After the extraction process, the seeds were identified and calculated using a stereo microscope. The result showed that soil-seed bank density was lower at the invaded location (7,566.88 seeds/m3) as compared to the uninvaded location (16,798.3 seeds/m3). The soil-seed bank was found in the invaded site comprising 12 species of broadleaved weeds and 5 species of grasses from 7 families, whereas those in the uninvaded area consisted of 10 species of broadleaved weeds and 7 species of grass from 8 families. This study showed that the invasion of A. nilotica significantly affected the amount and composition of soil-seed bank in various soil depths of Bekol savanna.

The Bet-Hedging Strategies for Seedling Emergence of Calligonum mongolicum to Adapt to the Extreme Desert Environments in Northwestern China.

Calligonum mongolicum is a dominant native perennial shrub on sand dunes in arid deserts of northwestern China, and is therefore widely used in sand dune stabilization in these regions. However, it remains largely unknown how seedling emergence of C. mongolicum has adapted to unpredictable sand movement and extreme drought. Here we examined effects of seed burial depth, light intensity, and seed age on seedling emergence, and considered seed germination and seedling emergence strategies for the shrub’s adaption to the desert environment. In our pot experiment, the optimum seeding depth for emergence of C. mongolicum was 2 cm, indicating that for germination and seedling emergence only moderate sand burial is required. Light intensity at the surface soil (0 cm) was important for seedling emergence, while there was no significant difference between 50 and 20% light flux density, at burial depths of 1 and 2 cm, indicating that C. mongolicum seeds had adapted to sand burial, while not exposure from sand erosion. We also found C. mongolicum seedlings emerged in spring and in late summer to early autumn. Meanwhile, seedling emergence percentage for 3-year-old seeds was similar to that of 1-year-old seeds, which meant that C. mongolicum seeds were well preserved under normal sand dune conditions, thus were capable of developing a persistent, but shallow soil seed-bank. These results indicated that germination and seedling emergence take a bet-hedging strategies to adapt to variable desert environments. Our study confirmed that C. mongolicum desert shrubs combine strategies in its adaption to arid and variable sand environments.

Seedsvsfungi: an enzymatic battle in the soil seedbank

AbstractDepleting the soil weed seedbank is an important integrated weed management strategy that has the potential to foster lasting weed control. Long-term dormancy and decay resistance of weed seeds pose a challenge to weed eradication efforts. Select soil fungi have been shown to cause significant decay of weed seeds. The physical and chemical mechanisms by which seeds in the seedbank defend themselves against pathogens have been well researched. However, very few studies have purposefully investigated the biochemical defence response of seeds. Enzyme-based biochemical seed defences have been detected in dormant and non-dormant seeds, and research supports their function in pathogen defence. This review summarizes current knowledge of the seed defence enzymes polyphenol oxidase, peroxidase, chitinase and oxalate oxidase. The fungal enzymes chitinase, protease and xylanase that function in pathogenesis of seeds in the soil seedbank are also reviewed. Progress in the development and standardization ofin situenzyme analyses fosters our understanding of actual enzyme activity present in soils, while high-throughput microplate techniques promote efficiency and enable greater scope. Application of genomic, proteomic and transcriptomic techniques to glean a deeper and more holistic understanding of the enzymatic interactions of weed seeds and soil fungi in the soil seedbank will support the development of improved integrated weed management strategies.

The Influence of Environmental Factors on Germination of Burcucumber (Sicyos angulatus) Seeds: Implications for Range Expansion and Management

AbstractBurcucumber (Sicyos angulatusL.) is a highly invasive vine that has become naturalized in the humid Black Sea region of Turkey, but previous to this study there was no information on the germination biology of this weed. The germination biology of three naturalized populations ofS. angulatusfrom the Black Sea region was studied in laboratory and greenhouse experiments. The germination of nondormant seeds was observed under different photoperiods, constant temperatures, and varying levels of pH, salinity, and osmotic potential. Furthermore, seedling emergence from various soil depths was investigated. The seeds of all populations proved nonphotoblastic (82% to 90%, 55% to 66%, and 48% to 56% germination under 12-, 24-, and 0-h photoperiod, respectively) and germinated over a wide range of temperatures (5 to 40 C). Seedlings emerged from all seed burial depths (0 to 15 cm); however, germination was drastically reduced (>90% reduction) beyond 6 to 8 cm. Seed germination was 30% to 38% for seeds placed on the surface and increased to 78% to 88% for seeds buried 2 cm deep, while germination was severely reduced for seeds buried 10 and 15 cm deep (8 to 12% and 0 to 6%, respectively). Seeds of all populations were found to be sensitive to osmotic and salinity stress and to highly acidic and alkaline pH levels. All populations had similar requirements for germination that are directly related to their area of naturalization. These results indicate that the species has limited potential for range expansion to arid, semiarid (nonirrigated), and relatively saline areas. However, humid, salinity-free, and frequently irrigated areas of the country are at high risk of invasion. In arable lands, deep tillage followed by shallow tillage and effective management of emerging seedlings could deplete the soil seedbank in the long run. However, there is an urgent need for effective strategies to manage the species in other nonarable areas.

Contribution of the soil SEED bank to the recovery of a Cytisus oromediterraneus shrubland after fuel reduction treatments

Land managers need scientifically-based information to enable them to select the most appropriate treatments for reduction of high-severity wildfires in shrubland areas. The soil seed bank is known to play a key role in the post-disturbance recovery of shrubland communities, although information about how it is affected by fuel reduction treatments is still scarce. We carried out a combined greenhouse and field study to evaluate the effects of prescribed burning, clearing and mastication on the response of the soil seed bank and vegetation recovery in a Cytisus oromediterraneus (Spanish golden broom) shrubland area in central Spain. We determined the following variables: total seedling density in the greenhouse, broom density (in the greenhouse and field), vegetation cover recovery in the field, species richness (in the greenhouse and field) and similarity index between the floristic composition of the above-ground vegetation and soil seed bank. We also evaluated how the remaining soil organic cover and depth affected seedling emergence after treatments in the field. In addition, we explored the effect of soil thermal regime during prescribed burning on posterior seedling emergence.In the greenhouse experiment, a significantly greater number of seedlings emerged from the soil seed bank samples obtained after burning (1297 seedlings m−2) than from the seedlings obtained before burning (775 seedlings m−2) and after clearing (801 seedlings m−2) or mastication (705 seedlings m−2). The mechanical treatments did not induce any changes in the seedling emergence from the soil seed bank. Species richness in the soil seed bank was not altered by fuel reduction treatments. Post-burning seedling density was not significantly related to any of the soil thermal regime parameters during burning. Soil organic cover after the treatments negatively affected the response of the soil seed bank.The field study revealed no differences between treatments in relation to total vegetation cover, broom cover or grass cover. However, forbs cover was significantly higher in the prescribed burning treatment that is related with the higher density of seedlings of these species measured in the greenhouse experiment. C. oromediterraneus regenerated strongly via sprouting, being the seed germination rate in the field very low. That suggests that the soil seed bank makes little contribution to recovery of this species after fuel reduction treatments, and the same was observed for the remaining plant community.

Effect of Simulated Tillage in Combination with Post-Shattering Temperature Conditions on Senna obtusifolia and Xanthium strumarium Seed Survival, Seedling Emergence and Seedbank Potential

Two of the most troublesome weeds in soybean, cotton, and corn in cropping systems of mid-south United States (US) are Senna obtusifolia and Xanthium strumarium. Understanding their population dynamics, particularly weed seedling emergence patterns, is important for the timely implementation and the success of weed management strategies. Identifying the sources of variation of emergence patterns could greatly improve our ability to predict emergence timing. A three-years field study was conducted to determine the effect of environmental conditions on S. obtusifolia and X. strumarium seedling emergence and seedbank potential. The experiment was conducted with two seed sources; X. strumarium burs and S. obtusifolia seeds from a single maternal plant source, and X. strumarium burs and S. obtusifolia seeds from multiple maternal plant sources, both being exposed either to 5 cm burial depth (buried) or left on the soil surface (soil surface) in the fallow or planted in spring after their storage under chilled (chill) or room temperature (no chill) conditions. X. strumarium and S. obtusifolia seedling emergence was lower from burs and seeds that were planted in the soil in September as compared with the chill and/or no chill seeds/burs stored for six months. X. strumarium seedling emergence was reduced from 37 to 1% when burs were left on the soil surface when compared to buried burs. S. obtusifolia seedling emergence was reduced from 47 to 13% when seeds were left on the soil surface as compared to buried. At the end of the experimental period, the soil seedbank of X. strumarium had been significantly depleted, whereas the remaining seeds of S. obtusifolia were viable.

Weed abundance and soil seedbank responses to tillage systems in continuous maize crops

ABSTRACTWeed abundance in crops undergoes frequent changes, often due to changes in tillage practices. Annual species, with quick germination, a short vegetative stage, profuse seed production and long-lived seeds become problematic under zero-tillage systems. Portulaca oleracea L. and Amaranthus blitoides L. are widespread weeds in the Mediterranean area, prominent in irrigated crops. We studied the total weed abundance in the field, and specifically these two species (Portulaca oleracea and Amaranthus blitoides) with high frequency of occurrence in monoculture maize, from 2012 to 2014, in the field and soil seedbank. Results showed significant differences between zero-tillage (ZT) and conventional tillage (CT) systems on total weed abundance and relative abundance of Portulaca oleracea. Total weed abundance decreased in ZT plots (from 136 plants m−2 to 25 and 46 plants m−2, in 2013 and 2014 respectively). The same trend was observed in Portulaca oleracea recorded in ZT plots, but the abundance of Amaranthus blitoides did not vary in this system. Weed seedling germination and weed seed numbers both of total weed seedbank and Portulaca oleracea, were greater in ZT plots compared to CT, regarding Amaranthus blitoides seedling germination and seed count, the values did not increase with ZT, in continuous maize crops.

Effect of heat on soil seedbank of three contrasting physiognomies in Shasha forest reserve, Southwestern Nigeria

The effects of soil heating which usually occur during forest fires on the floristic composition and seed density of the soil seed bank of Shasha forest reserve in Southwestern Nigeria was investigated and the potential of the soil seedbank in forest restoration process (especially after a fire) was examined. Three distinct sites (Regrowth forest, Gmelina and Pinus plantations) were selected in the forest reserve. Species enumeration, identification and distribution into families of the standing vegetation were carried out. Soil samples were collected at 0–15 cm depth from each plot in March 2012. One set of replicate samples was heated in an oven until the soil reached 80 °C (to simulate typical temperature at soil surface during forest fires) while the other serves as a control. They were subjected to seedling emergence for six months to determine the density and species composition of the seed banks of the study sites. Seedling emergence result for heated and unheated soil samples showed that the seedbank density was higher in control than heated samples in the three sites. Few woody species emerged from the soil seedbank of three study sites and in both control and heated samples. There was a significant difference in total seed density when treatments were compared (P < 0.05) and no significant difference (P > 0.05) when sites were compared. Diversity and evenness indices follow the order Regrowth forest > Pinus plantation > Gmelina plantation. NMDS (non-metric multi-dimensional scaling) ordination revealed low similarity in the species composition of extant vegetation and seedbank. The potential of vegetation restoration of the disturbed forest reserve from seed bank is limited, and heat from fire had negative effects on the seed bank characteristics of the forest but selectively enhanced the emergence of species like Pinus carribaea.

Vegetation and seed banks of arid ephemeral gilgai wetlands subject to contrasting grazing regimes

Ephemeral gilgai wetlands of the stony-plains of arid Australia have a relatively high diversity of native plant species and are extensively utilised for livestock grazing. We sampled the standing vegetation (SV) and germinable soil seed bank (SSB) of 40 gilgais, comparing gilgais near and far from watering points, and continually stocked versus rarely stocked. Despite historically heavy stock grazing, we found no significant differences in native species richness between treatments, indicating the general resilience of gilgai vegetation. One contributing factor is the abundance of Atriplex nummularia ssp. omissa. Cover of this long-lived shrub did not differ significantly between treatments and was positively correlated with “highly palatable” species’ cover, suggesting that it may act as a nurse species. In contrast, two other long-lived species, Atriplex vesicaria and Astrebla pectinata, had significantly reduced cover or were absent near to watering points. These and other long-lived species had a poorly developed SSB and thus limited ability to regenerate from seed if killed by sustained heavy grazing. The absence of fifteen locally rare species (including 12 short-lived species) from water-near gilgais indicates the need for more intensive survey to determine whether the proliferation of watering points poses a threat to such species.