Exotic Ecosystem Engineers Change the Emergence of Plants from the Seed Bank of a Deciduous Forest

The anthropogenic spread of exotic ecosystem engineers profoundly impacts native ecosystems. Exotic earthworms were shown to alter plant community composition of the understory of deciduous forests previously devoid of earthworms. We investigated the effect of two exotic earthworm species (Lumbricus terrestris L. and Octolasion tyrtaeum Savigny) belonging to different ecological groups (anecic and endogeic) on the emergence of plants from the seed bank of a northern North American deciduous forest using the seedling emergence method. We hypothesized that (1) exotic earthworms change the seedling emergence from the plant seed bank, (2) L. terrestris increases the emergence of plant seedlings of the deeper soil layer but decreases that of the upper soil layer due to plant seed burial, and (3) O. tyrtaeum decreases plant seedling emergence due the damage of plant seeds. Indeed, exotic earthworms altered the emergence of plant seedlings from the seed bank and the functional composition of the established plant seedlings. Surprisingly, although L. terrestris only marginally affected seedling emergence, O. tyrtaeum changed the emergence of native plant species from the seed bank considerably. In particular, the number of emerging grass and herb seedlings were increased in the presence of O. tyrtaeum in both soil layers. Moreover, the impacts of earthworms depended on the identity of plant functional groups; herb species benefited, whereas legumes suffered from the presence of exotic earthworms. The results highlight the strong effect of invasive belowground ecosystem engineers on aboveground ecosystem characteristics and suggest fundamental changes of ecosystems by human-spread earthworm species.     

Smoke and heat: influence on seedling emergence from the germinable soil seed bank of mesic grassland in South Africa

We examined if germination and seedling emergence of species from the soil seed bank of mesic grassland in South Africa differed in their response to smoke or heat treatments alone or combined. Soil seed bank samples taken from 0 to 5 cm depth of the topsoil were treated with smoke-water solution, heat and heat + smoke-water combined and subsequent emergence of seedlings monitored over 90 days. In total, 790 individuals from 11 different plant families representing 37 graminoid (Poaceae) and non-graminoid species of flowering plants were identified. The most abundant plant families that emerged were Poaceae followed by Asteraceae. Grasses contributed 18% of the germinable seed bank, while non-grass (forbs and trees) species contributed >80%. The most abundant grass species that emerged was Themeda triandra and the most common forb species was Centella asiatica. Compared to the control, smoke-water (SW) and/or smoke-water + heat (H + SW) treatment resulted in a 1.6-fold increase in mean number of seedling emergence. SW and H + SW treatment of soil seed bank also resulted in fourfold to fivefold greater biomass production. These results suggest that emergence of some smoke-responsive perennial grasses (e.g. Themeda triandra) from the soil seed bank can be enhanced using smoke techniques. Moreover, plant-derived smoke could potentially have a significant role in the restoration of degraded grasslands in South Africa and elsewhere.     

Ecological longevity of Polaskia chende (Cactaceae) seeds in the soil seed bank,seedling emergence and survival

• Soil seed banks are essential elements of plant population dynamics, enabling species to maintain genetic variability, withstand periods of adversity and persist over time, including for cactus species. However knowledge of the soil seed bank in cacti is scanty. In this study, over a 5‐year period we studied the seed bank dynamics, seedling emergence and nurse plant facilitation of Polaskia chende, an endemic columnar cactus of central Mexico.
• P. chende seeds were collected for a wild population in Puebla, Mexico. Freshly collected seeds were sown at 25 °C and 12‐h photoperiod under white light, far‐red light and darkness. The collected seeds were divided in two lots, the first was stored in the laboratory and the second was use to bury seeds in open areas and beneath a shrub canopy. Seeds were exhumed periodically over 5 years. At the same time seeds were sown in open areas and beneath shrub canopies; seedling emergence and survival were recorded over different periods of time for 5 years.
• The species forms long‐term persistent soil seed banks. The timing of seedling emergence via germination in the field was regulated by interaction between light, temperature and soil moisture. Seeds entered secondary dormancy at specific times according to the expression of environmental factors, demonstrating irregular dormancy cycling.
• Seedling survival of P. chende was improved under Acacia constricta nurse plants. Finally, plant facilitation affected the soil seed bank dynamics as it promoted the formation of a soil seed bank, but not its persistence.

     

Seed dormancy,soil type and protective shelters influence seedling emergence at Shark Bay,Western Australia: Insight into global dryland revegetation

Seedling emergence is a major constraint on dryland revegetation success. In this study, we investigated seedling emergence of six framework shrub species as influenced by seed treatment, soil type and protective shelters using a large field trial in arid Western Australia. We observed the main effects of seed treatment and soil type to account for the majority of the variation in emergence. For species that exhibit pronounced dormancy, we found emergence of dormancy‐alleviated or treated (T) seed to be significantly greater than dormant or untreated (UT) seed, with responses varying across species (e.g. 41 times greater for Acacia ligulata Benth., and 10 times greater for Stylobasium spathulatum Desf.). For shallowly or nondormant species like Senna glutinosa (DC) Randall, UT seed emergence was slightly greater than for T seed. Compared to subsoil, topsoil was more receptive to infiltration (3.44 vs. 0.38 mm/min), and less prone to compaction (1.24 vs. 1.67 g/cm³) and crusting (0.6 vs. 1.3 kg/cm²); however, subsoil had greater moisture retention. Shelters failed to benefit soil moisture retention in either soil type, but enhanced emergence for most species. This study provides insight into how various cost‐effective treatments can be utilized to manipulate seed dormancy to optimize seedling emergence, the intrinsic value of topsoil as a superior growth medium and the benefit of novel, low‐cost shelters for enhancing seedling emergence. In arid environments, sowing T seed in combination with UT seed increases the likelihood of capitalizing on inherently variable precipitation events.     

Dispersal and recruitment dynamics in the fleshy‐fruited Persoonia lanceolata (Proteaceae)

Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy‐fruited obligate seeding plant species in fire‐prone habitats? Location: Southeastern Australia. Methods: We used a long‐term study of a shrubby, fleshy‐fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post‐fire seedling densities 6‐7 times pre‐fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77‐100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0‐5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7–8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five‐fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished.     

Controlling the seed bank of the invasive plant <Emphasis Type="Italic">Acacia saligna</Emphasis>: comparison of the efficacy of prescribed burning,soil solarization,and their combination

Reducing the seed bank of invasive plants is a prerequisite for successful restoration of invaded ecosystems. The Australian legume tree Acacia saligna is one of the worst invasive plants in Mediterranean climate regions. This fire-adapted species possesses a large persistent seed bank characterized by physical dormant seeds. The present research was aimed to compare the efficacy of prescribed burning, soil solarization by solar heating of moist soil, and their use in combination on A. saligna seed bank reduction, using the buried seed method, and on seedling emergence from the natural seed bank, as a model of controlling fire-adapted plants. The data obtained show that the direct effect of prescribed burning on the buried seed dynamics was highly variable, and it only reduced seed viability from 98% to about 56%. Soil solarization, particularly in combination with prescribed burning, was much more effective than prescribed burning alone, reducing seed viability to about 29 and 4%, respectively. These results were confirmed by recording seedling emergence from the natural seed bank during two successive germination years following the treatments. Only a relatively very small number of seedlings emerged in the soil solarization treatment and none in the combined treatment. Based on the above data, it is recommended to apply prescribed burning as a pretreatment for soil solarization, or to utilize wild fires followed by soil solarization to reduce the seed bank of invasive fire-adapted plants. In situations in which fire cannot be used as a pretreatment, soil solarization alone is reasonably effective.     

Long-term orchard groundcover management systems affect soil microbial communities and apple replant disease severity

Apple replant disease (ARD) is a soil-disease syndrome of complex etiology that affects apple tree roots in replanted orchards, resulting in stunted tree growth and reduced yields. To investigate whether different groundcover management systems (GMSs) influence subsequent ARD severity, we grew apple seedlings in an outdoor nursery in pots containing orchard soil from field plots where four GMSs had been maintained for 14 years in an orchard near Ithaca, NY, USA. The GMS treatments were: (1) pre-emergence herbicide (Pre-H), bare soil strips maintained by applying tank-mixed glyphosate, norflurazon and diuron herbicides annually; (2) post-emergence herbicide (Post-H), sparse weed cover maintained by applying glyphosate in May and July each year; (3) mowed sod grass (Mowed Sod); and (4) bark mulch (Mulch). Soils were also sampled from the grass drive lane maintained between the trees in the orchard (Grass Lane). Sampled soils (Orchard soil) were either pasteurized or left untreated, placed into 4-L pots, and planted with one apple seedling per pot. After 3 months of growth, soil (Bioassay soil) and apple tree roots (Bioassay roots) were sampled from each pot and microbial populations colonizing samples were characterized. Seedling growth was reduced in soils sampled from all four GMS treatments compared to the Grass Lane soils. Among the GMS treatments, seedling biomass was greater in Pre-H than in the Post-H soil. Soil microbial communities and nutrient availability differed among all four GMS treatments and the Grass Lane. Root-lesion (Pratylenchus sp.) nematode populations were higher in the Mowed Sod than in the other GMS treatments. Soil bacterial and fungal community composition was assessed in Orchard and Bioassay soils and Bioassay roots with a DNA fingerprinting method (T-RFLP). Redundancy analysis indicated that soils sampled from the different GMS treatments differentially influenced seedling biomass. A clone library of 267 soil bacteria was developed from sampled Orchard soils and Bioassay roots. These communities were dominated by Acidobacteria (25% of sequences), Actinobacteria (19%), δ-Proteobacteria (12%), β-Proteobacteria (10%), and these ratios differed among the GMS soils. Members of the family Comamonadaceae were detected only in tree-row soil, not in the Grass Lanes. The dominant sequences among 145 cloned fungi associated with apple seedling roots were Fusarium oxysporum (16% of sequences), an uncultured soil fungus submitted under DQ420986 (12%), and Rhodotorula mucilaginosa (9%). In a redundancy analysis, factors including fungal and oomycete community compositions, soil respiration rates, population sizes of culturable bacteria and fungi, soil organic matter content, and nutrient availability, were not significant predictors of apple seedling biomass in these soils. Different GMS treatments used by apple growers may influence subsequent ARD severity in replanted trees, but edaphic factors commonly associated with soil fertility may not reliably predict tree-root health and successful establishment of replanted orchards.     

Factors influencing the natural regeneration of the pioneering shrub Calligonum mongolicum in sand dune stabilization plantations in arid deserts of northwest China

Calligonum mongolicum is a successful pioneer shrub to combat desertification, which is widely used for vegetation restoration in the desert regions of northwest China. In order to reveal the limitations to natural regeneration of C. mongolicum by asexual and sexual reproduction, following the process of sand dune stabilization, we assessed clonal shoots, seedling emergence, soil seed bank density, and soil physical characteristics in mobile and stabilized sand dunes. Controlled field and pot experiments were also conducted to assess germination and seedling emergence in different dune soil types and seed burial depths. The population density of mature C. mongolicum was significantly different after sand dune stabilization. Juvenile density of C. mongolicm was much lower in stabilized sand dunes than mobile sand dune. There was no significant difference in soil seed bank density at three soil depths between mobile and stabilized sand dunes, while the emergence of seedlings in stabilized dunes was much lower than emergence in mobile dunes. There was no clonal propagation found in stabilized dunes, and very few C. mongolicum seedlings were established on stabilized sand dunes. Soil clay and silt content, air‐filled porosity, and soil surface compaction were significantly changed from mobile sand dune to stabilized dunes. Seedling emergence of C. mongolicm was highly dependent on soil physical condition. These results indicated that changes in soil physical condition limited clonal propagation and seedling emergence of C. mongolicum in stabilized sand dunes. Seed bank density was not a limiting factor; however, poor seedling establishment limited C. mongolicum's further natural regeneration in stabilized sand dunes. Therefore, clonal propagation may be the most important mode for population expansion in mobile sand dunes. As a pioneer species C. mongolicum is well adapted to propagate in mobile sand dune conditions, it appears unlikely to survive naturally in stabilized sand dune plantations.     

The independent effects of heat,smoke and ash on emergence of seedlings from the soil seed bank of a heathy Eucalyptus woodland in Grampians (Gariwerd) National Park,western Victoria

Abstract The independent effects of smoke, ash, and wet and dry heat treatments on seedling emergence from the soil seed bank were tested for soils from fire-prone heathy woodlands in western Victoria. A total of 763 individuals from 56 species were recorded from the surface soil samples (which covered a total area of 1 m²). Both species richness and density of seedlings was greater for smoke- and heat-treated samples than for controls and ash-treated samples. However, only the density differences were significant. Mean seed bank densities for the smoke and heat treatments ranged from 855 ± 70m^?2 to 1080 ± 58 m^?2 and are similar to estimates obtained elsewhere in Australia for heat-treated soils from dry sclerophyll communities. Of the 56 species recorded, 46 occurred in the smoke and heat treatments but only 33 in the control and ash treatments. The sudden increase in surface soil pH, exchangeable cations and extractable phosphorus which was associated with the ash treatment did not act as a trigger for germination in any of the species recorded here. Chemical constituents from smoke do appear to provide a stimulus separate from the effects of heat, but were not identified with any particular taxa.     

Can the soil seed bank contribute to revegetation of the drawdown zone in the Three Gorges Reservoir Region?

The drawdown zone of the Three Gorges Reservoir Region was assumed to be completely formed in 2009 and the water level would range from ~145 m in flood season (summer) to ~175 m during non-flood season (winter). The soil seed bank is an important propagule source for vegetation restoration. In order to evaluate the potential of the soil seed bank to revegetate the drawdown zone of this region, we examined the quantitative relationships between the germinable soil seed bank and the established vertical and horizontal vegetation patterns. A total of 45 soil samples at four sites was collected to examine seed bank density, species richness, and composition using the seedling-emergence method. Forty-five species (from 20 families) germinated from the soil seed bank, and the average seed density was 4578 m⁻². The seed bank was dominated by annual plants, suggesting reestablishment of some above-ground species was plausible. However, most established woody plants and perennials were absent from the seed bank indicating a low probability of reestablishment for non-annuals through the seed bank. Thus, due to low species compositional similarity to extant vegetation and the dominance of annual plants, the soil seed bank had a low potential to restore pre-dam vegetation in the drawdown zone of the Three Gorges Reservoir Region, but its potential as a propagule source should be considered regarding the management of the drawdown zone for vegetation cover.     

Persistent soil seed banks and floristic diversity in Fagus orientalis forest communities in the Hyrcanian vegetation region of Iran

We assessed the size of seed bank, species diversity and similarity between seed bank and standing vegetation in four oriental beech (Fagus orientalis Lipsky) community types of the central Hyrcanian forests of northern Iran. For this purpose a total of 52 relevés was established in two associations and two subassociations of the beech forests, and six soil samples (20 × 20 cm square and to a depth of 10 cm) were collected in each relevé in mid-spring, after the germination season had ended. Soil seed bank was investigated using the seedling emergence method. A total of 63 species, 57 genera and 36 families was represented in the persistent soil seed bank of the forest communities. The seed bank contained 28 species not found as adult plants in the vegetation, but these were mostly early successional species. Size of the seed bank ranged from 3740 to 4676 individuals m⁻² in the Rusco hyrcani-Fagetum orientalis and Danae racemosae-Fagetum orientalis associations, respectively. Species composition of seed banks and aboveground vegetation had low similarity with an average of 24.3% in the four plant communities, because only 38% of the species were the same in the vegetation and the seed banks. Most seeds in the seed bank were from early successional species, and the only tree with a large persistent seed bank was the fast-growing pioneer Alnus subcordata. DCA ordination also demonstrated low similarity between soil seed bank and vegetation. The soil seed banks of the four beech communities did not differ significantly in size, composition, diversity and uniformity. Although above ground vegetation in the four community types is floristically distinct, there is considerable overlap among the soil seed banks because they contain in a similar way early successional species. Further, the absence of typical forest species in the soil seed bank indicates that restoration of forest tree species cannot rely on the soil seed bank.     

Fire and flood: Soil‐stored seed bank and germination ecology in the endangered Carrington Falls Grevillea (Grevillea rivularis,Proteaceae)

Abstract Seed germination is dependent on the interaction between the dormancy state of a seed and the presence of favourable environmental conditions. Thus, the spectacular pulse of seedling recruitment in many Australian vegetation communities following disturbances such as fire can be attributed to changes in microsite conditions and/or the dormancy‐breaking effect of the disturbance on accumulated seed banks. Grevillea rivularis is a threatened species endemic to the area immediately above Carrington Falls in the NSW Southern Highlands. Most of the population is confined to the riparian vegetation zone in woodland and heath, and is therefore subject to periodic disturbance from fire and flood. For this species, a pulse of seedling recruitment has been recorded after fire, flood and mechanical soil disturbance. The aims of this study were to examine the density and vertical distribution of the soil‐stored seed bank and to investigate the role of heat and scarification as cues for germination of fresh and soil‐stored seed. There was a large seed bank under the canopies of established individuals (194 ± 73 seeds m^?2) and most seeds were found in the 0–2 cm and leaf‐litter layers of the soil profile. The germination response of soil‐stored and fresh seed was examined using a hierarchical series of laboratory experiments. Seeds of G. rivularis showed marked dormancy polymorphism. Thirty‐six percent of soil‐stored seed germinated without treatment, whereas no untreated fresh seeds germinated. Scarification or heating caused significant germination of dormant soil‐stored seed, but only scarification resulted in germination of dormant fresh seeds. These results highlight important differences in the dormancy state of soil‐stored and fresh seed. Thus, being a riparian species in a fire‐prone environment, the dormancy mechanisms in seeds of G. rivularis suit this species to disturbance by both fire and flood.     

Experimental assessment of initial revegetation on abandoned paths in temperate deciduous forest

Question: Do soil treatments and addition of seed facilitate rapid vegetation restoration on forest paths excluded from trampling? Location: Six mesophilic mixed deciduous Querco‐Fagetea forests in Flanders, northern Belgium. Methods: Enclosures on paths were excluded from trampling by fencing. In a full factorial design, plots were subjected to seeding, soil scarification, addition of organic material and inoculum. The following two years, seedling establishment and growth were sampled during spring and summer. Soil treatments and seeding effect was tested and seedling occurrence was analysed in relation to species' origin. Results: Spontaneous re vegetation was significant in all plots since fencing. Throughout the observation period seedling cover and height continued to increase. Seeding had an overall effect on seedling density, cover and height. Some soil treatment interactions significantly enhance re vegetation, although each individual soil treatment had no significant effect. Regardless of the seeded individuals, invading species mostly originated from the surrounding area and the seed bank. Conclusion: The preliminary results of this experiment imply that seeding is the only treatment which has a positive effect on re vegetation success in all circumstances, provided that the exclusion from trampling is effective.     

Emergence of the Introduced Grass Agropyron cristatum and the Native Grass Bouteloua gracilis in a Mixed-grass Prairie Restoration

Abstract Prairie restoration at the northern edge of the Great Plains can be frustrated by previously established non‐native perennial grasses. We compared the emergence of a widely introduced grass, Agropyron cristatum, and a common native grass, Bouteloua gracilis, in a 4‐year‐old field experiment in which the Agropyron‐dominated vegetation had either been left intact or treated annually with herbicide. This was done at two levels of water supply, reflecting conditions expected in wet and dry years, to examine the effects of among‐year variability in precipitation. Water addition significantly increased the emergence of both surface‐sown and buried (1 cm deep) seeds. Herbicide treatment of neighbors did not increase the emergence of experimentally added seeds. Emergence was much greater for buried (80%) than surface‐sown seeds (20%). Significantly more Bouteloua than Agropyron germinated from experimentally buried seeds. Whereas only a single seedling of Bouteloua emerged from the existing seed bank, the mean density of Agropyron seedlings emerging from the seed bank was 930/m² (range, 0 to 6,455/m²). Surprisingly, the emergence of Agropyron from the seed bank was not decreased by 4 years of herbicide treatment, possibly because herbicide may release Agropyron from intraspecific competition and allow increased seed production to compensate for decreased plant abundance. In summary, we found few differences between Agropyron and Bouteloua in spring and summer emergence at high or low water availability. The persistence of Agropyron stands despite repeated herbicide application may be partly due to increased seed production.     

Aerial seed storage in <Emphasis Type="Italic">Melaleuca ericifolia</Emphasis> Sm. (Swamp Paperbark): environmental triggers for seed release

Aerial seed banks are potentially the main source of sexual recruitment for woody wetland plants. Whilst the importance of soil seed banks for the persistence and recruitment of wetland plants has been examined in many studies, the role of aerial seed banks has been largely neglected. We used seed traps and the seedling emergence technique to quantify the seed rain from aerial seed banks of the Swamp Paperbark Melaleuca ericifolia Sm. (Myrtaceae) in Dowd Morass, a Ramsar-listed, brackish-water wetland in south-eastern Australia. Nine plant species germinated from material collected in seed traps over 2004–2005, but emergents were dominated (80–97%) by M. ericifolia. The mean number of M. ericifolia emergents ranged from <1 to <100 seedlings m⁻² day⁻¹, and showed a peak in the summer–autumn period. Regression analysis showed a significant negative correlation (r ² = 0.738) between the number of M. ericifolia emergents and water depth. Water depth and salinity were negatively correlated (r ² = 0.819), and increases in the number of M. ericifolia emergents as water levels fell were also associated with high salinities. Increasing air temperature and vapour pressure deficit also stimulated seed release during periods of drying. This study is one of the first to demonstrate the importance of aerial seed banks for sexual recruitment in woody wetland plants and the release of seed in relation to environmental factors. Aerial seed banks warrant consideration alongside soil seed banks for the establishment and long-term survival of woody plants in wetlands. Handling editor: Luis Mauricio Bini     

Plant Establishment from the Seed Bank of a Degraded Floodplain Wetland: A Comparison of Two Alternative Management Scenarios

There has been little research examining the soil seed banks of degraded floodplain wetlands and their contribution to wetland rehabilitation in Australia. Our aim was to assess the establishment of plants from the seed bank that may occur following the delivery of an environmental water allocation to Kanyapella Basin, a 2950 ha wetland located on the floodplain of the Goulburn and Murray Rivers in northern Victoria, Australia. Two hypothetical water regimes were investigated (flooded and dry) in a glasshouse experiment, where plants were left to establish from the seed bank over a period of 124 days. Differences in the establishment of plants from the seed bank indicated that the return of a flooding regime is likely to have a significant effect on the composition of the wetland vegetation. Mapping of the distribution of plant species indicated that propagules were highly dispersed across the wetland for the majority of taxa, in contrast to the localised distribution of many of the plant species represented in the extant vegetation. Inundation favoured the establishment of native wetland and floodplain plants, although many areas of Kanyapella Basin that are currently ‘weed-free’ have the potential to become colonised and potentially dominated by introduced plants if the wetland is not managed appropriately. Overall, results supported the aim of management to reestablish a wetting and drying regime through use of an environmental water allocation. This study presents a significant example of the application of seed bank investigations in wetland ecology and management.     

How much seed remains in the soil after a fire?

Soil seed banks that persist after a fire are important in fire-prone habitats as they minimise the risk of decline or local extinction in plants, should the fire-free interval be less than the primary juvenile periods of the species. In two common woody plant genera (Acacia and Grevillea) in southeastern Australia, we examined the size and location of the residual seed bank after fire across areas of varying seedling densities at three locations in comparison to the distribution of seeds in the soil at an unburnt site. We found viable dormant seeds remaining in the soil after fire (evidence of residual soil seed bank). A significantly lower proportion of seeds remained in the top 5 cm of soil than at 5–10 cm or 10–15 cm soil depths, independent of seedling density or plant genus. This was due to greater germination, and possibly some seed mortality, near the soil surface. Reduced germination below 5 cm was probably due to the reduced efficacy of the fire cues that break seed dormancy, a declining ability of seeds to emerge successfully from such depths, and the lower abundance of seeds in the soil at such depths. The magnitude of the residual seed bank was similar across 0–5, 5–10 and 10–15 cm soil depths in Acacia suaveolens. For two Grevillea species, most residual seeds were at 0–5 and 5–10 cm. The residual soil seed bank in the top 10 cm of soil after fire varied across sites with estimates of 0, 19 and 27% in G. speciosa and 23, 35, and 55% in A. suaveolens. At two sites, both species had similar residual seed bank sizes, while at a third, there were large differences between the species (0–55%). The observed patterns imply that the fire-related cues that break seed dormancy generally declined with soil depth. For Acacia, seed dormancy is broken by heat shock, a fire-cue that declines with soil depth. Some 250 species (approx 15% of the fire-prone flora) in the region are thought to have dormancy broken by heat shock. For Grevillea, where seed dormancy is broken by the interaction of smoke and heat shock, at two sites, we suggest three possibilities: (i) the smoke cue declined with soil depth; (ii) both heat and smoke are obligatory for breaking seed dormancy; or (iii) the cues may be independent and additive and below the zone of soil heating, only a proportion of available seeds had dormancy broken by smoke alone. At a third site (no residual seed bank detected) the smoke cue was predicted not to have declined with soil depth. Up to 900 species (just under half the fire-prone flora) in the study region are thought to have seed dormancy broken by the interaction of heat and smoke during the passage of a fire.     

Seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence on desert sand dunes

Seedling emergence is a critical stage in the establishment of desert plants. Soil microbes participate in plant growth and development, but information is lacking with regard to the role of microbes on seedling emergence. We applied the biocides (captan and streptomycin) to assess how seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence of Artemisia sphaerocephala on the desert sand dune. Fungal and bacterial community composition and diversity and fungal–bacterial interactions were changed by both captan and streptomycin. Mucilage increased soil enzyme activities and fungal–bacterial interactions. Highest seedling emergence occurred under streptomycin and mucilage treatment. Members of the phyla Firmicutes and Glomeromycota were the keystone species that improved A. sphaerocephala seedling emergence, by increasing resistance of young seedlings to drought and pathogen. Seed mucilage directly improved seedling emergence and indirectly interacted with the soil microbial community through strengthening fungal–bacterial interactions and providing favourable environment for soil enzymes to affect seedling emergence. Our study provides a comprehensive understanding of the regulatory mechanisms by which soil microbial community and seed mucilage interactively promote successful establishment of populations of desert plants on the barren and stressful sand dune.     

A preliminary assessment of the response of a native reptile assemblage to spot‐spraying invasive Bitou Bush with glyphosate herbicide

During recent work examining the effects of Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) invasion on native reptile assemblages in coastal heathland vegetation in Eastern Australia, unplanned spot‐spraying of glyphosate occurred at some of our experimental sites invaded by Bitou Bush. We used this unexpected herbicide application as an opportunity to provide a preliminary assessment of the short‐term impacts on reptiles of glyphosate spot‐spraying of Bitou Bush. Using an M‐BARCI design, we compared reptile assemblages among uninvaded (reference) sites, invaded (control) sites and invaded and sprayed (impact) sites before and after spraying. We found no significant short‐term (7 – 10 months) differences in reptile abundance, species richness or assemblage composition among invaded, uninvaded and sprayed sites before and after glyphosate application. We cautiously interpret our results to generate a preliminary finding that spot‐spraying of Bitou Bush with glyphosate appears not to have a deleterious effect on reptile assemblages at seven and ten months following herbicide application. While we would not recommend basing management decisions on the outcomes of our study alone, we suggest that our findings can be used to assist in the development of strategic analyses of glyphosate impacts on native flora and fauna.     

Microhabitat variations and seed bank-vegetation relationships in a desert wadi ecosystem

Due to extreme variability in patterns of rainfall, plant seed banks are an important component of desert habitats. Here I report on effects of standing vegetation and three different microhabitats (channel, bank and terrace) on the soil seed bank of a desert wadi ecosystem in the Eastern Desert of Egypt. A total of 450 soil samples at 45 stands were collected to represent the different wadi microhabitats. The germinable seed bank was estimated by controlled counts of seedling emergence. The floristic composition, functional properties and diversity of the soil seed bank, as well as its similarity with the standing vegetation varied among wadi microhabitats. Such variation could be attributed to differences in disturbance intensity among microhabitats (terrace < bank < channel) and variation of soil factors along the microtopographic gradient. Channel showed the highest species richness and size of soil seed bank, followed by bank and then terrace. Moreover the Shannon index of diversity of the seed bank and its similarity with standing vegetation were significantly greater in both channel and bank microhabitats than in terrace. At the level of plant functional groups, number of seeds of annuals was higher in both channel and bank than in terrace. Shrubs were more abundant in seed banks of channel compared to terrace. The size and species richness of seed bank were increased with the total plant cover, annual/perennial ratio and species richness of the standing vegetation.