Effects of potnetial trap crops and planting date on soil infestation with potato cyst nematodes and root-knot nematodes

In 1997 and 1998 the stimulation of hatch of potato cyst nematodes (PCN) by a trap crop was studied at various times during the growing season in a container and a field experiment. Solanum nigrum‘90‐4750‐188’was used as the trap crop in both experiments and was sown on 1 May, 16 June or 1 August in two successive years on different plots. Neither experiment revealed much seasonal variation in hatchability of PCN juveniles under a trap crop. In the container experiment, the hatch of the Globodera pallida Pa3 population was equally and strongly stimulated (89%) at all sowing dates in both years, except for the 1 August sowing in 1998 (when the hatch was 77% under extremely wet soil conditions). In the control treatment with non‐hosts (flax followed by barley) the total spontaneous hatch was 50% over 2 yr. In the field experiment, the hatch of PCN, averaged over the four populations, was also equally stimulated (71%) at all sowing dates in both years. In the control treatment with non‐hosts (flax‐barley) the total spontaneous hatch was 36% over 2 yr. Total hatch under the trap crop over 2 yr varied between the four PCN populations from 63% to 80%. In 1998 and 1999, control of potato cyst nematodes (PCN) by the potential trap crops Solanum sisymbriifolium and S. nigrum‘90‐4750‐188’was studied in the field. Potato was also included as a trap crop. In the 1998 experiment, potato, S. sisymbriifolium and S. nigrum strongly stimulated the hatch of PCN compared with the non‐host white mustard (Sinapis alba). Roots of potato and white mustard were mainly found in the top 10 cm of soil, whereas roots of S. sisymbriifolium and S. nigrum were also abundant at depths of 10–20 cm and 20–30 cm. In the 1999 experiment, soil infestation with PCN decreased markedly with potato and S. sisymbriifolium as trap crops. In plots moderately to severely infested with 2‐yr old cysts (2–29 juveniles ml^?1 air dried soil), potato reduced soil infestation by 87% and S. sisymbriifolium by 77%. In plots moderately to severely infested with 1‐yr old cysts the reductions were 74% and 60%, respectively. The reduction was least on plots very severely infested with PCN (110–242 juveniles ml^?1 soil): 69% and 52% for potato and S. sisymbriifolium, respectively. Soil infestations of plots that were initially slightly to severely infested with the root‐knot nematode Meloidogyne hapla were greatly reduced under fallow and S. sisymbriifolium but increased under potato. From these and previous experiments it was concluded that, for several reasons, S. sisymbriifolium is a promising trap crop.     

Experimental demography of the rare Gentianella germanica: seed bank formation and microsite effects on seedling establishment

The persistence of populations of short-lived species requires regular reproduction and seedling establishment. A persistent seed bank can buffer populations against extinction in unfavourable years. We experimentally investigated seed fate in Gentianella germanica, an endangered biennial species characteristic for species-rich nutrient-poor calcareous grasslands in central Europe. We studied the effect of experimental gaps on seedling establishment from sown seeds and the fate of seeds buried in bags over two years. In December 1993 experiments were established at seven calcareous grassland sites in the Swiss Jura mountains. In spring 1994 seedlings emerged in all plots where seeds had been sown, including previously unoccupied patches. This suggests that limited dispersal within sites contributes to small population sizes. Significantly more seedlings emerged at sites with current populations of G. germanica than at unoccupied sites (5.95% vs 3.40%). Because this difference was not explained by germinations from the natural seed bank it indicates differences in habitat quality. Clipping of the vegetation and disturbance of the soil reduced vegetation cover in the following spring and enhanced seedling emergence. In undisturbed plots 4.5% of seeds sown produced a seedling in spring 1994, whereas in plots with clipped vegetation 9.9% and in disturbed plots 12.7% produced seedlings (p>0.01). This suggests that management measures which create gaps in the vegetation (e.g. grazing) could positively influence population size and persistence of G. geymanica. On average, we recovered 7.55% viable seeds after one year of burial in bags, and 4.05% after two years, indicating that G. geymanica has a persistent seed bank. The demographic data indicate that the number of viable seeds in the seed bank exceeds the number of established plants in a population at least by a factor of 20. Restoration of extinct populations of the species from the seed bank may thus be possible if appropriate management measures are taken within a few years.     

Germination and population structure of spear thistle Cirsium vulgare in relation to experimentally controlled sheep grazing

Summary The size and number of rosettes of Cirsium vulgare were censused in a 4 ha sheep grazing trial on lowland calcareous grassland in paddocks receiving controlled winter, spring and summer grazing treatments. Spring grazing significantly increased thistle rosette numbers, and there were always fewer rosettes in size classes 250mm–300 mm under the heavier grazing treatments. The emergence of seeds of Cirsium vulgare sown by hand into each of the grazing treatments was monitored and showed a positive effect of spring grazing. When the percent emergence of sown seeds was used as a covariate in the analysis of rosette numbers in the experimental paddocks, it was found to account for 77% of the variance in thistle numbers. It was concluded that the main effect of grazing on thistle rosette numbers is an indirect one exercised through the effects of grazing on germination conditions. Seeds of Cirsium vulgare were sown into artificial gaps at another grassland site, to determine the effect of gap-size upon seedling emergence. Germination was poor, but significantly more seedlings emerged in gaps 10–20 cm diameter, than in 5 cm gaps or in control plots without a gap. A computer simulation model was used to explore the relationship between gap density and thistle population dynamics. A threshold density of gaps was found to exist, below which thistle populations went extinct, and above which the thistle population grew geometrically. The degree of aggregation of dispersed seeds did not alter the threshold gap-density for plant extinction, but did affect the rate of increase of the thistle population when the threshold gap-density was exceeded. It is concluded that strategies for controlling Cirsium vulgare populations by grazing manangement will be most effective if aimed at reducing suitable sites for establishment in spring. The success of such attempts will depend upon the soil fertility of the site, and sudden outbreaks of Cirsium vulgare infestation can be expected if a sward gradually deteriorates through over-grazing.     

Determining the Optimal Sowing Density for a Mixture of Native Plants Used to Revegetate Degraded Ecosystems

No standardized, objective methodology exists for optimizing seeding rates when establishing herbaceous plant cover for pastures, hay fields, ecological restoration, or other revegetation activities. Seeding densities, fertilizer use, season of seeding, and the interaction of these treatments were tested using native plants on degraded sites in northern British Columbia, Canada. A mixture of 20% Achillea millefolium, 20% Carex aenea, 20% Elymus glaucus, 20% Festuca occidentalis, 16% Geum macrophyllum, and 4% Lupinus polyphyllus seed was applied at 0, 375, 750, 1,500, 3,000, and 6,000 pure live seed (PLS) per m² in 2.5 × 2.5–m rototilled test plots, established in the fall and spring, with and without fertilizer. There was no significant difference in plant cover of sown species between fall seeding and spring seeding, and few treatment interactions were identified in the first 2 years after sowing. There was no significant difference in cover between seed densities of 3,000 and 6,000 PLS/m² in the first year, nor among 1,500, 3,000, and 6,000 PLS/m² treatments in the second year. Seed densities as low as 375 PLS/m² produced year 2 plant cover equivalent to that observed at 3,000 PLS/m² in year 1. Plots sown to seed densities less than or equal to 750 PLS/m² generally exhibited an increase (infilling) in plant density from year 1 to year 2, whereas plots sown to seed densities greater than or equal to 1,500 PLS/m² generally exhibited a decrease (density‐dependent mortality) in plant density. These results imply a most efficient sowing density between 750 and 1,500 PLS/m² (corresponding to 190–301 established plants^.m^?2 after two growing seasons). It is suggested that net changes in plant populations observed over a range of sowing densities are a robust and objective means of determining optimal sowing densities for the establishment of herbaceous perennials.     

Restored meadow harvestman communities (Opiliones) in the Bílé Karpaty Protected Landscape Area, Czech Republic

Harvestman communities inhabiting plots treated differently for grassland restoration were investigated at the Vyzkum site near Malá Vrbka village (Bílé Karpaty Protected Landscape Area). Harvestman were sampled by pitfall trapping from 1999 to 2003 on plots sown with native haymeadow seed mixture, also on plots where narrow strips of regional seed mixtures were sown either within a matrix of commercial grass mixture or within vegetation cover in natural regeneration state and on plots in a natural regeneration state. Additionally, harvestman were collected in a field under permanent crop rotation and in a neighbouring xerothermic deciduous forest. In total, 5,086 individuals of harvestman representing 15 species from three families were obtained. Phalangium opilio was dominant (78%) and P. opilio, Rilaena triangularis and Zachaeus crista were the most frequent species. The results confirmed colonisation and subsequent development of harvestman communities on meadows in various state of restoration, including plots with spontaneous plant succession. Nevertheless, biotope character and successive formation of plant cover evidently influenced the structure of harvestman communities. The highest number of taxa (12) was recorded on plots with natural regeneration; the lowest one (9) was recorded in the field with permanent crop rotation. The highest values of diversity and equitability indices of harvestman communities were found in neighbouring forest habitats representing possible sources of harvestman migration.     

Agronomic factors in the establishment of tetraploid seeded Miscanthus × giganteus

To meet US renewable fuel mandates, perennial grasses have been identified as important potential feedstocks for processing into biofuels. Triploid Miscanthus × giganteus, a sterile, rhizomatous grass, has proven to be a high‐yielding biomass crop over the past few decades in the European Union and, more recently, in the United States. However, high establishment costs from rhizomes are a limitation to more widespread plantings without government subsidies. A recently developed tetraploid cultivar of M. × giganteus producing viable seeds (seeded miscanthus) shows promise in producing high yields with reduced establishment costs. Field experiments were conducted in Urbana, Illinois from 2011 to 2013 to optimize seeded miscanthus establishment by comparing seeding rates (10, 20, and 40 seeds m^?2) and planting methods (drilling seeds at 38 and 76 cm row spacing vs. hydroseeding with and without premoistened seeds) under irrigated and rainfed conditions. Drought conditions in 2011 and 2012 coincided with stand establishment failure under rainfed conditions, suggesting that seeded miscanthus may not establish well in water‐stressed environments. In irrigated plots, hydroseeding without premoistening was significantly better than hydroseeding with premoistening, drilling at 38 cm and drilling at 76 cm with respect to plant number (18%, 54%, and 59% higher, respectively), plant frequency (13%, 30%, and 40% better, respectively), and the rate of canopy closure (18%, 33%, and 43% faster, respectively) when averaged across seeding rates. However, differences in second‐year biomass yields among treatments were less pronounced, as plant size partially compensated for plant density. Both hydroseeding and drilling at rates of 20 or 40 seeds m^?2 appear to be viable planting options for establishing seeded miscanthus provided sufficient soil moisture, but additional strategies are required for this new biomass production system under rainfed conditions.     

Density dependence of Anaphes sordidatus (Hymenoptera: Mymaridae) parasitism on eggs of Listronotus oregonensis (Coleoptera: Curculionidae)

Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) oviposits in carrot leaves and the larvae feed in carrot roots. Its eggs are parasitized by Anaphes sordidatus (Girault) (Hymenoptera: Mymaridae) throughout its oviposition period. This parasitoid is the major biotic mortality factor for L. oregonensis. Parasitism by A. sordidatus was studied for three years in sequentially sown plots of carrots, Daucus carota var. sativa. Over the scason, significantly fewer L. oregonensis eggs were oviposited in later sown carrots than in earlier sown carrots because oviposition started later in late sown plots of carrots. A positive temporal density-dependent relationship was observed each year between parasitism rates and host densities. This positive density dependence occurred in early and mid-summer for earlysown carrots where host density reached 1–2 host eggs per plant but disappeared in late summer when host density decreased while parasitism remained high. Latesown carrots had low host egg density (0.2 host egg per plant) and contributed little to the total number of eggs. In these late sown plots, parasitism increased rapidly to over 80% but no density dependence was observed. Spatially, few statistically significant regressions were found but all indicated a positive spatial density-dependence. Most non-significant regressions occurred because the range of egg density was too small between plots for a given date.     

Enhancement in the germination, growth and yield of okra (Abelmoschus esculentus) using pre-sowing magnetic treatment of seeds

The effect of pre-sowing magnetic treatments was investigated on germination, growth and yield of okra (Abelmoschus esculentus cv. Sapz pari). The dry okra seeds were exposed to sinusoidal magnetic field induced by an electromagnet. The average magnetic field exposure was 99 mT for 3 and 11 min and seeds with no magnetic field treatment were considered as control. Both treated and non-treated seeds were sown in experimental plots (120 m2) under similar conditions. Samples were collected at regular intervals for statistical analysis. A significant increase (P < 0.05) was observed in germination percentage, number of flowers per plant, leaf area (cm2), plant height (cm) at maturity, number of fruits per plant, pod mass per plant and number of seeds per plant. The 99 mT for 11 min exposure showed better results as compared to control.     

The effects on soil fauna of insecticides tested against wireworms (Agriotes spp.) in wheat

The organophosphorus insecticides Bayer 38156 (O-ethyl S-p-tolyl ethyl phosphonodithioate), trichloronate, Stauffer N 2790 (O-ethyl S-phenyl ethyl phosphonodithioate), thionazin and fenitrothion were compared with aldrin, dieldrin and γ-BHC for their effects on soil fauna, particularly wire-worms, and on crop yields in 1964 and 1965. At 1·5 lb active ingredient/acre, none of the organophosphates had as great an effect on wireworms as an aldrin spray at 2·25 lb a.i./acre or a dieldrin seed dressing at 2·25 lb a.i./acre. Some treatments significantly increased and some significantly decreased numbers of mites and Collembola. Except for Allolobophora chlorotica in plots treated with Bayer 38156, earthworm numbers were greater in plots sprayed with Bayer 38156 or aldrin, or sown with dieldrin-dressed seeds, than in untreated plots. In May 1964, one month after sowing, untreated plots had significantly fewer plants than plots sprayed with aldrin, trichloronate or Bayer 38156, or sown with γ-BHC or dieldrin-dressed seeds, but yields from untreated plots at harvest were high for such a large wireworm population and did not differ significantly from yields of treated plots in either year. The persistence of thionazin and Bayer 38156 in treated plots was measured by a bioassay using Collembola. Bayer 38156 was detected in plots 1 month after spraying but not after 6 months. Thionazin left detectable residues 1 month after spraying in the two acid plots but not in the two alkaline plots. More frequent samples taken from thionazin-treated plots in 1965 showed a similar pattern of persistence, and laboratory tests, using soil mixed with various amounts of powdered calcium carbonate, confirmed that thionazin persisted longer in more acid soils.     

BIODIVERSITY RESEARCH: Experimental introduction of the alien plant Hieracium lepidulum reveals no significant impact on montane plant communities in New Zealand

Aim There is debate over whether alien plants necessarily alter the communities they invade or can coexist with native species without discernable impacts. We followed the fate of montane plant communities in response to the experimental sowing of the alien weed Hieracium lepidulum, looking for changes in plant community composition and structure over 6 years. Location Craigieburn Range, New Zealand. Methods We used a replicated randomised block design, with 30 × 30 cm plots (n = 756) subdivided into 5 × 5 cm cells to examine and compare the effects of H. lepidulum at 0.09 m² (plot) and 0.0025 m² (cell) scales. Plots were sown with between 0 and 15,625 H. lepidulum seeds in 2003, forming gradients of invader density and cover. Measurements comprised community richness, evenness and diversity along with H. lepidulum density and cover at both scales. The relationships between the invader and local community attributes were modelled using hierarchical mixed‐effect models. Results Plant communities differed in the extent to which they became invaded, with H. lepidulum cover in the plots ranging from 0% to 52%, with a mean of only 1.89%. Plot species richness increased from 2003 to 2009, with a component of this increase (+0.002 species per year) associated with increasing H. lepidulum density. Other relationships between the plant community and H. lepidulum were generally non‐significant. Main conclusions In these montane plant communities, it appears H. lepidulum coexists with the native community with no measurable negative effects after 6 years on species richness, evenness or diversity, even where density and cover of the invader are highest. We suggest H. lepidulum has persisted preferentially at those sites with abiotic conditions sufficient to support a species‐rich assemblage.     

Effect of pea bacterial blight (Pseudomonas syringae pv. pisi) on the yield of spring sown combining peas (Pisum sativum)

Field trials to examine the effect of pea bacterial blight (Pseudomonas syringae pv. pisi) (Psp) on the yield of combining peas were carried out at five sites (HRI Wellesbourne, ADAS Rosemaund, ADAS Terrington, PGRO, SASA East Craigs) in the UK in 1990, 1991 and 1992. Healthy seed, cv. Solara, and seed naturally infected with Psp Race 2 was sown in large plots (c. 200 m²) in the open or under nets to prevent bird damage by pigeons. Despite relatively low disease severity levels (< 15% leaf area) and separation by at least 12 m of cv. Consort (resistant to Race 2) between plots there was considerable spread of disease into plots sown with healthy seed. Regression analysis demonstrated a significant relationship between yield and disease. Of the disease measurements examined, disease severity on the leaves (stipules) at growth stage 208 was found to be the best predictor of yield. A model containing environmental and bird damage terms, in addition to disease, suggested that a yield loss of 0.98 t/ha would be expected for a disease severity score of 1, equivalent to 5% leaf area affected, at growth stage 208.     

RECOLONIZATION OF SMALL DISTURBANCE PATCHES IN A NEW ENGLAND SALT MARSH

Availability of colonizers and edaphic conditions were tested in relation to rates of recolonization of open patches in salt marsh vegetation. The density of buried viable seeds was estimated by counting seedlings in undisturbed vegetation and germinating seeds in the laboratory. A low density of viable seeds (<50 per m²) found in these salt marsh soils indicated the absence of an important viable seed bank in this system. Rates of recolonization in natural open patches were monitored for three years. Vegetative expansion of Spartina alterniflora, at approximately 12 cm per year, accounted for most of the recolonization of open patches, although some colonization of annual Salicornia spp. occurred from seeds. Salinity and sulfide and ammonium concentrations were measured in pore water samples from depths of 2–7 cm and 10–15 cm of soil. Comparison of the concentrations from disturbed and undisturbed plots in the marsh did not show significant differences, indicating that none of the edaphic conditions measured would be more inhibitory to plant growth in the disturbed than the undisturbed plots. Therefore, the rate at which small open patches become recolonized is primarily controlled by proximity of Spartina alterniflora and its capacity for vegetative expansion.     

The fate of Datura ferox seeds in the soil as affected by cultivation, depth of burial and degree of maturity

Seeds of Datura ferox were collected in soybean fields, grouped into four categories according to the degree of fruit maturity and placed just level with the soil surface or buried to a depth of 7 or 15 cm. Seed survival after 8 months was c. 30% when the seeds were left on the soil surface, but between 40 and 90% when the seeds were buried. The riper seeds were the more persistent. A similar pattern was observed after 20 months. Seedling emergence was negatively related with the degree of seed maturity and depth of burial, but it was never great enough to explain seed losses. In another experiment seeds from ripe capsules were superficially sown and the soil was: (0) left undisturbed, (1) cultivated in late winter or (2) cultivated in late winter and late spring. In all cases there was a small flush of seedlings at the beginning of the first spring; other flushes occurred only after soil cultivation and were larger during the second spring than during the first. In the plots cultivated twice a year (2) the seedlings that emerged in the first spring represented c. 4% of the initial seed bank. Survival after 20 months was about 25% in all treatments. In an arable field under soybean cropping the seedling flushes during the spring months were related to the pattern of soil cultivation. The seedlings that emerged after crop drilling represented c. 18% of the seed bank (estimated before drilling). Implications for weed management are discussed.     

Effects of sowing date and volunteers on the infectivity of soil infested with Gaeumannomyces graminis var. tritici and on take-all disease in successive crops of winter wheat

In a field experiment on winter wheat, take‐all on plants and the infectivity of the soil were studied in crop sequences with different combinations of sowing dates. Take‐all was negligible in the first wheat crop, but thereafter the mean disease intensity (measured using a take‐all rating, TAR, with a maximum of 300) was 108, 190, 118 and 251 in the second to fifth successive crops. In each growing season, the disease differed amongst sequences and built up more rapidly and was more intense on plants sown in mid‐September than on plants sown in mid‐October. In late‐sown plots, where volunteers had been present during the mid‐September to mid‐October period, take‐all reached an intensity intermediate between that in early‐sown plots and that in late‐sown plots that had been kept free of volunteers. Volunteers, therefore, partially offset the expected beneficial effect of decreased disease with later sowing. Differences in take‐all amongst sequences were most pronounced in the second wheat crop and early sowing of the previous wheat increased intensity of disease. In the following (third) crop, differences in disease intensity amongst sequences were smaller. Soil infectivity (measured by seedling bioassay after harvest) built up progressively from a low level after the first crop to peak after the third crop. In this build‐up phase, soil infectivity estimates were always numerically greater after harvest of early‐sown treatments than after later‐sown treatments, although never significant at P= 0.05. The greatest difference (P= 0.06) was recorded in October before sowing of the third crop, where the comparison was between soil after two previous early sowings and soil after two previous later sowings and control of volunteers. In the same autumn, presence of green cover (i.e. volunteers) was associated with a smaller loss of soil infectivity between harvest and later sowing than occurred in an absence of green cover. In 2^nd–4^th crops, where comparisons were available and mean TARs indicated moderate levels of take‐all, sowing later had no yield benefit, despite more take‐all and greater soil infectivity associated with early sowing. Important considerations for the management of crops at risk of take‐all are 1) choosing appropriate sowing dates to minimize take‐all or to encourage take‐all decline and 2) controlling volunteers and weed hosts where crops are sown late to minimise take‐all.     

REPRODUCTIVE ECOLOGY OF JEFFERSONIA DIPHYLLA (BERBERIDACEAE)

The reproductive ecology of Jeffersonia diphylla (L.) Pers. (Berberidaceae) was investigated by studying its breeding system, ovule production, seed set, seed dispersal by ants and seed predation by rodents. This species flowers early in the spring and is facultatively autogamous. In a typical year fruit and seed set is high (90%), however, freezing temperatures from late spring frosts in 1983 and 1985 resulted in low fruit set (7% and 20%, respectively), and reduced seed set in those flowers that produced fruit. No differences in seed set between selfed and outcrossed flowers were observed over a two-yr period (1983–84). Ovule number per capsule increased with plant size as measured by leaf number. Seed set and seed wt were unaffected by leaf number unless leaves were removed after flowering was initiated. Jeffersonia diphylla is myrmecochorous. Ants removed seeds faster when seeds were placed in areas where J. diphylla plants were absent, suggesting that dispersal within J. diphylla populations is ant limited. Moreover, fresh (1 day old) seeds were removed by ants faster than 3 day old seeds. Seed predation by rodents prior to dehiscence from capsules is heavy in large populations (85–90%), and apparently negligible in small populations. Predation of seeds that are released from capsules is heavy (approx. 66%), particularly at night. Overall, seed predators consume about 96% of the seed crop in well established populations, but probably much less in small young populations. Hence, seedling recruitment is likely to be higher in small populations, whereas ramet production from rhizomes is the primary mode of propagation in large ones. The evolution of autogamy, early flowering, and myrmecochory are discussed in light of the results of this study.     

No effect of transgene and strong wild parent effects on seed dormancy in crop–wild hybrids of rice: implications for transgene persistence in wild populations

Soil seed banks act as a gene pool for local plant species and, as such, can buffer local populations, especially those experiencing challenging environmental conditions. Seed dormancy has important implications to dynamics of soil seed banks. Therefore, estimating the seed dormancy of transgenic crop–wild hybrids could shed light on the persistence of transgenes in wild‐plant soil seed banks. Individuals from eight populations of wild rice Oryza rufipogon were crossed with those of three insect‐resistant transgenic rice lines. Selfed (F2–F4) and backcrossed populations (BC1, BC1F2 and BC1F3) were then made from the hybrids. Seed germination was tested under three treatments: (a) normal; (b) overwintering in soil; and (c) one‐week heat‐shocking. The effects of transgene, wild parent and hybrid generation on hybrid seed germination were examined. No significant effect of insect‐resistant transgenes (Bt and CpTI) was detected on the seed dormancy of crop–wild hybrids, while a significant wild parent effect was found. The seeds of advanced generation hybrids have higher germination percentages and lower dormancy than do those of F1 and BC1 generations. The study showed that the dormancy of hybrid seeds was determined mainly by their genetic backgrounds. All hybrid seeds have higher germination percentages and lower dormancy (and, consequently, a poorer overwintering ability), compared with wild seeds, and reduce dormancy would contribute to a fitness disadvantage, compared with wild types. Therefore, such seeds might form part of naturally occurring soil seed banks, through which crop genes would persist in wild populations.     

Seed and microsite limitation in Rheum nobile,a rare and endemic plant from the subnival zone of Sino-Himalaya

Background: Species persistence, particularly in monocarpic species, depends on the successful recruitment of individuals. An understanding of the factors that limit the recruitment of rare monocarpic plant species is therefore vital for their conservation.

Aims: To identify the factors limiting the recruitment of Rheum nobile, a rare and highly specialised monocarpic giant herb endemic to the high eastern Himalayas.

Methods: Seed sowing (seeds added or not added) and seedling transplanting experiments were conducted in disturbed (vegetation removed) and undisturbed plots in the vicinity of established populations of R. nobile to explore the mechanisms of recruitment limitation. Four levels of photosynthetically active radiation (0, 15, 30 and 50 μmol m^?2 s^?1) and two sowing positions (beneath and above grass litter or moss layer) were manipulated in the laboratory to determine how ground cover limited seedling emergence.

Results: Seed addition increased seedling recruitment. Disturbance significantly increased seedling emergence and establishment. Seed germination significantly decreased with the reduction of light availability, but 31.7% of all seeds germinated in complete darkness. Seedling emergence was close to zero when seeds were sown on top of a layer of grass litter or moss, but rose to 34.5% when the seeds were sown beneath such layers.

Conclusions: Our results indicate that the recruitment of R. nobile is limited by a combination of seed and microsite availability. Therefore, in order to conserve this species, we suggest adding seeds to suitable sites and implementing soil disturbances in existing populations to create suitable microsites.     

Seed bank of Littorella uniflora (L.) Asch. in the Czech Republic,Central Europe: does burial depth and sediment type influence seed germination?

Littorella uniflora (Plantaginaceae) is a scarce and declining aquatic plant in Europe. Its population has been strongly reduced by changes in fishpond management (eutrophication) in the Czech Republic since the 1950s. We studied its seed bank in both recent (n = 8) and historical localities (the last found from 1972 to 2000; n = 10) and tested the effects of sediment type and burial depth on seed germination using extracted seeds from two recent populations. The seeds were found in 60% of the historical localities, mostly in low densities (≤6 seeds per 3.75 l of sediment), and also in 100% of the recent localities in various densities (8–1390 seeds per 3.75 l of sediment); however, low germination rates (0–13.3%) were estimated. The seeds germinated best on wet filter paper, followed by nutrient-rich fishpond sediment, but poorly on sand mixed with different substrates. Burial depth significantly affected seed germination. The seeds germinated only on the soil surface and at the depth of 1 cm but no seed germinated at the depth of 3 and 5 cm. Besides low water transparency, both high rate of sediment accumulation and the absence of summer drainage may endanger L. uniflora populations in fishponds.

     

Expanding horizons for herbaceous ecosystem restoration: the Grassy Groundcover Restoration Project

Summary The Grassy Groundcover Restoration Project (GGRP) has sown thirteen 1 ha plots of species‐rich grassland or herbaceous understorey in previously weedy agricultural paddocks in a range of rural locations across southern and western Victoria, Australia. The sown plots are intended as both experimental trials and ‘core’ areas for the restoration of herbaceous communities native to these regions. Approximately 200 species were grown in Seed Production Areas (SPAs) and successfully sown in the field. Species were most successfully established on areas that were scalped prior to seeding, and least successful on plots that were pre‐treated with 1, 2 or 3 years of traditional herbicide weed control. Weed presence was lowest in scalped plots and highest in non‐scalped plots. Long‐term monitoring will be required to understand the development trajectories and degree of persistence of the sown communities, but in the shorter term (3–6 years of post‐seeding) an average of 80% of sown species have established and remain as adult populations. Surveys indicate that in scalped plots (n = 130) vegetation composition, structure and quality has been maintained. Conversely, composition, structure and quality have declined markedly in non‐scalped plots (n = 130). Formal surveys and field observations have also revealed that all sites provide a range of habitats which have been colonized by fauna from a variety of trophic levels. The implications of building on these trials to realize complex grassy ecosystem restoration at larger scales are discussed including the securing of sufficient quantities of high‐quality seed, the use of mechanized broad‐scale direct‐seeding techniques and the effectiveness of using complex mixtures of species early in the restoration cycle.     

Seedling Survival from Locally and Commercially Obtained Seeds on Two Semiarid Sites

Local populations of plants are likely to be better adapted to a site than populations from elsewhere. Thus, local seeds should yield higher survival in restoration attempts than commercial seed stocks. We compared seedling survival from locally and commercially obtained seeds of seven species, Pseudoroegneria spicata (bluebunch wheatgrass), Elymus elymoides (squirreltail), Pascopyrum smithii (western wheatgrass), Stipa hymenoides (Indian ricegrass), Stipa comata (needle‐and‐thread), Chrysothamnus nauseosus (rubber rabbitbrush) and Ephedra nevadensis (Mormon tea) over three years on two sites in Utah (Dugway and Tintic) that were dominated by the introduced annual Bromus tectorum (cheatgrass). At the Dugway site we included burned and unburned seedbed treatments. For all species at Dugway, seedling survival to the first summer was higher on burned plots where B. tectorum densities were greatly reduced. First‐year seedling survival was 20–30% for most species on the Dugway burned plots and at Tintic. At the drier Dugway site, only S. hymenoides and Ephedra had substantial third‐year survival. Elymus and Pascopyrum survived to the third year only at the moister Tintic site. Survival to the third year was less than 3% for all species except S. comata (6% survival), and densities were low (0.2–1.0 plants/m²). However, third‐year plants were well established and the grasses flowered. Pseudoroegneria and Ephedra at Dugway (on burned plots) and S. comata and Elymus at Tintic had higher first‐year survival or higher survival based on survival curves from local than from commercial seeds. However, final survival was never significantly higher, although such a trend was suggested. Seed dormancy traits could also provide advantages to local populations, and we observed differences in dormancy between local and commercial S. comata and S. hymenoides seeds that may be an example.