Ant-mediated expansion of an obligate seeder species during the first years after fire

Most obligate seeder species build up a soil seed bank that is associated with massive seed germination in the year immediately after a fire. These species are also shade‐intolerant and disappear when vegetation cover closes, creating unsuitable conditions for seedling recruitment. The only way for these plants to expand their populations is when habitats suitable for seedling recruitment arise (i.e. in years immediately after a fire). However, short primary seed dispersal of obligate seeders does not allow these plants to colonise the suitable habitats, and these habitats can only be colonised by secondary seed dispersion. We hypothesised that Fumana ericoides, an obligate‐seeding small shrub, not only establishes abundantly in the first year after fire, but also expands its local range in the following years due to secondary dispersal by ants while suitable habitats are still available. We tested this hypothesis using experimental studies and a simulation model of potential population expansion in a recently burned area. Results showed that F. ericoides not only established prolifically in the year immediately after fire, but was also able to recruit new individuals and expand its population in the years following the fire, despite a low germination rate and short primary seed dispersal. Ant‐mediated seed dispersal and availability of suitable habitats were key factors in this phenomenon: ants redistributed seeds in suitable habitats while they were available, which accelerated the expansion of F. ericoides because new plants established far away from the core population.     

Seed bank persistence of clonal weeds in contrasting habitats: implications for control

The ability of weeds to form a seed bank is important for their population dynamics and management because it provides a refuge enabling reinvasion after established target plants have died. However, knowledge of the differential seed behaviour of individual species over multiple years and varying environmental conditions is surprisingly rare but necessary for effective control of diverse weed populations. We established a seed burial experiment in alpine habitats differing in management regime (i.e., forest, hay meadow and pasture) to determine whether seeds of the unpalatable perennial weeds, Veratrum album (white hellebore) and Gentiana lutea (yellow gentian) were able to delay germination and remain viable over 3 years. Our study shows that both species formed a short-term persistent seed bank; in the third-year, the soil seed banks of both species were nearly depleted, having declined to <5% of their original size. Both species had strikingly different germination strategies: G. lutea seeds mainly germinated in their first-year, whilst the majority of V. album seeds germinated in their second-year. The fraction of dormant G. lutea seeds increased with seed age, indicating that seeds remained viable after forgoing germination in the previous year. Habitat-specific differences in seed germination increased with seed age, with germination fractions being lowest in moist hay meadows. This suggests that the negative effects of anoxic conditions became more pronounced as seeds aged in hay meadows. Conversely, seed dormancy was equal among habitats. The absence of a long-term persistent seed bank has important implications for the management of both nuisance and endangered-plant populations. In the case of V. album and G. lutea, re-colonization of habitats from the seed bank is unlikely after established plants have been removed.     

Nurse‐plant effects on the seed biology and germination of desert annuals

Nurse‐plants generally have positive effects on understorey species by creating more suitable conditions for stress‐intolerant plants relative to open micro‐habitats. However, long‐term effects of this plant–plant facilitation system have been rarely examined. Seeds of five desert annual species from Atiquipa coastal desert in Southern Peru were used to examine whether different microenvironmental conditions under the nurse‐plants Caesalpinia spinosa Molina (Kuntze) lead to differences in seed biology and germinability of annual plants relative to open, canopy‐free conditions. Seeds collected from plants associated with nurse‐plants were predicted to be (i) larger due to more favourable growing conditions, (ii) more viable and with greater germination rates, (iii) less variable in size and viability due to reduced environmental heterogeneity, and (iv) to germinate faster to avoid apparent competition with other annuals. Seed attribute measurements and germination trials in growth chambers were used to test these predictions. Although the plant abundance of only 2 of 5 species was strongly facilitated by the nurse‐plant, no significant differences were found in seed mass, viability or relative variability between understorey and open micro‐habitats for any of the species. Contrary to our predictions, final seed germination rates of seeds from open micro‐habitats were higher, and the open micro‐habitat treatment was more favourable for germination of seeds from both open and understorey environments. Taken together, these results suggest that plant–plant facilitation does not necessarily affect seed biology traits. Further studies addressing larger distribution ranges and/or density gradients of understorey species will illuminate the potential evolutionary effects of nurse‐plants.     

Effects of habitat fragmentation and soil quality on reproduction in two heathland Genista species

Habitat fragmentation decreases plant population size and increases population isolation, as well as altering patterns of plant–animal interactions, all of which may reduce plant fitness. Here, we studied effects of habitat fragmentation (in terms of population size and isolation) and soil quality on the reproduction of two rare legume species, Genista anglica (13 populations) and Genista pilosa (14 populations), confined to remnants of acidic and nutrient‐poor Calluna heathlands. Single individuals of the Genista plants are impossible to distinguish; population size was therefore estimated according to the area occupied (referred to as population size hereafter). We collected soil samples in all heathland sites to determine content of soil water, C, N, P, Ca, K and Mg. In both species values of soil pH and C/N ratio, as well as content of soil P and base cations, reflected the highly acidic and nutrient‐poor environment of the heathlands. Population sizes were unrelated to soil quality. Although the two Genista species are similar in morphology and ecology, effects of explanatory variables on reproduction were largely inconsistent across species. In G. anglica, population size had a positive impact on all reproductive variables except germination rate, which, in contrast, was the only variable affected positively by population size in G. pilosa. In both species, mean total reproductive output, calculated as the product of total seed mass per shoot and total germination, increased with increasing water content and decreased with increasing P. In G. anglica, we found positive effects of the C/N ratio on all reproductive variables except mean single and total seed mass per shoot. In summary, in both species reproductive success per shoot decreased with increasing soil nutrient availability in the heathland sites. The infestation of two large populations of G. pilosa with the pre‐dispersal, seed‐predating weevil Apion compactum had no significant effect on reproduction of the populations.     

Soil water status influences plant nitrogen use: a case study

We studied differences in nitrogen use efficiency (NUE) among six species [Calamagrostis epigejos (L.) Roth., Carex duriuscula C.A. Mey., Phragmites communis (L.) Trin., Salix gordejevii Y.L. Chang, Salix cheilophila Schneid., and Typha minima Funk.] growing in two contrasting habitat types, i.e., a riverine wetland with high water supply and a riparian zone with low water supply. The two sites were different in soil water supply, but not in nitrogen supply. Here, NUE was defined as the total net primary production per unit nitrogen absorbed. There was no significant difference in NUE between the species growing in the riverine wetland (Carex duriuscula, P. communis, S. cheilophila, T. minima) and the species growing in the river bank (Carex duriuscula, Calamagrostis epigejos, P. communis, S. gordejevii). We further analyzed NUE as the product of the nitrogen productivity (A, the rate of dry matter production per unit of nitrogen in the plant) and the mean residence time of nitrogen (MRT, the period of time a unit of nitrogen is present in the plant). The species growing in the riverine wetland had larger A but lower MRT than the species growing in the river bank. There was an inverse relationship between A and MRT. Consequently, NUE was similar among species and habitats. These results suggested that environmental factors, such as soil water supply, can influence N use by plants.     

Biological characteristics of an invasive south African species

Senecio inaequidens, a south African species that has recently invaded parts of Europe, especially human disturbed habitats, was examined under laboratory and glasshouse conditions to assess the germination of achenes, soil seed banks, growth of seedlings and its breeding system. These observations allowed identification of ecological characteristics that may contribute to the invasiveness of the species. Achenes derived from three populations of S. inaequidens were germinated over a wide temperature range (from 14/6 °C day/night temperatures to a constant temperature of 30 °C). They exhibited a rapid achene germination especially when temperatures reached 20 °C. Germination of seeds from soil samples also exhibited a prolonged germination over time suggesting therefore different types of dormancy. Growth response was studied along a nitrogen gradient from 0.33 to 16.0 mmol l^–1 and data were interpreted using growth analysis. Seedlings of S. inaequidens exhibited a slow growth in low nutrient availability and a rapid growth rate when exposed to high nutrient availability, which contributed to producing a large leaf area and biomass. Four types of pollination were studied in S. inaequidens. Hand-pollinations showed that S. inaequidens was mostly self-incompatible. Self-pollinated capitula only showed 7.6% viable achenes, significantly lower than insect-pollinated and cross-pollinated capitula. Some individuals were more self-fertile than others ensuring the production of some offspring in a situation of colonisation. Natural pollination occurred with generalist insects. Most of these results confirm the invasive ability of S. inaequidens.     

Seed germination and antioxidant pattern in Lavandula multifida (Lamiaceae): A comparison between core and peripheral populations

We evaluated the environmental adaptability of Lavandula multifida L., a plant species presents in the Western Mediterranean Basin with a threatened peripheral population in Southern Italy. Germination capacity, activities of some hydrolyzing enzymes associated with germination and antioxidative pathway of Calabrian L. multifida were quantified in comparison with a Spanish core population. The Calabrian population showed a lower germination ability and it can be related to the small size of the population and associated inbreeding depression. Difference between two populations in enzymatic assays and antioxidative pattern during germination and early seedling development may in part explain a different ability of these two populations to respond to external cues and a diverse environmental adaptability. The study on germination strategies of isolated populations is important to define possible programmes to preserve genetic biodiversity of autochthon plants populations.     

Allelopathic Effects of Tree Species on Some Soil Microbial Populations and Herbaceous Plants

The allelopathic potential of four tree species on soil microbial populations and some herbaceous plants (two understory species and one general biotest species) was investigated. Effects of three nonindigenous tree species, Eucalyptus globulus Labill, Pinus radiata D.Don and Acacia melanoxylon R.Br., on microorganisms participating in the cycle of nitrogen were evaluated, comparing them with those produced by the autochthonous Quercus robur L. Influence of the trees on Lactuca sativa L., Dactylis glomerata L. and Trifolium repens L. was also checked in bioassays. Cell numbers of Nitrosomonas sp. were negatively affected by Acacia and Eucalyptus stands, mainly during spring, when flowers are especially abundant on the ground. Proteolytic microorganisms were also negatively affected by Eucalyptus and Pinus stands, whilst Quercus stand did not show any toxicity. Soil bioassays showed clear inhibitory effects on germination and growth of understory plants, particularly soils from Eucalyptus and Acacia stands. The greatest effects had the soil from Acacia stand, which was phytotoxic during the whole period of germination and growth of understory plants. Allelopathic phenomena could be, at least partially, responsible of the low species diversity in the understory of the nonindigenous tree stands.     

Seed production and germination in two rare and three common co‐occurring Acacia species from south‐east Australia

Abstract Seed set, size, viability and germination requirements were investigated for two rare (Acacia ausfeldii and A. willianisonii) and three common (A. pycnantha, A. genistifolia and A.paradoxa) co‐occurring congeners in box‐ironbark eucalypt forests near Bendigo, south‐east Australia to investigate correlates of rarity. Seed size was significantly smaller for the two rare species and germinants were less able to emerge from deeper sowing depths than were the larger seeded common congeners. All species had a strong heat‐stimulated germination response. While the rare A. ausfeldii showed strong germination only at the highest temperature treatment (100°C), the common and widespread A.pycnantha showed strong germination across a broad range of temperatures (60‐100°C), likely to be experienced by soil‐stored seeds during a fire. Seed viability, number of seeds per plant, and number of firm, aborted and eaten seeds per pod varied between species, but the pattern of variation was not related to rarity. Small seed size and a very specific temperature requirement for germination may help to explain rarity in A. ausfeldii, and to a lesser extent in A. willianisonii. Fires are often patchy and heating of the soil is likely to be highly spatially variable, so species with germination responses to a broad range of temperatures have an advantage over those that respond only to a narrow range. A narrower range of soil depths from which seeds can emerge will further reduce the proportion of the seed bank that might recruit following fire. Human impacts on species habitats, such as fragmentation, loss of topsoil through mining, timber harvesting, grazing and urbanization, and consequent reduction in fire intensity, are likely to have further contributed to rarity in these species. The role of pollination and other factors in relation to population size is the subject of further investigation.     

Plant species and nutritional-mediated control over rhizodeposition and root decomposition

This study focuses on the influence of nitrogen (N) availability and species on rhizodeposition and on decomposition of rhizodeposits, roots and soil organic matter. Four perennial grass species were studied that are characteristic of grassland habitats that differ in nutrient availability. These perennial grass species, Holcus lanatus L., Festuca rubra L., Anthoxanthum odoratum L. and Festuca ovina L., were homogeneously labeled with ¹⁴CO₂. Plants were grown on soil without N addition and with N addition (14 g N m^–2). After 8 weeks, plants were harvested and root production and the remaining amount of rhizodeposits in the soil were measured. ¹⁴C-labelled roots were incubated in fresh soil. Decomposition was measured of 1) the labeled rhizodeposits in the soil in which the plants had been growing and 2) the labeled dead roots incubated in fresh soil, by trapping the evolved ¹⁴CO₂, over 69 days.In general, decomposability of both roots and rhizodeposits increased when nitrogen availability increased. Moreover, the species differed in their response to N. Higher N supply increased total rhizodeposition of H. lanatus and the decomposability of rhizodeposited carbon compounds of this high fertility species was greater than of the low fertility species F. ovina, but lower than of A. odoratum. The presented study gives no evidence for a relation between root decomposition rate and the nutrient availability of the habitat of the four species. Overall, we suggest on the basis of the results that species can affect nutrient cycling by differences in rates of rhizodeposition and litter production. This offers a mechanism whereby species can influence species replacement during succession.     

The gradient between pre-dawn rhizoplane and bulk soil matric potentials, and its relation to the pre-dawn root and leaf water potentials of four species

Uptake of soil water by plants may result in significant gradients between bulk soil and soil in the vicinity of roots. Few experimental studies of water potential gradients in close proximity to roots, and no studies on the relationship of water potential gradients to the root and leaf water potentials, have been conducted. The occurrence and importance of pre-dawn gradients in the soil and their relation to the pre-dawn root and leaf water potentials were investigated with seedlings of four species. Pre-germinated seeds were grown without watering for 7 and lid in a silt loam soil with initial soil matric potentials of -0.02, -0.1 and -0.22 MPa. Significant gradients, independent of the species, were observed only at pre-dawn soil matric potentials lower than -0.25 MPa; the initial soil matric potentials were -0.1 MPa. At an initial bulk soil matric potential of -0.22 MPa, a steep gradient between bulk and rhizoplane soil was observed after 7 d for maize (Zea mays L. cv. Issa) and sunflower (Helianthus annuus L. cv. Nanus), in contrast to barley (Hordeum vulgare L. cv. Athos) and wheat (Triticum aestivum L. cv. Kolibri). Pre-dawn root water potentials were usually about the same as the bulk soil matric potential and were higher than the rhizoplane soil matric potential. Pre-dawn root and leaf water potentials tended to be much higher than rhizoplane soil matric potentials when the latter were lower than -0.5 MPa. It is concluded that plants tend to become equilibrated overnight with the wetter bulk soil or with wetter zones in the bulk soil. Plants can thus circumvent negative effects of localized steep pre-dawn soil matric potential gradients. This may be of considerable importance for water uptake and growth in drying soil.     

Heat effects on seeds and rhizomes of a selection of boreal forest plants and potential reaction to fire

To analyse the potential reaction to firegenerated heat pulses, seeds of 12 species of plants and rhizomes of three species were exposed to elevated temperatures for 10 min. The tested material split into three groups with respect to heat tolerance: (1) the rhizomes, for which the lethal temperatures were in the range 55–59° C; (2) the seeds of most of the species tested, for which the lethal temperatures were in the range 65–75° C; (3) The seeds of two species of Leguminosae and three species of Geranium for which the lethal temperatures were around 100° C. For all three Geranium species and for one of the legume species, Anthyllis vulneraria, exposure temperatures above ca. 45° C resulted in dormancy release, and maximum germination occurred above 60–65° C. Speed of germination was little affected for most species, except after exposure to nearlethal temperatures, where it slowed down dramatically, although the seedlings emerging were healthy. We conclude that due to sharp temperature gradients in the soil during fire, differences in heat tolerance between species in most cases are not large enough to be a decisive factor in their post-fire colonising success. There are exceptions: the seeds of certain taxa that are impermeable to water in the dormant state, some of which have heat triggered germination.     

Conspecific plant–soil feedback scales with population size in Lobelia siphilitica (Lobeliaceae)

Plant–soil interactions directly affect plant success in terms of establishment, survival, growth and reproduction. Negative plant–soil feedback on such traits may therefore reduce the density and abundance of plants of a given species at a given site. Furthermore, if conspecific feedback varies among population sites, it could help explain geographic variation in plant population size. We tested for among-site variation in conspecific plant–soil feedback in a greenhouse experiment using seeds and soils from 8 natural populations of Lobelia siphilitica hosting 30–330 plants. The first cohort of seeds was grown on soil collected from each native site, while the second cohort was grown on the soil conditioned by the first. Our goal was to distinguish site-specific effects mediated by biotic and/or abiotic soil properties from those inherent in seed sources. Cohort 1 plants grown from seeds produced in small populations performed better in terms of germination, growth, and survival compared to plants produced in large populations. Plant performance decreased substantially between cohorts, indicating strong negative feedback. Most importantly, the strength of negative feedback scaled linearly (i.e., was less negative) with increasing size of the native plant population, particularly for germination and survival, and was better explained by soil- rather than seed-source effects. Even with a small number of sites, our results suggest that the potential for negative plant–soil feedback varies among populations of L. siphilitica, and that small populations were more susceptible to negative feedback. Conspecific plant–soil feedback may contribute to plant population size variation within a species’ native range.     

Effects of crop residues,soil type and temperature on emergence and early growth of wheat

Summary Two controlled environment experiments were conducted to examine the germination and early growth of wheat (Triticum aestivum L. cv. Songlen) growing under crop residues of rape, sorghum, field pea and wheat. Additional treamments also included were soil type (Lithic Vertic Ustochrept and Plinthustalf) and temperature (8°C and 24°C to simulate winter and autumn sowing conditions). At low temperature, wheat and sorghum residues produced the most adverse effects on germination with all residues reducing emergence at high temperatures. Shoot lengths were also reduced by most residues at high temperatures whilst root lengths and shoot and root dry weights were unaffected by residue treatments. These results suggest major phytotoxic effects of residues during early growth (up to 14 days after sowing) with, in general, few interactions with soil type or temperature.     

Reduced soil contributes to the anomalous occupation of dwarf communities in N-richer habitats in a cool-temperate mire

Spatial patterns of the oxidation–reduction potential (Eh) of soil, water level and chemistry were examined in the fen area of the Tohfutsu mire, northern Japan, where horse pasturage has been carried out throughout the growing season every year. The fen vegetation consisted mosaically of communities mono- or codominated by Eleocharis kamtschatica, Iris setosa and Carex lyngbyei. The highest concentration of total dissolved nitrogen of soil water was observed in the dwarf community dominated by E. kamtschatica with smaller biomass, whereas the nutrient level was lower in the community monodominated by C. lyngbyei with larger biomass. Principal component analysis denoted well that Eh, N, K, and pH contributed to the differentiation of these communities significantly. During the growing season that was investigated, the highest nitrogen concentration was observed in midsummer, when plants are expected to absorb nutrients intensely, indicating that the supply of dissolved nitrogen far exceeded the nutrient uptake of plants. Multiple habitats with reduced soil were formed by submergence and by an excess of nitrogen due to pasturage, and the soil reduction indirectly inhibited the incursion of species with large biomass at such sites. It was demonstrated that soil Eh contributed to the anomalous pattern of vegetation where the supply of available nitrogen exceeds the uptake by plants.     

SEED GERMINATION TIMING PATTERNS IN INTERMOUNTAIN PENSTEMON (SCROPHULARIACEAE)

Regulation of seed germination timing is an important component of population persistence, especially for short-lived plants in seasonal environments with unpredictable year-to-year weather variation. Seed germination patterns were examined in the laboratory for seeds from 135 populations belonging to 38 species and 13 sections of the genus Penstemon (Scrophulariaceae), from habitats ranging from warm desert to alpine tundra. Seeds of most species were dormant at dispersal and required a period of moist chilling to become germinable. Response to chilling was related to probable chilling duration at the collection site. Populations from habitats with severe winters produced seeds with long chilling requirements, while those from habitats with mild winters produced seeds with short chilling requirements. Populations from midelevation habitats produced seeds with intermediate chilling requirements but with a sizeable fraction whose dormancy was not broken by chilling of any length. Another pattern observed mostly in warm desert populations was little primary dormancy at autumn temperatures combined with induction of a fraction into secondary dormancy by short chilling. Species with a wide habitat range included populations with contrasting germination patterns. Parallel habitat-correlated patterns were observed in different sections. Most species showed germination patterns that combined predictive mechanisms with potential for carryover of a persistent seed bank. Results of common garden experiments suggested that germination differences had a strong genetic basis both among populations and among plants in a population. Adaptive radiation in the genus Penstemon has thus included the evolution of habitat-specific germination timing strategies in multiple lineages within the genus.     

Mycorrhizal specificity does not limit the distribution of an endangered orchid species

What factors determine the distribution of a species is a central question in ecology and conservation biology. In general, the distribution of plant species is assumed to be controlled by dispersal or environmentally controlled recruitment. For plant species which are critically dependent on mycorrhizal symbionts for germination and seedling establishment, specificity in mycorrhizal associations and availability of suitable mycorrhizal fungi can be expected to have a major impact on successful colonization and establishment and thus ultimately on a species distribution. We combined seed germination experiments with soil analyses and fungal assessments using 454 amplicon pyrosequencing to test the relative importance of dispersal limitation, mycorrhizal availability and local growth conditions on the distribution of the orchid species Liparis loeselii, which, despite being widely distributed, is rare and endangered in Europe. We compared local soil conditions, seed germination and mycorrhizal availability in the soil between locations in northern Belgium and France where L. loeselii occurs naturally and locations where conditions appear suitable, but where adults of the species are absent. Our results indicated that mycorrhizal communities associating with L. loeselii varied among sites and plant life cycle stages, but the observed variations did not affect seed germination, which occurred regardless of current L. loeselii presence and was significantly affected by soil moisture content. These results indicate that L. loeselii is a mycorrhizal generalist capable of opportunistically associating with a variety of fungal partners to induce seed germination. They also indicate that availability of fungal associates is not necessarily the determining factor driving the distribution of mycorrhizal plant species.     

Effect of soil drying on growth,biomass allocation and leaf gas exchange of two annual grass species

Influence of short-term water stress on plant growth and leaf gas exchange was studied simultaneously in a growth chamber experiment using two annual grass species differing in photosynthetic pathway type, plant architecture and phenology:Triticum aestivum L. cv. Katya-A-1 (C₃, a drought resistant wheat cultivar of erect growth) andTragus racemosus (L.) All. (C₄, a prostrate weed of warm semiarid areas). At the leaf level, gas exchange rates declined with decreasing soil water potential for both species in such a way that instantaneous photosynthetic water use efficiency (PWUE, mmol CO₂ assimilated per mol H₂O transpired) increased. At adequate water supply, the C₄ grass showed much lower stomatal conductance and higher PWUE than the C₃ species, but this difference disappeared at severe water stress when leaf gas exchange rates were similarly reduced for both species. However, by using soil water more sparingly, the C₄ species was able to assimilate under non-stressful conditions for a longer time than the C₃ wheat did. At the whole-plant level, decreasing water availability substantially reduced the relative growth rate (RGR) ofT. aestivum, while biomass partitioning changed in favour of root growth, so that the plant could exploit the limiting water resource more efficiently. The change in partitioning preceded the overall reduction of RGR and it was associated with increased biomass allocation to roots and less to leaves, as well as with a decrease in specific leaf area. Water saving byT. racemosus sufficiently postponed water stress effects on plant growth occurring only as a moderate reduction in leaf area enlargement. For unstressed vegetative plants, relative growth rate of the C₄ T. racemosus was only slightly higher than that of the C₃ T. aestivum, though it was achieved at a much lower water cost. The lack of difference in RGR was probably due to growth conditions being relatively suboptimal for the C₄ plant and also to a relatively large investment in stem tissues by the C₄ T. racemosus. Only 10% of the plant biomass was allocated to roots in the C₄ species while this was more than 30% for the C₃ wheat cultivar. These results emphasize the importance of water saving and high WUE of C₄ plants in maintaining growth under moderate water stress in comparison with C₃ species.     

Seed germination strategies of five perennial weeds

Summary The germination responses of seeds of Achillea millefolium L., Artemisia vulgaris L., Cirsium arvense (L.) Scop., Taraxacum officinale Weber, sensu lato, and Tussilago farfara L. to light, nitrate, alternating temperatures, chilling, light quality, and water availability were studied in laboratory tests, using fresh seed and seed stored for 6 months at 27°C and buried in the soil. A factorial experiment with light, nitrate, alternating temperatures, and seed age as factors found that all four affected germination except in T. farfara. All three external factors were stimulatory, especially in combinations. Fresh seed of A. vulgaris and C. arvense showed a light x alternating temperature synergism, responded to chilling, and after-ripened in cold dry storage. That of T. farfara had no dormancy and rapid germination, and germinated well on substrates with a water content too low for the other species. Seed of A. millefolium and A. vulgaris had good survival in both experimental storage conditions, while that of C. arvense and T. officinale did not, and that of T. farfara did not survive. Longevity in both conditions was associated with depth of initial dormancy. The two conditions caused different changes in dormancy in both A. vulgaris and A. millefolium. The germination behaviour, and the size, morphology and dispersal of the seeds of the species are discussed as strategies adapted to intermittently available situations for seedling establishment.     

Reduced light availability and increased competition diminish the reproductive success of wet forest sedge Carex loliacea L.

Wet forest ecosystems in temperate regions have been heavily drained and logged, often with significant negative consequences for biodiversity in these habitats. Our research focused on population maintenance mechanisms of a declining wet forest sedge Carex loliacea L. We studied germination under different light regimes and seedling survival under different vegetation densities using an in situ removal experiment. For successful germination, seeds of C. loliacea need light; germination in reduced light conditions is depressed. The seeds of C. loliacea are able to accumulate a seed bank and exhibit seasonal dormancy cycles. Survival of seedlings strongly depends on competition with other plant species. Our results imply that changes in habitat conditions (draining, forest cutting) affect the successful generative reproduction of C. loliacea primarily via a change in light conditions, which is a strong factor both at the stage of germination and seedling growth. However, adult plants are able to persist over a much broader range of habitat conditions without detectable vitality loss.