Effect of high temperatures and ash on germination of ten species from gorse shrubland

Seeds of ten species of Cistaceae, Ericaceae and Poaceae were examinated to compare their responses to high temperatures and ash, simulating the direct effect of fire on germination. A variable response to these factors between families and within species from the same family was detected.In Cistaceae, heat treatment pre-sowing stimulated germination. In Ericaceae, germination was stimulated by thermic shock, but a wide range of response was detected (between all four species), from Erica ciliari, very sensitive, to Daboecia cantabrica and Calluna vulgaris which showed no significant response. The range of reaction shown by the species of this family suggest that the size of the seeds is directly related to the difference in response, at least in species with a similar structure. In Poaceae, germination was not found to be dependent upon thermic shock.The effect of ash varies in magnitude. Although it decreased the germination percentage in all species, in Avenula marginata (Poaceae) the effect was not statistically significant, whilst in Ericaceae, particularly in those showing the highest levels of germination in the control (C. vulgaris and E. umbellata), the effect is to inhibit germination completely. In respect to the effect of ash the families could be arranged in the order Ericaceae>Cistaceae>Poaceae.Complex interactions between various dormancy types and seed size could explain these results. In species which depend on physical dormancy temperature has an important role. When other dormancy type is dominant in the control of germination, the medium characteristics could have a relevant role on seed response. In addition, the seed-size could determine the threshold of tolerance to temperature.     

Variability in seed germination at the interpopulation,intrapopulation and intraindividual levels of the shrub Erica australis in response to fire-related cues

In Mediterranean ecosystems, as well as in other fire prone ones, seedling establishment by some species is particularly favorable right after fire. It has been well established that many plants from these ecosystems have enhanced germination after exposing their seeds to heat or to chemicals related to the passage of fire. Less known it is how variable is this germination response among seeds from different sources (populations, individuals within a population, or parts of the plant within an individual) and whether such differences persist after exposing the seeds to germination-triggering, fire-related cues. In this work we studied the germination response to several fire-related factors of the Mediterranean, lignotuberous shrub Erica australis. This species produces a very combustible fuel, and resprouts vigorously after fire, but conditions for seedling establishment are poorly known. The objective of this study was to evaluate how variable was the germination response of this species among seeds from different sources, and whether this variability changed after exposing the seeds to fire-related factors. Seeds from three different sites, from different individuals at each site, and from different branches within each individual were set to germinate under control conditions or after exposing them to heat or to additions of nitrogenous compounds. Germination was highly variable among populations, individuals within populations or branches within individuals. Exposure to moderate heat promoted germination, but high temperatures were lethal. Differences at the various provenance levels were, however, also observed after heat exposure. Germination of seeds exposed to nitrogenous compounds increased, but differences among populations were always significant. These results indicate that the germination of Erica australis may be linked to disturbances, but it does not seem to be particularly related to passage of fire. On the contrary, this type of response appears more common in plants from heterogeneously disturbed environments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heather-feeding psyllids of the genus Strophingia (Homoptera)

Multivariate analysis of morphological characters suggests that the genus Strophingia comprises eight distinct species, namely ericae (Curtis) [the type-species], australis sp.n., fallax Log., cinereae Hod., proxima sp.n., hispanica Hod. & Hollis, harteni sp.n., and arborea Log. Each species is fully characterized and an identification key is provided. A tentative phylogeny of the groups is proposed. Among the newly described species, australis (host plant: Erica australis) occurs in Portugal, proxima (host plant: Erica arborea and possibly Calluna vulgaris) is found throughout the Iberian peninsula, while harteni (host plant: Erica azorica) is found on the Azores.     

Effects of altitude and seed size on germination and seedling survival of heathland plants in north Spain

The effects of altitude and seed size on germination and seedling survival were studied in Calluna vulgaris, Erica cinerea and Erica vagans. Experiments were carried out in the laboratory over a one year period. Seeds collected from heathlands of different altitudes were divided in two size classes. They were sowed on moist filter paper inside Petri dishes which were placed in chambers at 20 °C and a photoperiod of 12 h light/12 h darkeness. The seeds of Calluna vulgaris were the first to begin germination and had the highest rate and percentage of germination. The germination of Erica vagans was moderate, while seeds of Erica cinerea germinated later and the germination was very low. Seeds of Calluna vulgaris and E. cinerea collected at the highest altitudes had the highest germination percentages. Seed size in Calluna vulgaris and E. cinerea did not affect germination. However, large seeds of Erica vagans had higher germination rates and percentages than small seeds. The large seed size of Calluna vulgaris contributes to a better survival and growth of its seedlings.     

Seed banks of Erica australis and Calluna vulgaris in a heathland subjected to experimental fire

Abstract. Soil samples were collected before and after an experimental fire on a heathland in the province of León (Spain). The seed banks were assessed by counting the numbers of seedlings appearing of Erica australis and Calluna vulgaris. A total of 2285 germinable seeds/m² before burning and 1177 germinable seeds/m² after the fire were estimated for Erica australis, and 90 and 690 germinable seeds/m², respectively, for Calluna vulgaris. After the fire the number of germinable seeds/m² of Erica australis had decreased, whilst there was a considerable increase in the number of germinable seeds/m² of Calluna vulgaris. Neither seedlings nor sprouts of Calluna vulgaris had appeared in the field plots 10 months after the fire. Erica australis did recover mainly by sprouting after fire.     

The dynamics of mediterranean shrubs species over 12 years following perturbations

The response of woody species to experimental burning, cutting andploughing was studied for a period of twelve years in a shrub community in NWSpain. The treatments represent the perturbations most frequently imposed bymanon these shrub communities throughout history. The response to burning is muchfaster than the response to cutting. The response to ploughing is slower due tothe regeneration mechanism that species use: germination. In general, thedominant species, Erica australis, influences theregeneration patterns of the rest of the species, which make up the community.There is a significant increase in the cover of woody species until the fourthyear, and of herbaceous species until the third year. Subsequently,Erica australis attains dominance, returning to itsoriginal spatial occupancy and cover values, removing the herbaceous speciesandnegatively influencing the growth of woody ones like Halimiumumbellatum, Halimium alyssoides and Quercuspyrenaica. Both Erica australis andChamaespartium tridentatum regenerated by sprouting in theburnt and cut plots, and by germination in the ploughed plot.Arctostaphylos uva-ursi only recovers after burning andploughing. Halimium alyssoides, Halimium umbellatum, Ericaumbellata and Calluna vulgaris regenerate bygermination in the three plots. Differences in cover values and spatialoccupancy during the first years of succession tend to be eliminated twelveyears after treatment and most of the species tend to recover their initialcover values. These shrubland communities have a high degree of resilience dueto the strong sprouting potential of the component species.     

Enhancement of photosynthesis in post-disturbance resprouts of two co-occurring Mediterranean <Emphasis Type="Italic">Erica</Emphasis> species

The higher growth rates of resprouting shoots compared with those of mature plants in resprouter woody species are supported by higher rates of photosynthesis and transpiration. In this contribution we hypothesize that species with higher resprouting vigour will show a larger enhancement of photosynthesis in resprouting shoots. We test this hypothesis by comparing gas exchange and leaf parameters between resprouting and mature plants in Erica scoparia and E. australis. These two Erica species co-occur in Mediterranean heathlands of the Strait of Gibraltar. Erica scoparia has a higher rate of post-disturbance starch recovery than E. australis, which makes it more resistant to recurrent disturbance. We tested the hypothesis that enhancement of photosynthesis and water use characteristics of resprouting shoots compared with mature plants should be more pronounced in E. scoparia. In both species, resprouts had higher efficiency in the use of light and higher maximum net photosynthesis than mature shoots. However, contrary to expectations, differences in the photosynthetic performance between resprouts and mature plant shoots were larger in E. australis. Higher root to shoot ratios in resprouting E. australis plants, determined by their slower above-ground recovery, together with stronger demand from carbon sinks might explain this result.     

Resistance to wildfire and early regeneration in natural broadleaved forest and pine plantation

The response of an ecosystem to disturbance reflects its stability, which is determined by two components: resistance and resilience. We addressed both components in a study of early post-fire response of natural broadleaved forest (Quercus robur, Ilex aquifolium) and pine plantation (Pinus pinaster, Pinus sylvestris) to a wildfire that burned over 6000 ha in NW Portugal. Fire resistance was assessed from fire severity, tree mortality and sapling persistence. Understory fire resistance was similar between forests: fire severity at the surface level was moderate to low, and sapling persistence was low. At the canopy level, fire severity was generally low in broadleaved forest but heterogeneous in pine forest, and mean tree mortality was significantly higher in pine forest. Forest resilience was assessed by the comparison of the understory composition, species diversity and seedling abundance in unburned and burned plots in each forest type. Unburned broadleaved communities were dominated by perennial herbs (e.g., Arrhenatherum elatius) and woody species (e.g., Hedera hibernica, Erica arborea), all able to regenerate vegetatively. Unburned pine communities presented a higher abundance of shrubs, and most dominant species relied on post-fire seeding, with some species also being able to regenerate vegetatively (e.g., Ulex minor, Daboecia cantabrica). There were no differences in diversity measures in broadleaved forest, but burned communities in pine forest shared less species and were less rich and diverse than unburned communities. Seedling abundance was similar in burned and unburned plots in both forests. The slower reestablishment of understory pine communities is probably explained by the slower recovery rate of dominant species. These findings are ecologically relevant: the higher resistance and resilience of native broadleaved forest implies a higher stability in the maintenance of forest processes and the delivery of ecosystem services.     

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.     

Interaction of light and temperature on seed germination of Rumex obtusifolius L.

Germination of Rumex obtusifolius L. seeds (nutlets) is low in darkness at 25° C. Germination is stimulated by exposure to 10 min red light (R) and also by a 10-min elevation of temperature to 35° C. A 10-min exposure to far-red light (FR) can reverse the effect of both R (indicating phytochrome control) and 35° C treatment. Fluence-response curves for this reversal of the effect of R and 35° C treatments are quantitatively identical. Treatment for 10 min with light of wavelenght 680, 700, 710 and 730 nm, after R and 35° C treatment, demonstrates that germination induced by 35° C treatment results from increased sensitivity to a pre-existing, active, far-red-absorbing form of phytochrome (Pfr) in the seeds.Abbreviations FR far-red light - P phytochrome - Pr red-absorbing form of P - Pfr far-red-absorbing form of P - R red light     

Response to recurrent disturbance in two co-occurring resprouter heath species: the ecological consequences of withstanding herbivores

Resprouting woody plants are vulnerable to large mammal herbivores in the early stages of regeneration after disturbance (e.g., fire, slashing), because herbivory reduces the storage of below-ground starch reserves and may thus compromise regeneration success. Defence from herbivory may incur a cost to resprouter plants in terms of lengthening the time to recovery of pre-disturbance starch levels. Erica scoparia and E. australis (Ericaceae), two resprouter woody species that co-occur in Mediterranean heath-communities of the Strait of Gibraltar, differ in the way they cope with herbivory: E. scoparia is browsing-tolerant and E. australis is a browsing-avoider. Our experimental field study demonstrated that exposure to a moderate density of ungulate herbivores markedly lowered starch re-storage after resprouting in E. scoparia, but not in E. australis. Nevertheless, time to recover pre-disturbance starch levels was shorter in the tolerant E. scoparia, even under exposure to herbivores. The slower starch recovery rate of E. australis is a likely outcome of its resource-demanding browsing-avoidance mechanism. Differences in starch recovery rates after disturbance between the two Erica species partly explains their ecological segregation at the landscape scale.     

Interaction of light and temperature on the germination of Rumex obtusifolius L.

Seeds (nutlets) of Rumex obtusifolius L. fail to germinate in darkness at 25° C, but are stimulated by short exposure to red light (R) the effectiveness of which can be negated by a subsequent short exposure to far red light (F) indicating phytochrome control. Short periods of elevated temperature treatment (e.g. 5 min at 35° C) can induce complete germination in darkness. Although short F cannot revert the effect of 35° C treatment, cycling the phytochrome pool by exposure to short R before short F results in reversion of at least 50% of the population. Prolonged or intermittent F can also revert the germination induced by 35° C treatment. The effect of elevated temperature treatment is interpreted on the basis of two possible models; (i) that it increases the sensitivity of the seeds to a low level of pre-existing active form of phytochrome (Pfr) (ii) that it induces the appearance of Pfr in the dark. In both cases it is envisaged that elevated temperature treatment and Pfr control germination at a common point in the series of reactions that lead to germination.Abbreviations D Dark - F far red light - P phytochrome - Pr red absorbing form of P - Pfr far red absorbing form of P - R red light     

Effect of high temperature on moisture loss,imbibition and germination of seeds ofTrianthema Govindia Buch.-Ham. ex DC

Summary Seeds of erect and prostrate plants ofTrianthema govindia Buch. ham. ex DC., growing in shade and open respectively, differed significantly in seed weight and percentage germination. Effect of high temperature exposure to these seeds has been studied in view of water depletion, imbibition and seed germination. The seeds of both the types were subjected to temperatures of 40, 50, 60, and 70° C for 24, 48, 96, and 144 hours. The three factors viz., loss of water, water imbibition and germination of seeds were positively correlated to the duration of treatment at different temperatures. A highly significant positive correlation was also observed between moisture depletion and imbibition, and between imbibition and germination. The percentage germination was favoured at 40° C in both the types of seeds and was increased with the increase of treatment duration. However, at higher temperatures (50 and 60° C) the percentage declined while at 70° C the seeds lost their vitality.     

Effects of temperature,light and gibberellic acid on the germination of seeds of 43 species native to Western Australia

Abstract. Species native to the southwest of Western Australia, representing a range of plant families, life-history strategies, fire-response syndromes, seed-store types and seed weights, were tested for viability using tetrazolium chloride and for germination under combinations of constant temperatures of 15 °C or 23 °C, constantly dark or 12 h diurnal whitelight conditions, and with, or without, addition of gibberellic acid (GA₃, 50 mg/l). Species previously known to require a heat-shock treatment to overcome dormancy due to an impervious testa were pre-treated prior to imposition of temperature, light and GA₃ conditions. The test environmental conditions related to differences between winter and autumn temperatures and surface and buried seed germination positions of post-fire habitats. The viability of the selection of native Western Australian species ranged from 0 to 100 %, averaging 71 %. For all taxa, no combination of temperature, light and gibberellic acid treatment induced all viable seeds to germinate. The greatest percentage germination achieved in any combination of treatments averaged 71 % of all viable seeds for all species. Larger seeds (> 10 mg seed weight) tended to have greater viability percentages, but no overall patterns of viability or germinability were attributable to seed storage syndrome, strategy of fire recovery response or life-form type. Germination of most of the dominant tree representatives (Eucalyptus calophylla, E. diversicolor, E. erythrocorys, E. gomphocephala, and E. patens) was indifferent to the trial conditions of temperature, light and GA₃. However, Eucalyptus marginata showed reduced germination in the light, which was overcome with GA₃. GA₃ also overcame the inhibition resulting from exposure to light in some understorey species (e.g. Allocasuarina campestris, Regelia ciliata, Xanthorrhoea gracilis and X. preissii). Germination of many hard-seeded, understorey shrub and herbaceous perennial species, especially those with small (< 10 mg) seeds (e.g. Bossiaea ornata, B. aquifolium and Acacia drummondii ssp. candolleana) was greater at the lower trial temperature and in the dark. Some large (> 10 mg) seeded, understorey species (e.g. Acacia extensa, Kennedia coccinea, K. prostrata, Hovea trisperma and Hardenbergia comptoniana) germinated in high percentages in both temperatures, but maximum germination percentages still tended to be at 15 °C. Large-seeded species were less sensitive to exposure to light compared to the smaller seeded species. The largest seeded species tested, Paraserianthes lophantha, germinated best in the warmer incubation temperature and in the light. The ecological significance of the tests would be that species which have seed dormancy mechanisms capable of delaying germination until the cool temperature, winter rainy period of this mediterranean-type climate would be more likely to survive than if germination followed summer rain showers or the first, intermittent rains of autumn. Burial of seeds becomes more important if germination occurs when rains first begin as this period has less available soil moisture and temperatures are high. Also survival of seedlings could be enhanced if germination of seed was restricted to the positions protected from high light, higher temperatures and lower soil moisture by the presence of a forest canopy. Therefore, seeds which have an ability to sense the presence of a previous fire in the habitat, conditions in light environment and appropriate temperature level have an adaptive advantage to time emergence to situations of time and space where survival is maximized. Variation in viability and germination percentages were apparent in some cases where more than one seed collection of available for testing, indicating that further aspects, such as seed age, maturity at collection, storage conditions and depth of seed dormancy, remain to be considered.     

Light and temperature interaction in the photocontrol of germination of seeds in Ludwigia octovalvis

Summary The germination response of seeds of Ludwigia octovalvis (Jacq.) (=Jussiaea suffruticosa L.; Raven, 1963), to continuous light and to various types of intermittent irradiations is determined at 25, 30, 35 and 40° at different light intensities. At 25 and 40° intermittent irradiations are an effective substitute for continuous ones, while at 30 and 35° no promotion of germination is observed in the intermittent irradiations tested, except if the dark interval between light pulses is reduced to 1 min. Previous results obtained in the photocontrol of germination in this species are confirmed and extended to a variety of light cycles and intensities, indicating that the response to temperature is bimodal unless light is supplied continuously with high intensity, and that germination depends on light intensity more markedly in the temperature region of minimum germination (30–35°). As germination in this species is controlled by the red far-red system, hypothesis to account for the temperature dependence are based on the interaction between temperature and the reactions in which phytochrome is involved.Abbreviations L light - D darkness     

FACTORS AFFECTING GERMINATION IN GREENHOUSE-PRODUCED SEEDS OF OXALIS CORNICULATA,A PERENNIAL WEED

A study was conducted to investigate the physiological responses of greenhouse-produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 μmol m^-2 s^-1, 400–700 nm) to germinate. Seeds germinated over a broad, yet seasonally-dependent range of incubation temperatures. Seeds produced in winter had the narrowest temperature range of germination (15 to 25 C) and the lowest germination percent (44% at 2 wk) at optimum temperature (17 C); seeds produced in summer had the widest temperature range of germination (10 to 30 C) and the highest germination percent (93% at 2 wk) at optimum temperature (17 C). Incubation at non-optimum temperatures between 5 and 40 C suppressed or slowed the rate of germination until seeds were placed at optimum temperature, where full germination subsequently occurred. Moist heat treatment at temperatures over 40 C resulted in varying degrees of inhibition of subsequent germination. When seeds were stored dry in laboratory conditions, three of four seed lots examined retained over 80% germination capacity until ca. 8 months; 50% capacity remained after ca. 15 months. These results indicate that the seasonal temperature and daylength effects on maternal plants in the greenhouse environment are major determinants of seed germination characteristics of O. corniculata.     

Biodiversity in different successional stages of Mediterranean enclaves distributed along Sinop Peninsula (Turkey)

The aim of this research was to evaluate plant diversity and the relationships between the distribution of Raunkiaer life forms and community structure, and species richness, at different successional stages in communities of Quercus ilex L., Erica arborea L. and Sarcopoterium spinosum (L.) Spach., distributed as enclaves in Sinop Province. Permanent sample plots were selected to determine plant diversity. The cover percentage of each plant species was recorded monthly during two vegetation periods. Raunkiaer life forms, and the Shannon–Wiener, Evenness, Simpson and Margalef indexes were determined. Twenty-three species in Quercus ilex, 96 species in Erica arborea, and 148 species in Sarcopoterium spinosum were identified. Hemicryptophyte dominancy was observed followed by phanerophytes in the Q. ilex community, and therophyte and hemicryptophyte dominancy in the E. arborea and S. spinosum communities, respectively. It was determined that the S. spinosum community was the most heterogeneous community while the Q. ilex community was more uniform than other communities. The variation in diversity indexes, homogeneity, and composition of life forms among communities adopting a similar climatic environment could result from a differentiation of environmental factors, which impact on community structuring, from biotic to abiotic at different successional stages of Mediterranean communities.     

Low-temperature stratification strategies and growth regulators for rapid induction of Paris polyphylla var. yunnanensis seed germination

The seeds of Paris polyphylla var. yunnanensis are deeply dormant, and they remain dormant for 18 months or longer in their natural environment. Periodic exposure of the seeds to a low-temperature of 4 °C broke the dormancy in about 16 weeks (112 days). The most effective temperature stratification scheme was an interval of 14 days at 4 °C and 14 days at 22 °C. Both GA₃ and ethephon significantly enhanced the germination rate during the stratification treatment. The seed coat, particularly the mesophyll outer layer of the seed coat, strongly inhibited the germination. With removal of the seed coat and exposure of the uncoated seeds to 600 mg/l GA₃ for 48 h before the temperature stratification of 14 days at 4 °C and 14 days at 22 °C for 112 days, a germination percentage as high as 95.3% of the seeds was attained in about 160 days.     

Browser selectivity alters post-fire competition between <Emphasis Type="Italic">Erica arborea</Emphasis> and <Emphasis Type="Italic">E. trimera</Emphasis> in the sub-alpine heathlands of Ethiopia

Mammalian herbivores have the potential to alter the competitive relations of woody species, if consumption is unevenly distributed between species. At elevations above 3,500 m in the southern Ethiopian highlands, vegetation is dominated by Erica arborea and E. trimera. Both species can potentially grow into short trees, but are burnt on a rotation of 6–10 years, and regenerate by re-sprouting from belowground lignotubers. The regenerating scrub is heavily browsed by cattle. We set up browsing exclosures at three burnt sites to quantify the impact of browsing over a 3-year period. When protected from browsing, E. trimera had similar or better height growth than E. arborea, but in browsed vegetation, E. arborea instead grew taller. Browsing was more intense on E. trimera in the first years after fire, indicating a difference in palatability between the species. We checked if browse quality differed, by analysing shoot contents of acid detergent fibre (ADF), protein, phenolics and tannins. Contrary to expectations, the preferred E. trimera contained more ADF, less protein and had a higher tannin activity than E. arborea. Although the vegetative growth of E. arborea is favoured relative to E. trimera under high browsing pressure, rapid change in abundance would not be expected, since short-interval fire will repeatedly eradicate any gains in vegetative growth. However, within the typical fire return interval of less than 10 years, E. trimera barely reach a reproductive state, whereas E. arborea flower profusely. Under the current regime of fire and browsing, this may in the long run be more important than differences in height growth, leading to a gradual increase in the proportion of E. arborea.     

An unusual effect of the far-red absorbing form of phytochrome: Photoinhibition of seed germination inBromus sterilis L.

Seeds ofBromus sterilis L. germinated between 80–100% in darkness at 15° C but were inhibited by exposure to white or red light for 8 h per day. Exposure to far-red light resulted in germination similar to, or less than, that of seeds maintained in darkness. Germination is not permanently inhibited by light as seeds attain maximal germination when transferred back to darkness. Germination can be markedly delayed by exposure to a single pulse of red light following 4 h inhibition in darkness. The effect of the red light can be reversed by a single pulse of far-red light indicating that the photoreversible pigment phytochrome is involved in the response. The response ofB. sterilis seeds to light appears to be unique; the far-red-absorbing form of phytochrome (Pfr) actually inhibiting germination.Abbreviations Pr red absorbing form of phytochrome - Pfr far-red absorbing form of phytochrome