1,720,965 research outputs found
Qualitative and quantitative assessment of the reproductive litter from Posidonia oceanica accumulated on a sand beach following a storm
No full textThe biomass of reproductive litter from Posidonia oceanica deposited on a 3.5 km stretch of beach in the north-western Mediterranean, as a consequence of a storm in May 2004, was quantified. The damage caused by this storm to the meadow from which fruits originated was evaluated in terms of loss of seed production. Intermediate fruits (i.e., developing fruits) were the most important reproductive component, followed by immature and damaged fruits. No fully mature fruits were found. No significant differences in the average number of fruits and biomass accumulated were detected among beach sections hundreds of metres apart. Extrapolation of the results at four beach sections indicated that about I million fruits were deposited on the entire (3.5 km) beach. This was equivalent to the seed production potential of about 313,217 inflorescences, or a flowered area of 1500 m(2). The organic input to the beach was 224 kg ash-free dry weight (AFDM). These results suggest that storms may provide an unpredictable source of seed mortality in P. oceanica. The reproductive material produced by storms, however, may constitute an important source of allochthonous organic matter to the beach
On the unusual flowering of plagiotropic shoots in the seagrass Posidonia oceanica
No full textThe seagrass Posidonia oceanica (L.) Delile can produce plagiotropic (horizontally oriented) and orthotropic (vertically oriented) axes. These axes differ in various morphological and growth characteristics and ecological functions. Only orthotropic shoots are likely to support flowering and seed production. To asses whether flowering may occur on plagiotropic shoots, we examined plagiotropic axes that grew at the edge of a meadow during the flowering of 2003. We identified and analysed 10 rhizome fragments that bore at least one reproductive plagiotropic shoot. We then investigated whether reproductive plagiotropic shoots differed from orthotropic ones in morphological characteristics and investment in flowering (i.e., number of hermaphroditic flowers per inflorescence). Multivariate analysis did not show any significant difference between plagiotropic and orthotropic shoots with regard to the characteristics examined and investment in flowering. Further studies are necessary to ascertain if the observed pattern of flowering is a common or an exceptional event in P oceanic
Combined effect of plastic litter and increased atmospheric nitrogen deposition on vegetative propagules of dune plants: a further threat to coastal ecosystems
Full text linkLarge amounts of non-biodegradable plastics are currently deposited on beach-dune systems, and biodegradable plastics could enter these already declining habitats in coming years. Yet, the impacts of plastics on vegetative recruitment, a plant strategy playing a key role in dune stabilization, are unknown. Whether these pollutants interact with increased atmospheric nitrogen (N) deposition, a major global driver of plant biodiversity loss, in affecting plant communities of such nutrient-poor habitats, and how plant-plant interactions mediate their effects need to be explored. In a one-year field experiments, we examined individual and combined effects of plastic (non-biodegradable, biodegradable), N deposition (ambient, elevated) and biotic condition (no interaction, interaction with a conspecific or with a hetero-specific) on the colonization success and growth of vegetative propagules of dune plants. Thinopyrum junceum and Sporobolus pumilus were chosen as models because they co-occur along Mediterranean dunes and differ in ecological role (dune- vs. non dune-building) and photosynthetic pathway (C3 vs. C4). For both species, survival probability was reduced by non-biodegradable plastic and elevated N by up to 100%. Thinopyrum junceum survival was also reduced by S. pumilus presence. Elevated N and biodegradable plastic reduced T. junceum shoot biomass when grown alone and with a conspecific, respectively; these factors in combination mitigated their negative individual effects on root biomass. Biodegradable plastic increased S. pumilus shoot and root biomass, and in combination with elevated N caused a greater biomass investment in belowground (root plus rhizome) than aboveground organs. Non-biodegradable plastic may be a further threat to dune habitats by reducing plant colonization. Biodegradable plastic and increased N deposition could favour the generalist S. pumilus and hinder the dune-building T. junceum. These findings highlight the urgency of implementing measures for preventing plastic deposition on beaches and reducing N input
Harnessing spatial nutrient distribution and facilitative intraspecific interactions in soft eco-engineering projects to enhance coastal dune restoration
No full textPlanting engineer species is widely used to restore coastal dune ecosystems, but the success of this nature-based practice is often low. Increasing nutrient availability through fertilization and using plant density promoting facilitative plant-plant interactions are increasingly advocated to improve dune restoration. However, how fertilizer application (homogeneous or heterogeneous spatial distribution) influences plant interaction intensity in dune species is still poorly known. We conducted a field-mesocosm experiment assessing the effects of spatial nutrient distribution and planting density on functional traits and intraspecific interactions in two dune plants with contrasting clonal growth architecture. Fragments of Calamagrostis arenaria (phalanx architecture) and Sporobolus virginicus (guerrilla architecture) were grown in monoculture either at low or at high density with the same total supply of fertilizer applied either heterogeneously or homogeneously. We hypothesized that these species would respond differentially to nutrient distribution and plant density. C. arenaria allocated less biomass below- than aboveground under homogeneous than heterogeneous conditions and produced less shoots at low than high density. Conversely, under homogeneous conditions, S. virginicus plants grown at low density had a greater rhizome, root, and total biomass than those at high density. For C. arenaria, intraspecific interactions on aboveground, root, and total biomass shifted from positive to neutral under heterogeneous conditions while those on rhizome biomass switched from neutral to negative. S. virginicus intraspecific interactions on all biomass variables shifted from negative to neutral. Our results demonstrate that nutrient distribution affected functional traits and intraspecific interactions differentially in phalanx and guerrilla species. Notably, in nutrient homogeneous substrates high planting density increased phalanx species performance but reduced that of guerrilla species due to competition. Instead, in heterogeneous substrates both species performed similarly at low and high density. These findings may help restoration practitioners in identifying suitable fertilization/planting schemes and implementing effective dune restoration programs
Adverse effects of non-biodegradable and compostable plastic bags on the establishment of coastal dune vegetation: First experimental evidences
No full textNon-biodegradable and compostable plastic bags on beaches negatively affect the development of coastal dune vegetation by drastically reducing seedling emergence and growth
First evidence of root morphological and architectural variations in young Posidonia oceanica plants colonizing different substrate typologies
No full textRoot morphology and root system architecture of young Posidonia oceanica plants established on two contrasting substrate types, sand and rock, were examined to provide insights into the strategy of adaptation of seagrasses to their environment. After germination, seedlings were planted on sandy patches and on rock within the same area, and survived plants were collected five years later for measurements of the size of the entire root complex and analysis of individual morphological and architectural root traits. Collected plants exhibited up to nine highly intermingled root systems and approx. 2.5 m of total root length. Maximum horizontal extension, total biomass and total length of roots were not significantly affected by substrate. However, on sand roots grew vertically reaching up to 13 cm, while on rock they extended more horizontally and did not penetrate deeper than 5-7 cm leading to the formation of a shallow, densely packed root complex. On rock, the number and the length of second-order laterals on an individual root system were reduced and the topological index higher than on sand (0.8 vs. 0.7) reflecting a more simple (herringbone) branching pattern. Again, root diameter was greater than on sand. The results suggest that P. oceanica can adjust root traits early during plant development according to substrate typology to maximize anchorage and substrate exploration efficiency. This plasticity enables the species to establish and persist also on rocky bottoms which generally prevent establishment of the majority of seagrasses
Effect of seed density and sediment nutrient heterogeneity on recruitment and early patch growth in the seagrass Cymodocea nodosa
Full text linkTwo mesocosm experiments were performed to examine the effects of seed density and small-scale nutrient heterogeneity on seedling recruitment and early development of patches of Cymodocea nodosa. In the first experiment, seeds were sown at 4 densities selected after determining mean natural density of seeds in the field, and the emergence and survival rates of seedlings were monitored for 1 yr. In the second experiment, seedlings were grown individually for 2 yr, either on substrate made heterogeneous or homogeneous with the addition of a fertiliser or on unfertilised substrate. The emergence rate and proportional survival of seedlings decreased significantly with increasing seed density. Seedlings grown on fertilised substrates were able to form patches, while those grown on unfertilised substrate failed to branch, providing experimental evidence of the role of nutrient limitation as a constraint for patch initiation. The size of seed-generated patches was significantly larger (in terms of total length of the rhizome network and number of shoots) on heterogeneous substrate than on homogeneous substrate at the same overall level of nutrient supply. Apparently, no preferential proliferation of shoots and branches occurred in the nutrient-rich half of the heterogeneous substrate. The results support our hypothesis that negative density dependence at the seed-seedling stage plays an important role in regulating population size. They also reveal that seedlings experiencing nutrient heterogeneity are capable of exploiting resources more efficiently than those in homogeneous environments, but are probably unable to escape from unfavourable patches or to select favourable ones, at least at the scale examined here
Storm-generated fragments of the seagrass Posidonia oceanica from beach wrack - A potential source of transplants for restoration
No full textAnalysis of factors influencing the microbial population dynamics of the activated-sludge process
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