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991.
Question: Do contrasting biotic contexts in nutrient‐poor grasslands affect the predictability of invasion by exploitative species following fertilization? Location: French Alps. Methods: We examined community responses after 2 years of nutrient addition for two nutrient‐poor European calcareous grasslands, a mesoxeric community dominated by the short bunchgrass Bromus erectus and a mesic community dominated by the tall rhizomatous grass Brachypodium rupestre. We also performed reciprocal transplantations of these two dominant slow‐growing species and Arrhenatherum elatius, a tall fast‐growing grass that dominates nutrient‐rich communities and is likely to invade nutrient‐poor communities after fertilization. Transplants were grown with or without neighbors, in order to measure their individual responses (without neighbors) and competition intensity (by comparing performances with and without neighbors using the Relative Neighbor Effect index – RNE) during one growing season in all three communities. Results: In the Bromus community, fertilization induced a strong increase in fast‐growing grasses (including A. elatius). Competition intensity was low for the three transplanted grasses, but strongly increased with resource addition, to reach values observed in the Arrhenatherum community. In the Brachypodium community, no change in competition intensity with fertilization was detected, because of the high mortality of the two “non‐resident” species, irrespective of the presence of neighbors. Conclusions: Community responses to nutrient improvement are context‐dependent and vary as a function of the biotic environment. Soil processes are proposed as the main drivers of community resistance to the invasion of fast‐growing species in the mesic, nutrient‐poor grassland dominated by the large conservative competitor B. rupestre. 相似文献
992.
To supply essential information for improving mass production and biocontrol efficacy, two-stage cultivation on agar plates
was used to evaluate the environmental conditions affecting mycelial growth and sporulation of seven biocontrol fungi. Maximum
growth and sporulation occurred on acid media for Paecilomyces (Pa.) lilacinus IPC-P, Pochonia (Po.) chlamydosporia HSY-12-14, and Lecanicillium lecanii CA-1-G, and on alkaline media for Metarhizium anisopliae isolates. All fungi preferred a certain water potential and temperature for sporulation. Light greatly inhibited the growth
of P. lilacinus IPC-P, M. anisopliae SQZ-1-21, and L. lecanii CA-1-G but enhanced the sporulation of P. lilacinus M-14, P. chlamydosporia HSY-12-14, and L. lecanii CA-1-G. 相似文献
993.
We surveyed ectomycorrhizae, ectomycorrhizal fungal fruit bodies, and soil physical properties in one heavily damaged and
two lightly damaged pine stands on Mt. Tsukuba, central Japan. The rate of ectomycorrhizal root tips was not different between
heavily and lightly damaged pine stands. For ectomycorrhizae, Cenococcum geophilum had high relative abundance in the heavily damaged pine stand. The number of ectomycorrhizal fungal fruit bodies in the heavily
damaged pine stand was much lower than that in the lightly damaged pine stands. 相似文献
994.
Many studies have been conducted to quantify the possible ecosystem/landscape response to the anticipated global warming. However, there is a large amount of uncertainty in the future climate predictions used for these studies. Specifically, the climate predictions can be very different based on a variety of global climate models and alternative greenhouse emission scenarios. In this study, we coupled a forest landscape model, LANDIS-II, and a forest process model, PnET-II, to examine the uncertainty (that results from the uncertainty in the future climate predictions) in the forest-type composition prediction for a transitional forest landscape [the Boundary Water Canoe Area]. Using an improved global-sensitivity analysis technique [Fourier amplitude sensitivity test], we also quantified the amount of uncertainty in the forest-type composition prediction contributed by different climate variables including temperature, CO2 , precipitation and photosynthetic active radiation (PAR). The forest landscape response was simulated for the period 2000–2400 ad based on the differential responses of 13 tree species under an ensemble of 27 possible climate prediction profiles (monthly time series of climate variables). Our simulations indicate that the uncertainty in the forest-type composition becomes very high after 2200 ad , which is close to the time when the current forests are largely removed by windthrow disturbances and natural mortality. The most important source of uncertainty in the forest-type composition prediction is from the uncertainty in temperature predictions. The second most important source is PAR, the third is CO2 and the least important is precipitation. Our results also show that if the optimum photosynthetic temperature rises due to CO2 enrichment, the forest landscape response to climatic change measured by forest-type composition may be substantially reduced. 相似文献
995.
The kinetics of metal uptake by gel and dry calcium alginate beads was analysed using solutions of copper or lead ions. Gel beads sorbed metal ions faster than the dry ones and larger diffusivities of metal ions were calculated for gel beads: approximately 10−4 cm2/min vs. 10−6 cm2/min for dry beads. In accordance, scanning electron microscopy and nitrogen adsorption data revealed a low porosity of dry alginate particles. However, dry beads showed higher sorption capacities and a mechanical stability more suitable for large-scale use. Two sorption models were fitted to the kinetic results: the Lagergren pseudo-first order and the Ho and McKay pseudo-second order equations. The former was found to be the most adequate to model metal uptake by dry alginate beads and kinetic constants in the orders of 10−3 and 10−2 min−1 were obtained for lead solutions with concentrations up to 100 g/m3. The pseudo-first order model was also found to be valid to describe biosorbent operation with a real wastewater indicating that it can be used to design processes of metal sorption with alginate-based materials. 相似文献
996.
Alpine snowbeds are characterized by a long-lasting snow cover and low soil temperature during the growing season. Both these
key abiotic factors controlling plant life in snowbeds are sensitive to anthropogenic climate change and will alter the environmental
conditions in snowbeds to a considerable extent until the end of this century. In order to name winners and losers of climate
change among the plant species inhabiting snowbeds, we analyzed the small-scale species distribution along the snowmelt and
soil temperature gradients within alpine snowbeds in the Swiss Alps. The results show that the date of snowmelt and soil temperature
were relevant abiotic factors for small-scale vegetation patterns within alpine snowbed communities. Species richness in snowbeds
was reduced to about 50% along the environmental gradients towards later snowmelt date or lower daily maximum temperature.
Furthermore, the occurrence pattern of the species along the snowmelt gradient allowed the establishment of five species categories
with different predictions of their distribution in a warmer world. The dominants increased their relative cover with later
snowmelt date and will, therefore, lose abundance due to climate change, but resist complete disappearance from the snowbeds.
The indifferents and the transients increased in species number and relative cover with higher temperature and will profit
from climate warming. The snowbed specialists will be the most suffering species due to the loss of their habitats as a consequence
of earlier snowmelt dates in the future and will be replaced by the avoiders of late-snowmelt sites. These forthcoming profiteers
will take advantage from an increasing number of suitable habitats due to an earlier start of the growing season and increased
temperature. Therefore, the characteristic snowbed vegetation will change to a vegetation unit dominated by alpine grassland
species. The study highlights the vulnerability of the established snowbed vegetation to climate change and requires further
studies particularly about the role of biotic interactions in the predicted invasion and replacement process. 相似文献
997.
We have studied the underlying factors responsible for the heterogeneous ecophysiological status of a semiarid Stipa tenacissima L. steppe in a subcatchment of SE Spain by assessing population composition and habitat structure of S. tenacissima stands. To do this, we measured and estimated 18 variables (11 biotic and seven abiotic) in 15 plots randomly distributed
in the subcatchment, and then zoned this area by plot affinity using PCA. This analysis produced three sectors determined
mainly by S. tenacissima cover and soil depth variables. The linear relationship fitted between S. tenacissima tussock biomass and tussock density in monospecific stands (both logarithmic) indicated a curve close to −1, suggesting that
the system is close to the maximum constant yield state. Ecophysiological measurements (gas exchange, fluorescence and individual
leaf area index) were taken in two periods with different water availability in a representative plot in each sector. The
intraspecific competition (inferred from the density dependence of green biomass) and rock outcrops were the main factors
influencing the ecophysiological status in the study area. While, in the wet season, intraspecific competition regulated water
consumption in zones where S. tenacissima tussocks (monospecific stands) are dominant, during the dry season, stands in zones with extensive rock outcrops and stone
cover (tussocks in “soil pockets”) had no access to non-rainfall water gains because of the adjacent bare soil, and so in
these stands, gas exchange was lower and photoinhibition higher. This article stresses the importance of considering the connection
between tussocks and bare-ground interspace in the functional and structural analysis of semiarid steppes. 相似文献
998.
Many areas in Europe are dominated by agricultural land use, and as a consequence, many typical forest plant species suffer
from habitat loss and fragmentation. Hedgerows, one of the common elements of rural landscapes, have been considered as potential
refuges for these species. The main objective of this study was to examine whether forests and hedgerows differ in environmental
conditions, and whether important life-history attributes of the populations differ between the two habitat types. We selected
five species commonly found in the region in both forests and hedgerows (Adoxa moschatellina, Anemone nemorosa, Circaea lutetiana, Polygonatum multiflorum and Stellaria holostea), and sampled data on 10 populations of each species in each habitat type, including measurements of light and various soil
factors. Hedgerows had higher relative light availability and tended to have higher soil nutrient contents and lower soil
water values than forests. The comparison of plant performance values between habitat types did not show consistent patterns
across species. Anemone and Polygonatum performed equally well in hedgerows and forests, whereas Stellaria appeared to have a higher fitness in hedgerows. In contrast, Circaea showed a higher reproduction under forest conditions. For Adoxa, the results were somewhat contradictory: whereas the reproductive output of this species was higher in forests, population
density was higher in hedgerows. The abiotic factors most closely related to the performance values were relative light and
soil water availability. The majority of plant performance values did not differ between hedgerows and forests. We therefore
conclude that the tested forest species are capable of growing also in hedgerows and will survive equally well in forest and
its “surrogate” habitat. 相似文献
999.
Knapweeds (Centaurea spp.) are damaging invaders of grasslands and other North American rangelands. A field study was conducted to determine conditions
that promote diffuse knapweed (C. diffusa) emergence and establishment in a native Colorado grassland (North America). Knapweed was planted in native grassland under
treatments with different opening sizes, levels of competition, knapweed seed burial and season of seeding. There was no effect
of opening size where competing natives were alive, but knapweed emergence in 5- and 15-cm openings was higher than 0-cm openings
where natives were killed. Reducing competition reduced fall diffuse knapweed emergence, but did not affect spring emergence.
Seed burial increased knapweed emergence, but the effect varied by season. Although diffuse knapweed emergence reached 35%,
only four plants survived from 3,600 seeds. This native grassland did not prevent knapweed emergence or establishment, but
both were so low that rapid knapweed invasion is unlikely. 相似文献
1000.
Flóra Tinya Sára Márialigeti Ildikó Király Balázs Németh Péter ódor 《Plant Ecology》2009,204(1):69-81
A vegetation survey was carried out in a relatively intact Atlantic blanket bog in Southwest Ireland to study the vegetation
patterns in relation to environmental variation, and to quantify the effect of artificial and natural borders on compositional
variation. The data were analysed using canonical correspondence analysis. In terms of both vegetation and water chemistry,
the study site can be categorized as typical of Atlantic blanket bogs in the maritime regions of North-western Europe. The
distribution of plant species was explained mainly by depth of the water table. The distribution of bryophytes was secondarily
explained by the pH of the bog water, while the distribution of vascular plants was secondarily explained by concentrations
of ammonia. The vegetation distribution exhibited little variation between the central sector of the peatland and its disturbed
edges (hill-grazing and restoration areas), but a substantial variation was observed between the area along a natural edge
(stream) and the areas close to the other peatland borders or centre. Similarly, the internal variation within each sector
(centre, hill-grazing edge and restoration area edge) was small, but substantial vegetation variation was observed within
the area located along the stream. The area along the stream was associated with relatively deep water table, shallow peat
depth, high water colour, pH and NH4
+ concentrations, and low Cl− concentrations in the bog water. Our results suggest the existence of strong centre-natural margin gradients, as in raised
bogs, and indicate that human or animal disturbance do not give rise to the marked transition zones that often characterize
natural margins of mire systems. This indicates that even small areas and remnants of Atlantic blanket bogs are worthy of
conservation and that their conservation value would benefit from the inclusion of sectors close to the natural peatland borders,
which would increase the plant biodiversity of the conserved area. 相似文献