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1.
Grazing-induced changes in plant composition affect litter quality and nutrient cycling in flooding Pampa grasslands 总被引:5,自引:0,他引:5
Changes in plant community composition induced by vertebrate grazers have been found to either accelerate or slow C and nutrient
cycling in soil. This variation may reflect the differential effects of grazing-promoted (G+) plant species on overall litter
quality and decomposition processes. Further, site conditions associated with prior grazing history are expected to influence
litter decay and nutrient turnover. We studied how grazing-induced changes in plant life forms and species identity modified
the quality of litter inputs to soil, decomposition rate and nutrient release in a flooding Pampa grassland, Argentina. Litter
from G+ forbs and grasses (two species each) and grazing-reduced (G−) grasses (two species) was incubated in long-term grazed
and ungrazed sites. G+ species, overall, showed higher rates of decomposition and N and P release from litter. However, this
pattern was primarily driven by the low-growing, high litter-quality forbs included among G+ species. Forbs decomposed and
released nutrients faster than either G+ or G− grasses. While no consistent differences between G+ and G− grasses were observed,
patterns of grass litter decay and nutrient release corresponded with interspecific differences in phenology and photosynthetic
pathway. Litter decomposition, N release and soil N availability were higher in the grazed site, irrespective of species litter
type. Our results contradict the notion that grazing, by reducing more palatable species and promoting less palatable ones,
should decrease nutrient cycling from litter. Plant tissue quality and palatability may not unequivocally link patterns of
grazing resistance and litter decomposability within a community, especially where grazing causes major shifts in life form
composition. Thus, plant functional groups defined by species’ “responses” to grazing may only partially overlap with functional
groups based on species “effects” on C and nutrient cycling. 相似文献
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Abstract. Woodland colonization on wetlands is considered to have a detrimental effect on their ecological value, even though detailed analysis of this process is lacking. This paper provides an evaluation of the ecological changes resulting from succession of poor fen (base‐poor mire) to willow wet woodland on Goss Moor NNR in Cornwall, UK. Different ages of willow carr were associated with eight understorey communities. During willow colonization, in the ground flora, there was a progressive decrease in poor fen species and an associated increase in woodland species, which appeared to be related to an increase in canopy cover and therefore shade. The most diverse community was found to be the most recent willow and was dominated by poor fen species. The oldest willow was the second most diverse and was associated with a reduction in poor fen species and an increase in woodland species. Architectural features were used successfully to assess the general condition and structure of willow. Tree height and DBH were identified as useful parameters to accurately assess willow age in the field. The implications of active intervention to remove willow in order to conserve the full range of communities within the hydrosere are discussed. 相似文献
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María Busch Carol Knight Cristina Noemí Mazía Karina Hodara Emiliano Muschetto Enrique Chaneton 《Ecological Research》2012,27(2):369-376
Woody plant invasion in grassland ecosystems is a worldwide phenomenon, and biotic interactions as competition and predation
have been invoked as a possible barrier to woody encroachment in many ecosystems. We evaluated the role of rodents as seed
predators in Pampean grasslands, and we assessed the differences in removal by rodents between one native species, Prosopis caldenia (Caldén) and one exotic species, Gleditisia triacanthos (Honey locust). The experiment was conducted at different phases of the rodent population cycle in two grassland communities,
a remnant of a native grassland and a post agriculture grassland (old field). The amount of seed loss caused by predation
was estimated by a bait-removal experiment in foraging stations. We estimated the frequency of foraging stations with consumption,
the overall amount of seed predation and the individual rate of seed predation. The total amount of seed removal and the individual
rate of seed removal were higher for P. caldenia than for G. triacanthos, in the native grassland than in the old field, and in autumn when rodent density was maximum. Overall, the role of rodents
on woody seed removal varied according to the plant species and depending on the local conditions that vary through time and
space. 相似文献
6.
Do foliar endophytes affect grass litter decomposition? A microcosm approach using Lolium multiflorum 总被引:3,自引:0,他引:3
Symbiotic infection with fungal endophytes has been shown to decrease herbivory in several temperate grasses. We tested the hypothesis that foliar endophytes of grasses may also affect below-ground processes upon their host death, by altering the litter quality for detritivores or the microenvironment for decomposition. Microcosm–litterbag experiments were used to assess decay rates for litter produced by endophyte ( Neotyphodium sp.) infected vs uninfected Lolium multiflorum plants, and to examine endophyte-mediated effects of prior site occupants on current litter decomposition. We found that litter from endophyte-infected L. multiflorum decomposed more slowly than litter from endophyte-free conspecifics and from a naturally uninfected grass, Bromus unioloides . Furthermore, the endophyte–grass association modified the decomposition environment, so that B. unioloides litter decomposed faster when placed underneath a thick layer of endophyte-free L. multiflorum litter. Litter decay rates increased with the amount of root debris remaining in situ from the previous season, but were not affected by the infection status of prior site occupants. The lower decomposability of litter from infected L. multiflorum plants persisted across a range of microenvironments, as determined by different amounts of above-ground litter and soil moisture conditions. Endophyte infection tended to reduce the N content of decaying litter; however, litter N and C/N ratio mainly accounted for interspecific differences in decomposition. Our results imply that fungal endophytes not only can affect herbivory food chains, but also soil organisms and the ecosystem processes they regulate. This study suggests a novel role for symbiotic foliar endophytes in linking above-ground and below-ground sub-systems. 相似文献
7.
Plant cover plays a major role in shaping the nature of recruitment microsites through direct (resource mediated) and indirect
(consumer mediated) interactions. Understorey plants may differentially affect seedling establishment, thus contributing to
regeneration-niche separation among canopy tree species. We examined patterns of early tree seedling survival resulting from
interactive effects of understorey bamboo (Chusquea culeou) and resident consumers in a mixed temperate Patagonian forest, Argentina. Newly germinated seedlings of Nothofagus dombeyi and Austrocedrus chilensis were planted in bamboo thickets and non-bamboo patches, with or without small-vertebrate exclosures. We found species-specific
patterns of seedling survival in relation to bamboo cover. Nothofagus survival was generally low but increased under bamboo, irrespective of cage treatment. Desiccation stress accounted for most
Nothofagus mortality in open, non-bamboo areas. In contrast, Austrocedrus survival was highest in non-bamboo microsites, as most seedlings beneath bamboo were killed by small vertebrates through
direct consumption or non-trophic physical damage. There was little evidence for a negative impact of bamboo on tree seedling
survival attributable to resource competition. The balance of simultaneous positive and negative interactions implied that
bamboo presence facilitated Nothofagus early establishment but inhibited Austrocedrus recruitment via apparent competition. These results illustrate the potential for dominant understorey plants to promote microsite
segregation during early stages of recruitment between tree seedlings having different susceptibilities to water stress and
herbivory. We recognise, however, that patterns of bamboo–seedling interactions may be conditional on moisture levels and
consumer activity during establishment. Hence, both biotic and abiotic heterogeneity in understorey environments should be
incorporated into conceptual models of regeneration dynamics and tree coexistence in forest communities. 相似文献
8.
Plants infected with vertically transmitted fungal endophytes carry their microbial symbionts with them during dispersal into
new areas. Yet, whether seed-borne endophytes enhance the host plant’s ability to overcome colonisation barriers and to regenerate
within invaded sites remains poorly understood. We examined how symbiosis with asexual endophytic fungi (Neotyphodium) affected establishment and seed loss to predators in the invasive annual grass Lolium multiflorum (Italian ryegrass) across contrasting successional plots. Italian ryegrass seeds with high and low endophyte incidence were
sown into three communities: a 1-year-old fallow field, a 15-year-old grassland, and a 24-year-old forest, which conformed
to an old-field chronosequence in the eastern Inland Pampa, Argentina. We found that endophyte infection consistently increased
host population recruitment and reproductive output. Endophyte presence also enhanced aerial biomass production of ryegrass
in a low recruitment year but not in a high recruitment year, suggesting that symbiotic effects on growth performance are
density dependent. Endophyte presence reduced seed removal by rodents, although differential predation may not account for
the increased success of infected grass populations. Overall, there was no statistical evidence for an endophyte-by-site interaction,
indicating that the fungal endosymbiont benefitted host establishment regardless of large differences in biotic and abiotic
environment among communities. Our results imply that hereditary endophytes may increase the chances for host grass species
to pass various ecological filters associated with invasion resistance across a broad range of successional habitats. 相似文献
9.
Annemarie MM Vlaar Angela EP Bouwmans Marinus JPG van Kroonenburgh Werner H Mess Selma C Tromp Piet GWM Wuisman Alfons GH Kessels Ania Winogrodzka Wim EJ Weber 《BMC neurology》2007,7(1):28
Background
Parkinson's disease (PD) is the second most common neurodegenerative disorder. As there is no definitive diagnostic test, its diagnosis is based on clinical criteria. Recently transcranial duplex scanning (TCD) of the substantia nigra in the brainstem has been proposed as an instrument to diagnose PD. We and others have found that TCD scanning of substantia nigra duplex is a relatively accurate diagnostic instrument in patients with parkinsonian symptoms. However, all studies on TCD so far have involved well-defined, later-stage PD patients, which will obviously lead to an overestimate of the diagnostic accuracy of TCD. 相似文献10.
BŁAŻEJ BERKOWSKI CHRISTIAN KLUG 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2012,45(1):24-33
Berkowski, B & Klug, C. 2011: Lucky rugose corals on crinoid stems: unusual examples of subepidermal epizoans from the Devonian of Morocco. Lethaia, Vol. 45, pp. 24–33. In the fossil record, evidence for true epizoans, i.e. living animals inhabiting other living host‐animals, is rather rare. A host reaction is usually needed to proof the syn vivo‐settling of the epizoan. Herein, we provide a first report of such an epizoan biocoenosis from various strata of the Early Devonian of Hamar Laghdad, the world‐renowned Moroccan mud‐mound locality. In this case, solitary rugose corals settled as larvae on crinoid stems, perhaps at a spot where the epidermis was missing for some reason (injury, disease). Both the crinoid and the coral began to grow around each other. By doing so, the affected crinoid columnals formed a swelling, where ultimately only an opening slightly larger than the coral orifice remained. We discuss both macroecological and small‐scale synecological aspects of this biocoenosis. The coral profited from its elevated home because it reached into more rapid currents providing the polyp with more food than at the densely populated seafloor, which was probably covered by a coral‐meadow around the mounds and hydrothermal vents. □Corals, crinoids, Early Devonian, epizoans, Morocco, Rugosa. 相似文献