In order to study the effects of temperature enhancement on alpine calcareous grassland species, a warming experiment was carried out in the Berchtesgaden National Park (Southeast Germany, Northern Calcareous Alps) between 2002 and 2004. The study was conducted in stands of the Carex sempervirens and the Carex firma communities; the two most widespread grassland types in the alpine zone of the Northern Calcareous Alps. The temperature of the vegetation stand and the upper soil was passively enhanced using open top chambers (OTCs). The construction of the OTCs was appropriate since temperature was clearly increased while water conditions (humidity, soil water content) were not changed.
By comparing manipulated (temperature enhancement) with non-manipulated plots, the effects of warming on growth and reproduction of selected key species were studied. To test if vegetation response to temperature enhancement is at least partly due to increases in nutrient availability, soil solution concentrations of nitrate and ammonium were analysed.
We found that most of the studied plant species are sensitive to temperature enhancement. Growth and/or reproduction of 12 of the 14 studied species were significantly stimulated by warming. Only two species showed no response; none of the species experienced decreases in growth or reproduction. Dwarf shrubs and graminoids showed a stronger response than herbaceous perennials. A significant effect of warming on nutrient availability could not be detected. The observed response of vegetation is therefore mainly caused by direct and not by indirect temperature effects. 相似文献
Biological invasions are an increasing global challenge, for which single-species studies and analyses focused on testing
single hypotheses of causation in isolation are unlikely to provide much additional insight. Species interact with other species
to create communities, which derive from species interactions and from the interactions of species with the scale specific
elements of the landscape that provide suitable habitat and exploitable resources. I used logistic regression analysis to
sort among potential intrinsic, community and landscape variables that theoretically influence introduction success. I utilized
the avian fauna of the Everglades of South Florida, and the variables body mass, distance to nearest neighbor (in terms of
body mass), year of introduction, presence of congeners, guild membership, continent of origin, distribution in a body mass
aggregation or gap, and distance to body-mass aggregation edge (in terms of body mass). Two variables were significant predictors
of introduction success. Introduced avian species whose body mass placed them nearer to a body-mass aggregation edge and further
from their neighbor were more likely to become successfully established. This suggests that community interactions, and community
level phenomena, may be better understood by explicitly incorporating scale. 相似文献
Colonization of mycorrhizal fungi was studied in a Pinus muricata forest on the coast in California, USA, burned by a stand-replacing wildfire in October 1995. Naturally established field seedlings of P. muricata were harvested 1 yr after the fire. The species composition of the mycorrhizal fungi on these field seedlings was dominated by Rhizopogon species, Wilcoxina mikolae and Tomentella sublilacina . Bioassays, set up with soil collected immediately after the fire, were used to determine which mycorrhizal species had colonized the burned area from resistant propagules. The P. muricata seedlings in these bioassays were dominated by suilloid and ascomycetous fungi, the same fungi which dominated the mycorrhizal flora of seedlings in pre-fire bioassays derived from the same forest site, suggesting that resistant propagules were the primary inoculum source for naturally establishing seedlings. Drying of post-fire soil for 1 month raised the number of bioassay seedlings associated with Rhizopogon olivaceotinctus , while the number of bioassay seedlings associated with Rhizopogon ochraceorubens was reduced. Fire appeared to have either stimulated or provided a competitive advantage to R. olivaceotinctus , which increased in abundance on the post-fire bioassay and field seedlings. Soil collected from the burned area was diluted with sterile soil in three different concentrations, and the number and frequency of mycorrhizal taxa on bioassay seedlings decreased with increased dilution. Although precise quantification was not possible, propagules of the Rhizopogon species were much more abundant than those of Tomentella or Wilcoxina species. Differences between the mycorrhizal associates of bioassay seedlings, naturally regenerated seedlings, and different inoculum sources are discussed. 相似文献
Detecting marine invasions can be challenging, especially for lesser-known taxa, and requires (a) thorough field surveys of the region of interest for members of the taxon, (b) systematic analyses to identify all species found, (c) literature searches for the worldwide distribution of these species and for previous records of the taxon in this region, and (d) application of rigorous criteria to assess whether each species found is native or introduced. We carried out these steps in order to detect and document kamptozoan (entoproct) invasions on the American mid-Atlantic coast. We report on the occurrence of two colonial kamptozoans (Barentsia benedeni, Loxosomatoides laevis) in Chesapeake Bay (Maryland and Virginia, USA). On the American Atlantic coast, B. benedeni had previously only been reported from Massachusetts, although this species has a worldwide distribution in bays and harbors. The genus Loxosomatoides had not previously been reported from North America and L. laevis was known only from India. Since the genus Loxosomatoides was very poorly characterized, we briefly review all four of its species, which differ only slightly from each other. We have also synonymized L. japonicum with L. laevis. We did not find any of the kamptozoan species previously recorded in surveys of Chesapeake Bay and the American Atlantic coast. This is the first detailed consideration of anthropogenic influences on kamptozoan distributions, and we emphasize that most kamptozoan species are cryptogenic pending further investigation. 相似文献
Power densities produced by microbial fuel cells (MFCs) in natural systems are changed by exposure to light through the enrichment of photosynthetic microorganisms. When MFCs with brush anodes were exposed to light (4000 lx), power densities increased by 8–10% for glucose-fed reactors, and 34% for acetate-fed reactors. Denaturing gradient gel electrophoresis (DGGE) profiles based on the 16S rRNA gene showed that exposure to high light levels changed the microbial communities on the anodes. Based on 16S rRNA gene clone libraries of light-exposed systems the anode communities using glucose were also significantly different than those fed acetate. Dominant bacteria that are known exoelectrogens were identified in the anode biofilm, including a purple nonsulfur (PNS) photosynthetic bacterium, Rhodopseudomonas palustris, and a dissimilatory iron-reducing bacterium, Geobacter sulfurreducens. Pure culture tests confirmed that PNS photosynthetic bacteria increased power production when exposed to high light intensities (4000 lx). These results demonstrate that power production and community composition are affected by light conditions as well as electron donors in single-chamber air-cathode MFCs. 相似文献
Ocean acidification may have far‐reaching consequences for marine community and ecosystem dynamics, but its full impacts remain poorly understood due to the difficulty of manipulating pCO2 at the ecosystem level to mimic realistic fluctuations that occur on a number of different timescales. It is especially unclear how quickly communities at various stages of development respond to intermediate‐scale pCO2 change and, if high pCO2 is relieved mid‐succession, whether past acidification effects persist, are reversed by alleviation of pCO2 stress, or are worsened by departures from prior high pCO2 conditions to which organisms had acclimatized. Here, we used reciprocal transplant experiments along a shallow water volcanic pCO2 gradient to assess the importance of the timing and duration of high pCO2 exposure (i.e., discrete events at different stages of successional development vs. continuous exposure) on patterns of colonization and succession in a benthic fouling community. We show that succession at the acidified site was initially delayed (less community change by 8 weeks) but then caught up over the next 4 weeks. These changes in succession led to homogenization of communities maintained in or transplanted to acidified conditions, and altered community structure in ways that reflected both short‐ and longer‐term acidification history. These community shifts are likely a result of interspecific variability in response to increased pCO2 and changes in species interactions. High pCO2 altered biofilm development, allowing serpulids to do best at the acidified site by the end of the experiment, although early (pretransplant) negative effects of pCO2 on recruitment of these worms were still detectable. The ascidians Diplosoma sp. and Botryllus sp. settled later and were more tolerant to acidification. Overall, transient and persistent acidification‐driven changes in the biofouling community, via both past and more recent exposure, could have important implications for ecosystem function and food web dynamics. 相似文献