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Habitat patchiness affects decomposition and faunal diversity: a microcosm experiment on forest floor 总被引:10,自引:0,他引:10
Environmental heterogeneity has been intensively studied, but little is known about relationships between habitat patchiness
and soil processes. The aim of this study was to investigate (1) the impact of patchiness of the litter layer on the decomposer
community and litter decomposition rate, and (2) whether the impact of soil fauna on the rates of processes differs in relation
to patchiness. An experiment was carried out in microcosms with coniferous forest humus and four kinds of litter with different
C:N ratios or stages of decomposition, either separately (i.e. in patches) or mixed with each other. Microarthropod species
diversity was better maintained in the patchy systems. In the absence of soil fauna, community respiration was higher in the
patchy microcosms, but in the presence of fauna the opposite pattern was observed. The contribution of soil fauna to the rate
of decomposition was clearly greater in the mixed litter systems. Based on the results, a hypothesis is presented that in
the patchy litter layer the soil fungi can create connections between different materials located some centimeters apart,
thus enhancing decomposition, while in the mixed litter the scale of millimeters is more appropriate for the soil fauna, known
to accelerate the process rates.
Received: 10 November 1997 / Accepted: 20 April 1998 相似文献
178.
Bacterioplankton Dynamics in the McMurdo Dry Valley Lakes, Antarctica: Production and Biomass Loss over Four Seasons 总被引:4,自引:0,他引:4
Abstract Research of the microbial ecology of McMurdo Dry Valley lakes has concentrated primarily on phototrophs; relatively little is known about the heterotrophic bacterioplankton. Bacteria represent a substantial proportion of water column biomass in these lakes, comprising 30 to 60% of total microplankton biomass. Bacterial production and cell numbers were measured 3 to 5 times, within four Antarctic seasons (October to January), in Lakes Fryxell, Hoare, and Bonney. The winter-spring transition (September to October) was included during one year. Lake Fryxell was the most productive, but variable, lake, followed by Lakes Bonney and Hoare. Bacterial production ranged from 0 to 0.009 μg C ml-1 d-1; bacterial populations ranged from 3.2 x 10(4) to 4.4 x 10(7) cells ml-1. Bacterial production was always greatest just below the ice cover at the beginning of the season. A second maximum developed just above the chemocline of all the lakes, as the season progressed. Total bacterioplankton biomass in the lakes decreased as much as 88% between successive sampling dates in the summer, as evidenced by areal integration of bacterial populations; the largest decreases in biomass typically occurred in mid-December. A forward difference model of bacterial loss in the trophogenic zone and the entire water column of these lakes showed that loss rates in the summer reached 6.3 x 10(14) cells m-2 d-1 and 4.16 x 10(12) cells m-2 d-1, respectively. These results imply that bacteria may be a source of carbon to higher trophic levels in these lakes, through grazing. 相似文献
179.
We studied the effects of forest patch size and forest edge structure on nest predation in a boreal coniferous forest landscape. The following predictions were tested. Nest predation should be higher in small than in large stands, in edges than in interior areas of forest stands, and in barren forest/clear–cut edges created by forestry than in natural forest/open marsh edges. Four types of artificial above ground nests (total of 261) were used; open cup nests with reindeer Rangifer t. tarandus hair, open cup nests with domestic hen Gallus domesticus feathers, and unlined open cup and nest–box nests. Nests were baited with one Japanese quail Coturnix coturnix japonica egg. Nest–boxes were depredated significantly less than open cup nests of all types. No edge- or stand size–related nest predation was found. The predation rate, regardless of the nest type, did not differ relative to the edge type and vegetation characteristics. However, better horizontal visibility of open cup nests due to more open vegetation structure increased predation risk in man–made edges compared to inherent edges. The results suggest that edge–related nest predation is absent or weak in forest dominated landscapes. This may be due to predator types present in the landscape and/or predators habitat use in forest dominated areas. Therefore, it might be that findings documented in other areas, such as in agricultural dominated landscapes, cannot be directly applied to managed forest landscapes. 相似文献
180.
PCR-based assays of mendelian polymorphisms from anonymous single-copy nuclear DNA: techniques and applications for population genetics 总被引:5,自引:0,他引:5
This paper outlines a PCR-based approach for population genetics that
offers several advantages over conventional Southern blotting methods for
revealing restriction-fragment-length polymorphisms (RFLPs) in nuclear DNA.
Primers are constructed from clones isolated from a nuclear DNA library,
and these primers subsequently are employed in in vitro syntheses of
homologous regions. Amplified products are then screened directly for RFLPs
by using gel-staining procedures. Population applications for this
PCR-based approach, including potential strengths and weaknesses, are
exemplified by two RFLP data sets generated to estimate (a) male-mediated
gene flow in the green turtle (Chelonia mydas) and (b) geographic
population genetic structure in the American oyster (Crassostrea
virginica). Restriction assays of amplified products from 14 or 15
independent primer pairs in each species revealed polymorphisms at several
loci that proved highly informative in the population genetic analyses. In
general, the Mendelian polymorphisms produced by this PCR-based approach
will provide useful genetic markers for population studies, particularly in
situations where simpler and less expensive allozyme methods have failed,
for whatever reason, to provide adequate information.
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