Mechanisms of macroaggregation, carbon dynamics, and carbon sequestration were investigated in degraded mine tailings. Humic substances (HSs), wheat straw, lime, and their various combinations were added to the mine tailings and then incubated at 20 °C for 24 weeks. A significant increase (up to 79%) of water‐stable macroaggregates was observed in the HS‐amended tailings after the incubation. During the macroaggregation, 20–33% sand of the mine tailings was bound by HS‐derived active carbon pool. The organic carbon concentration of the macroaggregates significantly increased in the HS‐amended mine tailings compared to the control. Mineral‐associated organic matter carbon derived from the HSs was mainly responsible for the increased concentration of macroaggregate carbon and the increased amount of macroaggregates as well. This active pool of added organic matter was sequestered in aggregates during the process of macroaggregation and thus improved the structure of the mine tailings. 相似文献
The aggregation pheromone of strawberry blossom weevil [Anthonomus rubi Herbst (Col.: Curculionidae)], a 1:4:1 blend of Grandlure I, II and racemic lavadulol, has been available for pest monitoring for several years but shows low attractancy. Attempts to control A. rubi using the pheromone alone were also unsuccessful. This paper reports the finding that addition of the major flower volatile from wild strawberry flowers [Fragaria vesca L. (Rosaceae)], 1,4-dimethoxybenzene (comprising 98% of the volatiles emitted from wild strawberry flowers), to the aggregation pheromone increased trap catches by over two fold compared to the pheromone alone. There was no significant difference between the response of overwintered or summer emerged adults. Field trials in 2007–2008 in central and southern Norway, Denmark and southern England used green funnel traps with white cross vanes for the evaluations. (-)-Germacrene D, previously shown to be emitted by plants in increased amounts in the presence of pheromone producing weevils, did not improve trap catches. Thus, the combined use of the aggregation pheromone and 1,4-dimethoxybenzene is promising for improved monitoring and possibly control of this important pest of strawberry. 相似文献
Background: Pentoxifylline (PTX) possesses a number of vasomotor, immunomodulatory, and hemorheologic properties. Based upon the hypothesis that equine laminitis and navicular disease result from microthrombosis, the inhibitory effects of PTX on inflammatory cytokines, and its inhibitory effects on human platelet aggregation, PTX has been widely used to treat equine endotoxemia, navicular disease, and laminitis. Despite this, the effects of PTX on equine platelet aggregation have not been investigated previously. Hypothesis: PTX decreases platelet aggregation in equine whole blood at concentrations approximating those achieved in horses given clinically relevant doses of PTX. Animals: Seven healthy adult horses from a research herd. Methods: Whole blood impedance aggregometry using whole equine blood incubated with varying concentrations of PTX. Adenosine diphosphate (ADP) and collagen were used to initiate aggregation. Results: The onset time of collagen‐induced equine platelet aggregation was significantly shortened by PTX. The maximum slope of resistance change (dR/dt) and total resistance change of collagen‐induced platelet aggregation were unaffected by PTX. No effects of PTX on ADP‐induced onset time of aggregation, dR/dt, or total resistance change were observed. Conclusions and Clinical Importance: Our hypothesis is not supported by the results. PTX hastens the onset of collagen‐induced platelet aggregation in equine whole blood, but has no effect on the rate of collagen‐induced aggregation. PTX does not affect ADP‐dependent equine platelet aggregation. Given these findings, PTX may not be a reasonable therapeutic option to decrease platelet aggregation in horses. 相似文献
An analysis of spatial dispersion was conducted for individual tree species in the old-growth forest at the Davis-Purdue Research Forest in Indiana. This 20.6 ha stand has been left largely undisturbed by exogenous factors since its acquisition by Purdue in 1917. It is the only long-term study plot of its size for a temperate hardwood forest with x–y coordinates (rectangular plot) for all species above 10 cm diameter. Full censuses have been conducted spanning 60 years (1926, 1976 and 1986).
Ripley’s L(t) function revealed that most species are characterized by some form of aggregation, agreeing with a prior evaluation from 1981. Heterogeneity of spatial structure was evident between two large plots, indicating that differences in site quality and history had influenced spatial structure. Shade-intolerant species were numerically dominant and spatially aggregated in 1926 but have declined over the 60-year interval and become more random in spatial dispersion. Shade-tolerant species have increased in number and become more aggregated over time, or they exhibit little change in spatial structure. Examples of the latter include Acer saccharum and Ulmus americana, species that experienced explosive population growth. These contrasting patterns are masked by stand-level patterns that show a trend toward uniformity over the same time frame.
These data reveal that changes in dispersion accompany the demographic failure experienced by numerous tree species in Central Hardwood old-growth stands, and these changes may feed back into a negative population cycle and further impede regeneration. The simultaneous manipulation of dispersion and density should be considered as a tool for influencing forest succession and promoting regeneration of desired tree species. 相似文献
We determined if the structure and function of microbial communities associated with different aggregate size classes was influenced when the aggregate formation occurred under either nitrogen (N) limitation (straw only incubation treatment) or carbon (C) limitation (straw+N incubation treatment). Using a combination of community-level physiological (BD Oxygen Biosensor assay) and molecular (terminal restriction fragment length polymorphism; T-RFLP) profiling methods, we found differences in both microbial community composition and the physiological response of these communities between different aggregate size classes. The response of fungal and bacterial communities to ‘straw only’ and ‘straw+N’ treatments differed in that bacterial community composition was affected by the treatments, whereas fungal community composition was not. The magnitude of change in the bacterial community response increased with decreasing aggregate size. However, there were no significant differences in the mean bacterial community richness (number of different terminal restriction fragments; TRFs) between different aggregate size classes for the two treatments. In general, microbial communities associated with larger aggregate size fractions (large and small macroaggregates) were found to have a significantly faster respiratory response than the communities associated with microaggregates. Application of the fungal inhibitor cycloheximide resulted in a significant reduction in the utilization of cellulose, chitin, mannose, xylan, and xylose by the microbial communities associated with all aggregate size classes, indicating that fungi are significant contributors to the utilization of these compounds. Our results demonstrate that the BD Oxygen Biosensor assay offers a valuable new tool for community level physiological profiling. When used in combination with census-based methods such as T-RFLP, a greater level of resolution can be achieved. 相似文献
Building soil structure in agroecosystems is important because it governs soil functions such as air and water movement, soil C stabilization, nutrient availability, and root system development. This study examined, under laboratory conditions, effects of organic amendments comprised of differing proportions of labile and semi-labile C on microbial community structure and macroaggregate formation in three variously textured soils where native structure was destroyed. Three amendment treatments were imposed (in order of increasing C lability): vegetable compost, dairy manure, hairy vetch (Vicia villosa Roth). Formation of water stable macroaggregates and changes in microbial community structure were evaluated over 82 days. Regardless of soil type, formation of large macroaggregates (LMA, >2000 μm diameter) was highest in soils amended with vetch, followed by manure, non-amended control, and compost. Vetch and manure had greater microbially available C and caused an increase in fungal biomarkers in all soils. Regression analysis indicated that LMA formation was most strongly related to the relative abundance of the fungal fatty acid methyl ester (FAME) 18:2ω6c (r = 0.55, p < 0.001), fungal ergosterol (r = 0.58, p < 0.001), and microbial biomass (r = 0.57, p < 0.001). Non-metric multidimensional scaling (NMS) ordination of FAME profiles revealed that vetch and manure drove shifts toward fungal-dominated soil microbial communities and greater LMA formation in these soils. This study demonstrated that, due to their greater amounts of microbially available C, vetch or manure inputs can be used to promote fungal proliferation in order to maintain or improve soil structure. 相似文献