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The relationship between herbivores, plants and nutrient dynamics, has been investigated in many systems; however, how these relationships are influenced by changing climate has had much less attention. In the northeastern USA, both moose populations and winter climate have been changing. Moose, once extirpated from the region, have made a comeback; while locally, snow depth and duration of snow cover have declined. There is considerable uncertainty in how these changes will interact to influence forested systems. We used small experimental plots and transects along with snow removal (to elicit soil freezing and expose potential forage plants), mechanical browsing, and fecal additions (labeled with 15N) to examine ecosystem responses. We found that snow removal changed moose browsing behavior, with balsam fir more heavily browsed than sugar maple or Viburnum under low snow conditions. Soil freezing alone did not significantly alter N dynamics or selected plant responses, but there were significant interactions with moose activity. The combined effects of moose fecal additions, mechanical browsing, and soil freezing resulted in higher levels of NO3 ? leaching under fir and maple, whereas Viburnum had essentially no response to these multiple factors. Our results suggest that declines in snow depth can initiate a cascade of ecosystem responses, beginning with exposure of plants to increased browsing that then triggers a series of responses that can lead to higher N losses, precipitated by decreased N demand in plants compromised by soil freezing damage. Balsam fir may be particularly susceptible to this cascade of multiple stresses. 相似文献
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Rotating algal biofilm reactor and spool harvester for wastewater treatment with biofuels by-products 总被引:1,自引:0,他引:1
Maximizing algae production in a wastewater treatment process can aid in the reduction of soluble nitrogen and phosphorus concentrations in the wastewater. If harvested, the algae-based biomass offers the added benefit as feedstock for the production of biofuels and bioproducts. However, difficulties in harvesting, concentrating, and dewatering the algae-based biomass have limited the development of an economically feasible treatment and production process. When algae-based biomass is grown as a surface attached biofilm as opposed to a suspended culture, the biomass is naturally concentrated and more easily harvested. This can lead to less expensive removal of the biomass from wastewater, and less expensive downstream processing in the production of biofuels and bioproducts. In this study, a novel rotating algal biofilm reactor (RABR) was designed, built, and tested at bench (8 L), medium (535 L), and pilot (8,000 L) scales. The RABR was designed to operate in the photoautotrophic conditions of open tertiary wastewater treatment, producing mixed culture biofilms made up of algae and bacteria. Growth substrata were evaluated for attachment and biofilm formation, and an effective substratum was discovered. The RABR achieved effective nutrient reduction, with average removal rates of 2.1 and 14.1 g m(-2) day(-1) for total dissolved phosphorus and total dissolved nitrogen, respectively. Biomass production ranged from 5.5 g m(-2) day(-1) at bench scale to as high as 31 g m(-2) day(-1) at pilot scale. An efficient spool harvesting technique was also developed at bench and medium scales to obtain a concentrated product (12-16% solids) suitable for further processing in the production of biofuels and bioproducts. 相似文献
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Succinate:quinone oxidoreductase (SQR) from Bacillus subtilis consists of two hydrophilic protein subunits comprising succinate dehydrogenase, and a di-heme membrane anchor protein harboring two putative quinone binding sites, Qp and Qd. In this work we have used spectroelectrochemistry to study the electronic communication between purified SQR and a surface modified gold capillary electrode. In the presence of two soluble quinone mediators the midpoint potentials of both hemes were revealed essentially as previously determined by conventional redox titration (heme bH, Em = + 65 mV, heme bL, Em = − 95 mV). In the absence of mediators the enzyme still communicated with the electrode, albeit with a reproducible hysteresis, resulting in the reduction of both hemes occurring approximately at the midpoint potential of heme bL, and with a pronounced delay of reoxidation. When the specific inhibitor 2-n-heptyl-4 hydroxyquinoline N-oxide (HQNO), which binds to Qd in B. subtilis SQR, was added together with the two quinone mediators, rapid reductive titration was still possible which can be envisioned as an electron transfer occurring via the HQNO insensitive Qp site. In contrast, the subsequent oxidative titration was severely hampered in the presence of HQNO, in fact it completely resembled the unmediated reaction. If mediators communicate with Qp or Qd, either event is followed by very rapid electron redistribution within the enzyme. Taken together, this strongly suggests that the accessibility of Qp depended on the redox state of the hemes. When both hemes were reduced, and Qd was blocked by HQNO, quinone-mediated communication via the Qp site was no longer possible, revealing a redox-dependent conformational change in the membrane anchor domain. 相似文献
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Synthetic glucocorticoids and progesterone were evaluated for their inhibitory action on estrus in ovariectomized pigs treated with estrogen. Triamcinolone acetonide (˜70 μg/kg BW), and dexamethasone (˜140 μg/kg BW) inhibited the estrous response to estradiol benzoate when these glucocorticoids were given during a period of 5 days before to 4 days after estradiol benzoate. The minimum effective dosage of progesterone that would inhibit estrus when given concurrently with estradiol benzoate was 600 (μg/kg BW. When triamcinolone acetonide (30 μg/kg BW) or dexamethasone (125 or 150 μg/kg BW) was given as a single injection in combination with progesterone (100 μg/kg BW), estrous response to estradiol benzoate was again inhibited. These steroids at these dosages had no significant effect when either was administered alone. Based on these results, the inhibitory action of these glucocorticoids on estrus in pigs is additive to the action of progesterone, and we suggest that triamcinolone acetonide and dexamethasone inhibit estrus through mechanisms related to those of progesterone. 相似文献
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Prolonged Salmonella Contamination of a Recreational Lake by Runoff Waters 总被引:5,自引:3,他引:2 下载免费PDF全文
David G. Claudon Donald I. Thompson Eleanor H. Christenson Gerald W. Lawton Elliot C. Dick 《Applied microbiology》1971,21(5):875-877
In the summer and fall of 1968, various Salmonella serotypes were isolated from a portion of Lake Mendota, the major recreational lake for Madison Wis. The apparent sources of these organisms were a residential storm sewer and a University of Wisconsin Experimental Farms' washwater drain. Salmonellae were isolated with regularity from a swimming beach located approximately 0.5 mile (0.8 km) from these sources. 相似文献