This study aimed to understand the mechanisms of the variations in carbon (C) and nitrogen (N) pools and examine the possibility of differentiating the burning effects from seasonal and pre-existed N limitations in a native suburban forest ecosystem influenced by prescribed burning in subtropical Australia.
Materials and methods
Soil and litterfall samples were collected from two study sites from 1 to 23 months since last burnt. Soil labile C and N pools, soil C and N isotopic compositions (δ13C and δ15N), litterfall mass production (LM), and litterfall total C, total N, δ13C and δ15N were analysed. In-situ gas exchange measurements were also conducted during dry and wet seasons for Eucalyptus baileyana and E. planchoniana.
Results and discussion
The results indicated that labile C and N pools increased within the first few months after burning, with no correlations with climatic factors. Therefore, it was possible that the increase was due to the burning-induced factors such as the incorporation of ashes into the soil. The highest values of soil and litterfall δ15N, observed when the study was commenced at the experimental sites, and their high correlations with climatic factors were indicative of long-term N and water limitation. The 13C signals showed that soil N concentrations and climatic factors were also two of the main factors controlling litterfall and foliage properties mainly through the changes in photosynthetic capacity and stomatal conductance.
Conclusions
Long-term soil N availabilities and climatic factors were the two of the main driving factors of C and N cycling in the studied forest sites. Further studies are needed to compare soil and litterfall properties before and after burning to profoundly understand the effects of prescribed burning on soil labile C and N variations.
Evidence mounts for the influence of climate variability on temporal trends in the phenology of many organisms including various species of fish. Accordingly, we examined variation in adult Atlantic salmon Salmo salar run timing in thirteen Newfoundland and Labrador rivers where returns were monitored at fishways or fish‐counting fences. Run timing varied significantly among rivers with the median date of return differing by up to 5 weeks. Duration of runs was generally short with most adults returning over a period of three to 5 weeks. A mixed model analysis incorporating a first‐order autoregressive error structure was used to generalise changes in run timing among all monitored rivers. Results indicated that the median date of return has advanced by almost 12 days over a 35‐year interval from 1978 to 2012, while several individual rivers have advanced by almost 21 days. The influence of climate on median timing was evident when the simultaneous effects of both climate and salmon abundance were controlled. We found earlier runs associated with overall warmer climate conditions on the Newfoundland and Labrador Shelf. Results contrast with those from the north‐east Atlantic where Atlantic salmon are returning later in some rivers coincident with warming climate conditions. 相似文献
To identify the tick-borne pathogens in dogs from Grenada, we conducted a serologic survey for Ehrlichia canis in 2004 (104 dogs) and a comprehensive serologic and molecular survey for a variety of tick-borne pathogens in 2006 (73 dogs). In 2004 and 2006, 44 and 32 dogs (42.3% and 43.8%) were seropositive for E. canis, respectively. In 2006, several tick-borne pathogens were identified by serology and PCR. DNA of E. canis, Anaplasma platys, Babesia canis vogeli, Hepatozoon canis, and Bartonella sp. were identified in 18 (24.7%), 14 (19.2%), 5 (7%), 5 (7%), and 1 (1.4%) dogs, respectively. Six (8.2%) dogs were seropositive for Bartonella vinsonii subsp. berkhoffii. All dogs were seronegative and PCR-negative for Rickettsia spp. Coinfection with two or three pathogens was observed in eight dogs. Partial 16S rRNA E. canis and A. platys sequences were identical to sequences in GenBank. Partial 18S rRNA gene sequences from the Grenadian H. canis were identical to each other and had one possible mismatch (ambiguous base) from H. canis detected from Spain and Brazil. Grenadian B. c. vogeli sequences were identical to B. c. vogeli from Brazil and Japan. All of the detected pathogens are transmitted, or suspected to be transmitted, by Rhipicephalus sanguineus. Results of this study indicate that dogs from Grenada are infected with multiple tick-borne pathogens; therefore, tick-borne diseases should be included as differentials for dogs exhibiting thrombocytopenia, leukopenia, fever, or lethargy. One pathogen, E. canis, is also of potential public health significance. 相似文献
Surveillance and monitoring are important for measuring the level of disease in a population, documenting changes in prevalence over time, determining high-risk areas for implementation of control measures, eradicating disease, and documenting freedom from disease. The documentation of freedom from disease has importance for international trade and the resumption of production after an outbreak. Johne's disease (JD) is an example of an endemic disease of cattle that has variable prevalence related to environmental and animal-level factors. Three methods of sample collection were used to describe the prevalence and distribution of JD seropositivity in Texas. Sampled cattle were: (1) extensively managed herds, (2) market cattle, and (3) clinically ill cattle examined by practicing veterinarians throughout Texas. Samples were evaluated for JD using a commercially available serum ELISA. Proportion of seropositive samples was compared and spatial distributions were evaluated for clustering. Difference of JD seropositivity was observed among the three sample populations suggesting that estimation of disease prevalence is dependant upon the source of samples. 相似文献
Accumulation and metabolism of the organophosphate pesticide, phorate by the free-living nematode Panagrellus redivivus was studied under anaerobic conditions and in the presence of carbon monoxide or SKF 525A, and compared with results obtained under normal, aerobic conditions and using heat-killed nematodes. Both phorate hydrolysis and side-chain oxidation were inhibited under anaerobic conditions and with heat-killed nematodes, but only hydrolysis was affected in the presence of carbon monoxide. The much greater phorate accumulation in the nematodes under anaerobic conditions and with carbon monoxide could be explained by this metabolic inhibition. SKF 525A had no significant effect on phorate metabolism or accumulation. The possible mechanisms involved in phorate breakdown by P. redivivus are discussed. 相似文献
A retrospective/prospective radiographic study documented 55 cases of moderate to severe hip dysplasia, with varying degrees of shallowing of the acetabulum, flattening or loss of the femoral head, widening or loss of the femoral neck, and femoral diaphyseal abnormalities in northern koalas (Phascolarctos cinereus) in the San Diego Zoo (San Diego, California, USA) collection. For the retrospective study, historic radiographs were examined when availble. For the prospective study, three standard views (ventrodorsal extended leg, ventrodorsal frog leg, and lateral extended leg) were used. A scoring system was developed using four areas (acetabulum, femoral head, femoral neck, and femur) and ranges of 0 to 5 (0 = not affected to 5 = severely affected) for each area, creating a total score out of 40. Scores were graded as follows: 0-2 = normal dysplasia; 3-6 = mild dysplasia; 10-19 = moderate dysplasia; and 20-40 = severe dysplasia. Thirty koalas were graded as severe, 25 koalas as moderate, and 38 koalas as excellent or mild. Affected koalas may or may not demonstrate gait abnormalities. Mild to severe degenerative joint disease may develop and symptoms may be alleviated with glucosamine/chondroitin sulfate and nonsteroidal anti-inflammatory drugs. The etiology of hip dysplasia in koalas is not currently understood. 相似文献