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81.
82.
Corianne Tatariw Jean D. MacRae Ivan J. Fernandez Marie-Cécile Gruselle Cayce J. Salvino Kevin S. Simon 《Ecosystems》2018,21(1):178-189
Increased N inputs through chronic atmospheric deposition has enriched temperate forest ecosystems, altering critical ecosystem functions such as decomposition and potentially resulting in a shift to P limitation. We used a combination of microbial biomass stoichiometry and enzymatic activity analyses to evaluate the potential for microbial nutrient limitation over the course of a growing season in response to multi-decadal, whole-watershed N enrichments and a one time, plot-scale P addition that occurred in the 22nd year of whole-watershed treatments. The one-time P addition increased microbial biomass threefold and reduced N-acetyl-glucosaminidase (NAG) and acid phosphatase (AP) activity 1 week after application, but there was no interaction with long-term experimental N enrichment to indicate a shift to P limitation. However, both N and P treatments increased C limitation independently of each other over the duration of the study based on measured increases in β-1,4-glucosidase (BG) activity relative to NAG and AP. Microbial biomass stoichiometry and enzyme activity indicated that BBWM is P limited regardless of N status. Our findings highlight the complex interactions between C, N, and P use and limitation in a forested ecosystem subjected to long-term N enrichment. 相似文献
83.
Fragmented and scrambled mitochondrial ribosomal RNA coding regions among green algae: a model for their origin and evolution 总被引:4,自引:1,他引:3
Mitochondrial ribosomal RNA coding regions in the only three green algal
taxa investigated to date are fundamentally different in that they are
continuous in Prototheca wickerhamii, but highly fragmented and scrambled
in Chlamydomonas reinhardtii and Chlamydomonas eugametos. To gain more
insight into the mode of evolution of fragmented and scrambled
mitochondrial ribosomal RNA (rRNA) genes within the green algal group, this
work (1) provides additional information on fragmentation patterns of
mitochondrial small- and large-subunit (SSU and LSU) rRNAs that strongly
supports the concept of a gradual increase in the extent of discontinuity
of mitochondrial rRNAs among chlorophycean green algae and (2) reports the
first example of fragmented and scrambled mitochondrial LSU rRNA coding
regions in a green algal taxon outside the Chlamydomonas group. The present
study (1) suggests that the scrambling of the mitochondrial rRNA coding
regions may have occurred early in the evolution of fragmented and
scrambled mitochondrial rRNA genes within the chlorophycean green algal
group, most likely in parallel with the fragmentation events, (2) proposes
recombination as a possible mechanism involved in the evolution of these
mitochondrial rRNA genes, and (3) presents a hypothetical pathway for
converting continuous mitochondrial rRNA genes into the highly fragmented
and scrambled rRNA coding regions of Chlamydomonas through a series of
recombinatorial events between short repeated sequences.
相似文献
84.
The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Schueten are used together and alone as biological control agents against tetranychid pest mites of apple. Their effectiveness as control agents may be impacted by intraguild predation. The effects of prey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated through a series of experiments. Adult female predators were given prey as mixed populations of phytoseiid larvae and larvae of a more preferred species, the spider mite, Tetranychus urticae Koch, at different densities and ratios. Typhlodromus pyri, more of a generalist predator, showed higher rates of predation and cannibalism on phytoseiid immatures at most prey densities and ratios. Manly preference indices indicated that T. pyri switched to feed on phytoseiid larvae at higher prey levels and ratios of T. urticae than M. occidentalis. This greater ability to use phytoseiid larvae as prey may help stabilize T. pyri populations when more preferred prey is unavailable. This may, in part, explain the observed persistence of T. pyri populations when M. occidentalis populations were decreasing in orchard test plots. 相似文献
85.
86.
Eleven of the major non-polar constituents of the dried bark of Virola elongata were isolated. A new neolignan, virolongin, two new lignans, dihydrosesartemin and β-dihydroyangambin, as well as the neolignan, eusiderin, the lignans, epi-sesartemin, epi-yangambin and yangambin, the cis and trans isomers of 3,5,4′-trimethoxystilbene and sitosterol were identified. The structures of virolongin, dihydrosesartemin and β-dihydroyangambin were determined. 相似文献
87.
The effects of two insecticides, DDT and lindane, and two herbicides, Dalapon-Na and 2, 4, 5-T, upon the growth and nitrogen-fixing
capacity ofAzotobacter vinelandii in pure culture were investigated using concentrations of the pesticides equivalent to the usual field application rates,
and fifty times these levels. The acetylene reduction technique was used to assay nitrogen fixation. No significant effects
of the pesticides at either concentration were detected upon growth or acetylene reduction.
This study was supported by a grant from the Rural Credits Development Fund of the Reserve Bank of Australia. 相似文献
88.
D. J. MacRae 《BMJ (Clinical research ed.)》1938,1(4032):849-850
89.
In primary infection tuberculosis, the infected hilar gland(s) may cause involvement of peripheral lung tissue not only by pressure but also by rupture and discharge of caseous material into a bronchus. Atelectasis or lung infection or both may result and bronchiectasis may ensue.Early bronchoscopy is required when this form of tuberculosis fails to subside promptly under treatment.Bronchography is indicated to detect residual bronchiectasis which should be removed surgically.Three of six proved cases of Group A tuberculous tracheobronchitis caused by an ulcerating hilar gland required pulmonary resection for removal of residual bronchiectasis; two of these were complicated by atelectasis. All six patients are alive and well. 相似文献
90.
X-ray diffraction patterns of alpha-fibrous proteins 总被引:2,自引:0,他引:2