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51.
Alexander Knohl Astrid R. B. Søe Werner L. Kutsch Mathias Göckede Nina Buchmann 《Plant and Soil》2008,302(1-2):189-202
Respiration has been proposed to be the main determinant of the carbon balance in European forests and is thus essential for
our understanding of the carbon cycle. However, the choice of experimental design strongly affects estimates of annual respiration
and of the contribution of soil respiration to total ecosystem respiration. In a detailed study of ecosystem and soil respiration
fluxes in an old unmanaged deciduous forest in Central Germany over 3 years (2000–2002), we combined soil chamber and eddy
covariance measurements to obtain a comprehensive picture of respiration in this forest. The closed portable chambers offered
to investigate spatial variability of soil respiration and its controls while the eddy covariance system offered continuous
measurements of ecosystem respiration. Over the year, both fluxes were mainly correlated with temperature. However, when soil
moisture sank below 23 vol.% in the upper 6 cm, water limitations also became apparent. The temporal resolution of the eddy
covariance system revealed that relatively high respiration rates occurred during budbreak due to increased metabolic activity
and after leaf fall because of increased decomposition. Spatial variability in soil respiration rates was large and correlated
with fine root biomass (r
2 = 0.56) resulting in estimates of annual efflux varying across plots from 730 to 1,258 (mean 898) g C m−2 year−1. Power function calculations showed that achieving a precision in the soil respiration estimate of 20% of the full population
mean at a confidence level of 95%, requires about eight sampling locations. Our results can be used as guidelines to improve
the representativeness of soil respiration measurements by nested sampling designs, being applied in long-term and large-scale
carbon sequestration projects such as FLUXNET and CarboEurope. 相似文献
52.
Wong CW Heng CL Wan Yee L Soh SW Kartasasmita CB Simoes EA Hibberd ML Sung WK Miller LD 《Genome biology》2007,8(5):R93
DNA microarrays used as 'genomic sensors' have great potential in clinical diagnostics. Biases inherent in random PCR-amplification, cross-hybridization effects, and inadequate microarray analysis, however, limit detection sensitivity and specificity. Here, we have studied the relationships between viral amplification efficiency, hybridization signal, and target-probe annealing specificity using a customized microarray platform. Novel features of this platform include the development of a robust algorithm that accurately predicts PCR bias during DNA amplification and can be used to improve PCR primer design, as well as a powerful statistical concept for inferring pathogen identity from probe recognition signatures. Compared to real-time PCR, the microarray platform identified pathogens with 94% accuracy (76% sensitivity and 100% specificity) in a panel of 36 patient specimens. Our findings show that microarrays can be used for the robust and accurate diagnosis of pathogens, and further substantiate the use of microarray technology in clinical diagnostics. 相似文献
53.
Locust phase polymorphism is an extreme example of behavioral plasticity; in response to changes in population density, locusts dramatically alter their behavior. These changes in behavior facilitate the appearance of various morphological and physiological phase characteristics. One of the principal behavioral changes is the more intense flight behavior and improved flight performance of gregarious locusts compared to solitary ones. Surprisingly, the neurophysiological basis of the behavioral phase characteristics has received little attention. Here we present density‐dependent differences in flight‐related sensory and central neural elements in the desert locust. Using techniques already established for gregarious locusts, we compared the response of locusts of both phases to controlled wind stimuli. Gregarious locusts demonstrated a lower threshold for wind‐induced flight initiation. Wind‐induced spiking activity in the locust tritocerebral commissure giants (TCG, a pair of identified interneurons that relay input from head hair receptors to thoracic motor centers) was found to be weaker in solitary locusts compared to gregarious ones. The solitary locusts' TCG also demonstrated much stronger spike frequency adaptation in response to wind stimuli. Although the number of forehead wind sensitive hairs was found to be larger in solitary locusts, the stimuli conveyed to their flight motor centers were weaker. The tritocerebral commissure dwarf (TCD) is an inhibitory flight‐related interneuron in the locust that responds to light stimuli. An increase in TCD spontaneous activity in dark conditions was significantly stronger in gregarious locusts than in solitary ones. Thus, phase‐dependent differences in the activity of flight‐related interneurons reflect behavioral phase characteristics. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 152–162, 2003 相似文献
54.
Background and Aims
The biological mechanisms of niche complementarity allowing for a stable coexistence of a large number of species in a plant community are still poorly understood. This study investigated how small-statured forbs use environmental niches in light and CO2 to explain their persistence in diverse temperate grasslands.Methods
Light and CO2 profiles and the corresponding leaf characteristics of seven small-statured forbs were measured in monocultures and a multi-species mixture within a biodiversity experiment (Jena Experiment) to assess their adjustment to growth conditions in the canopy.Key Results
Environmental conditions near the ground varied throughout the season with a substantial CO2 enrichment (>70 µmol mol−1 at 2 cm, >20 µmol mol−1 at 10 cm above soil surface) and a decrease in light transmittance (to <5 % deep in the canopy) with large standing biomass (>500 g d. wt m−2) in the multi-species assemblage. Leaf morphology, biochemistry and physiology of small-statured forbs adjusted to low light in the mixture compared with the monocultures. However, the net carbon assimilation balance during the period of low light only compensated the costs of maintenance respiration, while CO2 enrichment near the ground did not allow for additional carbon gain. Close correlations of leaf mass per area with changes in light availability suggested that small-statured forbs are capable of adjusting to exploit seasonal niches with better light supply for growth and to maintain the carbon metabolism for survival if light transmittance is substantially reduced in multi-species assemblages.Conclusions
This study shows that adjustment to a highly dynamic light environment is most important for spatial and seasonal niche separation of small-statured forb species in regularly mown, species-rich grasslands. The utilization of short-period CO2 enrichment developing in dense vegetation close to the ground hardly improves their carbon balance and contributes little to species segregation along environmental niche axes. 相似文献55.
56.
Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms 总被引:1,自引:0,他引:1
Niu S Luo Y Fei S Yuan W Schimel D Law BE Ammann C Arain MA Arneth A Aubinet M Barr A Beringer J Bernhofer C Black TA Buchmann N Cescatti A Chen J Davis KJ Dellwik E Desai AR Etzold S Francois L Gianelle D Gielen B Goldstein A Groenendijk M Gu L Hanan N Helfter C Hirano T Hollinger DY Jones MB Kiely G Kolb TE Kutsch WL Lafleur P Lawrence DM Li L Lindroth A Litvak M Loustau D Lund M Marek M Martin TA Matteucci G Migliavacca M Montagnani L Moors E Munger JW Noormets A Oechel W Olejnik J 《The New phytologist》2012,194(3):775-783
? It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. ? Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. ? We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. ? Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models. 相似文献
57.
58.
Erin L. Gross Clifford J. Beall Stacey R. Kutsch Noah D. Firestone Eugene J. Leys Ann L. Griffen 《PloS one》2012,7(10)
Dental caries in very young children may be severe, result in serious infection, and require general anesthesia for treatment. Dental caries results from a shift within the biofilm community specific to the tooth surface, and acidogenic species are responsible for caries. Streptococcus mutans, the most common acid producer in caries, is not always present and occurs as part of a complex microbial community. Understanding the degree to which multiple acidogenic species provide functional redundancy and resilience to caries-associated communities will be important for developing biologic interventions. In addition, microbial community interactions in health and caries pathogenesis are not well understood. The purpose of this study was to investigate bacterial community profiles associated with the onset of caries in the primary dentition. In a combination cross-sectional and longitudinal design, bacterial community profiles at progressive stages of caries and over time were examined and compared to those of health. 16S rRNA gene sequencing was used for bacterial community analysis. Streptococcus mutans was the dominant species in many, but not all, subjects with caries. Elevated levels of S. salivarius, S. sobrinus, and S. parasanguinis were also associated with caries, especially in subjects with no or low levels of S. mutans, suggesting these species are alternative pathogens, and that multiple species may need to be targeted for interventions. Veillonella, which metabolizes lactate, was associated with caries and was highly correlated with total acid producing species. Among children without previous history of caries, Veillonella, but not S. mutans or other acid-producing species, predicted future caries. Bacterial community diversity was reduced in caries as compared to health, as many species appeared to occur at lower levels or be lost as caries advanced, including the Streptococcus mitis group, Neisseria, and Streptococcus sanguinis. This may have implications for bacterial community resilience and the restoration of oral health. 相似文献
59.
60.
Maria J Overbeek Herman Groepenhoff Alexandre E Voskuyl Egbert F Smit Jochem WL Peeters Anton Vonk-Noordegraaf Marieke D Spreeuwenberg Ben C Dijkmans Anco Boonstra 《Respiratory research》2008,9(1):1-8