Seasonal and intraspecific variability of chlorophyll fluorescence, pigmentation and growth of Pinus ponderosa subjected to elevated CO{sub 2}

Atmospheric CO{sub 2}2 is expected to double in the next century, and these increases will have substantial impact on forest ecosystems. However, the database on the effects of elevated CO{sub 2} on forests is limited, and the extent of intraspecific variability remains unknown. We are investigating the effects of elevated CO{sub 2} on the intraspecific variability of quantum yield (as measured through chlorophyll fluorescence Fv/Fm ratio) and pigmentation, and how these are correlated to variability in growth. Four-year-old Pinus ponderosa seedlings were obtained from nine different sources across California. These seedlings were grown in standard outdoor exposure chambers for sixteen months at either ambient levels of CO{sub 2}, ambient+175ppm CO{sub 2}, or ambient+350ppm CO{sub 2}. The seedlings were periodically measured for growth, pigmentation, and chlorophyll fluorescence. The results showed a variable growth response of the nine sources during all measurement periods. Increasing CO{sub 2} resulted in a decrease in Fv/Fm among sources ranging from {minus}2.1% to {minus}23.2% in February, and 3.1% to {minus}12.5% in June. The source that had the best growth throughout the study, also had a minimal reduction in quantum yield (Fv/Fm) in the presence of elevated CO{sub 2}. For the seedlings of fastest growing sources, the correspondence between total growth and chlorophyll fluorescence was strongest during the February measurement period. Our results also showed a significant reduction in pigmentation due to increased CO{sub 2}. There are at least three explanations for the different responses during each measurement periods. First, the trees could be adapting favorably to increasing CO{sub 2}. Secondly, 1993 needles could be under less physiological stress than the current year needles. Third, there is a seasonal effect dependent upon temperature or light which is influencing the Fv/Fm ratio and pigmentation

Nonlinear Dynamic Modeling and Controls Development for Supersonic Propulsion System Research

This paper covers the propulsion system component modeling and controls development of an integrated nonlinear dynamic simulation for an inlet and engine that can be used for an overall vehicle (APSE) model. The focus here is on developing a methodology for the propulsion model integration, which allows for controls design that prevents inlet instabilities and minimizes the thrust oscillation experienced by the vehicle. Limiting thrust oscillations will be critical to avoid exciting vehicle aeroelastic modes. Model development includes both inlet normal shock position control and engine rotor speed control for a potential supersonic commercial transport. A loop shaping control design process is used that has previously been developed for the engine and verified on linear models, while a simpler approach is used for the inlet control design. Verification of the modeling approach is conducted by simulating a two-dimensional bifurcated inlet and a representative J-85 jet engine previously used in a NASA supersonics project. Preliminary results are presented for the current supersonics project concept variable cycle turbofan engine design

The effect of elevated carbon dioxide on a Sierra-Nevadan dominant species: Pinus ponderosa

The impact of increasing atmospheric C0{sub 2} has not been fully evaluated on western coniferous forest species. Two year old seedlings of Pinusponderosa were grown in environmentally controlled chambers under increased C0{sub 2} conditions for 6 months. These trees exhibit morphological, physiological, and biochemical alterations when compared to our controls. Analysis of whole plant biomass distribution has shown no significant effect to the root to shoot ratios, however needles subjected to elevated C0{sub 2} exhibited an increased overall specific needle mass and a decreased total needle area. Morphological changes at the needle level included decreased mesophyll to vascular tissue 91 ratio and variations in starch storage in chloroplasts. The elevated CO{sub 2} increased internal CO{sub 2} concentrations and assimilation of carbon. Biochemical assays revealed that ribulose-bisphosphate carboxylase specific activities increased on per unit area basis with C0{sub 2} treatment levels. Sucrose phosphate synthase (SPS) activities exhibited an increase of 55% in the 700 uL L{sup {minus}1} treatment. These results indicate that the sink-source relationships of these trees have shifted carbon allocation toward above ground growth, possibly due to transport limitations

The comet Halley dust and gas environment

Quantitative descriptions of environments near the nucleus of comet P /Halley have been developed to support spacecraft and mission design for the flyby encounters in March, 1986. To summarize these models as they exist just before the encounters, we review the relevant data from prior Halley apparitions and from recent cometary research. Orbital elements, visual magnitudes, and parameter values and analysis for the nucleus, gas and dust are combined to predict Halley's position, production rates, gas and dust distributions, and electromagnetic radiation field for the current perihelion passage. The predicted numerical results have been useful for estimating likely spacecraft effects, such as impact damage and attitude perturbation. Sample applications are cited, including design of a dust shield for spacecraft structure, and threshold and dynamic range selection for flight experiments. We expect that the comet's activity may be more irregular than these smoothly varying models predict, and that comparison with the flyby data will be instructive.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43774/1/11214_2004_Article_BF00175326.pd

Feedback control system analysis and synthesis

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