Atmospheric CO^sub 2^ concentration continues to rise. It is important, therefore, to determine what acclimatory changes will occur within the photosynthetic apparatus of wheat (Triticum aestivum L. ...cv. Yecora Rojo) grown in a future high-CO^sub 2^ world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO^sub 2^ concentration of ambient air 370 μmol (CO^sub 2^) mol^sup -1^; Control and air enriched to 200 μmol (CO^sub 2^) mol^sup -1^ above ambient using a Free-Air CO^sub 2^ Enrichment (FACE) apparatus (main plot). A High (35 g m^sup -2^) or Low (7 and 1.5 g m^sup -2^ for 1996 and 1997, respectfully) level of N was applied to each half of the main CO^sub 2^ treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (g ^sub s^) by 30% at mid-morning (2 h prior to solar noon), 36% at midday (solar noon) and 27% at mid-afternoon (2.5 h after solar noon), whereas under Low-N, g ^sub s^ was reduced by as much as 31% at mid-morning, 44% at midday and 28% at mid-afternoon compared with Control. But, no significant CO^sub 2^×N interaction effects occurred. Across seasons and growth stages, daily accumulation of carbon (A') was 27% greater in FACE than Control. High-N increased A' by 18% compared with Low-N. In contrast to results for g ^sub s^, however, significant CO^sub 2^×N interaction effects occurred because FACE increased A' by 30% at High-N, but by only 23% at Low-N. FACE enhanced the seasonal accumulation of carbon (A'') by 29% during 1996 (moderate N-stress), but by only 21% during 1997 (severe N-stress). These results support the premise that in a future high-CO^sub 2^ world an acclimatory (down-regulation) response in the photosynthetic apparatus of field-grown wheat is anticipated. They also demonstrate, however, that the stimulatory effect of a rise in atmospheric CO^sub 2^ on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.PUBLICATION ABSTRACT
The response of whole-canopy net CO^sub 2^ exchange rate (CER) and canopy architecture to CO^sub 2^ enrichment and N stress during 1996 and 1997 for open-field-grown wheat ecosystem (Triticum ...aestivum L. cv. Yecora Rojo) are described. Every Control (C) and FACE (F) CO^sub 2^ treatment (defined as ambient and ambient +200 μmol mol^sup -1^, respectively) contained a Low- and High-N treatment. Low-N treatments constituted initial soil content amended with supplemental nitrogen applied at a rate of 70 kg N ha^sup -1^ (1996) and 15 kg N ha^sup -1^ (1997), whereas High-N treatments were supplemented with 350 kg N ha^sup -1^ (1996 and 1997). Elevated CO^sub 2^ enhanced season-long carbon accumulation by 8% and 16% under Low-N and High-N, respectively. N-stress reduced season-long carbon accumulation 14% under ambient CO^sub 2^, but by as much as 22% under CO^sub 2^ enrichment. Averaging both years, green plant area index (GPAI) peaked approximately 76 days after planting at 7.13 for FH, 6.00 for CH, 3.89 for FL, and 3.89 for CL treatments. Leaf tip angle distribution (LTA) indicated that Low-N canopies were more erectophile than those of High-N canopies: 48° for FH, 52° for CH, and 58° for both FL and CL treatments. Temporal trends in canopy greenness indicated a decrease in leaf chlorophyll content from the flag to flag-2 leaves of 25% for FH, 28% for CH, 17% for CL, and 33% for FL during 1997. These results indicate that significant modifications of canopy architecture occurs in response to both CO^sub 2^ and N-stress. Optimization of canopy architecture may serve as a mechanism to diminish CO^sub 2^ and N-stress effects on CER.PUBLICATION ABSTRACT
We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO^sub 2^ concentration, and ample and limiting N supplies, within a field experiment using free-air CO^sub 2^ ...enrichment (FACE). To understand how leaf age and developmental stage affected any acclimation response, measurements were made on a vertical profile of leaves every week from tillering until maturity. The response of assimilation (A) to internal CO^sub 2^ concentration (C^sub i^) was used to estimate the in vivo carboxylation capacity (Vc^sub max^) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (A ^sub sat^). The total activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and leaf content of Rubisco and the Light Harvesting Chlorophyll a/b protein associated with Photosystem II (LHC II), were determined. Elevated CO^sub 2^ did not alter Vc^sub max^ in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vc^sub max^ and A ^sub sat^ was observed, and was found to correlate with reduced Rubisco activity and content. The dependency of acclimation on N supply was different at each developmental stage. With adequate N supply, acclimation to elevated CO^sub 2^ was also accompanied by an increased LHC II/Rubisco ratio. At low N supply, contents of Rubisco and LHC II were reduced in all leaves, although an increased LHC II/Rubisco ratio under elevated CO^sub 2^ was still observed. These results underscore the importance of leaf position, leaf age and crop developmental stage in understanding the acclimation of photosynthesis to elevated CO^sub 2^ and nutrient stress.PUBLICATION ABSTRACT
The rationale for this study is found in the probable higher temperatures and changes in rainfall patterns that are expected in the future as a result of increasing levels of CO₂ in the atmosphere. ...In particular, higher air temperatures may cause an increase in evapotranspiration demand while a reduction in rainfall could increase the severity and duration of drought in arid and semi-arid regions. Representation of the water transfer scheme includes water uptake by roots and the interaction between evapotranspiration and CO₂ enrichment. The predicted response of a spring wheat (Triticum aestivum L. cv. Yecora rojo) canopy in terms of energy exchange processes to elevated atmospheric CO₂ level was tested against measurements collected at the FACE (Free Air Enrichment Experiment) site in 1994. Simulated and measured canopy conductances were reduced by about 30% under elevated CO₂ under optimum conditions of water supply. Reductions in latent heat fluxes under elevated instead of ambient CO₂ caused reductions in both simulated and measured seasonal water use of 6% under optimum and 2% under suboptimum irrigation. The soil–plant–atmosphere water transfer scheme proposed here offers several advances in the simulation of land surface interactions. First, the stomatal resistance model minimizes assumptions in existing land surface schemes about the effects of interactions among environmental conditions (radiation, temperature, CO₂) upon stomatal behavior. These interactions are resolved in the calculation of CO₂ in which processes are already well understood.
To test the predictions that plants will have a larger flavonoid concentration in a future world with a CO2‐enriched atmosphere, wheat (Triticum aestivum L. cv. Yecora Rojo) was grown in a field ...experiment using FACE (free‐air CO2 enrichment) technology under two levels of atmospheric CO2 concentration: ambient (370 μmol mol−1) and enriched (550 μmol mol−1), and under two levels of irrigation: well‐watered (100% replacement of potential evapotranspiration) and half‐watered. We also studied the effects of CO2 on the concentration of total non‐structural carbohydrates (TNC) and nitrogen (N), two parameters hypothesized to be linked to flavonoid metabolism. Throughout the growth cycle the concentration of isoorientin, the most abundant flavonoid, decreased by 62% (from an average of 12.5 mg g−1 on day of year (DOY) 41 to an average of 4.8 mg g−1 on DOY 123), whereas the concentration of tricin, another characteristic flavone, increased by two orders of magnitude (from an average of 0.007 mg g−1 of isoorientin equivalents on DOY 41 to an average of 0.6 mg g−1 of isoorientin equivalents on DOY 123). Although flavonoid concentration was dependent on growth stage, the effects of treatments on phenology did not invalidate the comparisons between treatments. CO2‐enriched plants had higher flavonoid concentrations (14% more isoorientin, an average of 7.0 mg g−1 for ambient CO2 vs an average of 8.0 mg g−1 for enriched CO2), higher TNC concentrations and lower N concentrations in ukpper canopy leaves throughout the growth cycle. Well‐irrigated plants had higher flavonoid concentrations (11% more isoorientin, an average of 7.1 mg g−1 for half watered vs an average of 7.9 mg g−1 for well‐watered) throughout the growth cycle, whereas the effect of irrigation treatments on TNC and N was more variable. These results are in accordance with the hypotheses that higher carbon availability promoted by CO2‐enrichment provides carbon that can be invested in carbon‐based secondary compounds such as flavonoids. The rise in atmospheric CO2 may thus indirectly affect wheat‐pest relations, alter the pathogen predisposition and improve the UV‐B protection by changing flavonoid concentrations.
Dynamic crop-growth models are used to project the effects of rising atmospheric CO(2) concentration and associated climate change on crop yields. Such model predictions are largely untested in the ...field, for lack of experimental data. We tested the CERES -Wheat model, modified to include leaf-level photosynthesis response to elevated CO(2), using field data from 2 yr of Free-Air Carbon Dioxide Enrichment (FACE) experiments with spring wheat (Triticum aestivum L. cv. Yecora Rojo) in Maricopa, AZ. Two irrigation treatments (well-watered, WW; water-deficit stressed, WS) and two atmospheric CO(2) concentrations (ambient, 350 micromole mol(-1); elevated, 550 micromole mol(-1) were simulated. The model was evaluated using measurements of crop phenology, aboveground dry matter (DM) production, grain yield, and evapotranspiration (ET). Model calculations of crop phenology were within 2 to 3 d of observed values under WW, ambient CO(2) conditions in both years. The model did not simulate the accelerated crop phenology (5-8 d at physiological maturity) observed in the WW and elevated CO(2) treatments, indicating the need to include effects of increased stomatal resistance on canopy temperature. Simulations of DM and grain yield were within 10% of measured values, except for a tendency to overcalculate DM response to CO(2) by 10 to 15% in Year 1 for WS treatments. The model undercalculated cumulative ET under WW conditions by 15%; model sensitivity analyses suggest that simulation of potential evapotranspiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO2-water interactions. Simulated reductions in water loss due to elevated CO2 were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO2 under WS than under WW conditions. In Year 1, simulated crop response to CO2 was 2% larger (measured: 3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: 9%). The ability to simulate CO2-water interactions, though it needs to be further evaluated with additional experimental datasets, is an important attribute of models used to project crop yields under elevated CO2 and climate change.
The impressive maneuverability demonstrated by birds has so far eluded comparably sized uncrewed aerial vehicles (UAVs). Modern studies have shown that birds’ ability to change the shape of their ...wings and tail in flight, known as morphing, allows birds to actively control their longitudinal and lateral flight characteristics. These advances in our understanding of avian flight paired with advances in UAV manufacturing capabilities and applications has, in part, led to a growing field of researchers studying and developing avian-inspired morphing aircraft. Because avian-inspired morphing bridges at least two distinct fields (biology and engineering), it becomes challenging to compare and contrast the current state of knowledge. Here, we have compiled and reviewed the literature on flight control and stability of avian-inspired morphing UAVs and birds to incorporate both an engineering and a biological perspective. We focused our survey on the longitudinal and lateral control provided by wing morphing (sweep, dihedral, twist, and camber) and tail morphing (incidence, spread, and rotation). In this work, we discussed each degree of freedom individually while highlighting some potential implications of coupled morphing designs. Our survey revealed that wing morphing can be used to tailor lift distributions through morphing mechanisms such as sweep, twist, and camber, and produce lateral control through asymmetric morphing mechanisms. Tail morphing contributes to pitching moment generation through tail spread and incidence, with tail rotation allowing for lateral moment control. The coupled effects of wing–tail morphing represent an emerging area of study that shows promise in maximizing the control of its morphing components. By contrasting the existing studies, we identified multiple novel avian flight control methodologies that engineering studies could validate and incorporate to enhance maneuverability. In addition, we discussed specific situations where avian-inspired UAVs can provide new insights to researchers studying bird flight. Collectively, our results serve a dual purpose: to provide testable hypotheses of flight control mechanisms that birds may use in flight as well as to support the design of highly maneuverable and multi-functional UAV designs.
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