Development of C4 photosynthesis in sorghum leaves grown under free-air CO2 enrichment (FACE).

The developmental pattern of C4 expression has been well characterized in maize and other C4 plants. However, few reports have explored the possibility that the development of this pathway may be sensitive to changes in atmospheric CO2 concentrations. Therefore, both the structural and biochemical development of leaf tissue in the fifth leaf of Sorghum bicolor plants grown at elevated CO2 have been characterized. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) activities accumulate rapidly as the leaf tissue differentiates and emerges from the surrounding whorl. Rubisco was not expressed in a cell-specific manner in the youngest tissue at the base of the leaf, but did accumulate before PEPC was detected. This suggests that the youngest leaf tissue utilizes a C3-like pathway for carbon fixation. However, this tissue was in a region of the leaf receiving very low light and so significant rates of photosynthesis were not likely. Older leaf tissue that had emerged from the surrounding whorl into full sunlight showed the normal C4 syndrome. Elevated CO2 had no effect on the cell-specific localization of Rubisco or PEPC at any stage of leaf development, and the relative ratios of Rubisco to PEPC remained constant during leaf development. However, in the oldest tissue at the tip of the leaf, the total activities of Rubisco and PEPC were decreased under elevated CO2 implying that C4 photosynthetic tissue may acclimate to growth under elevated CO2.

Use of CC traps with different trap base colors for silverleaf whiteflies (Homoptera: Aleyrodidae), thrips (Thysanoptera: Thripidae), and leafhoppers (Homoptera: Cicadellidae).

During 1996, 1997, and 1999, studies were conducted in cotton, sugar beets, alfalfa, yardlong bean, and peanut fields to compare insect catches in CC traps equipped with different trap base colors. The studies were conducted in southwestern United States, China, and India. The nine colors, white, rum, red, yellow, lime green, spring green, woodland green (dark green), true blue, and black, varied in spectral reflectance in the visible (400-700 nm) and near-infrared (700-1050 nm) portions of spectrum. Lime green, yellow, and spring green were the three most attractive trap base colors for silverleaf whitefly, Bemisia argentifolii Bellows & Perring, and leafhopper, Empoasca spp. adults. The three trap base colors were moderately high in the green, yellow, and orange spectral regions (490-600 nm), resembling the spectral reflectance curve of the abaxial (underleaf) surfaces of green cotton leaves. True blue and white were the most attractive trap base colors for western flower thrips, Frankliniella occidentalis (Pergande), adults. The true blue and white trap bases were moderately high in the blue spectral region (400-480 nm).

Acclimation response of spring wheat in a free-air CO(2) enrichment (FACE) atmosphere with variable soil nitrogen regimes. 1. Leaf position and phenology determine acclimation response.

We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO(2) concentration, and ample and limiting N supplies, within a field experiment using free-air CO(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(2) concentration (C(i)) was used to estimate the in vivo carboxylation capacity (Vc(max)) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (A (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(2) did not alter Vc(max) in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vc(max) and A (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(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(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(2) and nutrient stress.

Acclimation response of spring wheat in a free-air CO(2) enrichment (FACE) atmosphere with variable soil nitrogen regimes. 2. Net assimilation and stomatal conductance of leaves.

Atmospheric CO(2) concentration continues to rise. It is important, therefore, to determine what acclimatory c hanges will occur within the photosynthetic apparatus of wheat (Triticum aestivum L. cv. Yecora Rojo) grown in a future high-CO(2) world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO(2) concentration of ambient air [370 mumol (CO(2)) mol(-1); Control] and air enriched to approximately 200 mumol (CO(2)) mol(-1) above ambient using a Free-Air CO(2) Enrichment (FACE) apparatus (main plot). A High (35 g m(-2)) or Low (7 and 1.5 g m(-2) for 1996 and 1997, respectfully) level of N was applied to each half of the main CO(2) treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (g (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 (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(2) x 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 (s), however, significant CO(2) x 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(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(2) on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.

Acclimation response of spring wheat in a free-air CO(2) enrichment (FACE) atmosphere with variable soil nitrogen regimes. 3. Canopy architecture and gas exchange.

The response of whole-canopy net CO(2) exchange rate (CER) and canopy architecture to CO(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(2) treatment (defined as ambient and ambient +200 mumol mol(-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(-1) (1996) and 15 kg N ha(-1) (1997), whereas High-N treatments were supplemented with 350 kg N ha(-1) (1996 and 1997). Elevated CO(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(2), but by as much as 22% under CO(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 degrees for FH, 52 degrees for CH, and 58 degrees 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(2) and N-stress. Optimization of canopy architecture may serve as a mechanism to diminish CO(2) and N-stress effects on CER.

[A Doppler ultrasound device for determining blood volume flow]. / Ein Doppler-Ultraschall-Gerät zur Bestimmung des Blut-Volumenflusses.

A novel ultrasonic quantitative Doppler procedure has been developed which allows for the measurement of real-time volume flow in large blood vessels. It makes use of a 2D array transducer, which enables parallel sampling of a measuring slice placed in normal position to the sound beam. With this arrangement, volume flow can be computed without measuring the angle of incidence. Moreover, the 2D velocity distribution can be assessed within intervals of 10 to 30 ms.

Complexities of nadir-looking radiometric temperature measurements of plant canopies.

Effective radiant temperatures (ERTs) of five wheat canopies in different stages of development were measured during morning and noon periods. The observed variability in nadir sensor response was quantitatively described as a function of canopy structure and the vertical temperature profile of canopy components. In many cases, the nadir sensor ERT was a poor measure of vegetation temperature due to effects of soil emissions. Strong vertical temperature profiles of vegetation components were also observed. The theory and measurements presented document that remote measurements of vegetation canopy temperatures cannot be made indiscriminately over large spatial regions without consideration of the underlying physical principles.

Plant stress detection by remote measurement of fluorescence.

Chlorophyll fluorescence of mature lemon trees was measured with a Fraunhofer line discriminator (FLD). An increase in fluorescence was correlated with plant water stress as measured by stomatal resistance and twig water potential.

Remote detection of biological stresses in plants with infrared thermometry.

Green leaves of mature sugar beets infected with Pythium aphanidermatum and cotton infected with Phymatotrichum omnivorum had midday radiant leaf temperatures 3 degrees to 5 degrees warmer than adjacent plants with no sign of disease. The temperature difference persisted under varying conditions of soil moisture and could be used to detect biological stress imposed by these soilborne root-rotting fungi.

Plant canopy information extraction from composite scene reflectance of row crops.

As an aid in the interpretation of remotely sensed data from row crops with incomplete canopies, a model was developed that allowed the calculation of the fractions of sunlit soil, shaded soil, sunlit vegetation, and shaded vegetation for each resolution element in a scan of a remote sensor for a given set of conditions (plant cover, plant height/width ratio, row spacing, row orientation, time of day, day of year, latitude, and size of resolution element). Using measured representative reflectances of the four surfaces, composite reflectances were calculated as a function of view angle. Also, representative temperatures for each surface were used to simulate composite temperatures viewed by an IR scanner. With composite reflectances and temperatures known as a function of view angle, ways were explored to extract plant cover and plant temperature data from the composite data.