Showing papers by "Bruce A. Kimball published in 2000"
TL;DR: In this paper, the predictions of three daily time step wheat simulation models (AFRCWHEAT2, FASSET and Sirius) were tested against data from wheat (Triticum aestivum L.) experiments in AZ in which the amount of applied N and the atmospheric CO2 concentration were both varied.
117 citations
TL;DR: In this paper, a 4-year research program was undertaken with wheat (Triticum aestivum L.) as a model system for forage grasses, to document the potential changes in leaf N concentration in response to global environment changes.
116 citations
TL;DR: In this article, the authors evaluated the performance of two spring wheat crops, grown in a well-watered, subsurface drip-irrigated field under ambient (about 370 mmol mol 1 during daytime) and enriched (200mmol mol 1 above ambient) CO2 concentrations during 1995-1996 and 1996-1997 in Free-Air CO2 Enrichment (FACE) experiments in central Arizona.
104 citations
TL;DR: Free-air carbon dioxide enrichment (FACE) provides a realistic, cost-effective method for evaluating the effects of supra-ambient CO 2 concentrations on growth, development, yield, and water use of agricultural crops and natural ecosystems with very few of the problems normally associated with glasshouse or chamber type research as discussed by the authors.
87 citations
TL;DR: It is submitted that odor alone, in the absence of toxicosis or nociception, is not a deterrent to herbivores that continually sample foods and adjust intake based on the postingestive effects of toxins and nutrients.
Abstract: In the traditional sense, food ingestion consists of prehending, masticating, swallowing, and digesting plant matter. It is also possible to ingest plants without eating them. Volatile compounds are inhaled directly into the lungs and transported from the lungs into the bloodstream. Volatiles in high concentrations could presumably produce toxicosis, without an herbivore ever ingesting a plant in the customary sense. Volatile compounds may be aposematic, serving to warn potential predators of toxins in plants. We conducted three experiments to explore the roles of odor, taste, and toxicity in the food preferences of lambs. The first experiment determined if brief exposure to a novel odor followed by lithium chloride (LiCl)-induced toxicosis caused lambs to avoid a familiar food that contained the odor. Lambs that sniffed coconut-flavored barley and then received LiCl subsequently ate less coconut-flavored barley than lambs that did not receive LiCl. The second experiment determined if lambs were deterred from eating a familiar food by the odor of Astragalus bisulcatus. A. bisulcatus is a malodorous (to humans) sulfur-containing herb considered unpalatable and toxic. Neither odor nor intraruminal infusions of A. bisulcatus deterred lambs from feeding. The third experiment also determined how the degree of familiarity with the odor of A. bisulcatus, along with toxicosis, influenced preference of lambs for food with or without the odor of A. bisulcatus. Lambs with 8 d exposure to the odor but not given LiCl ate similar amounts of food, with and without the odor of A. bisulcatus, whereas lambs given LiCl showed a mild aversion to food with the odor during testing. Lambs with 1 d exposure to the odor but no LiCl ate similar amounts of food, with and without the odor, whereas lambs given LiCl showed a strong but transient aversion to food with the odor. Collectively, these findings show that lambs responded strongly to novel odors, but their response was transient and depended on the postingestive consequences of toxins and nutrients associated with odor inhalation. Thus, we submit that odor alone, in the absence of toxicosis or nociception, is not a deterrent to herbivores that continually sample foods and adjust intake based on the postingestive effects of toxins and nutrients. It also is unlikely that non-toxic plants can mimic the odors of toxic plants to avoid herbivory (Batesian mimicry), unless the odors are indistinguishable by herbivores, again because herbivores constantly sample foods.
66 citations
TL;DR: The premise that in a future high-CO2 world an acclimatory (down-regulation) response in the photosynthetic apparatus of field-grown wheat is anticipated is supported and it is demonstrated that the stimulatory effect of a rise in atmospheric CO2 on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.
Abstract: Atmospheric CO2 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-CO2 world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO2 concentration of ambient air [370 μmol (CO2) mol−1; Control] and air enriched to ∼200 μmol (CO2) mol−1 above ambient using a Free-Air CO2 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 CO2 treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (gs) 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, gs was reduced by as much as 31% at mid-morning, 44% at midday and 28% at mid-afternoon compared with Control. But, no significant CO2 × 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 gs, however, significant CO2 × 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-CO2 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 CO2 on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.
61 citations
TL;DR: Evaluated grain-filling rate and duration for spring wheat found later-formed tiller spikes were more responsive to elevated CO 2 and drought stress than main stem spikes, and grain weight increase under Elevated CO 2 was due to a faster rate of grain filling.
Abstract: Wheat grain weight is a function of rate and duration of grain growth and is affected by photosynthate supply. Drought stress reduces photosynthate production because of stomatal closure. However, this might be partially overcome by an increase in air CO 2 concentration. This study was conducted to evaluate elevated CO 2 and drought stress effects on grain-filling rate and duration for spring wheat (Triticum aestivum L.). Spring wheat (cv. Yecora Roja) was grown at two CO 2 concentrations, 550 (elevated) or 370 (ambient) μmol mol -1 and two water treatments in a Free-Air CO 2 Enrichment (FACE) system at the University of Arizona Maricopa Agricultural Center. Plant samples were collected every 3 to 4 d from 6 d after anthesis until plant maturity. Main stem spikes were separated into upper, middle, and lower sections. Grain weight data for the intact main stem spike, each of its sections, and intact tiller spikes were fitted to a cumulative logistic model. Both elevated CO 2 and water treatments significantly influenced the grain-filling processes. Under drought stress conditions, elevated CO 2 increased grain weight in the upper and lower sections of the main stem spike by 10 and 24%, respectively. In well-watered plants, final grain weight in the midsection of the main stem spike was 8% higher than that measured under drought stress conditions. Grain weight increase under elevated CO 2 was due to a faster rate of grain filling. Effects of elevated CO 2 on the statistically derived duration of grain filling were inconclusive because of the confounding effect of blower-induced temperature changes on the process. An increase in grain weight of well-watered plants was due to a longer grain-filling period. Later-formed tiller spikes were more responsive to elevated CO 2 and drought stress than main stem spikes. Information from this study will help us understand the grain growth of wheat and provide information to establish grain growth mechanism.
57 citations
TL;DR: Results indicate that significant modifications of canopy architecture occurs in response to both CO2 and N-stress, and optimization of canopy Architecture may serve as a mechanism to diminish CO2and N- stress effects on CER.
Abstract: The response of whole-canopy net CO2 exchange rate (CER) and canopy architecture to CO2 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) CO2 treatment (defined as ambient and ambient +200 μmol 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 CO2 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 CO2, but by as much as 22% under CO2 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 CO2 and N-stress. Optimization of canopy architecture may serve as a mechanism to diminish CO2 and N-stress effects on CER.
52 citations
TL;DR: The results underscore the importance of leaf position, leaf age and crop developmental stage in understanding the acclimation of photosynthesis to elevated CO2 and nutrient stress.
Abstract: We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO2 concentration, and ample and limiting N supplies, within a field experiment using free-air CO2 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 CO2 concentration (Ci) was used to estimate the in vivo carboxylation capacity (Vcmax) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (Asat). 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 CO2 did not alter Vcmax in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vcmax and Asat 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 CO2 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 CO2 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 CO2 and nutrient stress.
49 citations
TL;DR: Two 2-yr crops of tropical spider lily plants were grown in field soil in clear-plastic-wall open-top enclosures in the Sonoran Desert environment of central Arizona and a mean active ingredient increase of 75% for the 75% increase in the air's CO(2) concentration was used in the authors' experiments.
Abstract: Two 2-yr crops of tropical spider lily (Hymenocallis littoralis) plants were grown in field soil in clear-plastic-wall open-top enclosures in the Sonoran Desert environment of central Arizona. Half of the plants were exposed to ambient air of 400 ppm atmospheric CO(2) concentration and half of them were exposed to air of 700 ppm CO(2). This 75% increase in the air's CO(2) content resulted in a 48% increase in aboveground plant biomass and a 56% increase in belowground (bulb) biomass. It also increased the concentrations of five bulb constituents that have been demonstrated to possess anticancer and antiviral activities. Mean percentage increases in these concentrations were 6% for a two-constituent (1:1) mixture of 7-deoxynarciclasine and 7-deoxy-trans-dihydronarciclasine, 8% for pancratistatin, 8% for trans-dihydronarciclasine, and 28% for narciclasine, for a mean active ingredient percentage concentration increase of 12%. Combined with the 56% increase in bulb biomass, these percentage concentration increases resulted in a mean active ingredient increase of 75% for the 75% increase in the air's CO(2) concentration used in our experiments.
43 citations
TL;DR: In this paper, the mid-day responses of wheat ear CO 2 and water vapour exchange to full-season CO 2 enrichment were investigated using a Free-Air CO 2 Enrichment (FACE) apparatus.
Abstract: The mid-day responses of wheat ear CO 2 and water vapour exchange to full-season CO 2 enrichment were investigated using a Free-Air CO 2 Enrichment (FACE) apparatus. Spring wheat [Triticum aestivum (L). cv. Yecora Rojo] was grown in two experiments under ambient and elevated atmospheric CO 2 (C a ) concentrations (approximately 370 μmol mol -1 and 550 μmol mol -1 , respectively) combined first with two irrigation (Irr) schemes (Wet: 100% and Dry: 50% replacement of evapotranspiration) and then with two levels of nitrogen (N) fertilization (High: 350, Low: 70 kg ha -1 N). Blowers were used for C a enrichment. Ambient C a plots were exposed to blower induced winds as well the C a x N but not in the C a x Irr experiment. The net photosynthesis for the ears was increased by 58% and stomatal conductance (g s ) was decreased by 26% due to elevated C a under ample water and N supply when blowers were applied to both C a treatments. The use of blowers in the C a -enriched plots only during the C a x Irr experiment (blower effect) and Low N supply restricted the enhancement of net photosynthesis of the ear due to higher C a . In the latter case, the increase of net photosynthesis of the ear amounted to 26%. The decrease in g s caused by higher C a was not affected by the blower effect and N treatment. The mid-day enhancement of net photosynthesis due to elevated C a was higher for ears than for flag leaves and this effect was most pronounced under ample water and N supply. The contribution of ears to grain filling is therefore likely to increase in higher C a environments in the future. In the comparison between Wet and Dry, the higher C a did not alter the response of net photosynthesis of the ear and g s to Irr. However, C a enrichment increased the drought tolerance of net photosynthesis of the glume and delayed the increase of the awn portion of net photosynthesis of the ear during drought. Therefore, the role of awns for maintaining high net photosynthesis of the ear under drought may decrease when C a increases.
01 Jan 2000
TL;DR: In this paper, a synergy between remote sensing and crop simulation models is proposed as a new method for managing irrigations in precision agriculture, where the remote sensing component provides the ability to assess plant water status at high spatial resolution and the crop model provides data at high temporal frequency.
Abstract: A synergy between remote sensing and crop simulation models is proposed as a new method for managing irrigations in precision agriculture. The remote sensing component provides the ability to assess plant water status at high spatial resolution and the crop model provides data at high temporal frequency. The objective of this study was to integrate the crop water stress index (CWSI) and the simulation model CERES-Wheat to provide data on within-field variability in plant water requirements and yield response. The accuracy of the procedure was evaluated using a data set collected during the Free Air Carbon Dioxide Enhancement (FACE) wheat experiments conducted at the Maricopa Agricultural Center in Arizona. The method was very sensitive to overestimation of the CWSI under dry conditions with a potential for inaccurately predicted soil water contents. However, the combined approach allowed the model to provide reasonable yield prediction of water stressed plots using only CWSI measurements during the season to indicate inadequate plant available water. These initial results are encouraging; however, additional analysis of the data on a plot-by-plot basis is necessary before specific conclusions can be made about the suitability of this method for precision farming applications.
TL;DR: In this paper, the authors investigated the role of aerial fertilization in the early drawdown of atmospheric CO2 and the subsequent advance of the seasonal CO2 cycle in northern temperate latitudes.
01 Jan 2000
TL;DR: Cabergoline is a potential reproductive inhibitor in coyotes and future studies should determine if the efficacy of cabergoline in terminating pregnancy in coyote could be improved with higher doses and at earlier stages of gestation.
Abstract: Author(s): Seglund, Amy E.; DeLiberto, Thomas J.; Kimball, Bruce A. | Abstract: Cabergoline, a prolactin inhibitor, was evaluated on its potential use as a reproductive inhibitor for coyotes (Canis latrans). Groups consisting of six female coyotes were randomly assigned to three treatments and a control group. At 25 to 35 days after fertilization, coyotes were palpated to verify pregnancy status. If an animal was confirmed pregnant, it was dosed with 50 μg, 100 μg, or 250 μg of cabergoline, or a placebo for seven consecutive days on approximately day 40 days of gestation. Five animals dosed with 50 μg of cabergoline, three dosed with 100 μg, and three animals receiving placebo whelped; no animals treated with 250 μg whelped. No drop in serum progesterone or prolactin levels were observed for the 50 μg and 100 μg treated groups. However, progesterone levels declined below 2 ng/ml in animals treated with 250 μg. Prolactin and progesterone levels in the control group followed typical patterns observed in pregnant canines. This study suggests that cabergoline is a potential reproductive inhibitor in coyotes. Future studies should determine if the efficacy of cabergoline in terminating pregnancy in coyotes could be improved with higher doses and at earlier stages of gestation.