Showing papers by "Bruce A. Kimball published in 2007"

Decreases in Stomatal Conductance of Soybean under Open-Air Elevation of [CO2] Are Closely Coupled with Decreases in Ecosystem Evapotranspiration

Abstract: Stomatal responses to atmospheric change have been well documented through a range of laboratory- and field-based experiments. Increases in atmospheric concentration of CO2 ([CO2]) have been shown to decrease stomatal conductance (gs) for a wide range of species under numerous conditions. Less well understood, however, is the extent to which leaf-level responses translate to changes in ecosystem evapotranspiration (ET). Since many changes at the soil, plant, and canopy microclimate levels may feed back on ET, it is not certain that a decrease in gs will decrease ET in rain-fed crops. To examine the scaling of the effect of elevated [CO2] on gs at the leaf to ecosystem ET, soybean (Glycine max) was grown in field conditions under control (approximately 375 μmol CO2 mol−1 air) and elevated [CO2] (approximately 550 μmol mol−1) using free air CO2 enrichment. ET was determined from the time of canopy closure to crop senescence using a residual energy balance approach over four growing seasons. Elevated [CO2] caused ET to decrease between 9% and 16% depending on year and despite large increases in photosynthesis and seed yield. Ecosystem ET was linked with gs of the upper canopy leaves when averaged across the growing seasons, such that a 10% decrease in gs results in a 8.6% decrease in ET; this relationship was not altered by growth at elevated [CO2]. The findings are consistent with model and historical analyses that suggest that, despite system feedbacks, decreased gs of upper canopy leaves at elevated [CO2] results in decreased transfer of water vapor to the atmosphere.

Dynamics of labile and recalcitrant soil carbon pools in a sorghum free-air CO2 enrichment (FACE) agroecosystem

Abstract: Experimentation with dynamics of soil carbon pools as affected by elevated CO2 can better define the ability of terrestrial ecosystems to sequester global carbon. In the present study, 6 N HCl hydrolysis and stable-carbon isotopic analysis (δ13C) were used to investigate labile and recalcitrant soil carbon pools and the translocation among these pools of sorghum residues isotopically labeled in the 1998–1999 Arizona Maricopa free air CO2 enrichment (FACE) experiment, in which elevated CO2 (FACE: 560 μmol mol−1) and ambient CO2 (Control: 360 μmol mol−1) interact with water-adequate (wet) and water-deficient (dry) treatments. We found that on average 53% of the final soil organic carbon (SOC) in the FACE plot was in the recalcitrant carbon pool and 47% in the labile pool, whereas in the Control plot 46% and 54% of carbon were in recalcitrant and labile pools, respectively, indicating that elevated CO2 transferred more SOC into the slow-decay carbon pool. Also, isotopic mixing models revealed that increased new sorghum residue input to the recalcitrant pool mainly accounts for this change, especially for the upper soil horizon (0–30 cm) where new carbon in recalcitrant soil pools of FACE wet and dry treatments was 1.7 and 2.8 times as large as that in respective Control recalcitrant pools. Similarly, old C in the recalcitrant pool under elevated CO2 was higher than that under ambient CO2, indicating that elevated CO2 reduces the decay of the old C in recalcitrant pool. Mean residence time (MRT) of bulk soil carbon at the depth of 0–30 cm was significantly longer in FACE plot than Control plot by the averages of 12 and 13 yr under the dry and wet conditions, respectively. The MRT was positively correlated to the ratio of carbon content in the recalcitrant pool to total SOC and negatively correlated to the ratio of carbon content in the labile pool to total SOC. Influence of water alone on the bulk SOC or the labile and recalcitrant pools was not significant. However, water stress interacting with CO2 enhanced the shift of the carbon from labile pool to recalcitrant pool. Our results imply that terrestrial agroecosystems may play a critical role in sequestrating atmospheric CO2 and mitigating harmful CO2 under future atmospheric conditions.

Seventeen years of carbon dioxide enrichment of sour orange trees: final results

Abstract: The long-term responses of trees to elevated CO2 are especially crucial (1) to mitigating the rate of atmospheric CO2 increase, (2) to determining the character of future forested natural ecosystems and their spread across the landscape, and (3) to determining the productivity of future agricultural tree crops. Therefore, a long-term CO2-enrichment experiment on sour orange trees was started in 1987, and the final results after 17 years are reported herein. Four sour orange trees (Citrus aurantium L.) were grown from seedling stage at 300lmolmol � 1 CO2 above ambient in open-top, clear-plastic-wall chambers at Phoenix, AZ. Four control trees were similarly grown at ambient CO2. All trees were supplied ample water and nutrients comparable with a commercial orchard. After a peak 2‐4 years into the experiment, there was a productivity plateau at about a 70% enhancement of annual fruit and incremental wood production over the last several years of the experiment. When summed over the duration of the experiment, there was an overall enhancement of 70% of total biomass production. Much of the enhancement came from greater numbers of fruits produced, with no change in fruit size. Thicker trunks and branches and more branches and roots were produced, but the root/shoot ratio was unaffected. Also, there was almost no change in the elemental composition of the biomass produced, perhaps in part due to the minimal responsiveness of root-symbiotic arbuscular mycorrhizal fungi to the treatment.

The floral volatile, methyl benzoate, from snapdragon ( Antirrhinum majus ) triggers phytotoxic effects in Arabidopsis thaliana

Abstract: Previously it has been shown that the Xoral scent of snapdragon Xowers consists of a relatively sim- ple mixture of volatile organic compounds (VOCs). These compounds are thought to be involved in the attraction of pollinators; however, little is known about their eVect on other organisms, such as neighboring plants. Here, we report that VOCs from snapdragon Xowers inhibit Arabidopsis root growth. Out of the three major snapdragon Xoral volatiles, myrcene, (E)--ocim- ene, and methyl benzoate (MB), MB was found to be primarily responsible for the inhibition of root growth. Ten micromoles MB reduced root length by 72.6%. We employed a microarray approach to identify the MB tar- get genes in Arabidopsis that were responsible for the root growth inhibition phenotype in response to MB. These analyses showed that MB treatment aVected 1.33% of global gene expression, including cytokinin, auxin and other plant-hormone-related genes, and genes related to seed germination processes in Arabidopsis. Accordingly, the root growth of cytokinin (cre1) and auxin (axr1) response mutants was less aVected than that of the wild type by the volatile compound: roots of the treated mutants were reduced by 45.1 and 56.2%, respectively, relative to untreated control mutants.

Do herbivores associate flavors with specific consequences in flavor aversion learning

Abstract: Goats were first offered a novel, maple-flavoured diet paired with either lithium chloride (LiCl) or oxalic acid (OA) delivered intraruminally. Aversion to maple diet persisted for 6 days, regardless of toxin. Following a 10-day intermission, aversion to maple diet was reacquired (spontaneous recovery) among subjects previously dosed with LiCl but not for subjects receiving OA. All subjects were then offered two diets: the maple diet previously paired with LiCl or OA and a novel grape-flavoured diet. Immediately following consumption of both diets, all subjects were dosed with LiCl. Preference for maple and grape diets was assessed by two-choice test. Goats avoided maple diet for only 1 day, regardless of their previous experience with maple diet (paired with LiCl or OA). These results indicate that goats generalized the postingestive consequences of the two toxins. Furthermore, presence of a novel flavour (grape) during toxin exposure contributed to rapid extinction of the aversion to maple flavour. # 2006 Elsevier B.V. All rights reserved.