Potentially high future carbon dioxide (CO sub(2)) levels that affect water use by wheat could have secondary effects on plant-water relations, plant physiological processes, growth, and net primary ...productivity. The effect of a rise in atmospheric CO sub(2) on pre-dawn, mid-day, and sunset total leaf water potential of wheat ( psi sub(W)) as the soil matric potential ( psi sub(M)) varied from -0.03 to -1.50 MPa was studied in an open field in Maricopa, AZ, in ambient and CO sub(2)-enriched air. Two soil moisture levels also were tested. Analysis of pressure chamber measurements of psi on upper canopy leaves at pre-dawn, mid-day, and sunset showed that as psi sub(M) rose, an increase in atmospheric CO sub(2) resulted in a curvilinear increase in drought stress alleviation (to 77% at pre-dawn, 67% at mid-day, and 79% at sunset). As CO sub(2) concentrations rose, drought avoidance and tolerance mechanisms were enhanced, resulting in improved water relations in wheat.
Controlled-environment plant growth cabinets may be used to investigate the long-term effect of elevated carbon dioxide concentration (CO2) on plant growth. Infrared gas analyzers (IRGAs) are ...normally used to monitor and control CO2 in plant cabinets. With many cabinets in use, however, it soon becomes impractical to purchase an individual IRGA for each cabinet. A more economical method of monitoring and controlling CO2 relies on the change in electrical conductivity when CO2 is dissolved in demineralized water. This work describes the design, implementation, and functionality of an inexpensive conductimetric system for controlling CO2 in plant growth cabinets. Regressing electrical conductivity against CO2 over the range 0 to 1000 microliters L-1 yields a quadratic response. Calibration drift inherent in the conductimetric CO2 analyzer requires that each analyzer be recalibrated periodically. Automatically recalibrating with an IRGA every 900 s gave control of the CO2 within the plant enclosures to within 10 to 15 microliters L-1 of the set point. The CO2 control system is robust enough to maintain this accuracy regardless of the desired CO2 set point or the mass of plant material within the plant growth cabinet. In this approach, only one IRGA is required to control CO2 in many plant growth cabinets if each cabinet has a dedicated conductimetric CO2 analyzer
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.
Conductimetric CO2 analyzers provide an economical means of monitoring and controlling carbon dioxide concentration (CO2) in enclosed plant growth cabinets. They rely on dissolving CO2 from an air ...sample in demineralized water and measuring the resulting change in electrical conductivity. Regressing the analog output from the conductivity meter against CO2 values over the range 200 to 1000 microliters L-1 yields a quadratic response. Calibration curves for conductimetric CO2 analyzers are affected primarily by temperature and air and water flow rates. Air and water flow rates are relatively fixed, whereas temperature varies over time in normal operation. A covariate analysis for a three-way treatment structure in a randomized complete block design determined how the intercept (B0) and the linear and quadratic parameter estimates (B1 and B2) varied with temperatures of 10, 20, 30, and 40 degrees C, air flow rates of 540, 1880, and 3700 mm3 s-1, and water flow rates of 1.0, 0.66, and 0.33 mL s-1. Temperature effects were greatest, with air flow rate causing minor changes, while water flow rate had no effect. Temperature and air flow rate significantly altered B0, with only minor changes in B1 and B2. Variations in B0 were sufficient enough to alter the CO2 around the desired set point by 70 microliters L-1 for all treatments evaluated. Deviations in CO2 control due to variation in B1 and B2 were within 10 to 15 microliters L-1; only the adjustment in B0 must be made every sampling period (every 900 s) to maintain CO2 control within 10 to 15 microliters L-1 of the set point
Conductimetric CO2 analyzers provide an economical means of monitoring and controlling carbon dioxide concentration (CO2) in plant growth cabinets. When conductimetric CO2 analyzers are being used to ...measure canopy CO2 uptake over a period and compare that with light received, it is essential to know the time between an air sample leaving the canopy and its CO2 being registered by the analyzer. A four-way analysis of variance in three replicates of a split split-plot design was used to examine the response time of the conductimetric CO2 analyzers to successive step changes in CO2 (deltaCO2) from 200 to 400, 600, 800, and 1000 microliters L-1, at temperatures of 10, 20, 30, and 40 degrees C, at air flows rates of 540, 1880, and 3700 mm3 s-1, and at water flow rates of 1.0, 0.66, and 0.33 mL s-1. Response times ranged from 30 to 542 s across all treatments. Significant differences were observed between individual conductimetric CO2 analyzers, with response time means ranging from 99 to 145 s. Each analyzer, therefore, is unique and must be recalibrated following a change in any one component. A significant water flow rate X temperature interaction was observed (response time means ranged from 86 to 177 s). Comparing these response time means to the 900-s sampling period indicates that an individual conductimetric CO2 analyzer will adjust to the new steady state following a change in control within 9.5 to 20% of the sampling period. Only 1 data record out of 96 within a diurnal cycle is lost if an alteration in the CO2 control set point for the plant growth cabinet is made. This data loss is acceptable
Summary
•
To determine the response of C4 plants to elevated CO2 it is necessary to establish whether young leaves have a fully developed C4 photosynthetic apparatus, and whether photosynthesis in ...these leaves is responsive to elevated CO2.
•
The effect of free‐air CO2 enrichment (FACE) on the photosynthetic development of the C4 crop Sorghum bicolor was monitored. Simultaneous measurements of chlorophyll a fluorescence and carbon assimilation were made to determine energy utilization, quantum yields of carbon fixation (φCO2) and photosystem II (φPSII), as well as photorespiration.
•
Assimilation in the second leaf of FACE plants was 37% higher than in control plants and lower apparent rates of photorespiration at growth CO2 concentrations were exhibited. In these leaves, φPSII : φCO2 was high at low atmospheric CO2 concentration (Ca) due to overcycling of the C4 pump and increased leakiness. As Ca increased, φPSII : φCO2 decreased as a greater proportion of energy derived from linear electron transfer was used by the C3 cycle.
•
The stimulation of C4 photosynthesis at elevated Ca in young leaves was partially due to suppressed photorespiration. Additionally, elevated Ca enhanced energy‐use efficiency in young leaves, possibly by decreasing CO2 leakage from bundle sheath cells, and by decreasing overcycling of the C4 pump.
• Understanding how trees are affected by a long-term increase in atmospheric CO2is crucial to understanding the future impact of global climate change. Measurements of photosynthetic characteristics ...were made in sour orange trees (Citrus aurantium) growing under an enhanced CO2atmosphere and N-replete soil for 14 yr to determine whether photosynthetic down-regulation had occurred. • Photosynthesis, A: Cigas exchange relationships and Rubisco activity and content were measured throughout the 14th year of the experiment. The CO2-induced enhancement ratio of photosynthesis was calculated and compared with estimates of the enhancement of cumulative wood biomass production. • Content of the large subunit of Rubisco was significantly reduced by CO2enrichment indicating that down-regulation had occurred. A high correlation between the CO2-induced enhancement of photosynthesis and the enhancement of cumulative wood biomass production suggested that the decline in wood biomass production was closely related to the decline in photosynthesis. • These results indicate that long-term CO2enrichment can result in photosynthetic down-regulation in leaves of trees, even under nonlimiting N conditions.
Understanding how trees are affected by a long-term increase in atmospheric CO sub(2) is crucial to understanding the future impact of global climate change. Measurements of photosynthetic ...characteristics were made in sour orange trees (Citrus aurantium) growing under an enhanced CO sub(2) atmosphere and N-replete soil for 14 yr to determine whether photosynthetic down-regulation had occurred. Photosynthesis, A : C sub(i) gas exchange relationships and Rubisco activity and content were measured throughout the 14th year of the experiment. The CO sub(2)-induced enhancement ratio of photosynthesis was calculated and compared with estimates of the enhancement of cumulative wood biomass production. Content of the large subunit of Rubisco was significantly reduced by CO sub(2) enrichment indicating that down-regulation had occurred. A high correlation between the CO sub(2)-induced enhancement of photosynthesis and the enhancement of cumulative wood biomass production suggested that the decline in wood biomass production was closely related to the decline in photosynthesis. These results indicate that long-term CO sub(2) enrichment can result in photosynthetic down-regulation in leaves of trees, even under nonlimiting N conditions.
Physiological responses in sour orange trees grown in open-top chambers and exposed to elevated carbon dioxide levels were studied. In particular, enriched/ambient differences in the concentrations ...of rubisco and other soluble proteins in sour orange leaves were examined. The unknown proteins were purified and identified to help understand why the enriched trees can sustain a long-term increase of about 80% in wood and fruit production. The abundances of these proteins generally were lower in CO sub(2)-enriched leaves than in ambient leaves, except in the early and late times of the year when the reverse was true. Evidence supporting the hypothesis that these proteins are vegetative storage proteins (VSPs) is presented. The decline from winter levels may provide a source of nitrogen (N) that is needed for spring branch growth in enriched trees. The N-terminal amino acid sequence is homologous to a VSP found in sweet potato tubers. And immunoelectron microscopy revealed these proteins in mesophyll cell vacuoles, where VSPs commonly are found. Elevated CO sub(2) had little effect on leaf rubisco, suggesting that enhanced branch and fruit growth under enriched CO sub(2) is not correlated with increased breakdown of rubisco.
Separating roots from soil is a laborious and costly process, but a commercially available hydropneumatic root elutriator can semi-automate the job. Hydraulic and pneumatic systems elutriate the ...roots from the soil, while the electrical system controls the on/off functions of the hydraulic system. The extruded steel frame of the elutriator serves a dual purpose; structural support and transport of water and compressed air. Water is transported in the lower and air in the upper part of the hollow inner cavity of the extruded steel frame. They exit the frame into polyethylene tubes that extend to the base of the elutriator. After prolonged use, however, this design feature can become problematic because flow to the elutriator of either system can be blocked at the nozzle inlets with rust particles that originate from the steel frame's inner walls. The blockage increases sample processing time due to dismantling, clearing, and reassembling, which eventually degrades the elutriator. To resolve these problems a 40-mesh (420 micron) in-line stainless steel water filter and a 40-micron in-line bronze air filter were installed in the polyethylene tube lines between the extruded steel frame and the base of the elutriator. These filters were found to reduce nozzle blockage, thereby increasing sample processing efficiency by 10% and improving sample quality.
PDF
