Photosynthesis and conductance of spring-wheat leaves: field response to continuous free-air atmospheric CO2 enrichment

Spring wheat was grown from emergence to grain maturity in two partial pressures of CO2 (pCO2): ambient air of nominally 37 Pa and air enriched with CO2 to 55 Pa using a free-air CO2 enrichment (FACE) apparatus. This experiment was the first of its kind to be conducted within a cereal field without the modifications or disturbance of microclimate and rooting environment that accompanied previous studies. It provided a unique opportunity to examine the hypothesis that continuous exposure of wheat to elevated pCO2 will lead to acclimatory loss of photosynthetic capacity. The diurnal courses of photosynthesis and conductance for upper canopy leaves were followed throughout the development of the crop and compared to model-predicted rates of photosynthesis. The seasonal average of midday photosynthesis rates was 28% greater in plants exposed to elevated pCO2 than in contols and the seasonal average of the daily integrals of photosynthesis was 21% greater in elevated pCO2 than in ambient air. The mean conductance at midday was reduced by 36%. The observed enhancement of photosynthesis in elevated pCO2 agreed closely with that predicted from a mechanistic biochemical model that assumed no acclimation of photosynthetic capacity. Measured values fell below predicted only in the flag leaves in the mid afternoon before the onset of grain-filling and over the whole diurnal course at the end of grain-filling. The loss of enhancement at this final stage was attributed to the earlier senescence of flag leaves in elevated pCO2. In contrast to some controlled-environment and field-enclosure studies, this field-scale study of wheat using free-air CO2 enrichment found little evidence of acclimatory loss of photosynthetic capacity with growth in elevated pCO2 and a significant and substantial increase in leaf photosynthesis throughout the life of the crop

Does Leaf Position within a Canopy Affect Acclimation of Photosynthesis to Elevated CO2? . Analysis of a Wheat Crop under Free-Air CO2 Enrichment

Previous studies of photosynthetic acclimation to elevated CO2 have focused on the most recently expanded, sunlit leaves in the canopy. We examined acclimation in a vertical profile of leaves through a canopy of wheat (Triticum aestivum L.). The crop was grown at an elevated CO2 partial pressure of 55 Pa within a replicated field experiment using free-air CO2 enrichment. Gas exchange was used to estimate in vivo carboxylation capacity and the maximum rate of ribulose-1,5-bisphosphate-limited photosynthesis. Net photosynthetic CO2 uptake was measured for leaves in situ within the canopy. Leaf contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), light-harvesting-complex (LHC) proteins, and total N were determined. Elevated CO2 did not affect carboxylation capacity in the most recently expanded leaves but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO2 uptake remained higher under elevated CO2. Acclimation at elevated CO2 was accompanied by decreases in both Rubisco and total leaf N contents and an increase in LHC content. Elevated CO2 led to a larger increase in LHC/Rubisco in lower canopy leaves than in the uppermost leaf. Acclimation of leaf photosynthesis to elevated CO2 therefore depended on both vertical position within the canopy and the developmental stage

Regioselectivity in Electrophilic Aromatic Substitution: Insights from Interaction Energy Decomposition Potentials

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Crop water relations under different CO2 and irrigation: testing of ecosys with free air CO2 enrichment (FACE) experiment.

Increases in crop growth under elevated atmospheric C

Combinaison de données multi-fréquence micro-ondes et optiques pour le suivi des cultures

[Departement_IRSTEA]GT [TR1_IRSTEA]GMA1-Fonctionnement hydrologique des bassins et des réseaux hydrographiquesInternational audienceThe potential for the combined use of microwave and optical data for farm management was explored based on images acquired in the visible, near-infrared, and thermal spectrum, and the synthetic aperture radar (SAR) wavelengths in the Ku (14.85 GHz) and C (5.3 GHz) bands. The images were obtained during June 1994, and covered an agricultural site composed of large fields of partial-cover cotton, near-full-cover alfalfa and bare soil fields of varying roughness. Results showed that the SAR Ku backscatter coefficient (Ku-band so) was sensitive to soil roughness and insensitive to soil moisture conditions when vegetation was present. When soil roughness conditions were relatively similar (e.g., for cotton fields of similar row direction and for all alfalfa fields), Ku-band so was sensitive to the fraction of the surface covered by vegetation. Under these conditions, the Ku-band so and the optical normalized difference vegetation index (NDVI) were generally correlated. The SAR C backscatter coefficient (C-band so) was found to be sensitive to soil moisture conditions for cotton fields with green leaf area index (GLAI) less than 1.0 and alfalfa fields with GLAI nearly 2.0. For both low-GLAI cotton and alfalfa, C-band so was correlated with measurements of surface temperature (Ts). A theoretical basis for the relations between Ku-band so and NDVI and between C-band so and Ts was presented, and supported with on-site measurements. Based on these findings, some combined optical/radar approaches were suggested for farm management applications.La possibilité de combiner des données de télédétection micro-ondes et optiques pour la suivi des cultures est étudié, en utilisant des images acquises dans le visible, le proche infrarouge, le thermique et dans les longueurs d'onde d'un SAR (radar à ouverture synthétique) dans les bandes Ku (14.85 GHz) et C (5.3 GHz). Les images ont été obtenues en juin 1994, et couvraient un site agricole composé de grandes parcelles de coton, luzerne et sol nu. Les résultats montrent que le coefficient de rétrodiffusion en bande Ku (Ku so) est sensible à la rugosité du sol et indépendant de l'humidité du sol en présence de végétation. Lorsque les conditions de rugosité du sol sont relativement similaires (p.ex. parcelles de coton dont les rangs sont orientés dans la même direction, parcelles de luzerne), Ku so est sensible au pourcentage de recouvrement de la végétation. Dans ces conditions, Ku so et l'indice de végétation NDVI sont en général corrélés. Le coefficient de rétrodiffusion en bande C (C so) est sensible aux conditions d'humidité du sol pour les parcelles de coton dont l'indice foliaire (GLAI) est inférieur à 1.0 et pour les parcelles de luzerne dont le GLAI est proche de 2 : dans les deux cas, C so est corrélé aux mesures de température de surface Ts. Une approche théorique des relations entre Ku so et NDVI, et entre C so et Ts est présentée, et validée par les mesures terrain. A partir de ces résultats, quelques approches combinant optique et radar sont proposées pour le suivi des cultures à l'échelle de l'exploitation

Soil Organic Carbon Isotope Tracing in Sorghum under Ambient CO2 and Free-Air CO2 Enrichment (FACE)

As atmospheric carbon dioxide concentrations, [CO2Air ], continue their uncontrolled rise, the capacity of soils to accumulate or retain carbon is uncertain. Free-air CO2 enrichment (FACE) experiments have been conducted to better understand the plant, soil and ecosystem response to elevated [CO2 ], frequently employing commercial CO2 that imparts a distinct isotopic signal to the system for tracing carbon. We conducted a FACE experiment in 1998 and 1999, whereby sorghum (C4 photosynthetic pathway) was grown in four replicates of four treatments using a split-strip plot design: (i) ambient CO2 /ample water (365 µmol mol−1, “Control–Wet”), (ii) ambient CO2 /water stress (“Control–Dry”), (iii) CO2-enriched (560 µmol mol−1, “FACE–Wet”), and (iv) CO2-enriched/water stressed (“FACE–Dry”). The stable-carbon isotope composition of the added CO2 (in FACE treatments) was close to that of free atmosphere background values, so the subsequent similar13 C-enriched carbon signal photosynthetically fixed by C4 sorghum plants could be used to trace the fate of carbon in both FACE and control treatments. Measurement of soil organic carbon content (SOC (%) = gC/ gdry soil × 100%) and δ13 C at three depths (0–15, 15–30, and 30–60 cm) were made on soils from the beginning and end of the two experimental growing seasons. A progressive ca. 0.5‰–1.0‰ δ13 C increase in the upper soil SOC in all treatments over the course of the experiment indicated common entry of new sorghum carbon into the SOC pools. The 0–15 cm SOC in FACE treatments was13 C-enriched relative to the Control by ca. 1‰, and according to isotopic mass balance, the fraction of the new sorghum-derived SOC in the Control–Wet treatment at the end of the second season was 8.4%, 14.2% in FACE–Wet, 6.5% in Control–Dry, and 14.2% in FACE–Dry. The net SOC enhancement resulting from CO2 enrichment was therefore 5.8% (or 2.9% y−1 of experiment) under ample water and 7.7% (3.8% y−1 of experiment) under limited water, which matches the pattern of greater aboveground biomass increase with elevated [CO2Air ] under the Dry treatment, but no parallel isotopic shifts were found in deeper soils. However, these increased fractions of new carbon in SOC at the end of the experiment do not necessarily mean an increase in total SOC content, because gravimetric measurements of SOC did not reveal a significant increase under elevated [CO2Air ], at least within the limits of SOC-content error bars. Thus, new carbon gains might be offset by pre-experiment carbon losses. The results demonstrate successful isotopic tracing of carbon from plants to soils in this sorghum FACE experiment showing differences between FACE and Control treatments, which suggest more dynamic cycling of SOC under elevated [CO2Air ] than in the Control treatment. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]