L. Hartwell Allen

Photosynthetic acclimation of young sweet orange trees to elevated growth CO2 and temperature

Summary Two-year old trees of ‘Ambersweet’ orange, a hybrid of ‘Clementine’ tangerine (Citrus reticulata Blanco) and ‘Orlando’ tangelo (C. paradisi Macf. × C. reticulata), were grown for twenty-nine months under two daytime [CO2] of 360 (ambient) and 720 (elevated) μmol mol−1, and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize the physiology and biochemistry of citrus photosynthesis in response to both elevated [CO2] and temperature, and to test if the photosynthetic capacity of sweet orange, in terms of rubisco activity and protein concentration, was down-regulated under long-term elevated growth [CO2]. Both mature (old) and expanding (new) leaves of trees grown under elevated [CO2] had higher photosynthetic rates, lower transpiration and conductance, and higher water-use efficiency (WUE), compared to those grown under ambient [CO2]. Although leaf WUE was reduced by high temperature, elevated [CO2] compensated for adverse effect of high temperature on leaf WUE. Activity and protein concentration of rubisco were down-regulated in both new and old leaves at elevated [CO2]. In contrast, the amount of total leaf soluble protein was not affected by elevated [CO2] and high temperature. Down-regulation of photosynthetic capacity was greater for the old leaves, although activity and protein concentration of rubisco in the new leaves were higher. Contents of soluble sugars and starch in all leaves sampled, which were higher under elevated [CO2], were generally not affected by high temperature. Within each specific CO2-temperature treatment and leaf type, total soluble sugars remained relatively unchanged throughout the day, as did the starch content of early morning and midday samples, and only a moderate increase in starch for the old leaves at late afternoon sampling was observed. In contrast, starch content in the new leaves increased substantially at late afternoon. Activities of sucrose-P synthase and adenosine 5′-diphosphoglucose pyrophosphorylase were reduced at elevated [CO2] in the old leaves, but not in the new leaves. The photosynthetic acclimation of Ambersweet orange leaves at elevated [CO2] allowed an optimization of nitrogen use by reallocation/redistribution of the nitrogen resources away from rubisco. Thus, in the absence of other environmental stresses, citrus photosynthesis would perform well under rising atmospheric [CO2] and temperature as predicted for this century.

C02 Enrichment Delays a Rapid, Drought-Induced Decrease in Rubisco Small Subunit Transcript Abundance

Summary Rice ( Oryza sativa L. cv. IR-72) was grown in sunlit chambers at 350 and 700 gmol CO 2 mol -1 under conditions of continuous flooding (control) or drought which was imposed at panicle initiation, to evaluate the effects of C0 2 enrichment and soil water deficit on photosynthesis and Rubisco gene expression. Leaf and canopy photosynthetic rates were enhanced by high [CO 2 ] but reduced by drought. High [CO 2 ] and severe drought both reduced rbcS transcript abundance, along with the activity, activation and protein content of Rubisco, but the K m (CO 2 ) was not affected. The transition from moderate to severe drought caused a rapid decline, within 24 h, in the rbcS transcript abundance. High [CO 2 ], however, delayed the adverse effects of severe drought on rbcS transcript abundance and activities of Rubisco, and permitted photosynthesis to continue for an extra day during the drought-stress cycle.

Up-regulation of sucrose phosphate synthase in rice grown under elevated CO2 and temperature

Rice (Oryza sativa L. cv. IR-30) was grown season-long in outdoor, controlled-environment chambers at 33 Pa CO2 with day/night/paddy-water temperatures of 28/21/25 °C, and at 66 Pa CO2 with five different day/night/paddy-water temperature regimes (25/18/21, 28/21/25, 31/24/28, 34/27/31 and 37/30/34 °C). Sucrose phosphate synthase (SPS) activities in leaf extracts at 21, 48 and 81 days after planting (DAP) were assayed under saturating and selective (limiting) conditions. Diel SPS activity data indicated that rice SPS was light regulated; with up to 2.2-fold higher rates during the day. Throughout the growth season, leaf SPS activities were up-regulated in the CO2-enriched plants, averaging 20 and 12% higher than in ambient-CO2 grown plants in selective and saturating assays, respectively. Similarly, SPS activities increased 2.4% for each 1 °C rise in growth temperature from 25 to 34 °C, but de creased 11.5% at 37 °C. Leaf sucrose content was higher, and mirrored SPS activity better, than starch, although starch was more responsive to CO2 treatment. Leaf sucrose and starch contents were significantly higher throughout the season in plants at elevated CO2, but the N content averaged 6.5% lower. Increasing growth temperatures from 25 to 37 °C caused a linear decrease (62%) in leaf starch content, but not in sucrose. Consequently, the starch:sucrose ratio declined with growth temperature. The data are consistent with the hypothesis that the up-regulation of leaf SPS may be an acclimation response of rice to optimize the utilization and export of organic-C with the increased rates of inorganic-C fixation in elevated CO2 or temperature growth regimes.

Changes in stomatal density in rice grown under various CO2 regimes with natural solar irradiance

Abstract Rice (Oryza sativa L. cv. IR-30), grown from seed under natural solar irradiance, was exposed to CO2 concentrations ranging from 160 to 900 μl CO2/l air from 9 days after planting until senescence. Stomatal density was determined from leaf impressions at two growth stages: on leaf number 7 (31 days after planting), and on flag leaves (104 days after planting). Increasing CO2 concentrations resulted in a rise in stomatal density of leaves at both growth stages. The effect was greatest on the flag leaves, which exhibited a 54% increase in abaxial stomatal density (from 550 to 810 stomata/mm2) at 500 as compared with 160 μl CO2/l. Stomatal density increased with increasing CO2 up to 330 μl CO2/l; enrichment above this level resulted in no further significant increase in stomatal density. For both leaf ages, the abaxial stomatal density was more influenced by increases in CO2 than the adaxial surface. The increase in stomatal density was largely the result of a rise in the number of stomata per row, although on the abaxial surface more rows across the leaf also contributed to the response. Flag leaf area was not significantly different among the CO2 treatments, so the number of stomata per leaf followed similar trends to the stomatal density. This indicated the CO2 effect was on stomatal, rather than leaf area, development. The response of stomatal density to rising CO2 seems to be a species-dependent phenomenon, that varies with leaf surface and CO2 range utilized.

Enhancement in leaf photosynthesis and upregulation of Rubisco in the C4 sorghum plant at elevated growth carbon dioxide and temperature occur at early stages of leaf ontogeny.

Rising atmospheric carbon dioxide (CO2) concentration and temperature will influence photosynthesis, growth and yield of agronomic crops. To investigate effects of elevated CO2 and high temperature on leaf gas exchanges, activities of Rubisco and phosphoenolpyruvate carboxylase (PEPC) and growth of grain sorghum (Sorghum bicolor L. Moench), plants were grown in controlled environments at day-time maximum/night-time minimum temperatures of 30/20°C or 36/26°C at ambient (350 µmol mol-1) or elevated (700 µmol mol-1) CO2. Gas-exchange rates, activities of Rubisco and PEPC and growth parameters (leaf, stem and total dry weights) were determined at different stages of leaf development. Between 6 and 25 days after leaf tip emergence, leaf carbon exchange rate (CER) of elevated CO2 plants was greater at 30/20°C and 36/26°C than that of ambient CO2 plants at the same temperatures. The positive response of CER to elevated CO2 was greater in young leaves than in old leaves. In young leaves, elevated CO2 enhanced Rubisco activity at 30/20°C and 36/26°C, whereas PEPC activity was not affected by elevated CO2 at 30/20°C but was marginally enhanced at 36/26°C. At 30/20°C, growth parameters were not affected by elevated CO2 until 50 days after sowing (DAS); at 36/26°C, they were progressively enhanced by elevated CO2 to as high as 49 to 62% by 50 DAS. Leaf CER and Rubisco activity were enhanced by elevated CO2 at early stages of leaf ontogeny for the C4 grain sorghum. Such enhancement should have a significant role in dry matter production under elevated CO2.

Subambient growth CO2 leads to increased Rubisco small subunit gene expression in developing rice leaves.

Summary To test the hypothesis whether low atmospheric [CO 2 ] can cause an increase of Rubisco small subunit gene expression, rice ( Oryza sativa L.) growing under ambient [CO 2 ] at 350μmol mol −1 was switched to subambient [CO 2 ] at 175μmol mol −1 during late vegetative stage. After the switch, photosynthesis rate of developing leaves initially declined but partially recovered after 8 days. Transcript levels of the Rubisco small subunit gene ( rbcS ) in developing leaves increased within three days to almost twice that of ambient-CO 2 controls, followed later by an up-regulation of Rubisco total activity and protein content.

Atmospheric Volatilization and Distribution of (Z)- and (E)-1,3-Dichloropropene in Field Beds with and without Plastic Covers

Abstract The fumigant 1,3-dichloropropene (1,3-D) is considered to be a potential replacement for methyl bromide when methyl bromide is phased out in 2005. This study on surface emissions and subsurface diffusion of 1,3-D in a Florida sandy soil was conducted in field beds with or without plastic covers. After injection of the commercial fumigant Telone II by conventional chisels to field beds at 30 cm depth which were covered with polyethylene film (PE), virtually impermeable film, or no cover (bare), (Z)- and (E)-1,3-D rapidly diffused upward. Twenty hours after injection, majority of (Z)- and (E)-1,3-D had moved upward from 30 cm depth to the layer of 5–20 cm depth. Downward movement of the two isomers in the beds with or without a plastic cover was not significant. (Z)-1,3-D diffused more rapidly than (E)-1,3-D. Virtually impermeable films (VIF) had a good capacity to retain (Z)- and (E)-1,3-D in soil pore air space. Vapor concentrations of the two isomers in the shallow subsurface of the field bed covered with VIF were greater than that in the two beds covered with polyethylene film (PE) or no cover (bare). In addition, VIF cover provided more uniform distribution of (Z)- and (E)-1,3-D in shallow subsurface than PE cover or no cover. Virtually impermeable film also had a better capability to retard surface emissions of the two isomers from soil in field beds than PE cover or no cover.

Comparison of surface emissions and subsurface distribution of cis- and trans-1,3-dichloropropne and chloropicrin in sandy field beds covered with four different plastic films

The purpose of this study was to conduct a field study at a Florida field site on surface emissions and subsurface distribution of cis-and trans-1,3-dichloropropene (1,3-D) and chloropicrin (CP) in raised beds injected with Telone C35 with four replications. A total of 16 beds were applied with Telone C35 by chisel injection and covered with four different plastic films, 4 beds for each film. Each bed was installed with five 20-cm long soil pore air probes and a surface air collection pan at arbitrarily locations along the length of each bed for sampling soil pore air and surface air, respectively, for analysis of the three biologically active compounds, cis- and trans-1,3-D and CP. We found that average concentrations of the three compounds at 20-cm depth among the beds covered with four different plastic films generally were not statistically different. Among the four beds covered with the same plastic film, average concentrations of the three compounds were statistically different only in the four metallic PE covered beds at 5 and 24 hours after injection. Volatilization rates of the three compounds among the beds covered with four different plastic films, with the exception of CP at 48 hours after injection, were not statistically different. It appeared that initial upward diffusion and volatilization flux were influenced by solar radiation. Initial subsurface concentrations of the three compounds and volatilization flux, especially cis-1,3-D, were greater in the beds on the east side of the field than that in the beds on the west side of the field. Whether or not difference in initial subsurface concentrations of the compounds between east side beds and west side beds may influence fumigant efficacy remains to be determined.

Emissions and distribution of methyl bromide in field beds applied at two rates and covered with two types of plastic mulches

A field experiment was conducted to compare two plastic mulches and two application rates on surface emissions and subsurface distribution of methyl bromide (MBr) in field beds in Florida. Within 30 minutes after injection of MBr to 30 cm depth, MBr had diffused upward to soil surface in all beds covered with polyethylene film (PE) or virtually impermeable film (VIF) and applied at a high rate (392 kg/ha) and a low rate (196 kg/ha). Due to the highly permeable nature of PE, within 30 minutes after injection, MBr volatilized from the bed surfaces of the two PE-covered beds into the atmosphere. The amount of volatilization was greater for the high rate-treatment bed. On the other hand, volatilization of MBr from the bed surfaces of the two VIF-covered beds were negligible. Volatilization losses occurred from the edges of all the beds covered with PE or VIF and were greater from the high rate-treatment beds. Initial vertical diffusion of MBr in the subsurface of the beds covered with PE or VIF was mainly upward, as large concentrations of MBr were detected from near bed surfaces to 20 cm depth in these beds 30 minutes after injection and little or no MBr was found at 40 cm depth. The two VIF-covered beds exhibited greater MBr concentrations and longer resident times in the root zone (0.5–40 cm depth) than corresponding PE-covered beds. Concentrations of MBr in the root zone of the high rate-treatment beds were 3.6–6.1 times larger than the low rate-treatment beds during the first days after application. In conclusion, VIF promoted retention of MBr in the root zone and, if volatilization loss from bed edges can be blocked, volatilization loss from VIF-covered beds should be negligible.

Regulation of Rubisco Activity by Carboxyarabinitol-1-Phosphate and Elevated Atmospheric CO2 in Rice and Soybean Cultivars

The activity of ribulose bisphosphate carboxylase-oxygenase (rubisco) is influenced by environmental factors: light, temperature, and nutrients. Light, via rubisco activase, regulates the in vivo CO2/Mg2+-activation of rubisco (10). Light also effects the metabolism of carboxyarabinitol-1-phosphate (CA1P), an endogenous inhibitor of rubisco that exists to varying degrees in many, but not all species (6,13). The recent concern with increasing atmospheric CO2 has led to studies of the effect of this nutrient on growth, photosynthesis, and rubisco activity (11,12). CO2 acts as a substrate and activator for the rubisco reaction, but it also seems to have growth regulatory effects. Thus in some species the initial increase in photosynthesis at elevated CO2 due to more substrate, is followed by a decline, as rubisco protein declines (9). Increasing atmospheric CO2 will alter climatic temperatures, but little is known as to how these two variables may interact to affect photosynthesis and growth. This preliminary report suggests that in rice and soybean cultivars, rubisco activity, activation, and dark inhibition is regulated by these, and developmental, parameters.