Carbon Exchange Rate Research Articles

Response of Leaf Photosynthesis during the Grain‐Filling Period of Maize to Duration of Cold Exposure, Acclimation, and Incident PPFD

Maize (Zea mays L.) leaf photosynthesis during the grain-filling period is affected by low (≈4°C) night temperatures. Three factors that are potentially involved in this phenomenon were examined: (i) duration of cold exposure, (ii) acclimation prior to exposure to light, and (iii) level of incident photosynthetic photon flux density (PPFD) following cold exposure. Studies were carried out with plants grown hydroponically under both field and controlled-environment conditions. Three hybrids (‘Pride 5’, ‘Pioneer 3902’, and ‘Cargill 1877’) were used in the field experiments and Pioneer 3902 was used in controlled-environment experiments. Plants were exposed to 4°C in the dark for either 2 or 16 h and, subsequently, acclimated for either 0 or 1 h in the dark before exposure to high PPFD. Four incident PPFD levels (400, 650, 1200, and 2000 μmol m−2 s−1) after cold exposure were examined. Both duration of cold exposure and acclimation after cold exposure affected the reduction in leaf carbon exchange rate (CER). Leaf CER was reduced by 18.0% after a 2-h exposure and by 30.4% after a 16-h exposure to 4°C, and leaf CER was reduced by 20.4 and 28.0% for 1- and 0-h acclimation, respectively. Dark-adapted Fv/Fm (Fv = variable fluorescence; Fm = maximum chlorophyll fluorescence), that is, maximum quantum efficiency of Photosystem II, was 0.71 after cold exposure during the night compared with 0.81 for the control. The Fv/Fm was affected by duration of cold exposure (0.74 and 0.68 for 2- and 16-h exposure, respectively) but not by acclimation. Reduction in leaf photosynthesis after cold exposure was linearly related to the incident PPFD level. Results support the contention that the reduction in CER due to low night temperature is not associated with photoinhibition.

Carbon assimilation, partitioning and export in mature cladophylls of two asparagus (Asparagus officinalis) cultivars with contrasting yield.

To assess the physiological aspects underpinning cultivar difference in asparagus (Asparagus officinalis L.) yield, diel carbon exchange, carbon partitioning and export and sucrose phosphate synthase (SPS) activity were examined in mature cladophyll tissue of two asparagus cultivars (ASP-69 and ASP-03) under field conditions. Both cultivars exhibited similar diel patterns in carbon exchange rate (CER) and carbohydrate partitioning. Rates of carbon export estimated from CER and dry mass changes were the highest at midday and coincided with maximum assimilation rate. Carbon export accounted for about 74% of carbon fixation during the photoperiod. No diel fluctuations were observed in SPS activity in either cultivar. A positive correlation between day CER and carbon export rate (r2 = 0.87) was found and this relationship did not differ between the two cultivars studied. The greater carbon export rate measured in the high-yielding cultivar (ASP-69) was associated with significantly higher CER in comparison to the low-yielding cultivar (ASP-03). However, a correlation between sucrose concentration and carbon export rate did not exist. Biochemical evidence indicated that the greater CER in ASP-69 was associated with a significantly greater SPS activity (P 0.05). Phloem 14C exudate analysis revealed that 14C flux out of cladophyll tissue in ASP-69 was significantly greater than in ASP-03. These results indicate a feed-forward effect of rate of photosynthesis on assimilate export in the two cultivars studied.

Automated closed-system canopy-chamber for continuous field-crop monitoring of CO 2 and H 2O fluxes

An automated transient-state closed-system canopy-chamber for gas-exchange determinations of field-crops was developed to allow unattended day and night, high frequency CO 2 and H 2O exchange measurements, with short measurement time (15 s) and high scanning rate (0.5 s). Environment tests on the chamber performance indicated that: atmospheric pressure variation during operation was 10–20 Pa and limited to a few seconds; leaks introduced maximum errors of 1% in the flux calculation; turbulence effect on CO 2 and H 2O fluxes was not detectable; during the measurement period, temperature build-up inside the chamber was typically within 1–2 °C range; photosynthetic photon flux density ( R p) attenuation by the chamber as a whole was in the 15–20% range; whereas, net radiation ( R n) inside the chamber was always higher than outside by 10–20%. The flux determinations of the automated canopy-chamber were compared with other methods. Daily evapotranspiration ( E) of artichoke obtained by canopy-chamber was at the most 4.2% lower than E obtained by high-precision weighing lysimeter. Diurnal E and carbon exchange rates ( A) of sugarbeet and marjoram crops obtained by canopy-chamber closely followed the pattern of those obtained by the Bowen-ratio/energy-balance (BREB) method, with maximum daily underestimations of 6–8 and 5–6% for E and A, respectively. No differences in flux calculations came out when the rate of change in CO 2 and H 2O concentrations was derived either by linear or quadratic regressions (QR). The results of all tests and comparisons showed that the automated chamber presented is a valuable and accurate tool for monitoring day and night CO 2 and H 2O fluxes.

Trials and tribulations: a review of the role of assimilate supply in soybean genetic yield improvement

The contribution of genetic improvement to overall soybean ( Glycine max (L.) Merrill) yield improvement has been estimated to range from 0.5 to 0.7% per year in continental North America. Therefore, breeding has had and potentially will play an important role in yield improvement. An understanding of the physiological traits associated with genetic improvement in yield holds the promise of increasing the efficiency of further advances in yield improvement. A number of theories have been put forward as to the physiological traits that may contribute to genetic yield improvement. However, in reviewing the research literature, a number of incongruencies among the theories become apparent. The objective of this paper was to discuss some of the contradictory theories on the physiological traits associated with yield, especially as they address the role of assimilate supply to genetic yield improvement. The genetic material used, the means of parameter calculation, the phenological stage at which treatments were imposed can all impact the conclusions that may be drawn from a study. The conclusions from a study must thus be seen within the constraints of its experimental approach. Total dry matter (DM) accumulation appears to be a more important contributor to yield improvement than harvest index. The association between DM accumulation and yield is most apparent after the beginning of reproductive development, although the physiological traits associated with this increase is contentious: neither selection for maximum leaf carbon exchange rate (CER) nor maintenance of leaf CER during the seed filling period (SFP) has proved to consistently improve yield. Soybean cultivars have a complex feedback system which maintains a cultivar-specific source–sink ratio. Manipulation of the ratio of source supply to sink demand has shown that plants generally readjust to maintain their inherent source–sink ratio. A possible explanation for the lack of gain in yield through selection for greater assimilate supply alone may be because it was ineffective in increasing the source–sink ratio of the cultivar. The source–sink ratio may prove to be a more potent trait than assimilate supply alone to further soybean genetic yield improvement.

Moisture-deficit-induced changes in leaf-water content, leaf carbon exchange rate and biomass production in groundnut cultivars differing in specific leaf area

Field experiments were conducted during two rainy seasons to study the effect of soil moisture deficit on total biomass, pod yield, harvest index (HI) and drought tolerance index (DTI) in groundnut ( Arachis hypogaea L.) cultivars possessing a wide range of specific leaf area (SLA, 144–241 cm 2 g −1). There were three soil moisture regimes: adequate irrigation (W 1), drought simulated under rain-out-shelter (W 2) and rain-fed (W 3). This experiment had two parts, in one, five cultivars were exposed to W 1, W 2 and W 3, and in a second, seven cultivars were exposed to W 1 and W 3. Using the same set of seven cultivars, pot-culture experiments were conducted to study relative water content (RWC), stomatal conductance ( g s) and single leaf carbon exchange rate (CER) during increasing moisture-deficit in two contrasting (rainy and summer) seasons. Variation in DTI was significant, and low SLA types had greater DTI under both W 2 and W 3. The ranking of SLA among cultivars was consistent between experiments conducted during the two seasons. The rate of reduction in leaf RWC during the progressive moisture-deficit was related directly to SLA ( r=0.78, P<0.01). The coefficient of determination of the slopes calculated between RWC and soil moisture during the experimental period was more in the summer ( r 2=0.82) than the rainy ( r 2=0.54) season. Under increasing moisture-deficit, the low SLA types were able to maintain higher RWC, CER and g s in both seasons. The relationships between RWC and CER ( r=0.91, P<0.01), and RWC and g s ( r=0.65, P<0.01) were significant. It is suggested that under water-limited conditions there is a significant inverse relationship between SLA and RWC. The low SLA types (water use efficient) were found to be drought tolerant in terms of total dry matter production in the field studies, and maintenance of higher RWC under drought like situations in pot-culture experiments. Thus the ability of the low SLA types (higher water use efficiency, WUE) to maintain higher RWC may form the basis for the differences in drought tolerance vis a vis WUE in groundnut cultivars differing in SLA. Suggestions are made to select parents for drought tolerance or WUE, and to initiate breeding to combine traits like high HI, and WUE in terms of lower SLA. Ultimately, selection for both WUE (measured in terms of SLA) and yield traits (HI) should result in cultivars with improved performance in rain-fed agriculture.

Photosynthetic light response of flooded cherrybark oak (Quercus pagoda) seedlings grown in two light regimes.

Two-year-old cherrybark oak (Quercus pagoda Raf.) seedlings raised in full or partial (27%) sunlight were flooded for 30 days to study the effects of light availability and root inundation on photosynthetic light response. Compared with seedlings receiving full sunlight, seedlings receiving partial sunlight developed leaves with 90% greater blade area, 26% less mass per unit volume, and 35% lower nitrogen (N) concentration per unit area, leading to a 15% reduction in leaf photosynthetic capacity when carbon exchange rates were based on blade area. However, when carbon exchange rates were based on leaf mass, leaves acclimated to partial sunlight exhibited a 15% greater photosynthetic capacity realized primarily through an increased initial slope of the photosynthetic light response (A/PPFD) curve and increased net photosynthesis at leaf saturation (Amax). Short-term flooding increased leaf mass per unit area more than 19%, reduced foliar N concentrations per unit dry mass by 19%, and initiated reductions in Amax and apparent quantum yield (phi) of seedlings in both light regimes. Greatest impairment of Amax (56% area basis, 65% mass basis) and phi (40%) were observed in leaves receiving full sunlight, and the declines were concomitant with a 35% decrease in chlorophyll concentration. Flooding also depressed instantaneous photosynthetic N-use efficiency (PPNUE) such that Amax decreased 54%, and the initial slope of PPNUE/PPFD curves decreased 33 and 50% for leaves acclimated to partial and full sunlight, respectively. The A/PPFD patterns indicated that the magnitude of flood-induced inhibition of the photosynthetic mechanism of cherrybark oak seedlings is determined partly by the light environment.

Carbon dioxide exchange in Norway spruce at the shoot, tree and ecosystem scale.

Net CO2 exchange in a 35-year-old boreal Norway spruce (Picea abies (L.) Karst.) forest in northern Sweden was measured at the shoot (NSE), tree (NTE) and ecosystem levels (NEE) by means of shoot cuvettes, whole-tree chambers and the eddy covariance technique, respectively. We compared the dynamics of gross primary production (GPP) at the three levels during the course of a single week. The diurnal dynamics of GPP at each level were estimated by subtracting half-hourly or hourly model-estimated values of total respiration (excluding light-dependent respiration) from net CO(2) exchange. The relationship between temperature and total respiration at each level was derived from nighttime measurements of NSE, NTE and NEE over the course of 1 month. There was a strong linear relationship (r2 = 0.93) between the hourly estimates of GPP at the shoot and tree levels, but the correlation between shoot- and ecosystem-level GPP was weaker (r2 = 0.69). However, the correlation between shoot- and ecosystem-level GPP was improved (r2 = 0.88) if eddy covariance measurements were restricted to periods when friction velocity was > or = 0.5 m s(-1). Daily means were less dependent on friction velocity, giving an r2 value of 0.94 between shoot- and ecosystem-level GPP. The correlation between shoot and tree levels also increased when daily means were compared (r2 = 0.98). Most of the measured variation in carbon exchange rate among the shoot, tree and ecosystem levels was the result of periodic low coupling between vegetation and the atmosphere at the ecosystem level. The results validate the use of measurements at the shoot and tree level for analyzing the contribution of different compartments to net ecosystem CO2 exchange.

Evaluation of Modeled Carbon Fluxes for a Slash Pine Ecosystem: SPM2 Simulations Compared to Eddy Flux Measurements

Abstract A process-based model (SPM2) was developed to simulate net hourly exchanges of carbon for slash pine (Pinus elliottii var. elliottii) ecosystems in north-central Florida, and simulated values were compared to those obtained using eddy covariance measurements above the canopy. The SPM2 simulated relatively low hourly rates of net carbon exchange at high irradiance during the day, especially during the month of May. This discrepancy contributed the most to differences between the two approaches, and suggests that the model underestimates the maximum rate of leaf-level net photosynthesis during the period of rapid growth in the spring. The SPM2 also simulated lower net carbon release during the nighttime across the range of air temperatures, relative to eddy covariance measurements. As a result of these discrepancies, accumulated daytime and nighttime sums were quite different between the two approaches. However, once results were aggregated over 24 hr, differences between simulations and measurements were insignificant at all but the highest and lowest daily net carbon gain values. Annual estimates for 1996 were similar: 693, 719, and 745 g C m-2 yr-1 for the SPM2 model, eddy covariance measurements and mass balance measurements, respectively. This model evaluation has lead to specific research questions for guiding further model development. FOR. Sci. 47(1):52–59.

Gas Exchange and Water Relations in Diploid and Tetraploid Russian Wildrye

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is a drought tolerant, cool‐season forage grass used in seeded pastures in the Northern Great Plains where water often limits production. Seedling vigor is generally poor in diploid cultivars, but tetraploid germplasm has improved seedling vigor. Objectives of this study were to determine the relationships between water‐use efficiency (WUE), carbon isotope discrimination (CID), and gas exchange rates for a diploid cultivar (Vinall) and a tetraploid entry over 3 yr, two water treatments (50 and 150% of mean monthly precipitation), and two fertilizer rates (10 and 134 kg N ha−1) in a rain shelter. The tetraploid entry exhibited higher carbon exchange rate (CER), stomatal conductance (gs), and transpiration (T) than the diploid entry at the 50% but not the 150% water treatment. Leaf water potentials (LWP) were 0.6 and 0.3 MPa less negative for the tetraploid entry than diploid entry at the 50 and 150% water treatment, respectively. Values of CER averaged 12.4 and 14.2 μmol m−2 s−1, T averaged 5.2 and 6.0 mmol m−2 s−1, and gs averaged 0.21 and 0.28 mol m−2 s−1 for the diploid and tetraploid entry, respectively. The diploid entry had a significantly greater CID, averaging 20.37‰ compared with 19.65‰ for the tetraploid entry and CID was negatively associated with WUE. The more favorable plant water relations, gas exchange, and dry matter production under limited soil water suggests tetraploid populations of Russian wildrye should be emphasized in future breeding and management programs.

Response of maize leaf photosynthesis to low temperature during the grain-filling period

The response of dry matter accumulation and leaf photosynthesis in maize ( Zea mays L.) to low temperature has been documented during early phases of development, but little is known about the low-temperature response of maize during later phases of development. Studies were conducted in 1999 at the Cambridge Research Station, Ontario, Canada, to quantify the effect of low night temperature during grain filling on leaf photosynthesis of short-season maize hybrids. Plants were grown in a hydroponic system in the field with plants in the low-night temperature treatments exposed to 4°C from late afternoon (17:00 h) to the next morning (9:00 h). Plants of three maize hybrids (i.e., an older hybrid, Pride 5, and two more recent hybrids, Pioneer 3902 and Cargill 1877) were exposed to one night or three consecutive nights of 4°C at weekly intervals from tasseling to 6 weeks after silking. Carbon exchange rate (CER) was measured at 10:00, 12:00, 14:00, and 16:00 h on the second leaf above that subtending the topmost ear. Dark-adapted chlorophyll fluorescence ( F v/ F m) was measured at 9:00 h at 6 weeks after silking. Leaf CER of control plants declined almost linearly from about 50 μmol m −2 s −1 at tasseling to about 20 μmol m −2 s −1 at 6 weeks after silking with the rate of decline in the older hybrid approximately two times greater than that in the two newer hybrids. No trend in the reduction in cold-stressed leaf CER relative to the field-grown control was apparent from tasseling to 6 weeks after silking. Reduction in CER was greater during the morning than during the afternoon after exposure to 4°C and the reduction in leaf CER increased from 19.4% after one night, to 25.8% after two nights, and 30.2% after three nights. Mean reduction in leaf CER after one night at 4°C differed significantly among the three hybrids and was 29.7% for Pride 5, 15.4% for Pioneer 3902, and 13.5% for Cargill 1877. The reduction in leaf CER due to low night temperature was associated with a reduction in leaf chlorophyll fluorescence. In conclusion, maize hybrids differ significantly in leaf CER response to cold night temperature during the grain-filling period.

Genotype Variability in Photosynthetic Characteristics in Finger Millet

High variability in leaf gas exchange and related traits were found in 30 genotypes of field grown finger millet. The variability in carbon exchange rate per unit leaf area (P N) can be partly attributed to the differences in the stomatal conductance (gs) and area leaf mass (ALM). The P N was positively correlated with total dry matter (TDM). However, no relationship between P N and seed yield was found. The leaf area showed a positive and significant correlation with total biomass. None of the other gas-exchange traits had significant relationship either with TDM or with seed yield. The ALM showed a strong positive association with P N. However, it was not correlated with either total biomass or seed yield. As a result, the use of ALM as surrogate for P N for identifying high biomass producing genotypes only had a limited value. Hence selection for high P N would result in higher biomass producing types.

Carbon Exchange Rates in Grazed and Ungrazed Pastures of Wyoming

The influence of cattle grazing on carbon cycling in the mixed grass prairie was investigated by measuring the CO(2) exchange rate in pastures with a 13 year history of heavy or light grazing and an ungrazed exclosure at the High Plains Grasslands Research Station near Cheyenne, Wyo. In 1995, 1996 and 1997 a closed system chamber, which covered 1 m(2) of ground, was used every 3 weeks from April to October to measure midday CO(2) exchange rate. Green vegetation index (similar to leaf area index), soil respiration rate, species composition, soil water content, soil temperature, and air temperature were also measured to relate to CO(2) exchange rates of the 3 grazing treatments. Treatment differences varied among years, but overall early season (mid April to mid June) CO(2) exchange rates in the grazed pastures were higher (up to 2.5 X) than in the exclosure. Higher early season CO(2) exchange rates were associated with earlier spring green-up in grazed pastures, measured as higher green vegetation index. As the growing season progressed, green vegetation index increased in all pastures, but more so in the ungrazed exclosure, resulting in occasionally higher (up to 2 X) CO(2) exchange rate compared with grazed pastures late in the season. Seasonal treatment differences were not associated with soil temperature, soil respiration rate, or air temperature, nor was there a substantial change in species composition due to grazing. We hypothesize that early spring green-up and higher early season CO(2) exchange rate in grazed pastures may be due to better light penetration and a warmer microclimate near the soil surface because of less litter and standing dead compared to the ungrazed pastures. When all the measurements were averaged over the entire season, there was no difference in CO(2) exchange rate between heavily grazed, lightly grazed and ungrazed pastures in this ecosystem. DOI:10.2458/azu_jrm_v53i2_lecain

Elevated atmospheric CO2 and increased nitrogen deposition: effects on C and N metabolism and growth of the peat moss Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) Warnst

Summary Sphagnum bogs play an important role when considering the impacts of global change on global carbon and nitrogen cycles. Sphagnum recurvum P. Beauv. var. mucronatum (Russ.) was grown at 360 (ambient) and 700 μL L−1 (elevated) atmospheric [CO2] in combination with different nitrogen deposition rates (6, 15, 23 g N m−2 y−1), in a short‐ and long‐term growth chamber experiment.After 6 months, elevated atmospheric [CO2] in combination with the lowest nitrogen deposition rate, increased plant dry mass by 17%. In combination with a high nitrogen deposition rate, biomass production was not significantly stimulated.At the start of the experiment, photosynthesis was stimulated by elevated atmospheric [CO2], but it was downregulated to control levels after three days of exposure. Elevated [CO2] substantially reduced dark respiration, which resulted in a continuous increase in soluble sugar content in capitula. Differences in growth response among different nitrogen and CO2 treatments could not be related to measured carbon exchange rates, which was mainly due to interference of microbial respiration.Doubling atmospheric [CO2] reduced total nitrogen content in capitula but not in stems at all nitrogen deposition rates. Reduction in total nitrogen content coincided with a decrease in amino acids, but soluble protein levels remained unaffected. Thus, elevated [CO2] induced a substantial shift in the partitioning of nitrogen compounds in capitula. Soluble sugar concentration was negatively correlated with total nitrogen content, which implies that the reduction in amino acid content in capitula, exposed to elevated [CO2], might be caused by the accumulation of soluble sugars.Growth was not stimulated by increased nitrogen deposition. High nitrogen deposition, resulting in a capitulum nitrogen content in excess of 15 mg g−1 dw, was detrimental to photosynthesis, reduced water content and induced necrosis. We propose a capitulum nitrogen content of 15 mg g−1 dw as a possible bioindicator for the detection of nitrogen pollution stress in oligo‐mesotrophic peat bog ecosystems.At the lowest nitrogen deposition level, nitrogen recovery was higher than 100%, which indicates substantial dry deposition and/or gaseous nitrogen fixation by bacteria, associated with Sphagnum. Increasing nitrogen deposition rates decreased nitrogen recovery percentages, which indicates reduced efficiency of nitrogen fixation.

Carbon and water exchanges of two contrasting central Siberia landscape types: regenerating forest and bog

Abstract1. In central Siberia Pinus sylvestris forests and bogs are common elements of the landscape and they show different functional behaviour in terms of energy and carbon exchanges.2. The two ecosystems show a remarkable difference in energy dissipation, with average Bowen ratios of 0·6 and 2·9, respectively.3. The alternation of bogs and forests with different energy partition at the surface could affect rainfall distribution and the disturbance regimes (lightening and fires) and drive the ecology of such a complex landscape.4. During summer, water shortage and poor nutrient conditions in the soil heavily affect carbon exchange rates of the regenerating forest (− 7·7 mmol m−2 day−1). Consequently the bog becomes a significant dominant carbon sequestration element of this particular landscape with higher rates of carbon uptake (− 104·2 mmol m−2 day−1).

Carbon exchange rates in grazed and ungrazed pastures of Wyoming

The influence of cattle grazing on carbon cycling in the mixed grass prairie was investigated by measuring the CO(2) exchange rate in pastures with a 13 year history of heavy or light grazing and an ungrazed exclosure at the High Plains Grasslands Research Station near Cheyenne, Wyo. In 1995, 1996 and 1997 a closed system chamber, which covered 1 m(2) of ground, was used every 3 weeks from April to October to measure midday CO(2) exchange rate. Green vegetation index (similar to leaf area index), soil respiration rate, species composition, soil water content, soil temperature, and air temperature were also measured to relate to CO(2) exchange rates of the 3 grazing treatments. Treatment differences varied among years, but overall early season (mid April to mid June) CO(2) exchange rates in the grazed pastures were higher (up to 2.5 X) than in the exclosure. Higher early season CO(2) exchange rates were associated with earlier spring green-up in grazed pastures, measured as higher green vegetation index. As the growing season progressed, green vegetation index increased in all pastures, but more so in the ungrazed exclosure, resulting in occasionally higher (up to 2 X) CO(2) exchange rate compared with grazed pastures late in the season. Seasonal treatment differences were not associated with soil temperature, soil respiration rate, or air temperature, nor was there a substantial change in species composition due to grazing. We hypothesize that early spring green-up and higher early season CO(2) exchange rate in grazed pastures may be due to better light penetration and a warmer microclimate near the soil surface because of less litter and standing dead compared to the ungrazed pastures. When all the measurements were averaged over the entire season, there was no difference in CO(2) exchange rate between heavily grazed, lightly grazed and ungrazed pastures in this ecosystem.

Diurnal Changes in Photosynthesis in Sugarcane Leaves: II. Enzyme activities and metabolite levels relating to sucrose and starch metabolism

SummaryDiurnal changes in carbohydrate contents, assimilate export, enzyme activities and metabolite levels associated with sucrose and starch synthesis in field-grown sugarcane (Saccharum sp. cv. NiF4) leaves were investigated during a natural 24 h day-night cycle. Eighty percent of the carbon fixed in sugarcane leaves at midday was exported immediately. Of the total carbon fixed during the day, 82% was exported in the daytime and 17% was accumulated as leaf starch which was exported at night. The activities of sucrose phosphate synthase (SPS), cytosolic fructose-1, 6-bisphosphatase (FBPase), UDP-glucose pyrophosphorylase (UDPG-PPase) and ADP-glucose pyrophosphorylase (ADPG-PPase), and the levels of triose phosphates (triose-P) and fructose-1,6-bisphosphate (FBP) showed distinct diurnal fluctuations during the day-night cycle. The levels of hexose phosphates fluctuated at smaller magnitudes compared with those in triose-P and FBP. The diurnal change in triose-P level was highly related to the changes in carbon exchange rate and sucrose content, while the sucrose content was closely related to the changes in activities of SPS, cytosolic FBPase and UDPG-PPase in leaves of sugarcane. The present results suggest that the availability of triose-P is a key factor in determining the rate of sucrose synthesis in sugarcane leaves.

Elevated CO2 increases wheat cer, leaf and tiller development, and shoot and root growth

Whole‐plant responses to elevated CO2 throughout the life cycle are needed to understand future impacts of elevated atmospheric CO2. In this study, Triticum aestivum L. leaf carbon exchange rates (CER) and carbohydrates, growth, and development were examined at the tillering, booting, and grain‐filling stages in growth chambers with CO2 concentrations of 350 (ambient) or 700 (high) μmol mol−1. Single‐leaf CER values measured on plants grown at high CO2 were 50% greater than those measured on plants grown at ambient CO2 for all growth stages, with no photosynthetic acclimation observed at high CO2. Leaves grown in high CO2 had more starch and simple sugars at tillering and booting, and more starch at grain‐filling, than those grown in ambient CO2. CER and carbohydrate levels were positively correlated with leaf appearance rates and tillering (especially third‐, fourth‐ and fifth‐order tillers). Elevated CO2 slightly delayed tiller appearance, but accelerated tiller development after appearance. Although high CO2 increased leaf appearance rates, final leaf number/culm was not effected because growth stages were reached slightly sooner. Greater plant biomass was related to greater tillering. Doubling CO2 significantly increased both shoot and root dry weight, but decreased the shoot to root ratio. High CO2 plants had more spikes plant−1 and spikelets spike−1, but a similar number of fertile spikelets spike−1. Elevated CO2 resulted in greater shoot, root and spike production and quicker canopy development by increasing leaf and tiller appearance rates and phenology.

Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow-poplar seedlings

Potted seedlings of black cherry ( Prunus serotina Ehrh.) (BC), green ash ( Fraxinus pennsylvanica Marsh.) (GA), and yellow-poplar ( Liriodendron tulipifera L.) (YP) were exposed to one of the four treatments: (1) charcoal-filtered air (CF) at ambient CO 2 (control); (2) twice ambient O 3 (2×O 3); (3) twice ambient CO 2 (650 μl l −1) plus CF air (2×CO 2); or (4) twice ambient CO 2 (650 μl l −1) plus twice ambient O 3 (2×CO 2+2×O 3). The treatments were duplicated in eight continuously stirred tank reactors for 10 weeks. Gas exchange was measured during the last 3 weeks of treatment and all seedlings were destructively harvested after 10 weeks. Significant interactive effects of O 3 and CO 2 on the gas exchange of all three species were limited. The effects of elevated CO 2 and O 3, singly and combined, on light-saturated net photosynthesis ( A max) and stomatal conductance ( g s) were inconsistent across species. In all three species, elevated O 3 had no effect on g s. Elevated CO 2 significantly increased A max in GA and YP foliage, and decreased g s in YP foliage. Maximum carbon exchange rates and quantum efficiencies derived from light-response curves increased, while compensation irradiance and dark respiration decreased in all three species when exposed to 2×CO 2. Elevated O 3 affected few of these parameters but any change that was observed was opposite to that from exposure to 2×CO 2–air. Interactive effects of CO 2 and O 3 on light-response parameters were limited. Carboxylation efficiencies, derived from CO 2-response curves ( A/C i curves) decreased only in YP foliage exposed to 2×CO 2–air. In general, growth was significantly stimulated by 2×CO 2 in all three species; though there were few significant growth responses following exposure to 2×O 3 or the combination of 2×CO 2 plus 2×O 3. Results indicate that responses to interacting stressors such as O 3 and CO 2 are species specific.

Radiation-use efficiency response to vapor pressure deficit for maize and sorghum

Variability within a crop species in the amount of dry mass produced per unit intercepted solar radiation, or radiation-use efficiency (RUE), is important for the quantification of plant productivity. RUE has been used to integrate (1) leaf area, (2) solar radiation interception, and (3) productivity per unit leaf area into crop productivity. Responsiveness of RUE to vapor pressure deficit (VPD) should relate closely to responsiveness of CO 2 exchange rate (CER) to VPD. The objective of this study was to compare independent RUE measurements to published response functions relating VPD with RUE of maize ( Zea mays L.) and grain sorghum [ Sorghum bicolor L. (Moench)]. Data sets from five locations covering a wide range of mean VPD values were compared to published response functions. Predicted RUE values were nearly always within the 95% confidence intervals of measurements. Measured RUE of maize decreased as VPD increased from 0.9 to 1.7 kPa. For sorghum, measured values of RUE agreed closely with predictions. RUE of sorghum decreased as VPD increased from 1.1 to 2.2 kPa. The relative RUE:VPD responses for these two species were similar to CER:VPD responses reported in the literature. Thus, these RUE:VPD responses may be general and appear to be related to carbon exchange rates. We calculated the expected impacts of VPD on RUE at three USA locations during maize and sorghum growing seasons. The RUE:VPD equations offer hope in describing location effects and time-of-year effects on RUE.

Photosynthesis and Chlorophyll Fluorescence in Blackleaf-Affected Concord Leaves

Blackleaf is a leaf disorder which is believed to be associated with low leaf and/or petiole potassium. Correlative evidence for potassium deficiency has been variable and increasing potassium fertilization has not eliminated the disorder. Additionally, blackleaf symptom development differs from classic potassium deficiency in several critical aspects, which include location within the canopy and individual leaves. We tested the hypothesis that blackleaf influences the photosynthetic process such that potential vine productivity is reduced. Coincident with veraison and appearance of visual symptoms in Concord grapevines, carbon exchange rate (CER) declined in blackleaf-affected source leaves (9.46 µmol CO₂ · m ^-2 · s^-l) compared to unaffected source leaves (12.46 µmol CO₂ · m ^-2 · s^-l). By September the decline in CER was &gt; 50% in affected leaves (6.18 µmol CO₂ · m ^-2 · s^-1). These data suggest blackleaf results in a 22% to 55% reduction in carbon on a daily basis. The level of chlorophyll fluorescence (Chl-F) decreased in affected leaves, which is opposite of the expected increase in Chl-F with a reduction in CER. Loss in CER did not appear to be associated with photoinhibition because the maximum intrinsic efficiency of Photosystem II (PSII), as measured by F/F_m, was unaffected. When CER, Chl-F and chlorophyll <i>a</i> and <i>b</i> concentrations for green and black portions of affected leaves were compared, there was no significant difference in CER. CER was reduced in green and black portions of affected leaves by <i>ca</i>. 55% compared to unaffected leaves. Green portions of affected leaves had the highest Chl-F values, thus less light energy was utilized in photosynthesis, suggesting the potential efficiency of the photosynthetic apparatus had been reduced. Measurement of chlorophyll concentrations confirmed that there was a loss in chlorophyll green and black portions of affected leaves. Collectively, the data suggest a possible transition in photosynthetic system damage between unaffected leaves, green tissue of affected leaves, and black tissue of affected leaves.