Diurnal Course Research Articles

Response of gas exchange and yield components of field-grown Triticum aestivum L. to elevated ozone in China

To assess photosynthesis and yield components' response of field-grown wheat to increasing ozone (03) concentration (based on diurnal pattern of ambient O-3) in China, winter wheat (Triticum aestivum L.) cv. Jia 403 was planted in open top chambers and exposed to three different O-3 concentrations: O-3-free air (CF), ambient air (NF), and O-3-free air with additional O-3 (CF+O-3). Diurnal changes of gas exchange and net photosynthetic rate (P-N) in response to photosynthetic photon flux density (PPFD) of flag leaves were measured at the filling grain stage, and yield components were investigated at harvest. High O-3 concentration altered diurnal course of gas exchange [PN, stomatal conductance (g,), and intercellular CO2 concentration (C-i)] and decreased significantly their values except for C-i. Apparent quantum yield (AQY), compensation irradiance (CI), and saturation irradiance (SI) were significantly decreased, suggesting photosynthetic capacity was also altered, characterized as reduced photon-saturated photosynthetic rate (P-Nmax). The limit of photosynthetic activity was probably dominated by non-stomatal factors in combination with stomatal closure. The significant reduction in yield was observed in CF+O-3 treatment as a result of a marked decrease in the ear length and the number of grains per ear, and a significant increase in the number of infertile florets per ear. Even though similar responses were also observed in plants exposed to ambient O-3 concentration, no statistical difference was observed at current ambient O-3 concentration in China.

Standard deviation of the wind vertical component and its dynamics in Moscow by the sodar data

For the first time long-term data on standard deviation of the vertical wind component in the lower 250 m air layer in Moscow are presented. They have been received by results of continuous sodar measurements during six last years. The climatologic features of its diurnal and annual course for various seasons have been discussed. In average this parameter varies usually from 0.6 to 0.8 m/s, in the afternoon in summer - up to 1 m/s. The diurnal course is flat in winter and has a clear daily maximum in the other seasons connected with the thermal convection. The annual course is characterized by a maximum in June and the lowest values in autumn and in winter. Clear asymmetry between the transitional seasons (spring and autumn) are detected. The values of this parameter are clearly depending on the synoptic conditions. They are highest in the rear of cyclones after the passing of the cold front and in cold air masses due to the intense development of thermal convection there.

Moving towards a more mechanistic approach in the determination of soil heat flux from remote measurements: II. Diurnal shape of soil heat flux

For vegetated surfaces, calculation of soil heat flux, G, with the Exact or Analytical method requires a harmonic analysis of below-canopy soil surface temperature, to obtain the shape of the diurnal course of G. When determining G with remote sensing methods, only composite (vegetation plus soil) radiometric brightness temperature is available. This paper presents a simple equation that relates the sum of the harmonic terms derived for the composite radiometric surface temperature to that of below-canopy soil surface temperature. The thermal inertia, Γ, for which a simple equation has been presented in a companion paper, paper I, is used to set the magnitude of G. To assess the success of the method proposed in this paper for the estimation of the diurnal shape of G, a comparison was made between ‘remote’ and in situ calculated values from described field sites. This indicated that the proposed method was suitable for the estimation of the shape of G for a variety of vegetation types and densities. The approach outlined in paper I, to obtain Γ, was then combined with the estimated harmonic terms to predict estimates of G, which were compared to values predicted by empirical remote methods found in the literature. This indicated that the method proposed in the combination of papers I and II gave reliable estimates of G, which, in comparison to the other methods, resulted in more realistic predictions for vegetated surfaces. This set of equations can also be used for bare and sparsely vegetated soils, making it a universally applicable method.

A stereo imaging system for measuring structural parameters of plant canopies

Plants constantly adapt their leaf orientation in response to fluctuations in the environment, to maintain radiation use efficiency in the face of varying intensity and incidence direction of sunlight. Various methods exist for measuring structural canopy parameters such as leaf angle distribution. However, direct methods tend to be labour-intensive, while indirect methods usually give statistical information on stand level rather than on individual leaves. We present an area-based, binocular stereo system composed of commercially available components that allows three-dimensional reconstruction of small- to medium-sized canopies on the level of single leaves under field conditions. Spatial orientation of single leaves is computed with automated processes using modern, well-established stereo matching and segmentation techniques, which were adapted for the properties of plant canopies, providing high spatial and temporal resolution (angle measurements with an accuracy of approx. +/-5 degrees and a maximum sampling rate of three frames per second). The applicability of our approach is demonstrated in three case studies: (1) the dihedral leaflet angle of an individual soybean was tracked to monitor nocturnal and daytime leaf movement showing different frequencies and amplitudes; (2) drought stress was diagnosed in soybean by quantifying changes in the zenith leaflet angle distribution; and (3) the diurnal course of the zenith leaf angle distribution of a closed soybean canopy was measured.

Urban/rural atmospheric water vapour pressure differences and urban moisture excess in Krefeld, Germany

AbstractUrban/rural humidity differences were analysed by means of a climate station pair in Krefeld (51° 20′N, 6° 33′E), Germany, during the period from 11/2001 to 10/2002, on the basis of hourly averages of water vapour pressure. Focus was put upon on the examination of frequency, timing and duration of the Urban Moisture Excess (UME) (Δeu−r > 0 hPa). It was found that the urban site was more humid (0 hPa < Δeu−r⩽0.5 hPa; weak UME) in 31.4% of the cases investigated and was only rarely significantly more humid (Δeu−r > 0.5 hPa; intense UME) in 4.6%. Weak and intense UME occur during every month of the year with different frequencies per month. A diurnal course of UME was found for summer but not for winter. Weak and intense UME events show frequency maxima in the second half of the night. Most of them are characterized by durations of 1 hour, in few cases several hours duration were observed for weak (up to 14 h) and intense UME (up to 12 h).The main reason for formation of UME events might be that the surface dew point at the rural station was reached more often, earlier and lasted longer in comparison to the urban environment. Copyright © 2007 Royal Meteorological Society

Seasonal evolution of diffusional limitations and photosynthetic capacity in olive under drought

This study tests the hypothesis that diffusional limitation of photosynthesis, rather than light, determines the distribution of photosynthetic capacity in olive leaves under drought conditions. The crowns of four olive trees growing in an orchard were divided into two sectors: one sector absorbed most of the radiation early in the morning (MS) while the other absorbed most in the afternoon (AS). When the peak of radiation absorption was higher in MS, air vapour pressure deficit (VPD) was not high enough to provoke stomatal closure. In contrast, peak radiation absorption in AS coincided with the daily peak in VPD. In addition, two soil water treatments were evaluated: irrigated trees (I) and non-irrigated trees (nI). The seasonal evolution of leaf water potential, leaf gas exchange and photosynthetic capacity were measured throughout the tree crowns in spring and summer. Results showed that stomatal conductance was reduced in nI trees in summer as a consequence of soil water stress, which limited their net assimilation rate. Olive leaves displayed isohydric behaviour and no important differences in the diurnal course of leaf water potentials among treatments and sectors were found. Seasonal diffusional limitation of photosynthesis was mainly increased in nI trees, especially as a result of stomatal limitation, although mesophyll conductance (g(m)) was found to decrease in summer in both treatments and sectors. A positive relationship between leaf nitrogen content with both leaf photosynthetic capacity and the daily integrated quantum flux density was found in spring, but not in summer. The relationship between photosynthetic capacity and g(m) was curvilinear. Leaf temperature also affected to g(m) with an optimum temperature at 29 degrees C. AS showed larger biochemical limitation than MS in August in both treatments. All these suggest that both diffusional limitation and the effect of leaf temperature could be involved in the seasonal reduction of photosynthetic capacity of olive leaves. This work highlights the need for models of plant growth and ecosystem function to incorporate new parameters affecting the distribution of photosynthetic capacity in canopies.

Modelling evapotranspiration in a Scots pine stand under Mediterranean mountain climate using the GLUE methodology

Canopy transpiration ( E c) and soil evaporation ( E s) in a Mediterranean Scots pine stand were simulated using a two-layer model, with a Jarvis-type submodel of canopy stomatal conductance ( G s) and a soil resistance to evaporation expressed as a function of superficial soil moisture. Sap flow measurements and soil evaporation data, together with meteorological and soil moisture variables were used to calibrate the model. G s was calibrated using the generalized likelihood uncertainty estimation (GLUE) methodology, first with data from the year 2004, a year characterised by mild meteorological conditions. Then, data from the year 2003, which included an intense summer drought, was used to update the results from the previous calibration. The discrepancy between the diurnal courses of modelled and measured E c using best-fit parameters was not related to any particular situation of meteorology or soil moisture. Model performance improved at the daily scale, but the model failed to simulate E c adequately during the year 2005. Maximum modelled E s rates were 0.7 mm day −1 with the ratio E s/ E c being typically under 0.3 during the growing season. The GLUE analysis revealed that parameters representing reference stomatal aperture at a vapour pressure deficit ( D) value equal to 1 kPa ( G s,ref), and sensitivity to D ( m) were the most relevant, and were consistent with the hydraulic theory of stomatal regulation. Parameters controlling the response to superficial soil moisture deficit only appeared sensitive in the calibration with data from the year 2003, suggesting that response to deeper soil layers should also be considered in the model. Updating the original calibration reduced predictive uncertainty and constrained the value of some parameters. Nevertheless, it seems that representations of variable plant and soil hydraulic resistances, are required to simulate long-term E c in seasonally-dry Mediterranean forest stands.

Forced depression of leaf hydraulic conductance in situ: effects on the leaf gas exchange of forest trees

Summary Recent work on the hydraulic conductance of leaves suggests that maximum photosynthetic performance of a leaf is defined largely by its plumbing. Pursuing this idea, we tested how the diurnal course of gas exchange of trees in a dry tropical forest was affected by artificially depressing the hydraulic conductance of leaves (Kleaf). Individual leaves from four tropical tree species were exposed to a brief episode of forced evaporation by blowing warm air over leaves in situ. Despite humid soil and atmospheric conditions, this caused leaf water potential (Ψleaf) to fall sufficiently to induce a 50–74% drop in Kleaf. Two of the species sampled proved highly sensitive to artificially depressed Kleaf, leading to a marked and sustained decline in the instantaneous rate of CO2 uptake, stomatal conductance and transpiration. Leaves of these species showed a depression of hydraulic and photosynthetic capacity in response to the ‘blow‐dry’ treatment similar to that observed when major veins in the leaf were severed. By contrast, the other two species sampled were relatively insensitive to Kleaf manipulation; photosynthetic rates were indistinguishable from control (untreated) leaves 4 h after treatment. These insensitive species demonstrate a linear decline of Kleaf with Ψleaf, while Kleaf in the two sensitive species falls precipitously at a critical water deficit. We propose that a sigmoidal Kleaf vulnerability enables a high diurnal yield of CO2 at the cost of exposing leaves to the possibility of xylem cavitation. Linear Kleaf vulnerability leads to a relatively lower CO2 yield, while providing better protection against cavitation.

Dew as a key factor for the distribution pattern of the lichen species Teloschistes lacunosus in the Tabernas Desert (Spain)

The role of different sources of water (rain, dew and water vapor) has been investigated under natural conditions in order to explain the activity and the distribution patterns of Teloschistes lacunosus (Rupr.) Sav. in the Tabernas Desert (Almeria, Spain). This field work was carried out at two neighboring sites: a pediment where T. lacunosus is well developed and an east-facing slope where only few small thalli are developed. Diurnal courses of photosynthetic activity were assessed by the use of chlorophyll a fluorescence measurements, at each site for a total of 12 days distributed among different seasons over the year. Microclimatic data (thallus temperature, relative humidity (RH) and light intensity) were recorded continuously for a period of 1 year including all the days on which fluorescence measurements were made. Dried T. lacunosus in its natural habitat only became photosynthetically active after re-hydration with liquid water (dew or rain). In contact with an atmosphere of high RH (higher than 90%) but without dew condensation, thalli were not able to obtain sufficient water to become physiologically active. The microclimatic study showed notably differences between the two studied expositions. After dawn, thalli from the east-facing slope were exposed to higher temperatures and light intensity (PPFD) levels than thalli from the pediment. This was reflected in the length of time that the air remained saturated and the lichen remained wet and active. The high incident PPFD and the resultant increased temperatures at the east-facing slope led to short dew duration and, therefore to shorter periods of morning photosynthetic activity than on the pediment as fluorescence measurements showed. Additionally, the microclimatic differences between the two sites indicated a high frequency of dew fall events on the thalli from the pediment. The time periods of thallus dew imbibition vary strongly with the exposure of the lichens.

Diurnal time course of pain perception in healthy humans

Rapid skin heating by infrared lasers can be used to investigate the integrity of the nociceptive system by activating A-delta and C fibers. The aim of our study was to analyze if healthy humans exhibit any clinically relevant diurnal variations in their heat pain sensitivity. Circadian A-delta fiber function was analyzed by studying N2 and P2 components of laser-evoked potentials (LEP) and pain thresholds evoked by laser stimulation of the foot every 2 h from 8 a.m. to 10 p.m. in 15 healthy subjects. Heat stimuli were generated by an infrared Tm-YAG laser and were delivered to an area of 4 cm × 4.5 cm on the dorsum of the right or left foot in 3 runs of incremental and decremental intensities. After each stimulus subjects were asked to classify the intensity of pain with a numeric rating scale (NRS). LEPs were recorded with fixed stimulus intensities that were 1.5× of the pain threshold. Data were collected with the SynAmps System (Neuroscan, El Paso, USA) and averaged across 35–40 trials. Laser-induced heat pain thresholds and circadian latencies of LEP did not significantly vary during the day. Our results correspond with previous studies that did not detect any consistent significant diurnal variations in perception of heat pain perception using contact thermodes. The intensity of pain perception did not demonstrate any correlation with mood or sleep parameters as measured with the Beck Depression Inventory (BDI), the subjective sleep scales Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS).

Tree water storage and its diurnal dynamics related to sap flow and changes in stem volume in old-growth Douglas-fir trees

Diurnal and seasonal tree water storage was studied in three large Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) trees at the Wind River Canopy Crane Research site. Changes in water storage were based on measurements of sap flow and changes in stem volume and tissue water content at different heights in the stem and branches. We measured sap flow by two variants of the heat balance method (with internal heating in stems and external heating in branches), stem volume with electronic dendrometers, and tissue water content gravimetrically. Water storage was calculated from the differences in diurnal courses of sap flow at different heights and their integration. Old-growth Douglas-fir trees contained large amounts of free water: stem sapwood was the most important storage site, followed by stem phloem, branch sapwood, branch phloem and needles. There were significant time shifts (minutes to hours) between sap flow measured at different positions within the transport system (i.e., stem base to shoot tip), suggesting a highly elastic transport system. On selected fine days between late July and early October, when daily transpiration ranged from 150 to 300 liters, the quantity of stored water used daily ranged from 25 to 55 liters, i.e., about 20% of daily total sap flow. The greatest amount of this stored water came from the lower stem; however, proportionally more water was removed from the upper parts of the tree relative to their water storage capacity. In addition to lags in sap flow from one point in the hydrolic pathway to another, the withdrawal and replacement of stored water was reflected in changes in stem volume. When point-to-point lags in sap flow (minutes to hours near the top and stem base, respectively) were considered, there was a strong linear relationship between stem volume changes and transpiration. Volume changes of the whole tree were small (equivalent to 14% of the total daily use of stored water) indicating that most stored water came from the stem and from its inelastic (sapwood) tissues. Whole tree transpiration can be maintained with stored water for about a week, but it can be maintained with stored water from the upper crown alone for no more than a few hours.

Photosynthetic regulation of C4 desert plant Haloxylon ammodendron under drought stress

About 20-year-old desert plants of C4 species, Haloxylon ammodendron, growing at the southern edge of the Badain Jaran Desert in China, were selected to study the photosynthetic characteristics and changes in chlorophyll fluorescence when plants were subject to a normal arid environment (AE), moist atmospheric conditions during post-rain (PR), and the artificial supplement of soil water (SW). Results showed that under high radiation, in the AE, the species down-regulated its net assimilation rate (A) and maximum photochemical efficiency of PS II (Fv/Fm), indicating photoinhibition. However, under the PR and SW environments, A was up-regulated, with a unimodal diurnal course of A and a small diurnal change in Fv/Fm, suggesting no photoinhibition. When the air humidity or SW content was increased, the light compensation points were reduced; light saturation points were enhanced; while light saturated rate of CO2 assimilation (A max) and apparent quantum yield of CO2 assimilation (ΦC) increased. ΦC was higher while the A max was reduced under PR relative to the SW treatment. It was concluded that under high-radiation conditions drought stress causes photoinhibition of H. ammodendron. Increasing air humidity or soil moisture content can reduce photoinhibition and increase the efficiency of solar energy use.

A decade of carbon, water and energy flux measurements of an old spruce forest at the Anchor Station Tharandt

At Tharandt/Germany eddy covariance (EC) measurements of carbon dioxide and heat fluxes are performed above an old spruce forest since 1996. The last ten years cover almost all meteorological extremes observed during the last 45 years: the coldest and warmest year with mean air temperature of 6.1°C (1996) and 9.6°C (2000) as well as the fourth wettest and the driest year with a precipitation of 1098 mm (2002) and 501 mm (2003), respectively. In general, the observed annual carbon net ecosystem exchange (NEE) indicates a high net sink from .395 g C m-2 a-1 (2003) to .698 g C m-2 a-1 (1999) with a coefficient of variation cv = 16.6%. The yearly evapotranspiration (ET) has a lower interannual variability (cv = 9.5%) between 389 mm (2003) and 537 mm (2000). The influence of flux correction and gap filling on the amount of annual NEE and ET is considerable. Using different methods of gap filling (non-linear regressions, mean diurnal courses) yields annual NEE totals that differ by up to 18%.Consistency analysis regarding energy balance closure, comparisons with independent soil respiration and biomass increment measurements indicate reliability of the fluxes. The average gap of the energy balance is 15% of the available energy based on regression slope with an intercept of 3 to 16 W m-2, but around zero for annual flux ratios. Between 47% and 63% of the net ecosystem productivity was fixed above ground according to up-scaled tree ring data and forest inventories, respectively. Chamber measurements of soil respiration yield up to 90% of nighttime EC based total ecosystem respiration. Thus, we conclude that the EC based flux represents an upper limit of the C sink at the site.

DIURNAL AND SEASONAL COURSE OF THE RATE OF THE PHOTOSYNTHESIS IN THE APPLE TREE CASE IN THE CONDITIONS FROM THE FRUIT-GROWING REGION PITESTI- MARACINENI

A great importance in developing the photosynthesis with the trees, bushes and herbal fruit plants is represented by the presence or absence of the inflorescences on the branches, the number of leaves, the foliar surface, the number of fruit. In this article we have studied the diurnal and seasonal course of the rate of photosynthesis with the apple tree. The photosynthesis process presents variations during day, characterized by high values in the morning, followed by a decrease in the rate of photosynthesis. During springtime the values of the photosynthesis intensity are low, with a rise in intensity during summer months, after which one can notice a decrease of the photosynthesis intensity. It has been established that the rate of photosynthesis is dependent on the position of the leaf on the twig (at the base, middle or at the top), as well as on the presence or absence of fruit in the bouquet. Maximum values of the rate of photosynthesis were obtained with the leaves positioned at the middle of the twig and with the fruit-bearing bouquet.

Comparison of Four Methods to Estimate Urban Heat Storage

Abstract The relative performance of four independent methods to estimate the magnitude and diurnal behavior of net heat storage fluxes (ΔQS) in a city center is assessed. This heat flux is a significant but understudied component of the urban surface energy balance (SEB). Direct measurement of this SEB term at the local scale (horizontal length scale ∼102–104 m) is practically unattainable primarily because of the complex array of materials and the three-dimensionality of urban systems. Results of an 8-day summertime observational study at a site in the center of Marseille, France, are presented. This locale is an ideal environment for such research because of the warm, dry climate (hence the SEB is dominated by sensible heat exchanges) and the high density of tall buildings with thick walls (hence it has a large thermal mass that favors heat storage as a component of the SEB). Estimates of ΔQS derived as residuals in the SEB, after the remaining terms are measured directly, (termed RES) are compared with those calculated from a parameterization scheme [objective hysteresis model (OHM)], a local-scale numerical model [Town Energy Balance model (TEB)], and a bulk heat transfer method [thermal mass scheme (TMS)]. Inputs to the methods include observed meteorological data and morphometric properties of the urban site. All approaches yield a similar diurnal course. The OHM and TEB methods tend to slightly overestimate storage uptake by day when compared with the RES, whereas TMS slightly underestimates it. All methods underestimate heat storage release at night when compared with RES and show some sensitivity to wind speed, especially above about 5 m s−1. OHM estimates perform satisfactorily in the mean but miss short-term variability and are poor at night. TEB simulations show the best agreement with RES results, particularly at night. TMS values are comparable to those from the other methods, but its extensive input requirements render it almost impractical. Overall, the convergence of results is reassuring but the lack of a standard for quantifying heat storage and the spread of results mean this term remains a source of imprecision in urban energy balance measurement and modeling.

Seasonal variation in carbon exchange and its ecological analysis over Leymus chinensis steppe in Inner Mongolia

Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.

A comparison of photosynthethetic characteristics in four poplar clones

The photosynthetic characteristics and the relationship of net photosynthetic rate,water use efficiency with the environmental factors and stomatal conductance in four new poplar clones(3~#、6~#、8~#、9~#) were studied.The results showed that the peak value of the diurnal courses of the photosynthetic rate generally appeared around 10:00,and then reduced gradually.The diurnal courses of transpiration rate in different months were different.The peak value of the diurnal courses of stomatal conductance generally appeared at 7:00~9:00.The total mean net photosynthetic rate(μmol CO_2·m~(-2)·s~(-1)),transpiration rate(mmol H_2O·m~(-2)·s~(-1)) and water use efficiency(mmol CO_2·mol~(-1) H_2O) had following order in June,July and August respectively: Clone 9~#(8.53)6~#(7.21)3~#(6.47)8~#(4.98);Clone 9~#(3.74)3~#(2.76)6~#(1.76)8~#(1.47);Clone 8~#(4.77)6~#(4.35)3~#(2.99)9~#(2.40).Clone 9~# had higher net photosynthetic rate and transpiration rate,with lower water use efficiency.On the contrary,clone 8~# had lower net photosynthetic rate and transpiration rate,with higher water use efficiency.Net photosynthetic rate and water use efficiency had a close relationship with the air temperature and relative humidity in 6~#,and had a close relationship with the photosynthetic active radiation and stomatal conductance in 3~#、8~# and 9~#.

Fluxo de seiva e fotossíntese em laranjeira 'Natal' com clorose variegada dos citros

O objetivo deste trabalho foi avaliar os efeitos da clorose variegada dos citros (CVC), no fluxo de seiva, trocas gasosas e atividade fotoquímica em laranjeira 'Natal', com e sem CVC, em condição de campo. O curso diário do fluxo de seiva, potencial da água na folha, assimilação de CO2, transpiração, condutância estomática e eficiência quântica máxima e efetiva do fotossistema II foram avaliados. O delineamento experimental foi em blocos ao acaso com cinco repetições. O fluxo de seiva foi 1,9 vez superior nas plantas sadias em relação às doentes. Em plantas doentes ocorreu queda de 43, 28 e 33% na assimilação de CO2, condutância estomática e transpiração, respectivamente. As plantas com CVC apresentaram fotoinibição dinâmica. Uma vez que a eficiência quântica efetiva apresentou um padrão de resposta semelhante, durante o dia, em ambos os tratamentos, o efeito protetor da fotorrespiração no aparato fotoquímico em plantas com CVC é discutido. As quedas de assimilação de CO2, transpiração e de fluxo de seiva, nas plantas com CVC, foram decorrentes do menor valor da condutância estomática, possivelmente causado pela colonização dos vasos do xilema pela Xylella fastidiosa.

Two Algorithms for Variable Power Control of Heat‐Balance Sap Flow Gauges under High Flow Rates

The advantages of variable power control for heat‐balance sap flow gauges are evident under high flow rates (e.g., >600 g h−1) where high rates of power must be applied. Under the very high flow rates (e.g., 1500–4000 g h−1) of mature grapevines (Vitis spp.), we evaluated two algorithms to control the power applied to heat‐balance sap flow gauges, and thus the temperature difference (ΔT) above and below gauge heaters: (i) a proportional‐derivative (PD) algorithm and (ii) an open‐loop controller following the theoretical diurnal course of irradiance. The PD algorithm was tuned for expected maximum flow rates and could keep ΔT within 0.1°C of its daytime (0800–1800 h) target value. Over 21 d, mean daytime ΔT was 1.32 ± 0.001°C (s.e.m.) for an 18‐gauge system. The algorithm was unstable early in the morning and in the evening as rates of sap flow were below those for which the algorithm had been tuned. In the open‐loop algorithm, power output was programmed to change according to a sine curve tied to daylength. In well‐watered vines, the power curve mimicked actual sap flow patterns. As flow rates varied it accommodated the changing dead time of the system, which is the delay or time required before any change in ΔT occurs. Daytime ΔT varied sinusoidally with a typical amplitude of 0.5 to 1.0°C. The coefficient of variation in daytime ΔT appeared to be higher (16–26%) under the open‐loop algorithm than under the PD algorithm (5–13%). Under weekly cycles of deficit irrigation, the variance in daytime ΔT increased with the number of days after irrigation, suggesting that the open‐loop algorithm might best be applied when the stem energy balance includes an estimate of heat storage.

Effects of Genotypes and Plant Density on Yield, Yield Components and Photosynthesis in Bt Transgenic Cotton

AbstractBt (Bacillus thuringiensis) transgenic cotton (Gossypium hirsutumL.), including the introduced, indigenous Chinese non‐hybrid and hybrid cotton, is spreading very rapidly in China. Agronomic and photosynthetic performance as well as the optimum plant density for planting Bt cotton may vary with genotypes. With three types of commercial Bt cotton varieties, two field experiments were conducted to study yield performance and leaf photosynthetic rate (Pn) during 2000 and 2001, and yield interaction between variety and plant density during 2001 and 2002 in Yellow River region in northern China. The first experiment showed that the indigenous Chinese Bt cotton significantly differed from the introduced Bt cotton (IBtC) in plant growth and yield components. As a result of manipulation of boll numbers, boll weight and lint percentage, there was no significant difference in lint yield between Chinese non‐hybrid Bt cotton (CBtC) and the IBtC, but two Chinese hybrid Bt cotton (HBtC) varieties exhibited significantly higher lint yield than all other varieties in either 2000 or 2001. Hybrid cotton SCRC15 showed a one‐peak curvilinear change in diurnal course of Pn throughout the growing season, while non‐hybrid cotton 33B and SCRC16 exhibited severe mid‐day depression in Pn in squaring, flowering or boll‐setting stage. The second experiment showed that the main effect of plant population on lint yield was not significant, and yield difference among all treatments was derived from varieties and the interaction between plant density and variety. The optimal plant densities in terms of lint yield for the introduced, indigenous CBtC and HBtC genotypes were 6.0, 4.5 and 3.0 plants m−2respectively.