Leaf Net CO2 Assimilation Rate Research Articles

Stomatal and Non-Stomatal Leaf Responses during Two Sequential Water Stress Cycles in Young Coffea canephora Plants

Understanding the dynamics of physiological changes involved in the acclimation responses of plants after their exposure to repeated cycles of water stress is crucial to selecting resilient genotypes for regions with recurrent drought episodes. Under such background, we tried to respond to questions as: (1) Are there differences in the stomatal-related and non-stomatal responses during water stress cycles in different clones of Coffea canephora Pierre ex A. Froehner? (2) Do these C. canephora clones show a different response in each of the two sequential water stress events? (3) Is one previous drought stress event sufficient to induce a kind of “memory” in C. canephora? Seven-month-old plants of two clones (’3V’ and ‘A1’, previously characterized as deeper and lesser deep root growth, respectively) were maintained well-watered (WW) or fully withholding the irrigation, inducing soil water stress (WS) until the soil matric water potential (Ψmsoil) reached ≅ −0.5 MPa (−500 kPa) at a soil depth of 500 mm. Two sequential drought events (drought-1 and drought-2) attained this Ψmsoil after 19 days and were followed by soil rewatering until a complete recovery of leaf net CO2 assimilation rate (Anet) during the recovery-1 and recovery-2 events. The leaf gas exchange, chlorophyll a fluorescence, and leaf reflectance parameters were measured in six-day frequency, while the leaf anatomy was examined only at the end of the second drought cycle. In both drought events, the WS plants showed reduction in stomatal conductance and leaf transpiration. The reduction in internal CO2 diffusion was observed in the second drought cycle, expressed by increased thickness of spongy parenchyma in both clones. Those stomatal and anatomical traits impacted decreasing the Anet in both drought events. The ‘3V’ was less influenced by water stress than the ‘A1’ genotype in Anet, effective quantum yield in PSII photochemistry, photochemical quenching, linear electron transport rate, and photochemical reflectance index during the drought-1, but during the drought-2 event such an advantage disappeared. Such physiological genotype differences were supported by the medium xylem vessel area diminished only in ‘3V’ under WS. In both drought cycles, the recovery of all observed stomatal and non-stomatal responses was usually complete after 12 days of rewatering. The absence of photochemical impacts, namely in the maximum quantum yield of primary photochemical reactions, photosynthetic performance index, and density of reaction centers capable of QA reduction during the drought-2 event, might result from an acclimation response of the clones to WS. In the second drought cycle, the plants showed some improved responses to stress, suggesting “memory” effects as drought acclimation at a recurrent drought.

Impacts of Dutch elm disease-causing fungi on foliage photosynthetic characteristics and volatiles in Ulmus species with different pathogen resistance.

Global warming affects the abiotic and biotic growth environment of plants, including the spread of fungal diseases such as Dutch elm disease (DED). Dutch elm disease-resistance of different Ulmus species varies, but how this is reflected in leaf-level physiological pathogen responses has not been investigated. We studied the impacts of mechanical injury alone and mechanical injury plus inoculation with the DED-causing pathogens Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana on Ulmus glabra, a more vulnerable species, and U. laevis, a more resistant species. Plant stress responses were evaluated for 12days after stress application by monitoring leaf net CO2 assimilation rate (A), stomatal conductance (gs), ratio of ambient to intercellular CO2 concentration (Ca/Ci) and intrinsic water-use efficiency (A/gs), and by measuring biogenic volatile (VOC) release by plant leaves. In U. glabra and U. laevis, A was not affected by time, stressors or their interaction. Only in U. glabra, gs and Ca/Ci decreased in time, yet recovered by the end of the experiment. Although the emission compositions were affected in both species, the stress treatments enhanced VOC emission rates only in U. laevis. In this species, mechanical injury especially when combined with the pathogens increased the emission of lipoxygenase pathway volatiles and dimethylallyl diphosphate and geranyl diphosphate pathway volatiles. In conclusion, the more resistant species U. laevis had a more stable photosynthesis, but stronger pathogen-elicited volatile response, especially after inoculation by O. novo-ulmi subsp. novo-ulmi. Thus, stronger activation of defenses might underlay higher DED-resistance in this species.

Crop Photosynthetic Performance Monitoring Based on a Combined System of Measured and Modelled Chloroplast Electron Transport Rate in Greenhouse Tomato.

Combining information of plant physiological processes with climate control systems can improve control accuracy in controlled environments as greenhouses and plant factories. Through that, resource optimization can be achieved. To predict the plant physiological processes and implement them in control actions of interest, a reliable monitoring system and a capable control system are needed. In this paper, we focused on the option to use real-time crop monitoring for precision climate control in greenhouses. For that, we studied the processes and external factors influencing leaf net CO2 assimilation rate (AL, µmol CO2 m-2 s-1) as possible variables of a plant performance indicator. While measured greenhouse environmental variables such as light, temperature, or humidity showed a direct relation between AL and light-quantum yield of photosystem II (Φ2), we defined three objectives: (1) to explore the relationship between climate variables and AL, as well as Φ2; (2) create a simple and reliable method for real‐time prediction of AL with continuously Φ2 measurements; and (3) calibrate parameters to predict chloroplast electron transport rate as input in AL modelling. Due to practical obstacles in measuring CO2 gas-exchange in commercial production, we explored a method to predict AL by measuring Φ2 of leaves in a commercial hydroponic greenhouse tomato crop (“Pureza”). We calculated AL with two different approaches based on either the negative exponential response model with simplified biochemical equations (marked as Model I) or the non-rectangular hyperbola full biochemical photosynthetic models (marked as Model II). Using Model I can only be used to predict AL with large uncertainty (R2 0.64; RMSE 2.21), while using Φ2 as input to Model II could be used to improve the prediction accuracy of AL (R2 0.71; RMSE 1.98). Our results suggests that (1) Φ2 light signals can be used to predict net photosynthesis rate with high accuracy; (2) a parameterized photosynthetic electron transport rate model is suitable predicting measured electron transport rate (J) and AL. The system can be used as decision support system (DSS) for plant and crop performance monitoring when leaf-dynamics are up-scaled to the plant or crop level.

Transgenic maize phosphoenolpyruvate carboxylase alters leaf\u2013atmosphere CO2 and 13CO2 exchanges in Oryza sativa

The engineering process of C4 photosynthesis into C3 plants requires an increased activity of phosphoenolpyruvate carboxylase (PEPC) in the cytosol of leaf mesophyll cells. The literature varies on the physiological effect of transgenic maize (Zea mays) PEPC (ZmPEPC) leaf expression in Oryza sativa (rice). Therefore, to address this issue, leaf–atmosphere CO2 and 13CO2 exchanges were measured, both in the light (at atmospheric O2 partial pressure of 1.84 kPa and at different CO2 levels) and in the dark, in transgenic rice expressing ZmPEPC and wild-type (WT) plants. The in vitro PEPC activity was 25 times higher in the PEPC overexpressing (PEPC-OE) plants (~20% of maize) compared to the negligible activity in WT. In the PEPC-OE plants, the estimated fraction of carboxylation by PEPC (β) was ~6% and leaf net biochemical discrimination against 13CO2left( {Delta_{text{bio}} } right) was ~ 2‰ lower than in WT. However, there were no differences in leaf net CO2 assimilation rates (A) between genotypes, while the leaf dark respiration rates (Rd) over three hours after light–dark transition were enhanced (~ 30%) and with a higher 13C composition left( {delta^{ 1 3} {text{C}}_{text{Rd}} } right) in the PEPC-OE plants compared to WT. These data indicate that ZmPEPC in the PEPC-OE rice plants contributes to leaf carbon metabolism in both the light and in the dark. However, there are some factors, potentially posttranslational regulation and PEP availability, which reduce ZmPEPC activity in vivo.

Knockdown of glycine decarboxylase complex alters photorespiratory carbon isotope fractionation in Oryza sativa leaves.

The influence of reduced glycine decarboxylase complex (GDC) activity on leaf atmosphere CO2 and 13CO2 exchange was tested in transgenic Oryza sativa with the GDC H-subunit knocked down in leaf mesophyll cells. Leaf measurements on transgenic gdch knockdown and wild-type plants were carried out in the light under photorespiratory and low photorespiratory conditions (i.e. 18.4 kPa and 1.84 kPa atmospheric O2 partial pressure, respectively), and in the dark. Under approximately current ambient O2 partial pressure (18.4 kPa pO2), the gdch knockdown plants showed an expected photorespiratory-deficient phenotype, with lower leaf net CO2 assimilation rates (A) than the wild-type. Additionally, under these conditions, the gdch knockdown plants had greater leaf net discrimination against 13CO2 (Δo) than the wild-type. This difference in Δo was in part due to lower 13C photorespiratory fractionation (f) ascribed to alternative decarboxylation of photorespiratory intermediates. Furthermore, the leaf dark respiration rate (Rd) was enhanced and the 13CO2 composition of respired CO2 (δ13CRd) showed a tendency to be more depleted in the gdch knockdown plants. These changes in Rd and δ13CRd were due to the amount and carbon isotopic composition of substrates available for dark respiration. These results demonstrate that impairment of the photorespiratory pathway affects leaf 13CO2 exchange, particularly the 13C decarboxylation fractionation associated with photorespiration.

Changes in Within-Shoot Carbon Partitioning in Pinot Noir Grapevines Subjected to Early Basal Leaf Removal.

Early leaf removal significantly alters the source-sink balance within grapevine shoots, leading to a reduction in fruit set. However, no research has previously examined the conditions controlling this process in terms of carbon allocation among major sink organs following defoliation. In this study, the impact of defoliation at bloom on the distribution dynamics of leaf assimilates among clusters and growing shoot apices was investigated on Vitis vinifera, cv. Pinot noir, grown in Michigan, a cool climate viticultural region. Three levels of defoliation: no leaves removed (LR-0); six leaves removed from six basal nodes (LR-6); and ten leaves removed from ten basal nodes (LR-10), were imposed at full bloom. A 13C pulsing was performed 1 week after the treatment application to the defoliated shoots. Single leaf gas exchange (Pn), diurnal changes of the leaf net CO2 assimilation rate, carbon distribution, fruit-set, yield, and fruit composition were measured. Higher Pn was recorded in diurnal measurements of gas exchange in leaf removal (LR) treatments compared to LR-0. The shoot apex of LR-10 experienced the highest 13C allocation (%) after 3 and 7 days following the carbon pulsing. LR-10 had lower percentage of 13C allocated to clusters, which decreased fruit set by 60%, compared to the control, and enhanced the concentration of phenolic compounds in fruit. Alteration of carbon portioning among shoot sink organs indicated that an increasing severity of leaf removal significantly reduced fruit set, and was linearly correlated to shoot apex sink strength, which occurred at the expense of the cluster.

Effects of Nitrogen Addition on the Drought Susceptibility of the Leymus chinensis Meadow Ecosystem Vary with Drought Duration.

It is not clear yet how extreme drought and nitrogen (N) deposition influence grassland ecosystem functions when they are considered together, especially in complex field conditions. To explore the response of the Leymus chinensis meadow ecosystem to manipulated extreme drought (45 days), N addition and their interaction, we measured leaf photosynthetic characteristics, aboveground phytomass on the community level and ecosystem C exchange in different treatments at the middle and the end of the drought period. The extreme drought treatment decreased the leaf net CO2 assimilation rate and ecosystem C exchange [gross ecosystem productivity (GEP), ecosystem respiration and net ecosystem CO2 exchange]. In contrast, the N addition treatment increased aboveground phytomass, GEP and net ecosystem CO2 exchange. The effects of N addition on the drought susceptibility of the L. chinensis meadow ecosystem varied with drought severity. The N addition treatment alleviated drought-induced suppression of CO2 exchange at the leaf and ecosystem levels in the middle of the drought period, whereas it exacerbated drought-induced suppression of the CO2 exchange and aboveground phytomass on the community level at the end of the drought period. Given that dominance by L. chinensis is a characteristic of the studied ecosystem, knowledge of the traits of L. chinensis and its response to multiple global change drivers will be crucial for predicting future ecosystem functions. Furthermore, increasing N deposition may affect the response of the L. chinensis meadow ecosystem to further droughts by increasing carbon allocation to roots and therefore root–shoot ratios.

Effect of high temperature on yield associated parameters and vascular bundle development in five potato cultivars

High temperature is one of the major abiotic stresses affecting performance of crop plants including potato yield. To gain an insight into whether high temperature effects tuber yield and its relation to translocation of photoassimilates in potato, a comparative study was conducted using five (Kufri jyoti, Kufri megha, Kufri pokraj, Rangpuria, and Badami) potato cultivars for two consecutive years. These cultivars were sown early in the season (mid August–November) when the temperature was high and normal growing season (ambient condition) (mid October–mid January) in an open field along in a polyhouse where the temperature was high. Early season planting experienced highest temperature (30–35°C) and temperature in the polyhouse was 2–4°C higher than the ambient condition. Leaf net CO2 assimilation rate, stem anatomy, xylem size, sugar-starch ratio, activity of sucrose phosphate synthase, tuber bulking rate and tuber yield were evaluated under all three conditions (early season, ambient condition and polyhouse conditions). Overall, compared to ambient conditions, under early season and polyhouse conditions, the net photosynthesis rate was significantly reduced but sugar starch ratio was significantly enhanced in all tested cultivars. Under both early planting and polyhouse conditions, the xylem cells were abnormally enlarged and deformed in all potato cultivars, however, the effects were minimal in case of cultivar Kufri megha (high yielding cultivar) and Rangpuria (local cultivar) which was correlated with the minimal yield reduction. Overall, the temperature induced abnormalities in vascular tissues appears to be critical for tuber bulking rate and tuber yield (42–55% in the high yielding cultivars and 44–54% in the local cultivars). The cultivars that could maintain xylem size and phloem structure tended to minimize the negative effects of high temperature on tuber yield.

Comparative Effects of Brassinosteroid and Brassinosteroid Mimic on Improving Photosynthesis, Lipid Peroxidation, and Rice Seed Set under Heat Stress

The application of brassinosteroids (BRs) has been reported to alleviate heat stress. This study investigated the effect of 7,8-dihydro-8α-20-hydroxyecdysone (DHECD)—a BR mimic—by comparison with 24-epibrassinolide (EBR) on the changes in photosynthetic performance, lipid peroxidation, and rice seed set. The results demonstrated that 10 −8 M EBR and 10 −7 M DHECD had the best actions to counteract the lethal heat temperature of 47 °C for 2 h indicated by a reduction in the number of wilted leaves and an increase in the relative water content and leaf greenness. Moreover, plants treated with EBR or DHECD were exposed to high day/night temperatures of 40/30 °C for 7 days. EBR-treated and DHECD-treated plants showed a high shoot fresh weight, leaf area, chlorophyll content, and carotenoid content. High temperature significantly decreased the leaf net CO2 assimilation rate as well as increased lipid peroxidation. The application of EBR and DHECD maintained the high level of the net CO2 assimilation rate by increasing the stomatal conductance and photochemical quenching. On the other hand, EBR and DHECD decreased the intracellular CO2 content and non-photochemical quenching leading to enhance photosynthesis under heat stress. EBR-treated and DHECD-treated plants significantly reduced their malondialdehyde and hydrogen peroxide contents as well as increasing their total soluble sugar contents. Moreover, BR treatments increased the filled seed of rice. This study confirmed that DHECD—a BR mimic—has activities of heat stress alleviation similar to EBR.

Plasmon analysis in wheat alloplasmic lines using morphological and chloroplast microsatellite markers

Inheritance of plant traits mainly depends upon nuclear genes, cytoplasmic factors and their interactions. In the present study, 32 alloplasmic lines accompanied by a euplasmic parental line (control) were evaluated using molecular (chloroplast microsatellite) and morpho-physiological traits during 2010–2011 and 2011–2012. The results of combined analysis of variance showed the significant effect of growing seasons on most of the studied traits as well as the significant effect of cytoplasm on plant height, leaf net CO2 assimilation rate and grain yield per plant. Results of cluster analysis divided the six plasmons based on their phenotypic effects into three groups: (1) R and Sv type, D (Aegilops typica and Ae. ventricosa) and D2 type, as well as B-type plasmon (euplasmic line); (2) a single plasmon of M type and three plasmons of B type; (3) all other B-type and a single D-type plasmon (Aegilops cylindrica). Molecular analysis showed that 20 primer pairs out of 26 chloroplastic microsatellite markers (cpSSR) produced polymorphic bands in the alloplasmic lines. A total of 50 alleles were identified with an average of 2.5 alleles per locus. In this study, polymorphism information content (PIC) ranged from 0.05 (WCt17 primer) to 0.49 (WCt9 primer). Cluster analysis of molecular data revealed that the alloplasmic lines belong to two major clusters, in which differentiation of cytoplasmic types belonging to the genus Triticum and Aegilops has been evident. Likewise, analysis of molecular variance showed significant differences between two studied groups (FST = 0.67, P < 0.001). Overall, our findings indicated that the cpSSR markers can be valuable resources of polymorphic markers for the analysis of cytoplasm of Triticeae species, with the potential for clear differentiation in close species and genera of this tribe.

Down-regulation of photosynthesis following girdling, but contrasting effects on fruit set and retention, in two sweet cherry cultivars

Sweet cherry (Prunus avium) trees were manipulated to analyse the contribution of soluble sugars to sink feedback down-regulation of leaf net CO2 assimilation rate (Anet) and fruit set and quality attributes. Total soluble sugar concentration and Anet were measured in the morning on fully expanded leaves of girdled branches in two sweet cherry cultivars, ‘Kordia’ and ‘Sylvia’ characterised typically by low and high crop load, respectively. Leaves on girdled trees had higher soluble sugar concentrations and reduced Anet than leaves on non-girdled trees. Moreover, RuBP carboxylation capacity of Rubisco (Vcmax) and triose-phosphate utilisation (TPU) were repressed in the girdled treatments, despite Jmax remaining unchanged; suggesting an impairment of photosynthetic capacity in response to the girdling treatment. Leaf Anet was negatively correlated to soluble sugars, suggesting a sink feedback regulatory control of photosynthesis. Although there were significantly less fruit set and retained in ‘Kordia’ than ‘Sylvia’; girdling had contrasting effects in each cultivar. Girdling significantly increased fruit set and fruitlet retention in ‘Sylvia’ cultivar, but had no effect in ‘Kordia’ cultivar. We propose that low inherent sink demand for photoassimilates of ‘Kordia’ fruit could have contributed to the low fruit retention rate, since both non-girdled and girdled trees exhibited similar retention rate and that increases in foliar carbohydrates was observed above the girdle. In ‘Sylvia’ cultivar, the carbohydrate status may be a limiting factor for ‘Sylvia’ fruit, since girdling improved both fruit set and retention, and leaf soluble solids accumulation.

Effects of 5-aminolevulinic acid on the H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;-content and antioxidative enzyme gene expression in NaCl-treated cucumber seedlings

The potential of 5-aminolevulenic acid (ALA) to enhance the salt tolerance of cucumber (Cucumis sativus L.) seedlings was investigated. ALA was applied at various concentrations (0, 1, 10, 25, 50, and 100 mg dm-3) as foliar spray or root watering. Then the seedlings were exposed to 0 or 75 mM NaCl for 5 d. NaCl stress reduced the root and leaf dry masses, leaf area, and the leaf net CO2 assimilation rate. These reductions were counteracted by exogenous ALA, and the most efficient was 50 mg dm-3 concentration via foliar spray. ALA decreased the H2O2 contents and increased the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) in NaCl-treated cucumber roots and leaves and the activity of catalase (CAT) in leaves. The ALA application also up-regulated the expressions of CAT and cAPX genes in roots and leaves and the expression of GR gene in roots of the NaCl treated cucumber plants.

Effects of applied water amounts at various fractions of evapotranspiration (ETc) on leaf gas exchange of Thompson Seedless grapevines

Aims: To determine the effects of applied water amounts at various fractions (0.2, 0.6, 1.0 and 1.4) of grapevine evapotranspiration on leaf gas exchange of Thompson Seedless grapevines. Methods and Results: Midday stomatal conductance (gs) decreased linearly as leaf water potential (Ψl) and soil water content decreased. Leaf net CO2 assimilation rate only decreased once midday Ψl values were less than −1.0 MPa and when ∼50% of the soil water content at field capacity had been depleted. The mean seasonal midday A/gs ratio (intrinsic water use efficiency) was greatest for the 0.2 irrigation treatment and decreased as applied water amounts increased. Diurnal A and gs for vines irrigated at the 0.6 level or greater reached a maximum prior to midday remained constant thereafter before decreasing late in the afternoon, while those for vines that received less water decreased subsequent to the first measurement of the day. Conclusions: A and gs responded differently to vine and soil water statuses under the conditions of this study. There was no midday depression in either A or gs for vines irrigated at full evapotranspiration. Significance of the Study: The values of Ψl, A and gs reported here would serve as criteria to indicate that vines were well watered.

Effects of potassium supply on limitations of photosynthesis by mesophyll diffusion conductance in Carya cathayensis

Potassium (K) influences the photosynthesis process in a number of ways; however, the mechanisms underlying the photosynthetic response to differences in K supply are not well understood. Concurrent measurements of gas exchange and chlorophyll fluorescence were made to investigate the effect of K nutrition on photosynthetic efficiency and mesophyll conductance (g(m)) in hickory seedlings (Carya cathayensis Sarg.) in a greenhouse. The results show that leaf K concentrations < 0.7-0.8% appeared to limit the leaf net CO2 assimilation rate (A), and that the relative limitation of photosynthesis due to g(m) and stomatal conductance (g(s)) decreased with increasing supplies of K. However, a sensitivity analysis indicated that A was most sensitive to the maximum carboxylation rate of Rubisco (V(c,max)) and the maximum rate of electron transport (J(max)). These results indicate that the photosynthetic rate is primarily limited by the biochemical processes of photosynthesis (V(c,max) and J(max)), rather than by g(m) and g(s) in K-deficient plants. Additionally, g(m) was closely correlated with g(s) and the leaf dry mass per unit area (M(A)) in hickory seedlings, which indicates that decreased g(m) and g(s) may be a consequence of leaf anatomical adaptation.

Effects of salt-tolerant rootstock grafting on ultrastructure, photosynthetic capacity, and H2O2-scavenging system in chloroplasts of cucumber seedlings under NaCl stress

Plant growth, photosynthetic parameters, chloroplast ultrastructure, and the ascorbate-glutathione cycle system in chloroplasts of self-grafted and rootstock-grafted cucumber leaves were investigated. Grafted plants were grown hydroponically and were exposed to 0, 50, and 100 mM NaCl concentrations for 10 days. Under NaCl stress, the hydrogen peroxide (H2O2) content in cucumber chloroplasts increased, the chloroplast ultrastructure was damaged, and the gas stomatal conductance, intercellular CO2 concentration, as well as shoot dry weight, plant height, stem diameter, leaf area, and leaf relative water content were inhibited, whereas these changes were less severe in rootstock-grafted plants. The activities of ascorbate peroxidase (APX; EC 1.11.1.11), glutathione reductase (GR; EC 1.6.4.2), and dehydroascorbate reductase (DHAR EC 1.8.5.1) were higher in the chloroplasts of rootstock-grafted plants compared with those of self-grafted plants under 50 and 100 mM NaCl. Similar trends were shown in leaf net CO2 assimilation rate and transpiration rate, as well as reduced glutathione content under 100 mM NaCl. Results suggest that rootstock grafting enhances the H2O2-scavenging capacity of the ascorbate–glutathione cycle in cucumber chloroplasts under NaCl stress, thereby protecting the chloroplast structure and improving the photosynthetic performance of cucumber leaves. As a result, cucumber growth is promoted.

Analysis of the photosynthetic parameters, the yield and the quality of winter wheat

The environmental adaptability of crop production is basically determined by the selection of biological background (plant species andvarieties) suitable for the region and the site. The aim of our work is to parametrize the plant assimilation, its intensity, dynamics and themost important characteristics and the relationships to the quality in winter wheat trials. The measurements were carried out at the researchsite of the University of Debrecen in small parcel experiments. We measured the leaf net CO2 assimilation rate, stomatal conductance,intercellular CO2 level, the transpiration, the leaf temperature and the air temperature by the LICOR LI-6400 portable photosynthesissystem in field trials on the nutrient supply. The soil of the experimental area is calciferous chernozem with favorable water regime.We have examined the photosynthetic activity, the productivity and yield stability of winter wheat varieties. We have compared the yieldresults, at similar agrotechnical conditions in seven cropyears. We also determined the quality parameters of the winter wheat varieties.Then we valued the yield stability of genotypes with the help of analysis of variance and linear regression equations. We have defined theconnections between assimilation parameters, the yield stability and quality parameters of wheat varieties.

Soluble sugars mediate sink feedback down-regulation of leaf photosynthesis in field-grown Coffea arabica

Source-sink relationships of field-grown plants of Coffea arabica L. cultivar 'Caturra' were manipulated to analyze the contribution of soluble sugars to sink feedback down-regulation of maximal leaf net CO2 assimilation rate (Amax). Total soluble sugar concentration (SSCm) and Amax were measured in the morning and afternoon on mature leaves of girdled branches bearing either high or low fruit loads. Leaf Amax was negatively correlated to SSCm, increased with fruit load and decreased during the day, indicating that limiting sink demand for carbohydrates caused SSCm to accumulate in the leaf tissue which results in down-regulation of Amax. To further analyze source-sink feedback on Amax, we compared Amax of mature, non-sink-limited coffee leaves fed with water or sucrose for 5, 10 or 30 min with that of non-fed control leaves. Sucrose-feeding reduced Amax compared with the control and water-feeding treatments, indicating that down-regulation of Amax is related to phloem sucrose concentration in coffee source leaves, independent of SSCm concentration in other leaf tissues. Although sucrose appeared to be more closely related to the mechanism underlying sink feedback down-regulation of Amax in coffee leaves than SSCm, Amax was closely related to SSCm by a nonlinear equation that may be useful for integrating sink limitations in coffee leaf photosynthetic models.

Simulating leaf net CO2 assimilation rate of C3 &amp; C4 plants and its response to environmental factors

Basic structure and algorithm of leaf mechanism photosynthesis model were described in first part of this study based on former researcher results. Then, considering some environmental factors influencing on leaf photosynthesis, three numerical sensitivity experiments were carried out. We simulated the single leaf net CO2 assimilation, which acts as a function of different light, carbon dioxide and temperature conditions. The relationships between leaf net photosynthetic rate of C3 and C4 plant with CO2 concentration intercellular, leaf temperature, and photosynthetic active radiation (PAR) were presented, respectively. The results show the numerical experiment may indicate the main characteristic of plant photosynthesis in C3 and C4 plant, and further can be used to integrate with the regional climate model and act as land surface process scheme, and better understand the interaction between vegetation and atmosphere.

Crop Load Effects on Irrigated and Non-irrigated Vitis vinifera L. cv. Thompson Seedless

A study was conducted to determine the effects of crop removal on gas exchange parameters of `Thompson Seedless' grapevines grown in the San Joaquin Valley of California. Vines were either irrigated at full ET or not irrigated throughout the growing season. Clusters were removed subsequent to veraison, when the fruit soluble solids were ≈15° Brix. Reductions in leaf net CO2 assimilation rate (A) were measured within 1 day of fruit removal for both irrigation treatments and remained such until the end of the experiment. The greatest reduction in A due to crop removal on a diurnal basis was with the non-irrigated vines between 0800 and 1000 hr. The reduction in A subsequent to crop removal was not the result of an accumulation of either starch or sugars in leaf tissue. The greater reduction in A of non-irrigated vines after fruit removal may have been due to the lack of strong, alternate sinks as vegetative growth was minimal due to water stress during the experimental period.

Crop Load Effects on Irrigated and Non-irrigated Vitis vinifera L. cv. Thompson Seedless

A study was conducted to determine the effects of crop removal on gas exchange parameters of `Thompson Seedless' grapevines grown in the San Joaquin Valley of California. Vines were either irrigated at full ET or not irrigated throughout the growing season. Clusters were removed subsequent to veraison, when the fruit soluble solids were ≈15° Brix. Reductions in leaf net CO2 assimilation rate (A) were measured within 1 day of fruit removal for both irrigation treatments and remained such until the end of the experiment. The greatest reduction in A due to crop removal on a diurnal basis was with the non-irrigated vines between 0800 and 1000 hr. The reduction in A subsequent to crop removal was not the result of an accumulation of either starch or sugars in leaf tissue. The greater reduction in A of non-irrigated vines after fruit removal may have been due to the lack of strong, alternate sinks as vegetative growth was minimal due to water stress during the experimental period.