The Contribution of Leaves from Different Levels within a Tomato Crop to Canopy Net Photosynthesis: An Experimental Examination of Two Canopy Models

The rates of net photosynthesis per unit ground area by a closedcanopy of tomato plants were measured over a range of naturallight flux densities. The canopy, of leaf area index 8.6, wasdivided into three horizontal layers of equal depth. On successivedays the canopy was progressively defoliated in layers fromthe ground upwards, allowing the photosynthetic contributionfrom individual leaf layers to be determined. The uppermostlayer, 23% of the total leaf area, assimilated 66% of the netCO₂ fixed by the canopy and accounted for a similar percentageof the total leaf respiration. Net photosynthesis versus light response curves for individualleaves from different positions within the canopy were alsoobtained. Leaf conductances to CO₂ transfer and the dark respirationrates of leaves from the uppermost leaf layer were approximatelyten times those from the lowest layer. The canopy data were analysed using a simple model which assumedthat the canopy was composed of leaves with identical photosyntheticand respiratory characteristics. The model fitted the data andallowed the characteristics of an ‘idealized’ leafto be estimated. The estimated values of the leaf light utilizationefficiency, ,and the leaf conductance CO₂ transfer, , were similarto values directly determined for individual leaves in the uppermostleaf layer and the estimated rate of leaf dark respiration,R_d, corresponded to measured rates for leaves much lower inthe canopy. The simple model may be used to examine gross effectsof crop environment on the leaf photosynthetic characteristicof an ‘idealized’ leaf, but cannot be used to predictaccurately canopy net photosynthesis from the photosyntheticand respiratory characteristics of any single real leaf. A moredetailed model, developed to allow explicitly for the observedvariation in and R_d within the canopy is appropriate for thispurpose.     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

Estimation of the anatomical, stomatal and biochemical components of differences in photosynthesis and transpiration of wild-type and transgenic (expressing yeast-derived invertase targeted to the vacuole) tobacco leaves

Photosynthesis and transpiration rates of transgenic (expressing yeast-derived invertase targeted to the vacuole) tobacco (Nicotiana tabacum L.) leaves were, respectively, 50 and 70% of those of a wild type at 20°C, 350 cm³ m^?3 CO₂ concentration, 450 μmol (photons) m^?2 s^?1 of light intensity, and 70% relative air humidity. These differences could be attributed: (a) to changes in leaf anatomy and, consequently, to changes in gases diffusion between the cells' surfaces and the atmosphere; (b) to different stomatal apertures, and, for the photosynthesis rate, (c) to the altered CO₂ assimilation rate. Our objective was to estimate the relative contributions of these three sources of difference. Measurements on the wild-type and the transgenic leaf cross-sections gave values for the cell area index (CAI, cell area surface per unit of leaf area surface) of 15.91 and 13.97, respectively. The two-dimensional model 2DLEAF for leaf gas exchange was used to estimate quantitatively anatomical, stomatal and biochemical components of these differences. Transpiration rate was equal to 0.9 for the wild-type and to 0.63 mmol m^?2 s^?1 for the transgenic leaf: 24.0% of the difference (0.066 mmol m^?2 s^?1 was caused by the greater cell area surface in the wild-type leaf, and 66.0% was caused by a smaller stomatal aperture in the transgenic leaf. Photosynthetic rate was 3.10 and 1.55 μmol m^?2 s^?1 for the wild-type and transgenic leaves, respectively. Only 10.3% of this difference (0.16 μmol m^?2 s^?1) was caused by the difference in CAI, and the remaining 89.7% was caused by altered CO₂ assimilation rate.     

An Analysis of Some Effects of Humidity on Photosynthesis by a Tomato Canopy under Winter Light Conditions and a Range of Carbon Dioxide Concentrations

The rates of net photosynthesis by closed canopies of tomatoplants were measured at three CO₂ concentrations and three humiditiesover a range of natural light flux densities. The data havebeen analysed using a model of canopy photosynthesis which allowsfor variation in leaf area index and other leaf and canopy characteristics.The model also deals explicitly with the effects of CO₂ concentration,leaf conductance, and photorespiration on the leaf photochemicalefficiency, . The leaves were found to have a photochemicalefficiency in the absence of photorespiration, _m, of 12?6 ?10^–9 kg (CO₂) J^–1. At a CO₂ concentration of 0?73 ? 10^–3 kg m^–3 (400vpm) the leaf photochemical efficiency, , and canopy light utilizationefficiency, _c, were 18 per cent greater at a vapour pressuredeficit of 0?5 kPa than at 1?0 kPa. At a CO₂ concentration of2?2 ? 10^–3 kg m^–3 (1200 vpm) they were only 5 percent greater.     

Photoperiod Sensitivity during Flower Development of Opium Poppy (Papaver somniferum L.)

Photoperiod is a major factor in flower development of the opiumpoppy (Papaver somniferum L. ‘album DC’) which isa long-day plant. Predicting time to flower in field-grown opiumpoppy requires knowledge of which stages of growth are sensitiveto photoperiod and how the rate of flower development is influencedby photoperiod. The objective of this work was to determinewhen poppy plants first become sensitive to photoperiod andhow long photoperiod continues to influence the time to firstflower under consistent temperature conditions. Plants weregrown in artificially-lit growth chambers with either a 16-hphotoperiod (highly flower inductive) or a 9-h photoperiod (non-inductive).Plants were transferred at 1 to 3-d intervals from a 16- toa 9-h photoperiod andvice versa . All chambers were maintainedat a 12-h thermoperiod of 25/20 °C. Poppy plants becamesensitive to photoperiod 4 d after emergence and required aminimum of four inductive cycles (short dark periods) beforethe plant flowered. Additional inductive cycles, up to a maximumof nine, hastened flowering. After 13 inductive cycles, floweringtime was no longer influenced by photoperiod. These resultsindicate that the interval between emergence and first flowercan be divided into four phases: (1) a photoperiod-insensitivejuvenile phase (JP); (2) a photoperiod-sensitive inductive phase(PSP); (3) a photoperiod-sensitive post-inductive phase (PSPP);and (4) a photoperiod-insensitive post-inductive phase (PIPP).The minimum durations of these phases forPapaver somniferum‘album DC’ under the conditions of our experimentwere determined as 4 d, 4 d, 9 d, and 14 d, respectively. Anthesis; days to flowering; flower bud; opium poppy; Papaver somniferum L.; photoperiod; photoperiod sensitivity; predicting time to flowering; transfer     

Growth Response of a Chrysanthemum Crop to the Environment. II. A Mathematical Analysis Relating Photosynthesis and Growth

Vegetative crops of chrysanthemum were grown for 5 weeks inthree replicate daylit assimilation chambers. Weekly harvestswere made from each crop for growth analysis, and on seven occasionsduring the 5-week period continuous measurements of the netCO₂ exchange rate of each crop were made over a 24 h period.A semi-empirical model for canopy photosynthesis was fittedto these data. The photosynthesis model was then incorporatedinto a simple, dynamic growth model. Using fitted values ofthe canopy photosynthesis parameters, the daily total radiationintegrals, and the experimentally observed relationship betweenthe leaf area index and crop dry matter per unit ground area,the crop growth model was used to simulate growth over the 5-weekperiod. The predicted and measured crop dry weights were inclose agreement over the whole period.     

Photosynthesis in Stands of Green Peppers. An Application of Empirical and Mechanistic Models to Controlled-environment Data

The photosynthetic response of stands of green peppers to lightand CO² is examined by means of various mathematical models.Several single leaf response equations are considered, fromthe simple and ubiquitous rectangular hyperbola, to more sophisticatedforms incorporating photorespiration and the oxygen effect.By making the usual assumptions about stand structure and lightpenetration, mechanistic crop response equations arc derivedfor each of the different leaf response equations. First, asa purely empirical approach, the leaf response equations areapplied directly to crop data, and it is concluded that therectangular hyperbola with a term for dark respiration [eqn(2)] gives an adequate summary of crop response to light andCO₂. Second, four mechanistic equations of crop response areapplied to the data, and, although the results are equivocal,it is suggested that the simpler crop equations [eqns (15) and(17)] are satisfactory at the present time, and it is not yetpossible to detect the results of photorespiration and the oxygeneffect directly in the crop data.     

Effects of Sucrose on Water Relations of Cut, Senescing, Carnation Flowers

Carnation flower stems were stood in water or sucrose solutionand changes in water content, water and osmotic potential, turgorpressure and solutes (sugars, nitrogen, phosphorus, potassium)of petals were measured throughout the flower life. In bothtreatments the petals had a higher specific water content atincipient wilting than when the flowers were first cut. In water,turgor pressure decreased rapidly after the seventh day becauseof a decrease in tissue solute content. In sucrose solution,loss, of solutes was delayed probably because the sugar provideda respiratory substrate to maintain cell membrane integrity.In these cells, sugars and water accumulated causing decreasesin water potential and osmotic potential. Solutes and waterwere lost at about day 15 and turgor pressure decreased. Therewas some evidence that from about day 11 cells were so gorgedwith sugars that they burst when they were placed in water duringthe adjustment of water content prior to water potential measurements. Most of the initial petal osmotic energy content could be accountedfor by sugar, potassium, and anions associated with potassium,but in water, as the petals aged and sugar content decreased,so the potassium ions contributed a larger proportion of theosmotic energy; with stems in sucrose, the endogenous sugarcontent (reducing sugars plus sucrose) contributed an increasingproportion of the total osmotic energy. Dianthus caryophyllus, carnation, flowers, water relations, senescence