Leaf photosynthesis can be influenced by many plant factorssuch as leaf age, leaf position, sink effects, and mutual shading, as well asenvironmental factors such as light, temperature, nutrition, and wateravailability (Constable and Rawson, 1980; Field and Mooney, 1983; Leech andBaker, 1983; Lieth and Pasian, 1990). Constable and Rawson (1980) suggestedthat leaf position and age influence leaf area, gas exchange, leafconductance, and saturated net photosynthetic rate. Lieth and Pasian (1990)also found young, expanding leaves had low net photosynthesis. Leaf age andstructure affected the number of mesophyll cells and subsequently influencedphotosynthesis (Araus et al., 1997). However, only a few studies have focusedon plant leaf position and age influencing photosynthesis, and no publishedreports were found on Asia pear.
concentration, and soil water deficit affect stomatalresponse, gas exchange and photosynthesis (Mooney and Harrison, 1970; Berryand Bjorkman, 1980; Lieth and Pasian, 1990; Xie et al., 1996; Moriana et al.,2002). Based on changes during the day or between days, Heinicke and Childers(1937) concluded that light was the major factor affecting whole-canopy NCERof apple trees, and temperature was second most important, although Sirois andCooper (1964) concluded CO2 was second. A recent study(Corelli-Grappadelli and Magnanini, 1993) reported short-term whole-canopyNCER measurements declined with gradually declining light levels for one appletree. Photosynthesis and transpiration were greatly influenced by stomatalbehavior. Stomatal opening is affected by CO2 concentration, vaporpressure gradient (VPG), light, turgor pressure caused by change in potassiumand organic acids, and by abscisic acid (ABA) (Raschke, 1970; Schulze andHall, 1982). Berry and Bjorkman (1980) found light intensity, CO2concentration, temperature, and soil water deficit may have affected gasexchange of plants in a greenhouse. Bunce (1984) reported photosynthesisincreased when humidity was increased in the environment. Transpiration atnoon under a high temperature after 48 h of acclimation was 400% higher thanunder a moderate temperature. Stomatal resistance reached a minimum at noon,in accordance with the transpiration rate. Leaf wa
(However, plants generate daily variations in concentrations of oxygen and carbon dioxide through their photosynthetic and respiratory activities.) Thermal profiles at midday in corn fields at various stages of growth are shown in Figure 4.4, demonstrating the marked reduction in ground temperature due especially to shading.
This process is also affected by the temperature surrounding the plant (the species of plant we experimented with, pond weed, photosynthesised best at around 20 degrees centigrade.) Light, temperature & CO2 are known as limiting factors, and each is as important as the next in photosynthes...
Abbreviations: Pn, net photosynthesis; Gs, stomatal conductance; Ci, intercellular CO2concentration; Rs, stomatal resistance; Rh, relative humidity;Cc, CO2 concentration in photosynthetic chamber; Tf,leaf temperature.
Leaf photosynthesis was measured using the LI-6200 portablephotosynthesis system (LI-COR, Lincoln, Nebraska 68504, USA) on attachedleaves in the field between 10:00 a.m. and 2:00 p.m. (Beijing time) on sunnydays. Air temperature (Ta), leaf temperature (Tf), relative humidity (Rh), netphotosynthesis (Pn), stomatal conductance (Gs), intercellular CO2concentration (Ci), stomatal resistance (Rs), and stomatal conductance (Cs)were measured or calculated. Leaf gas exchange readings were taken byquadrants (i.e., readings were taken from the eastern, southern, western, andnorthern quadrants of each tree) to minimize any potential environmentalimpacts.
Asian pear ( Rehd. cv. rehd.) is one of the most prevalent tree crops in southern China. Thesubtropical climate of this region provides for cloudy, rainy conditions withlow temperatures in the spring, when pears produce new shoots, expand leaves,flower and set fruit, increasing the demand for organic and inorganicnutrients. Plants meet these nutritional requirements three ways: (1) nutrientstorage, (2) uptake of inorganic nutrients from the soil through the rootsystem, and (3) synthesis of carbohydrate through leaves. Under unfavorableconditions, leaves have a stronger photosynthetic capacity to supplysufficient carbohydrates and organic nutrients to assure pears can finishvarious biochemical and physiological processes. Hancock and Flore (1989)reported the regression coefficient of net photosynthetic rates wassignificantly correlated with yield. Determining the leaf photosyntheticcharacteristics of pear is therefore important to maintaining yield andimproving fruit quality.
Lieth, J.H. and C.C. Pasian. 1990. A model forphotosynthesis of rose leaves as a function of photosynthtically activeradiation, leaf temperature, and leaf age. J. Amer. Soc. Hort. Sci. 115: 486-491.
Variables: The variables that might affect the rate of photosynthesis in this experiment are: Temperature: When the temperature rises so does the rate of photosynthesis; this is because as the temperature around the plant rises the enzymes controlling photosynthesis inside the chloroplasts heat up and start moving around faster, the fast moving molecules collide with other fast moving enzymes causing them to react....
A) sunlight concentration B) temperature C) chlorophyll concentration D) carbon dioxide availability Effects of the variables and there concentrations: The amount of sunlight will decide the rate of photosynthesis as there will be a an increased rate of photosynthesis due to the increased availability of photons of light....
Mooney, H.A. and A.T. Harrison. 1970. The influence ofconditioning temperature on subsequent temperature-related photosyntheticcapacity in higher plants. Prediction and Measurement ofPhotosynthetic Productivity. PUDOC, Wageningen, pp. 411-417.
This process is called photosynthesis. Temperature, carbon dioxide concentration and light intensity are factors that can limit the rate of photosynthesis.