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. Fig. 2. Changes in leaf photosynthetic rate ( P N ) ( A ), transpiration rate ( T r ) ( B ), stomatal conductance ( g S ) ( C ), and intercellular CO 2 concentration ( C i ) ( D ) in ‘Wuniuzao’ after N fertilization. Uppercase and lowercase letters
. On days 5, 8, 10, and 17 of the experimental period, six of nine plants per treatment were chosen to measure net P n , T r , g S , and intercellular CO 2 concentration ( C i ). A red/blue LED light LI-6400 Portable System (LI-COR, Lincoln, NE) was
water potential, ( B ) net photosynthetic rate (P n ), ( C ) stomatal conductance ( g S ), and ( D ) intercellular CO 2 concentration (Ci) of leaves of micropropagated apple trees in response to half-root water stress (▼) and whole-root water stress
continuously decreased up to day 16 ( Fig. 2B ). Fig. 2. ( A ) Net photosynthetic (P n ), ( B ) transpiration rate ( E ), ( C ) stomatal conductance ( g S ), ( D ) intercellular CO 2 concentration ( C i ,), and ( E ) water use efficiency (WUE) changes in
the main stem of five plants was randomly selected, and net photosynthetic rate (P n ), water use efficiency (WUE), stomatal conductance ( g S ), intercellular CO 2 concentration (C i ), and transpiration rate (T r ) were measured with a
d of transplantation, which were consistent with the change in SD ( Fig. 1A ). Fig. 4. Net photosynthesis rate (Pn) ( A ), stomatal conductance ( g S ) ( B ), intercellular CO 2 concentration (Ci) ( C ), and transpiration rate (Tr) ( D ) of
Photosystem II (PSII) efficiency and CO2 assimilation in response to photon flux density (PFD) and intercellular CO2 concentration (Ci) were monitored simultaneously in leaves of apple, pear, apricot, and cherry with a combined system for measuring chlorophyll fluorescence and gas exchange. When photorespiration was minimized by low O2 (2%) and saturated CO2 (1300 ppm), a linear relationship was found between PSII efficiency and the quantum yield for CO2 assimilation with altering PFD, indicating CO2 assimilation in this case is closely linked to PSII activity. As PFD increased from 80 to 1900 μmol·m–2·s–1 under ambient CO2 (350 ppm) and O2 (21%) conditions, PSII efficiency decreased by increased nonphotochemical quenching and decreased concentration of open PSII reaction centers. The rate of linear electron transport showed a similar response to PFD as CO2 assimilation. As Ci increased from 50 to 1000 ppm under saturating PFD (1000 μmol·m–2·s–1) and ambient O2, PSII efficiency was increased initially by decreased nonphotochemical quenching and increased concentration of open PSII reaction centers and then leveled off with further a rise in Ci. CO2 assimilation reached a plateau at a higher Ci than PSII efficiency because increasing Ci diverted electron flow from O2 reduction to CO2 assimilation by depressing photorespiration. It is concluded that PSII efficiency is regulated by both nonphotochemical quenching and concentration of open PSII reaction centers in response to light and CO2 to meet the requirement for photosynthetic electron transport.
Abstract
Differences in the photosynthetic capacity of leaves of peach [Prunus persica (L.) Batsch cv. Golden Glory] were investigated in conjunction with their leaf nitrogen and phosphorus content. Photosynthetic CO2 assimilation expressed on a leaf area basis, mesophyll conductance, and leaf conductance to water vapor were all linearly related to leaf nitrogen content expressed on a leaf area basis (R2 = 0.908, 0.921, 0.685, respectively). Leaf intercellular CO2 concentrations tended to decrease slightly with increasing CO2 assimilation rates and leaf N contents, indicating that CO2 assimilation was not being restricted by low intercellular CO2 concentrations and leaf conductances in leaves with lower assimilation capacity. CO2 assimilation, mesophyll conductance, and leaf conductance to water vapor were also linearly related to leaf phosphorus content, but these relationships were not as clear as for leaf nitrogen content. (R2 = 0.601, 0.687, 0.324, respectively). The maximum CO2 assimilation rate per unit of leaf nitrogen for peach leaves in this experiment was between 6.0 and 7.0 nmol CO2 mg N−1 s−1.
Abstract
The CO2 assimilation characteristics of walnut leaves (Juglans regia L.) were measured on excised branches using controlled, open-system, infrared gas analysis techniques in the laboratory and on large bearing trees with a CO2 depletion method in the field. The mean maximum rate of net CO2 assimilation measured by both techniques was 1.3 nM CO2 cm-2s-l on a leaf area basis of 6.0 nm CO2 mg N-1s-1 on a leaf nitrogen basis. Leaves approached light saturation at 600-800 µEs-1m-2, and exhibited an otpimum range for CO2 assimilation at 18 to 26°C. CO2 assimilation increased linearly with increases in intercellular CO2 concentrations between 60-250 µl liter-1. The daily pattern of field CO2 assimilation was highly correlated with leaf conductance to H2O but exhibited a midday depression that was independent of the daily pattern of incident photosynthetic photon flux density at the surface of the leaves.
93 POSTER SESSION 11 (Abstr. 159–188) Crop Physiology Tuesday, 25 July, 1:00–2:00 p.m.