Seok Chan Koh

Novel Patterns of Seasonal Photosynthetic Acclimation, Including Interspecific Differences, in Conifers over an Altitudinal Gradient

Abstract Photosynthesis, as the basis of most food chains and a crucial global carbon sink, makes chief contributions to overall ecosystem carbon budgets, but specific responses of the plant component cannot be obtained from such budgets. To gain much-needed further information on possible interspecies differences in seasonal patterns of photosynthesis, capacities for light- and CO2-saturated rates of oxygen evolution at 25°C (photosynthetic capacity) were determined during the summer-fall-winter transition for five conifer species over their natural distribution along a steep altitudinal gradient. Findings include (i) a transient upregulation of photosynthetic capacity during the summer-to-fall transition in all five conifer species that preceded the previously reported winter downregulation in conifers. However, there were (ii) interspecific differences in this response at the highest altitudes, with higher maximal photosynthetic capacities displayed by pine and spruce species compared to fir species. Lastly, the winter downregulation of photosynthetic capacity was not as complete in the present study (winter of 2006) as that which has been reported for previous winter seasons, which has implications for the winter survival strategy of conifers in response to global warming.

Growth, photosynthesis and chlorophyll fluorescence of Chinese cabbage in response to high temperature.

In order to gain insight into the physiological responses of plants to high temperature stress, the effects of temperature on Chinese cabbage (Brassica campestris subsp. napus var. pekinensis cv. Detong) were investigated through analyses of photosynthesis and chlorophyll fluorescence under 3 different temperatures in the temperature gradient tunnel. Growth (leaf length and number of leaves) during the rosette stage was greater at ambient and ambient temperatures than at ambient temperature. Photosynthetic fixation rates of Chinese cabbage grown under the different temperatures did not differ significantly. However, dark respiration rate was significantly higher in the cabbage that developed under ambient temperature relative to elevated temperature. Furthermore, elevated growth temperature increased transpiration rate and stomatal conductance resulting in an overall decrease of water use efficiency. The chlorophyll a fluorescence transient was also considerably affected by high temperature stress; the fluorescence yield , , and decreased considerably at ambient and ambient temperatures, with induction of and decrease of . The values of RC/CS, ABS/CS, TRo/CS, and ETo/CS decreased considerably, while DIo/CS increased with increased growth temperature. The symptoms of soft-rot disease were observed in the inner part of the cabbage heads after 7, 9, and/or 10 weeks of cultivation at ambient and ambient temperatures, but not in the cabbage heads growing at ambient temperature. These results show that Chinese cabbage could be negatively affected by high temperature under a future climate change scenario. Therefore, to maintain the high productivity and quality of Chinese cabbage, it may be necessary to develop new high temperature tolerant cultivars or to markedly improve cropping systems. In addition, it would be possible to use the non-invasive fluorescence parameters , , and , as well as , , , RC/CS, ETo/CS, , and (which were selected in this study), to quantitatively determine the physiological status of plants in response to high temperature stresses.

Seasonal Photoprotective Responses in Needles of Korean Fir (Abies koreana) Over an Altitudinal Gradient on Mount Halla, Jeju Island, Korea

Abstract Chloroplast pigments and chlorophyll fluorescence were characterized in needles of Korean fir (Abies koreana) in summer, winter, and spring at three altitudes on Jeju Island, Korea. High light-harvesting efficiency (intrinsic photosystem II efficiency) and indirect evidence for high photosynthetic rates (high levels of&bgr;-carotene and chlorophyll b) during the growing season contrasted with mid-winter downregulation of light-harvesting efficiency involving retention of high zeaxanthin levels and locked-in photoprotective thermal dissipation (from low chlorophyll fluorescence emission). Neoxanthin levels were inversely correlated with sustained photoprotection in the winter, and lutein to xanthophyll cycle carotenoid levels decreased from summer to winter, suggesting that zeaxanthin plays the prominent role in winter photoprotection of Korean fir needles. Summer was apparently most conducive to photosynthesis, consistent with high levels of summer precipitation on Jeju Island, and in contrast to fir and other conifers in a climate with dry summers at high altitudes in Colorado, U.S.A., where studies have shown that the wet spring is the season most favorable for photosynthesis. Lastly, despite there being only 300 m difference in altitude among the three sites, there were discernible differences in (i) accumulation of zeaxanthin in winter (as an indicator for the severity of conditions, with highest levels at the highest altitude), (ii) apparent photosynthesis rates in summer (from &bgr;-carotene levels, with highest levels at the highest altitude), and (iii) transition to increased photosynthesis in spring (from fluorescence emission levels, slowest at the highest altitude).

Photosynthesis of Chinese cabbage and radish in response to rising leaf temperature during spring

Photosynthesis in leaves, exposed to temperature change, was measured during spring to provide information for modeling of cropping systems for Chinese cabbage (Brassica campestris subsp. napus var. pekinensis) and radish (Raphanus sativus) in Jeju Island. The net photosynthetic rates (A) of Chinese cabbage and radish were depressed at temperatures above approximately 25°C (corresponding to the optimum temperature for photosynthesis), due in part to high rates of respiration above 25 or 30°C. Chinese cabbage was more sensitive to high temperature than radish. Above 25°C, stomatal conductance (gs) declined steeply with a sharp increase in the vapor pressure deficit (VPD) and transpiration rate (E), suggesting that stomatal closure could not be associated with transpiration rate, particularly in Chinese cabbage. Dramatic declines in water use efficiency (WUE), instantaneous transpiration efficiency (ITE), and carboxylation efficiency (CE) above 30°C indicated that the plants could be severely affected negatively by high temperatures above 30°C. However, compared to Chinese cabbage, radish had high light use efficiency and potential to assimilate CO2, judged by their high quantum yield (φ) and maximum photosynthetic rate (Amax). Radish utilized high levels of photosynthetic photon flux and strongly acclimated to the light environment, considering their high light saturation point (Qsat) and low light compensation point (Qcomp). These results suggested that rising temperature might substantially alter water availability of plants by itself and/or through effects on the rate of water loss from leaves of Chinese cabbage and radish under diurnal and/or seasonal fluctuations of temperature, and/or global temperature change. To maintain the high productivity and quality of these crop species, it may be necessary to harvest them until early June, when the daily maximum temperature is below 25°C in Jeju Island.

Photosystem II photochemical efficiency and photosynthetic capacity in leaves of tea plant ( Camellia sinensis L.) under winter stress in the field

The effects of winter stress on photosynthesis of the tea plant (Camellia sinensis L.) were determined over the course of a year. Changes in gas exchange and chlorophyll fluorescence parameters largely tracked seasonal changes of temperature, precipitation, and atmospheric vapor pressure deficit. Intrinsic photosystem II (PSII) efficiency (estimated from the ratio of variable over maximal chlorophyll fluorescence, Fv/Fm) was at maximal levels (0.80–0.83) during the summer, then decreased in the fall and remained below 0.6 from January to March. The low levels of Fv/Fm in the winter were accompanied by the strongest quenching of maximal (Fm) and initial (Fo) fluorescence, presumably reflecting engagement of photoprotective thermal energy dissipation. Net photosynthetic rate, transpiration rate, and stomatal conductance were highest in the summer and lowest from late fall to early spring. These data suggested that PSII photochemical efficiencies and photosynthetic capacity of tea plant were limited under low temperature in the winter. On the other hand, a greater water use efficiency, lower light compensation point, and lower light intensity at which photosynthesis became saturated might be advantageous for tea plants acclimated to the lower precipitation levels and light intensities of winter. Analysis of the relationships between temperature or humidity and photosynthetic variables suggested that tea plants might benefit from irrigation in winter.

Chlorophyll a Fluorescence Response to Mercury Stress in the Freshwater Microalga Chlorella Vulgaris

【The response of the freshwater microalga Chlorella vulgaris to mercuric ion (

Analysis of CO 2 Fixation Capacity in Leaves of Ten Species in the Family Fagaceae

Hg^{2+}

Effects of Different Day / Night TemperatureRegimes on Growth and Clove Development inCool-type Garlic ( Allium sativum L.)

) stress was examined using chlorophyll a fluorescence image analysis and O-J-I-P analysis as a way to monitor the toxic effects of mercury on water ecosystems. The levels of photosynthetic pigments, such as chlorophyll a and b and carotenoids, decreased with increasing

Photosynthesis and Growth Responses of Soybean (Glycine max Merr.) under Elevated CO2 Conditions

Hg^{2+}

Photosynthetic and Growth Responses of Chinese Cabbage to Rising Atmospheric CO2

concentration. The maximum photochemical efficiency of photosystem II(Fv/Fm) changed remarkably with increasing