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The Sclerophyllous Eucalyptus camaldulensis and Herbaceous Nicotiana tabacum Have Different Mechanisms to Maintain High Rates of Photosynthesis

View Article: PubMed Central - PubMed

ABSTRACT

It is believed that high levels of mesophyll conductance (gm) largely contribute to the high rates of photosynthesis in herbaceous C3 plants. However, some sclerophyllous C3 plants that display low levels of gm have high rates of photosynthesis, and the underlying mechanisms responsible for high photosynthetic rates in sclerophyllous C3 plants are unclear. In the present study, we examined photosynthetic characteristics in two high-photosynthesis plants (the sclerophyllous Eucalyptus camaldulensis and the herbaceous Nicotiana tabacum) using measurements of gas exchange and chlorophyll fluorescence. Under saturating light intensities, both species had similar rates of CO2 assimilation at 400 μmol mol−1 CO2 (A400). However, E. camaldulensis exhibited significantly lower gm and chloroplast CO2 concentration (Cc) than N. tabacum. A quantitative analysis revealed that, in E. camaldulensis, the gm limitation was the most constraining factor for photosynthesis. By comparison, in N. tabacum, the biochemical limitation was the strongest, followed by gm and gs limitations. In conjunction with a lower Cc, E. camaldulensis up-regulated the capacities of photorespiratory pathway and alternative electron flow. Furthermore, the rate of alternative electron flow was positively correlated with the rates of photorespiration and ATP supply from other flexible mechanisms, suggesting the important roles of photorespiratory pathway, and alternative electron flow in sustaining high rate of photosynthesis in E. camaldulensis. These results highlight the different mechanisms used to maintain high rates of photosynthesis in the sclerophyllous E. camaldulensis and the herbaceous N. tabacum.

No MeSH data available.


Monthly climatic data collected from 1961 to 1980. (A) monthly average air temperature, monthly average maximum and minimum temperatures; (B) monthly precipitation and total irradiance.
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Figure 1: Monthly climatic data collected from 1961 to 1980. (A) monthly average air temperature, monthly average maximum and minimum temperatures; (B) monthly precipitation and total irradiance.

Mentions: We compared the photosynthetic characteristics of N. tabacum and Eucalyptus camaldulensis Dehnh. The latter is a fast-growing species native to Australia that has been widely introduced into China for forest plantations. For this study, Eucalyptus samples were collected from plants grown in an open field at an elevation of 700 m in Dongchuan County, Kunming City, Yunnan Province, China. The monthly air temperature, total radiation and precipitation were displayed in Figure 1 (data were collected from 1961 to 1980). Seedlings of N. tabacum cv. k326 were cultivated in plastic pots in a phytotron at Kunming Institute of Botany, Yunnan, China. Growing conditions were 24/18°C (day/night), 60% relative humidity, and an atmospheric CO2 concentration maintained at 400 μmol mol−1. The phytotron used sunlight as the source of illumination, and plants were exposed to approximately 95% of full sunlight (maximum at noon ≈ 1990 μmol photons m−2 s−1). Photosynthetic parameters were measured in June of 2014. Measurements were made using four mature leaves from four independent plants per species. Fully expanded mature leaves on 13-week-old plants of N. tabacum were used for photosynthetic measurements. For E. camaldulensis, mature leaves that flushed in the spring on 3-year-old plants were used for measurements.


The Sclerophyllous Eucalyptus camaldulensis and Herbaceous Nicotiana tabacum Have Different Mechanisms to Maintain High Rates of Photosynthesis
Monthly climatic data collected from 1961 to 1980. (A) monthly average air temperature, monthly average maximum and minimum temperatures; (B) monthly precipitation and total irradiance.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121285&req=5

Figure 1: Monthly climatic data collected from 1961 to 1980. (A) monthly average air temperature, monthly average maximum and minimum temperatures; (B) monthly precipitation and total irradiance.
Mentions: We compared the photosynthetic characteristics of N. tabacum and Eucalyptus camaldulensis Dehnh. The latter is a fast-growing species native to Australia that has been widely introduced into China for forest plantations. For this study, Eucalyptus samples were collected from plants grown in an open field at an elevation of 700 m in Dongchuan County, Kunming City, Yunnan Province, China. The monthly air temperature, total radiation and precipitation were displayed in Figure 1 (data were collected from 1961 to 1980). Seedlings of N. tabacum cv. k326 were cultivated in plastic pots in a phytotron at Kunming Institute of Botany, Yunnan, China. Growing conditions were 24/18°C (day/night), 60% relative humidity, and an atmospheric CO2 concentration maintained at 400 μmol mol−1. The phytotron used sunlight as the source of illumination, and plants were exposed to approximately 95% of full sunlight (maximum at noon ≈ 1990 μmol photons m−2 s−1). Photosynthetic parameters were measured in June of 2014. Measurements were made using four mature leaves from four independent plants per species. Fully expanded mature leaves on 13-week-old plants of N. tabacum were used for photosynthetic measurements. For E. camaldulensis, mature leaves that flushed in the spring on 3-year-old plants were used for measurements.

View Article: PubMed Central - PubMed

ABSTRACT

It is believed that high levels of mesophyll conductance (gm) largely contribute to the high rates of photosynthesis in herbaceous C3 plants. However, some sclerophyllous C3 plants that display low levels of gm have high rates of photosynthesis, and the underlying mechanisms responsible for high photosynthetic rates in sclerophyllous C3 plants are unclear. In the present study, we examined photosynthetic characteristics in two high-photosynthesis plants (the sclerophyllous Eucalyptus camaldulensis and the herbaceous Nicotiana tabacum) using measurements of gas exchange and chlorophyll fluorescence. Under saturating light intensities, both species had similar rates of CO2 assimilation at 400 μmol mol−1 CO2 (A400). However, E. camaldulensis exhibited significantly lower gm and chloroplast CO2 concentration (Cc) than N. tabacum. A quantitative analysis revealed that, in E. camaldulensis, the gm limitation was the most constraining factor for photosynthesis. By comparison, in N. tabacum, the biochemical limitation was the strongest, followed by gm and gs limitations. In conjunction with a lower Cc, E. camaldulensis up-regulated the capacities of photorespiratory pathway and alternative electron flow. Furthermore, the rate of alternative electron flow was positively correlated with the rates of photorespiration and ATP supply from other flexible mechanisms, suggesting the important roles of photorespiratory pathway, and alternative electron flow in sustaining high rate of photosynthesis in E. camaldulensis. These results highlight the different mechanisms used to maintain high rates of photosynthesis in the sclerophyllous E. camaldulensis and the herbaceous N. tabacum.

No MeSH data available.