title: The SclerophyllousEucalyptus camaldulensisand HerbaceousNicotiana tabacumHave Different Mechanisms to Maintain High Rates of Photosynthesis.
abstract: It is believed that high levels of mesophyll conductance (gm) largely contribute to the high rates of photosynthesis in herbaceous C3plants. However, some sclerophyllous C3plants that display low levels ofgmhave high rates of photosynthesis, and the underlying mechanisms responsible for high photosynthetic rates in sclerophyllous C3plants are unclear. In the present study, we examined photosynthetic characteristics in two high-photosynthesis plants (the sclerophyllousEucalyptus camaldulensisand the herbaceousNicotiana tabacum) using measurements of gas exchange and chlorophyll fluorescence. Under saturating light intensities, both species had similar rates of CO2assimilation at 400 μmol mol-1CO2(A400). However,E. camaldulensisexhibited significantly lowergmand chloroplast CO2concentration (Cc) thanN. tabacum. A quantitative analysis revealed that, inE. camaldulensis, thegmlimitation was the most constraining factor for photosynthesis. By comparison, inN. tabacum, the biochemical limitation was the strongest, followed bygmandgslimitations. In conjunction with a lowerCc,E. camaldulensisup-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 inE. camaldulensis. These results highlight the different mechanisms used to maintain high rates of photosynthesis in the sclerophyllousE. camaldulensisand the herbaceousN. tabacum.
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of SciencesMengla, China; Department of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of SciencesKunming, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Huang
authors.affiliation: Forestry Bureau of Dongchuan County Kunming, China.
authors.forename: You-Gui
authors.initials: YG
authors.lastname: Tong
authors.affiliation: Forestry Bureau of Dongchuan County Kunming, China.
authors.forename: Guo-Yun
authors.initials: GY
authors.lastname: Yu
authors.affiliation: Forestry Bureau of Dongchuan County Kunming, China.
authors.forename: Wei-Xian
authors.initials: WX
authors.lastname: Yang
keywords: CO2 assimilation; alternative electron flow; mesophyll conductance; photorespiration; sclerophyllous