Influence of light and nitrogen on the photosynthetic efficiency in the C4 plant Miscanthus × giganteus
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There are numerous studies describing how growth conditions influence the efficiency of C4 photosynthesis. However, it remains unclear how changes in the biochemical capacity versus leaf anatomy drives this acclimation. Therefore, the aim of this study was to determine how growth light and nitrogen availability influence leaf anatomy, biochemistry and the efficiency of the CO2 concentrating mechanism in Miscanthus × giganteus. There was an increase in the mesophyll cell wall surface area but not cell well thickness in the high-light (HL) compared to the low-light (LL) grown plants suggesting a higher mesophyll conductance in the HL plants, which also had greater photosynthetic capacity. Additionally, the HL plants had greater surface area and thickness of bundle-sheath cell walls compared to LL plants, suggesting limited differences in bundle-sheath CO2 conductance because the increased area was offset by thicker cell walls. The gas exchange estimates of phosphoenolpyruvate carboxylase (PEPc) activity were significantly less than the in vitro PEPc activity, suggesting limited substrate availability in the leaf due to low mesophyll CO2 conductance. Finally, leakiness was similar across all growth conditions and generally did not change under the different measurement light conditions. However, differences in the stable isotope composition of leaf material did not correlate with leakiness indicating that dry matter isotope measurements are not a good proxy for leakiness. Taken together, these data suggest that the CO2 concentrating mechanism in Miscanthus is robust under low-light and limited nitrogen growth conditions, and that the observed changes in leaf anatomy and biochemistry likely help to maintain this efficiency.
KeywordsCarbon isotope discrimination C4 photosynthesis Miscanthus Nitrogen Light
This research was supported by the National Natural Science Foundation of China [Grant Nos. 41071032, 31270445], the 9th Thousand Talents Program of China, the US Department of Energy, Office of Basic Energy Science [DE-FG02_09ER16062] and Office of Science, Office of Biological and Environmental Research [DE-AC02-05CH11231]. Instrumentation was obtained through an NSF Major Research Instrumentation Grant [#0923562]. JLH was supported by an Australian Research Council Future Fellowship [FT130101165]. We thank C. Cody for plants growth management, Dr. Steve Long for Miscanthus plant material and the Franceschi Microscopy and Imaging Center of Washington State University for use of its facilities.
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