The resistances inside leaves that restrict the uptake of CO2 by photosynthesis impact how efficiently crops and other plants use water and fertilizers. This efficiency is also impacted by how photosynthesis and respiration interact through sharing of reactants and products. This project will examine the resistances to CO2 diffusion in leaves and interactions between photosynthesis and respiration through analyses of how leaves differentially use heavy and light isotopes of carbon in CO2, a task that has become easier, faster, and less expensive with the development of a new technology - the tunable diode laser spectrometer (TDL). Recent discoveries suggest that providing high light intensities to a leaf immediately preceding a dark period can have a large effect on the exchange of isotopes during darkness. This implies a larger role of the enzyme phosphoenolpyruvate carboxylase (PEPC) than is expected and this could impact interpretation of isotopic data used to measure internal leaf resistance to CO2 diffusion and interactions between photosynthesis and respiration. Daily and seasonal variation in carbon isotope usage by woody and herbaceous species will be analyzed along with plants containing high amounts of PEPC. This study will help to define the role of PEPC in controlling isotopic usage by plants and its influence on photosynthetic and respiratory interactions.
Broader impacts: In addition to potential crop improvements, increases in understanding of isotopic exchange within leaves will refine the fundamental assumptions used to understand ecosystem metabolism and generate data needed to model regional carbon cycles. The TDL is straightforward and inexpensive to use making it ideal for classroom education and laboratory training of graduate and undergraduate students at the University of New Mexico (a Minority Serving Institution where 36% of UNM Biology's 1300 majors are Hispanic and another 7% are Native American) and at Portland State University (where many students are the first member of their family to attend college or are non-traditional re-entry students). Experience with this equipment will help prepare students for research careers at universities, national labs, and in the private sector.
