Exploring the acclimation of leaf anatomical traits to high CO2 and their relevance to photosynthesis

Greenhouse crops are frequently grown under high CO2 concentrations due to the application of supplementary CO2. Leaves developed under high CO2 could differ in their anatomical traits compared with leaves developed under normal CO2 concentrations. For example, leaves developed at high CO2 often show increased leaf thickness specifically in palisade layers but not in spongy mesophyll, and an increased chloroplast density in the leaf tissue; high CO2 acclimated leaves also tend to have decreased stomatal density. These changes in leaf anatomical traits may affect both stomatal conductance (gs) and mesophyll conductance (gm), which could potentially limit photosynthesis in terms of both its steady state and dynamics. Previous research of two master theses already showed that tomato and cucumber grown at high CO2 showed increased leaf mass per area, which potentially indicates that leaf anatomy may be affected and thus gm; cucumber grown at high CO2 also had lower stomatal density, but the results for tomato was not statistically clear. The objectives of this project are to (1) study the effect of growth CO2 concentration on leaf anatomy for three commercially important greenhouse crops (i.e. tomato, cucumber and chrysanthemum) that have distinct differences in stomatal anatomy, and (2) explore how the acclimation of leaf anatomy to high CO2 affects steady-state and dynamic photosynthesis.
Furthermore, in this project, we will use novel methods to measure leaf anatomy and gm. First, a multiphoton microscope / confocal laser scanning microscope will be used to obtain 3D pictures of leaf tissue, which will be much faster than the normal leaf fixation processes for making cross-sections of leaf anatomy. Those pictures will give us an idea about the vertical distribution of chlorophyll content in the leaf tissue and the distribution of chloroplasts inside the leaf. Second, gm will be measured using isotope discrimination method, based on the different diffusion rate of C12 and C13 in the leaf tissue. This will provide a direct measurement of gm, instead of estimating gm from modelling methods, which provide different estimations based on the specific modelling approach used.

Type of research:
Performing climate chamber experiments using a gas exchange and chlorophyll fluorescence system (LI‐6400 or LI‐6800). Measuring leaf cross-section and the distribution of chlorophyll inside the leaf using multiphoton microscope / confocal laser scanning microscope. If the confocal microscope is not available during the thesis period, leaf cross-sections will be made by normal leaf fixation process. Taking leaf imprints samples and measuring stomatal density and size. Measuring gm using isotope discrimination method in the joint-photosynthesis lab of HPP and CSA.

Interested in doing a BSc or MSc thesis at HPP? Please contact the HPP student coordinator Katharina Hanika.