Abstract: Plants assimilate CO₂ through photosynthesis, converting it into carbohydrates that sustain growth, development and maintenance. However, a substantial portion of this fixed carbon is returned to the atmosphere via respiration, with terrestrial plants releasing 60-80 Gt C y⁻¹—a flux five times greater than annual anthropogenic CO₂ emissions. Depending on species and environmental conditions, up to 70% of the carbohydrates produced through photosynthesis may be respired within the same day. Consequently, understanding the mechanisms underlying respiratory carbon flux is essential for improving climate models and predicting ecosystem responses to environmental change.

In current Earth System Models, leaf dark respiration (R_dark) is commonly parameterized through its relationship with leaf nitrogen (N) and maximum carboxylation capacity (V_cmax), due to the linkage between N investment in photosynthetic capacity and the energy required for cellular maintenance processes. While these models can explain much of the observed variation in R_dark, they largely represent maintenance costs and overlook other energy-intensive processes such as sugar export and tissue-specific metabolism.

Building on this framework, my PhD investigates how environment stress, sugar export, and tissue specialization contribute to R_dark beyond the modelled factors. First, I examine how drought alters R_dark and V_cmax to understand how environmental stress modifies substrate availability, energy demand, and the R_dark-V_cmax scaling. Drought significantly reduced V_cmax but exerted no effect on R_dark as increased maintenance respiration (R_m) was balanced by decreased export-related respiration (R_e). Second, I quantify how the rate of starch degradation and associated energy costs of export affect R_dark, which increased nonlinearly with starch degradation rose, indicating sugar export becomes cheaper at high starch degradation rates. Third, I investigated how functional differences between vascular and mesophyll tissues contribute to R_dark variation. Vascular tissue exhibited higher R_dark at a given N concentration, suggesting faster protein turnover and greater energy demand compared with mesophyll tissue. Together, these studies provide a mechanistic framework to explain variation in R_dark, moving beyond maintenance-only assumptions to incorporate with sugar export process and tissue specialization.

Biography: I completed my master’s degree at Nanjing University (China), where I developed pH-sensitive fluorescence dyes and used them to create 2D planar optode foils for high temporal-spatial resolution sensing. Since 2021, I’ve been doing my PhD in Owen’s lab at ANU, studying what drives of variation in leaf dark respiration. My research uses high-throughput fluorescence approach with planar optode to explore how respiration respond to environmental changes. I have found that sugar export plays an important role in mediating leaf dark respiration, and that the export and long-distance transport functions of vascular tissues lead to a heterogeneous respiration patten across the leaf.