General trait relationships in stems: a study on the performance and interrelationships of several functional and structural parameters involved in corticular photosynthesis

We addressed corticular photosynthesis, focusing on parameters of underlying dark and light reactions as well as structural differentiation. To unveil general stem traits and underlying principles that may be valid across several tree species, CO₂ exchange rates and chlorophyll-fluorescence parameters were measured in current-year to 3-year-old stems of five deciduous tree species (including climax and pioneer species). Across species, dark CO₂ efflux rates (Rd) of stems exhibited a common regression relationship with photosynthetic rates (A) and light-adapted quantum efficiency of photosystem II (PSII) (ΔF/Fm'), a pattern analogous to leaf trait correlations. Furthermore, A and ΔF/Fm' were closely interrelated to each other. Consistent correlations of stem structure and function were also assessed among species. Changes in tissue structure during ageing significantly affected several stem functional parameters. Stem CO₂ efflux during the dark and corticular photosynthetic rates declined with increasing stem age as well as light-adapted quantum efficiency of PSII. Furthermore, a strong relationship between stem Rd and peridermal PFD-transmittance (T) as well as between Rd and total bark chlorophyll was evident. Consistent results were found for the relationships between corticular photosynthesis (or primary photosynthetic reactions like ΔF/Fm') and selected structural traits. The found correlation patterns among functional and/or structural traits of stems and their concordance with leaf trait relationships may aid in identifying underlying mechanisms and scaling relationships that link traits to plant and ecosystem function.