Exogenous sugar addition can exacerbate root carbon limitation in trees

Area of Science:

• Plant Physiology
• Forest Ecology
• Plant Carbon Metabolism

Background:

• Roots are critical carbon sinks in trees, vulnerable to carbon limitation during reduced assimilation.
• Advancements in sugar infusion techniques offer new insights into root carbon dynamics.

Purpose of the Study:

• To investigate the impact of exogenous sugar supply on carbon allocation and physiological responses in maple and pine saplings.
• To determine species-specific differences in response to sugar infusion under simulated carbon limitation.

Main Methods:

• Glasshouse experiment with Acer pseudoplatanus and Pinus sylvestris saplings.
• Defoliation followed by controlled 13C-labeled glucose infusion (slow, fast, or none).
• Measurement of photosynthetic parameters, nonstructural carbohydrates (NSC), and stable isotope ratios (δ13C) in plant tissues and respired CO2.

Main Results:

• Maple saplings exhibited photosynthetic downregulation and leaf senescence following sugar infusion, linked to high leaf NSC.
• Pine saplings maintained stable photosynthesis and NSC levels, indicating successful mitigation of root carbon limitation.
• Species-specific responses highlight differences in sugar transport and source-sink dynamics.

Conclusions:

• Exogenous sugar supply can exacerbate root carbon limitation by negatively impacting plant photosynthesis.
• The effectiveness of sugar infusion to alleviate root carbon limitation is contingent on species-specific physiological resilience.
• Alleviating root carbon limitation through sugar addition requires that photosynthesis remains unimpeded.