Nitrogen-driven changes in leaf anatomy affect the coupling between leaf mass per area and photosynthesis

Area of Science:

• Plant Physiology
• Plant Ecology
• Leaf Economics

Background:

• Leaf mass per area (LMA) and photosynthetic rate (A) are key traits defining plant growth strategies within the leaf economic spectrum.
• Nitrogen (N) availability influences photosynthetic rate (A) and growth, but its effect on LMA is genotype-dependent.
• Leaf structural traits are known to mediate the relationship between LMA and A, suggesting N supply could alter this coupling through structural modifications.

Purpose of the Study:

• To investigate how nitrogen (N) supply affects leaf anatomical traits and their subsequent impact on the relationship between LMA and photosynthetic rate (A).
• To determine the role of specific structural traits, such as mesophyll cell density and palisade tissue thickness, in mediating LMA-A coupling under varying N conditions.
• To explore the potential for optimizing plant growth and resistance by manipulating leaf structure and N allocation.

Main Methods:

• Measurements of photosynthetic rate (A), LMA, leaf anatomical traits (e.g., mesophyll cell density, palisade tissue thickness), and nitrogen allocation to leaf components were conducted.
• Experiments involved 9 Brassica napus cultivars grown under two distinct nitrogen supply levels.
• Analysis focused on the influence of structural traits and N allocation on mesophyll conductance (gm) and Rubisco content (Nrub).

Main Results:

• Palisade tissue thickness (Tp) positively influenced LMA, chloroplast surface area, Rubisco content (Nrub), mesophyll conductance (gm), and photosynthetic rate (A).
• Mesophyll cell density (ρcell) increased LMA but negatively affected Nrub under low N conditions.
• Higher LMA led to increased allocation to cell walls (Ncw), reducing Nrub and A, an effect mitigated by the positive impact of palisade tissue thickness (Tp) on A.

Conclusions:

• Leaf structural plasticity, particularly in palisade tissue thickness (Tp) and mesophyll cell density (ρcell), plays a crucial role in regulating mesophyll conductance (gm) and the trade-off between nitrogen allocation to Rubisco (Nrub) and cell walls (Ncw).
• These findings provide insights into how simultaneous increases in LMA and A can be achieved, potentially enhancing both rapid growth and stress resistance in plants.
• Understanding these structural and physiological relationships under varying N supply is vital for crop improvement and predicting plant responses in different environments.