Nitrogen allocation and partitioning in invasive and native Eupatorium species

Area of Science:

• Plant Ecology
• Invasive Species Biology
• Photosynthetic Physiology

Background:

• Nitrogen (N) allocation in plants involves a trade-off between photosynthesis and defense.
• Invasive species, lacking natural enemies, might reallocate N from defense to photosynthesis.
• This reallocation could confer a competitive advantage to invasive plants.

Purpose of the Study:

• To test if invasive Eupatorium adenophorum allocates more leaf N to photosynthesis than native Eupatorium species.
• To compare photosynthetic N-use efficiency (PNUE) and related physiological traits between invasive and native species.
• To determine if enhanced photosynthetic efficiency contributes to the invasiveness of E. adenophorum.

Main Methods:

• Comparative analysis of nitrogen allocation, photosynthetic rates (Pmax), and PNUE in invasive E. adenophorum and native E. chinense and E. heterophyllum.
• Quantification of N partitioning within photosynthetic components (carboxylation vs. light-harvesting).
• Measurement of related physiological efficiencies including water-use efficiency and respiration efficiency.

Main Results:

• Contrary to hypothesis, the invasive species did not allocate a higher fraction of leaf N to photosynthesis.
• The invader exhibited more efficient photosynthetic N partitioning, allocating more N to carboxylation.
• Invasive species showed higher Pmax, PNUE, water-use efficiency, respiration efficiency, and apparent quantum yield compared to natives.

Conclusions:

• Invasive E. adenophorum demonstrates superior photosynthetic N-use efficiency through optimized N partitioning to carboxylation, not increased allocation.
• These physiological advantages, coupled with a higher leaf area ratio, likely contribute to the invasive success of E. adenophorum.
• Understanding N partitioning provides insights into the mechanisms driving plant invasions.