Nitrogen addition affects eco-physiological interactions between two tree species dominating in subtropical forests

Area of Science:

• Forest Ecology
• Plant Physiology
• Biogeochemistry

Background:

• Nitrogen (N) deposition is a significant environmental factor influencing forest ecosystems.
• Understanding interspecific interactions under N enrichment is crucial for subtropical forest management.

Purpose of the Study:

• To investigate the effects of nitrogen deposition on the growth and eco-physiological interactions of Cunninghamia lanceolata and Phoebe chekiangensis.
• To determine how N addition influences competition dynamics and resource acquisition between these two dominant subtropical tree species.

Main Methods:

• A 6-month greenhouse experiment with monocultures and mixtures of C. lanceolata and P. chekiangensis.
• Two nitrogen (N) addition levels (0 and 45 kg ha⁻¹ yr⁻¹) were applied.
• Measurements included plant growth, root architecture, biomass distribution, element content, and photosynthetic physiology.

Main Results:

• Interspecific competition was higher in mixtures without N addition, with P. chekiangensis outperforming C. lanceolata.
• Nitrogen addition increased net photosynthetic rates but reduced height, diameter, and crown width for both species in mixtures.
• N addition shifted belowground biomass distribution, decreasing it in C. lanceolata and increasing it in P. chekiangensis.

Conclusions:

• Nitrogen addition exacerbates competition between C. lanceolata and P. chekiangensis, primarily through altered root architecture and biomass allocation.
• These changes negatively impact the growth of both species in mixed stands under elevated N deposition.
• Findings offer insights into managing subtropical forests facing increased nitrogen deposition.