Global change progressively increases foliar nitrogen-phosphorus ratios in China's subtropical forests

Area of Science:

• Ecology
• Biogeochemistry
• Plant Science

Background:

• Rising global nitrogen (N) to phosphorus (P) ratios (N/P) impact terrestrial ecosystems.
• Long-term foliar N/P dynamics and drivers in subtropical forests remain understudied.
• Understanding foliar N/P is crucial for predicting forest nutrient status under global change.

Purpose of the Study:

• To detect temporal trends in foliar N/P in China's subtropical forests.
• To quantitatively estimate drivers of foliar N/P changes.
• To analyze interactions between plant types (evergreen vs. deciduous, trees vs. shrubs).

Main Methods:

• Analysis of 1811 herbarium specimens from 12 species collected between 1920-2010.
• Statistical estimation of drivers including atmospheric CO2, N deposition, mean annual temperature (MAT), and vapor pressure deficit.
• Projection of future foliar N/P trends under Shared Socioeconomic Pathway (SSP) scenarios.

Main Results:

• Significant decrease in foliar P concentration (23.1%) and increase in foliar N/P (21.2%) observed over time.
• Foliar N/P increased more in evergreen (22.9%) than deciduous (16.9%) species.
• Atmospheric CO2, N deposition, and MAT were key drivers for evergreens; CO2, MAT, and vapor pressure deficit for deciduous species.

Conclusions:

• Global change has intensified N-P imbalance in subtropical forests, altering ecosystem functioning.
• Future climate and CO2 changes will likely exacerbate this imbalance, particularly in deciduous species.
• Projected increases in foliar N/P under SSP scenarios will further impact forest community composition and ecosystem processes.