Phosphorus constrains global photosynthesis more than nitrogen does.

Area of Science:

• Ecology
• Biogeochemistry
• Plant Physiology

Background:

• Nitrogen (N) is traditionally considered the primary nutrient limiting global vegetation growth.
• Recent observations suggest a potential shift in nutrient limitation dynamics.

Purpose of the Study:

• To investigate the comparative limitation of global photosynthesis by phosphorus (P) and nitrogen (N) over the past four decades.
• To quantify the impact of declining foliar nutrient concentrations on vegetation photosynthesis and terrestrial carbon sinks.

Main Methods:

• Utilized a global dataset of over 80,000 field observations of foliar nutrients (1980-2017).
• Employed a machine learning approach to generate long-term global foliar N and P concentration data.
• Analyzed trends in foliar P and N concentrations and their effects on global photosynthesis.

Main Results:

• Foliar P concentration declined at a significantly faster rate (-0.80%/yr) than foliar N concentration (-0.31%/yr).
• Phosphorus limitation on global photosynthesis increased, becoming over 1.5 times stronger than N limitation.
• Declining foliar P and N reduced the increasing trend in global photosynthesis by approximately 17.2% and 6.7%, respectively.

Conclusions:

• Phosphorus limitation is emerging as a stronger constraint on global photosynthesis than nitrogen.
• The weakening of terrestrial carbon sinks due to P limitation necessitates stricter anthropogenic emission reduction strategies.
• This study underscores the critical role of phosphorus in regulating Earth's carbon cycle and climate.