Long-term decline in grassland productivity driven by increasing dryness.

Area of Science:

• Ecology
• Climate Science
• Biogeochemistry

Background:

• Increasing aridity and drought severity threaten the global carbon (C) sink.
• Distinguishing direct drying effects from CO2 enrichment and nitrogen (N) deposition impacts is challenging.
• Long-term data is crucial for understanding climate-ecosystem dynamics.

Purpose of the Study:

• To quantify grassland production decline over four decades.
• To identify the specific climatic drivers of this decline.
• To assess the roles of CO2 enrichment and N deposition.

Main Methods:

• Analysis of grassland biomass production over 40 years.
• Stable isotope analysis (C and N) of plant biomass.
• Utilizing a long-term snow-addition experiment for causal inference.

Main Results:

• A >50% decline in native C3 grassland production was documented.
• Increasing aridity, particularly declining late-summer rainfall, was identified as the primary cause.
• CO2 enrichment provided a slight amelioration of productivity loss; N changes had no significant effect.

Conclusions:

• Late-summer dryness is a critical factor impacting grassland productivity.
• Climate change, specifically altered rainfall patterns, has lasting consequences for terrestrial ecosystems.
• Understanding past climate-ecosystem interactions is key to predicting future carbon sink capacity.