Slower Soil Nitrogen Transformations Under Longer-Term Warming and the Consequences for Plant Growth

Area of Science:

• Soil Science
• Ecology
• Global Change Biology

Background:

• Climate warming is projected to enhance soil nitrogen (N) transformations, potentially boosting plant growth and carbon (C) assimilation.
• Uncertainty exists regarding the long-term persistence of warming's stimulatory effects on soil N cycling and its impact on plant N uptake.

Purpose of the Study:

• To investigate the long-term response of soil N transformations to warming.
• To elucidate the mechanisms driving these responses and their effects on plant growth.
• To challenge traditional views on warming's impact on soil N cycling.

Main Methods:

• A global meta-analysis was conducted.
• A 7-year local warming experiment was implemented.
• Gross soil N transformation rates (mineralization, nitrification, immobilization) were measured.
• Biotic and abiotic factors influencing N transformations were analyzed.
• Plant growth and N uptake were assessed under experimental warming.

Main Results:

• Longer-term warming (≥6 years) did not stimulate, but significantly inhibited, gross nitrification and nitrate (NO3-) immobilization rates.
• Biotic factors, rather than abiotic factors, were the primary drivers of altered N transformation rates.
• Despite slower soil N transformations, plant growth and ammonium (NH4+) uptake increased under warming.
• Inhibition of NH4+ consumption by nitrifiers led to increased NH4+ availability for plants.

Conclusions:

• Long-term warming can slow soil N transformations, contradicting the assumption of a persistent stimulatory effect.
• Warming-induced changes in soil N cycling can still enhance plant growth and N uptake through altered N availability and plant preferences.
• Findings highlight a crucial soil-plant N coordination, necessitating adjustments in land management and C-N cycling models.