Postfire Phosphorus Enrichment Mitigates Nitrogen Loss in Boreal Forests

Area of Science:

• Ecology
• Soil Science
• Microbial Ecology

Background:

• Wildfires in boreal forests disrupt nitrogen (N) cycling and slow vegetation recovery.
• Postfire phosphorus (P) enrichment is observed, but its impact on microbial N transformations is poorly understood in N-limited boreal systems.
• Soil N availability and loss are regulated by net nitrogen mineralization (Nmin) and nitrification.

Purpose of the Study:

• To investigate the effects of postfire N-P interactions on soil N transformations in boreal forests.
• To understand how microbial responses to P enrichment influence N availability and loss after wildfires.
• To assess the risk of N loss in boreal forest soils compared to other climatic zones.

Main Methods:

• Regional-scale soil sampling across 17 boreal forests in the Greater Khingan Mountains.
• Laboratory P-addition incubation experiments.
• Continental-scale meta-analysis of postfire N loss.

Main Results:

• Postfire soils exhibited accelerated Nmin and nitrification, increasing N loss risk, especially with low plant N demand during early recovery.
• Postfire N/P imbalance from P enrichment inhibited Nmin but not nitrification, acting as a N retention strategy.
• Enhanced microbial N-use efficiency and N immobilization were key mechanisms behind N retention.

Conclusions:

• Postfire N-P interactions are crucial for mitigating N limitation and maintaining nutrient balance in boreal forests.
• Boreal forest soils face a higher risk of N loss post-wildfire compared to other regions.
• Microbial responses to P enrichment play a vital role in regulating soil N dynamics after disturbances.