Climate change has become a catastrophic event that has altered Earth's ecosystems. Global warming and increasing atmospheric greenhouse gases (GHGs), such as CO2 and methane, have caused a drier climate, thereby affecting the water availability and its impacts on carbon (C) and nitrogen (N) cycles within terrestrial ecosystems. Wildfires also play an important role in C and N cycling in terrestrial ecosystems. Extreme wildfires are known to increase both CO2 and N emissions into the atmosphere and can alter C and N cycling processes. The objectives of this study were to quantify the effects of climate change on long-term tree water-use efficiency, N availability and growth in boreal forest ecosystems of northern China, and to evaluate the signatures and intensities of wildfires and climate extremes (such as drought and flooding) by using 15N natural abundance in tree rings in the context of climate change. Tree rings were extracted from 4 Larix gmelinii sample trees and 4 Pinus sylvestris sample trees, located in a boreal plantation forest of Mohe City, Heilongjiang Province, China. [...]