Trajectories of plant nitrogen availability globally during 1984-2022 uncovered by satellite-derived nitrogen stable isotope ratio

Abstract

Abstract Nitrogen (N) availability regulates the productivity of terrestrial plants and the ecological services they provide. There is evidence for both increasing and decreasing plant N availability in different biomes, but the data are fragmentary. How plant N availability responds to climate change, N deposition and increasing atmospheric CO2 concentration remains a major uncertainty in the projection of the terrestrial carbon sink. The foliar N stable isotope ratio (δ15N) is an indicator of plant N availability but its usefulness to infer long-term global patterns has been limited by data scarcity. Combining ground-based δ15N and Landsat spectra, we derived annual global maps of Landsat-based foliar δ15N as estimates of plant N availability during 1984-2022. We found significant decreases in plant N availability for 44% and increases in 16% of vegetated Earth’s surface with large spatial heterogeneity. Plant N availability declined in woody-dominated ecosystems but increased in herbaceous-dominated ones. These δ15N trends were consistently and negatively correlated with the trends of Normalised-Difference-Vegetation-Index as they varied across ecosystems, suggesting increasing plant cover could have led to decreasing plant N availability. Our results indicate possible future reductions in plant N availability in many terrestrial ecosystems and provide a useful way to monitor those changes globally.