Long‐term nitrogen loading alleviates phosphorus limitation in terrestrial ecosystems

Increased human‐derived nitrogen (N) deposition to terrestrial ecosystems has resulted in widespread phosphorus (P) limitation of net primary productivity. However, it remains unclear if and how N‐induced P limitation varies over time. Soil extracellular phosphatases catalyze the hydrolysis of P from soil organic matter, an important adaptive mechanism for ecosystems to cope with N‐induced P limitation. Here we show, using a meta‐analysis of 140 studies and 668 observations worldwide, that N stimulation of soil phosphatase activity diminishes over time. Whereas short‐term N loading (≤5 years) significantly increased soil phosphatase activity by 28%, long‐term N loading had no significant effect. Nitrogen loading did not affect soil available P and total P content in either short‐ or long‐term studies. Together, these results suggest that N‐induced P limitation in ecosystems is alleviated in the long‐term through the initial stimulation of soil phosphatase activity, thereby securing P supply to support plant growth. Our results suggest that increases in terrestrial carbon uptake due to ongoing anthropogenic N loading may be greater than previously thought. Current Earth System Models predict strong P limitation of plant productivity, based on the assumption that anthropogenic N enrichment shifts plant growth from N to P limitation. However, empirical evidence for P limitation following prolonged N additions is equivocal, and temporal variations in P limitation have not been systematically assessed. Using soil phosphatase activity as an indicator of P limitation, we show that N‐induced P limitation acclimates to long‐term N addition. This finding highlights the importance of plant and microbial adaptation strategies to control P availability. Absence of these strategies in models underestimates the potential of vegetation to slow climate change.