Global change progressively increases foliar nitrogen–phosphorus ratios in China's subtropical forests

Foliar nitrogen (N) to phosphorus (P) ratios (N/P) indicate N versus P
limitation in terrestrial ecosystems. Quantifying the long-term dynamics
of foliar N/P and their potential drivers is crucial for predicting
nutrient status in forest ecosystems under global change. Using 1811
herbarium specimens collected during 1920-2010 in subtropical forests of
China, we detected significant increases in foliar N/P (21.2%) and
decreases in foliar P concentrations (23.1%). Foliar N/P increased more in
evergreen species (22.9%) than in deciduous species (16.9%). Changes in
atmospheric CO2 concentrations (Pco2), N deposition and mean annual
temperature (MAT) dominantly contributed to the increased foliar N/P of
evergreen species, while Pco2, MAT, and vapor pressure deficit, to that of
deciduous species. Under future Shared Socioeconomic Pathway scenarios,
increasing MAT would continuously increase foliar N/P by more than
6.5-26.0%. The results suggest that global change progressively and
non-uniformly aggravates the N-P imbalance of plant species in subtropical
forests.