Wang, XY; Wu, CY; Zhang, XY; Li, ZL; Liu, ZJ; Gonsamo, A; Ge, QS (2020). Satellite-observed decrease in the sensitivity of spring phenology to climate change under high nitrogen deposition. ENVIRONMENTAL RESEARCH LETTERS, 15(9), 94055.

Spring phenology is a sensitive indicator of climate change and has substantial impacts on the carbon cycle. The global N cycle has been greatly disturbed by anthropogenic activities resulting in altered atmospheric N deposition worldwide. Research has been focused on the changes in the spring phenology and its covariations with climatic factors. However, the influences of N deposition on spring phenology have not been well documented to date. Herein, we investigated the effects of N deposition on the start of growing season (SOS) in continental United States (CONUS) during the years 1986-2015 using the normalized difference vegetation index (NDVI) datasets derived from both the third generation NDVI dataset and the Moderate Resolution Imaging Spectroradiometer (MODIS). We observed that N deposition could only explain approximately 5% of temporal variation in SOS in CONUS. However, the sensitivities of SOS in response to unit change in both temperature (S-T) and precipitation (S-P) showed clear decreasing spatial patterns with increasing N deposition. The S(T)generally decreased from -6 d/degrees C in low N deposition regions (<2 kg ha(-1)) to -4 d/degrees C in areas with N deposition >4 kg ha(-1). Furthermore, the positive S(P)also showed a continuously decreasing pattern with the increase in N deposition, but the negative S(P)was gradually weakened when N deposition was >1.0 kg ha(-1). The results have important implications as it reveals the role of N deposition on spring plant phenology, and strongly suggest the consideration of N deposition effects when analyzing or predicting spring phenology in response to future climate change.