Nitrogen Deposition Significantly Altered the Climatic Sensitivity of Vegetation Phenology

Nitrogen deposition substantially alters nutrient absorption by plant root systems, which has far-reaching consequences for leaf growth and development. However, its effects on plant phenology and climatic sensitivity remain unclear. This study investigated the effects of nitrogen deposition on vegetation phenology and its sensitivity to moisture and temperature from 1982 to 2022 by combining data from field experiments, remote-sensing observations, and land surface models. The results revealed that the start of the growing season (SOS) has become more sensitive to vapor pressure deficit (VPD), whereas its sensitivity to temperature and soil moisture (SM) has decreased in recent decades. Conversely, there was no notable trend in climatic sensitivity at the end of the growing season (EOS). The model results show that SOS's sensitivity to VPD (SVPD) and temperature (STem) increased with higher nitrogen deposition levels (SVPD, a = 1.07 d unit–1, P < 0.01; STem, a = 0.10 d unit–1, P < 0.01). The sensitivity of EOS to soil moisture (SSM) decreased significantly with increasing nitrogen deposition (a = –1.82 d unit–1, P < 0.05), whereas SVPD decreased (a = –0.38 d unit–1, P < 0.01). Attribution analysis indicated that nitrogen deposition was the primary driver of changes in the climatic sensitivity of SOS, whereas atmospheric CO2 predominantly influenced changes in the SSM of EOS. These results emphasize the critical role of nitrogen deposition in determining the climatic sensitivity of vegetation phenology and provide a novel perspective for understanding and predicting vegetation phenology dynamics under ongoing global change.