The variability in sensitivity of vegetation greenness to climate change across Eurasia

Climate change is one of dominators driving the greening of vegetation worldwide, which is expected to enhance land carbon sink and mitigate global warming. The sensitivity of vegetation greenness to climate change is fluctuant and regulated by other environmental factors. However, the drivers and mechanisms behind remain unclear so far. Here, we hired long-term satellite-based vegetation index (NDVI), climatic variables, nitrogen deposition, and atmospheric CO2 records to investigate variations of greenness climatic sensitivity and its drivers across Eurasia. To obtain the timeseries of temperature (γNDVITEM) and precipitation sensitivity (γNDVIPRE), we applied multi-regression models and regressed temperature and precipitation on NDVI in each 9-year moving windows. The results showed that the area of vegetation greenness limited by low temperatures substantially shrunk, while the area of vegetation greenness limited by precipitation deficit increased during 1982–2015. Specifically, significantly decreasing γNDVITEM and γNDVIPRE accounted for 29.8% and 20.1%, respectively, while remarkably increasing γNDVITEM and γNDVIPRE accounted for about 18.2% and 24.5%, respectively, of the vegetated lands across Eurasia. Declining γNDVITEM was widely observed in most biomes, including tropical and subtropical moist broadleaf forests, temperate broadleaf and mixed forests, temperate coniferous forests, croplands, and deserts and xeric shrublands. Substantially increasing γNDVIPRE was merely found in montane grasslands and shrublands, and tropical and subtropical dry broadleaf forests, while decreasing γNDVIPRE and nonlinear regimes was widely proved in other biome types. Spatially, rather than elevated CO2 and nitrogen deposition, climate factors (temperature, precipitation, and radiation) jointly dominated γNDVITEM and γNDVIPRE variations across nearly 45% and 48% of Eurasia respectively. Our results uncovered the apparent pattern of greenness climate sensitivity changes across Eurasia and highlighted the necessity to unfold the underlying mechanisms based on plant physiology and traits.