Elevational differences in the net primary productivity response to climate constraints in a dryland mountain ecosystem of northwestern China

Dryland mountain ecosystems regulate global terrestrial carbon cycling and show high sensitivity to climate variability. The Qilian Mountains (QLMs) typify dryland mountain ranges in northern temperate belts and offer fundamental ecosystem services including forage production and water conservation. However, dominant controls on the interannual trend and variability of net primary productivity (NPP) in this region are unknown. Thus, we examined magnitude and direction of the NPP trend and quantified NPP sensitivity to temperature and precipitation under different biomes and altitudes using ground and remote sensing data. Our results showed that 12% of the QLMs had a reversed NPP trend from increasing to decreasing from 2000 to 2016, particularly in the western and southern parts, where NPP reductions were related to precipitation deficits. About 34% of the QLMs showed accelerated or persistent increasing NPP trends, mainly from the mid-altitude between 3,100 and 4,300 m. The growth rate of NPP was higher in deserts and grasslands than in forests and increased in deserts but decreased in forests and grasslands with increasing elevation. Precipitation showed a stronger effect on the interannual variability in NPP than temperature did. The temperature sensitivity of NPP was similar along elevation gradients in forest steppes but decreased with increasing elevation in alpine deserts. The precipitation sensitivity of NPP reached highest in shrubby meadows when compared with coniferous forests and alpine deserts. This research provides new insights into climate controls of the NPP over the QLMs and to present drought as a growing threat to shrubby meadows and alpine deserts.