Contrasting responses of fruiting phenology and folia phenology to water additiontreatments in the Desert Shrub Nitraria tangutorum

Abstract: Climate models often predict that more extreme precipitation events will occur in arid and semiarid regions, where plant phenology is particularly sensitive to precipitation changes. To understand how increases in precipitation affect plant phenology, this study conducted a manipulative field experiment in a desert ecosystem of northwest China. In this study, a long-term in situ water addition experiment was conducted in a temperate desert in northwestern China. The following five treatments were used: natural rain plus an additional 0, 25, 50, 75, and 100% of the local mean annual precipitation. A series of phenological events, including leaf unfolding, fruit setting (onset, summit and end), fruit ripening (onset, summit and end) and leaf coloration of the locally dominant shrub Nitraria tangutorum were observed from 2012 to 2018. The results showed that on average, over the seven-year-study and in all treatments water addition treatments advanced the leaf unfolding date by 1.29–3.00 days, but delayed the leaf coloration date by 1.18–11.82 days. Therefore, the length of the growing season was prolonged by 2.11–13.68 days. However, water addition treatments had no significant effects on all six fruiting events in almost all years, and the occurrence time of almost all fruiting events remained relatively stable compared with leaf phenology. The inter-annual variations of fruiting events were driven by the preceding flowering events rather than temperature or precipitation.