Shifts in plant phenology induced by environmental changes are small relative to annual phenological variation

Climate change and resource availability increasingly influence plant phenology. Previous research has shown that global warming and nitrogen (N) enrichment reduce the effectiveness of arbuscular mycorrhizal fungi (AMF). However, the mechanism by which global change drivers and AMF interactively affect plant phenology is still poorly understood. We examined the impact of warming, N addition and AMF reduction on plant phenology in an in-situ experiment for two grasses over 3 years. Year-to-year variations in the phenology of the two species were more apparent than those caused by the experimental treatments. For Puccinellia tenuiflora (P. tenuiflora), only 1 out of our 9 phenological measurements was significant: AMF reduction shortened the reproductive duration. For Leymus chinensis (L. chinensis), 5 out of the 9 phenological measurements were significant: warming advanced both flowering and fruiting times, N addition shortened the reproductive duration, and AMF reduction delayed both the flowering and fruiting times. Significant interactive effects of warming and N addition, warming and AMF reduction on the reproductive and fruiting time of L. chinensis were observed: warming plus N addition advanced fruiting times and shortened reproductive duration, and warming plus AMF reduction delayed fruiting time and shortened reproductive duration of L. chinensis. Furthermore, for both species, no interactive effect between the experimental treatments and annual climate variation was detected. These results indicate that the effects of warming, N addition and AMF reduction on plant phenology are largely independent and consistent over time. However, the annual variation in the phenology of both species is much larger than any experimental induced changes, suggesting no mismatch for species in terms of their phenology tracking annual climate fluctuations under future global change.