Climate change is expected to result in more extreme rainfall regimes that are characterized by intensified rainfall events and prolonged dry intervals. However, to date, the response of the dryland ecosystems to changes in the rainfall regime has remained unresolved. To better understand the effects of individual dry intervals and extreme rainfall regimes on the aboveground/belowground net primary productivity (ANPP/BNPP) and species diversity of semi-arid sandy grassland, this study aimed to assess the influence of the timing and frequency of prolonged dry intervals on the function of a degraded sandy grassland under a constant total growing-season rainfall. A field rainfall manipulation experiment was carried out in northeast China. The results showed that the 30 day dry interval caused a significant decrease in ANPP and plant cover, except for April. The 30 day dry interval substantially increased the allocation of total net primary productivity (NPP) to BNPP in July, while decreasing the species richness in May and June. The extreme rainfall regimes with lower frequency and longer dry intervals significantly decreased the ANPP, BNPP, plant cover, species richness and species diversity index, while increasing the allocation of the NPP to BNPP and plant density. The mean duration of the dry interval exhibited significant negative correlations with the ANPP, plant cover, species richness, and Simpson index. Variability in dry interval’s mean length also had a negative correlation with ANPP, plant cover, and species richness. Our results suggest that annuals in the semiarid sandy land were highly responsive to changes in rainfall regime. Even if rainfall amount remained constant, increases in duration of the dry intervals and the frequency of extreme intervals were more likely to reduce net primary productivity and species diversity in semiarid sandy annual grasslands, and even contribute to desertification. The findings also provide new evidence for the vital roles of dry interval frequency, duration, and timing, as determinants of semiarid ecosystem function and structure.
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