Responses of plant reproductive phenology and productivity to drought timing depend on root depth and flowering time

Abstract The water demands of plant vary across seasons. However, how the seasonal drought affect plant reproductive phenology, and whether the phenological shifts mediate their aboveground biomass remains poorly understood. Methods: We examined the effects of decreased precipitation during early (April-June), late (July-September), and entire (April-September) growing season on the phenology and productivity of two functional groups with differential root depth (shallow vs. deep) and flowering time (early, mid, and late) in a temperate steppe in Northern China. Decreased precipitation during the early growing season prolonged reproductive duration of shallow-rooted, late-flowering group and reduced its productivity. Decreased precipitation during the late growing season advanced the first flowering time and fruiting time of the mid-flowering group, but increased the productivity of early-flowering group and reduced the productivity mid- and late-flowering group. Decreased precipitation in the entire growing season advanced the first flowering time for the shallow-rooted, early-flowering groups and first fruiting time for the shallow-rooted, mid-flowering groups, but only the productivity of shallow-rooted, mid-flowering group was decreased. In contrast, except for decreased precipitation during the entire growing season advanced the reproductive duration of the deep-rooted functional group, other treatments of drought timing had no effects on either the phenology or productivity of deep-rooted group. Our study suggests that reproductive phenology and productivity of shallow-rooted, mid-flowering group are more sensitive to decreased precipitation in the late growing season, and highlight that the responses of plant phenology and productivity to precipitation changes largely depend on their root depth and flowering time.