Precipitation and environmental constraints on three aspects of flowering in three dominant tallgrass species

1. Flower production can comprise up to 70% of above-ground primary production in grasslands. Yet we know relatively little about how the environment and timing of rainfall determine flower productivity. Evidence suggests that deficits or additions of rainfall during phenlologically relevant periods (i.e. growth, storage, initiation of flowering and reproduction) can determine flower production in grasslands. 2. We used long-term data from the Konza Prairie LTER to test how fire, soil topography and precipitation amounts during four phenologically relevant periods of the growing season constrain three aspects of flowering in three dominant C4 grass species. Specifically, we examined the probability of flowering, flowering stalk density and individual flowering stalk biomass for Andropogon gerardii, Schizachyrium scoparium and Sorghastrum nutans. 3. We found that each of the three species responded to the amount of precipitation during phenologically relevant periods in unique ways. All aspects of A. gerardii flowering were sensitive to precipitation during the flowering stalk elongation period (20 June-3 August). The probability of S. nutans flowering was partly determined by precipitation during the rapid growth phase (21 April-4 June), whereas flowering stalk density of this species depended on rainfall during flowering stalk elongation (20 June-3 August). In contrast, all aspects of flowering of S.scoparium were relatively independent of rainfall during any period. 4. Our results demonstrate that three functionally similar, co-dominant C4 grass species respond differently to phenologically relevant precipitation periods. As a result, drought during any phenological window during the growing season can adversely impact biomass and flowering production of grasslands via species-specific reductions in flowering stalk density and biomass.