Phenology, timing of biological events, is critical for species persistence because it influences survival and reproduction. The timing of flowering and seed production, two important aspects of plant phenology, strongly determine reproductive success. Although it is clear that climate change is leading to earlier phenological events in response to warmer temperatures, the effects of precipitation on phenology are far less understood. Seasonal precipitation patterns, particularly in moisture-limited environments such as temperate grasslands, can also determine phenological outcomes. Therefore, we examined how flowering and fruiting responded to experimental precipitation manipulations in a mixed-grass prairie. We used a randomized block split-plot design with seven precipitation treatments (precipitation reduction [-20 %, -40 %, -60 %, -80%, and -100%], precipitation addition [+50%], and control [0%, no change in precipitation]) across twenty-one 2 x 2 m plots (n=3). Rain-out shelters were established in Spring 2016. Starting in Spring 2019, we monitored the phenology and abundance of flowers and fruits of 11 common occurring species twice per week. We asked: (1) Does altered precipitation influence reproductive phenology (timing and abundance) of temperate grassland plant species? (2) How does precipitation interact with plant species identity to influence reproductive phenology of a mixed-grass prairie ecosystem?
Results/Conclusions
We found that the precipitation gradient altered both the abundance of flowers and fruits, with marginal effects influencing the timing of such events. Flowers (F= 4.48, P=0.03) and fruits (F= 5.63, P=0.01) were more abundant in -20% precipitation plots but less abundant in -80% precipitation plots, compared to the control. Further, precipitation affected the initiation and duration of fruiting across species. For instance, fruiting day delayed 17±2 days in -100% precipitation plots and 39±2 days in +50% precipitation plots, compared to the control (F=10.11, P=0.01). Precipitation reduction treatments made fruiting duration longer, 10 to 14 days compared to the control (F=23.95, P=0.00). The effect of precipitation depended on species for phenological and abundance responses, except for the date of first flowering. Most species delayed flowering and fruit maturation in dry treatments, especially the common graminoids. By showing the impacts of a drought gradient on fruit timing and abundance of both flowers and fruits, our findings suggest that future decreases in precipitation, as predicted under climate change, will likely reduce fruit production and potentially hinder species persistence over the long-term. Further, our study highlights that is crucial to consider precipitation effects on plant phenology in the context of climate change.