Pollen Supplementation Alters How Flowering Phenology Affects Reproduction in a Spring-Flowering Herb

Abstract

The timing of flowering and other components of phenology such as duration and synchrony can affect reproductive success and recruitment by influencing the environment a plant will experience throughout its flowering period. Pollination is a common explanation for why flowering phenology may affect reproduction, but it is not well understood how variation in pollination might interact with the abiotic environment to affect plant reproduction. Here we monitored a population of spring ephemerals, Claytonia virginica, for one flowering season and examined the effects of flowering phenology and the environment on plant reproduction in two treatments: plants supplemented with additional outcross pollen and unmanipulated control plants. Different aspects of reproduction were measured at both the population and within-plant levels: number of seeds produced by individual plants (seed production), per-fruit seed viability (the proportion of viable seeds out of the total number of seeds per fruit), percent germination, and number of days to germination. Soil surface temperature, light, and moisture data were also collected. The flowering phenology and environmental predictors most important for each measurement of reproduction differed between control and pollen-supplemented plants. For example, in both pollen treatment groups, more days in flower was consistently a positive predictor of seed production, but the environmental factors affecting seed production varied, with increasing pollinator visitation mostly affecting seed production in the nonsupplemented group and soil moisture positively affecting it in supplemented plants. Phenological and environmental predictors also differed for proportion of viable seeds and timing of germination. Our germination results support the hypothesis that the mechanisms that control early flowering time in the maternal plant may affect the timing of other life history events such as seed germination. Additionally, we show some evidence that changes in the maternal abiotic environment, particularly temperature, may alter progeny phenotype. No clear seasonal resource trade-offs were evident, as has been shown in other studies of spring ephemerals. Our results show that the abiotic environment interacts with the pollination environment to affect plant reproduction, with different environmental factors predicting reproduction in control versus pollen-supplemented plants.