LATE PLANTING SHORTENS THE FLOWERING PERIOD AND REDUCES FECUNDITY IN LASTHENIA CALIFORNICA

Abstract

Modifications in the timing of life-history events can alter the biotic and abiotic environments experienced during an organism's lifetime. In plants, germination timing plays a critical role in relation to seasonal environmental conditions, pollinator availability, competitive dynamics, etc. Individuals can compensate for a change in timing of germination by modifying their growth and flowering time. However, biotic and abiotic factors may affect these compensatory responses. In this study we assess how biotic and abiotic differences due to planting date influence the timing of flowering, survival, and reproduction. To do this we manipulated germination timing of the annual California Goldfields (Lasthenia californica DC. ex Lindl., Asteraceae) in a serpentine grassland in northern California, by seeding three times during the growing season (November, January, and March). Neighbor removal plots were compared with control plots to examine influences of close neighbors and seasonal priority effects (due to early individuals pre-empting resources) on flowering time and duration, growth, and reproductive success (survival to reproduction and inflorescence production). Both planting date and neighbor removal treatments significantly impacted flowering time and duration, growth, and reproduction in this species. Later planting dates did delay flowering time, but this delay was minimal as flowering time was constrained within set biotic and abiotic boundaries. In addition, we find that a mixture of planting times and levels of neighbor removal can extend the duration of flowering on the landscape. Inflorescence production and survival declined with later planting dates, but neighbor removal counteracted this decline. We find that L. californica exhibits graded growth allocation, as well as plasticity in flowering time in response to planting date. This study has implications for the timing of restoration projects, as planting time influences both the timing of flowering as well as the overall reproductive success of planted individuals. Our results suggest that practitioners should aim to plant earlier in the season, but that neighbor removal may counteract some of the costs of late planting.