Temporal emergence patterns of seedlings from playa wetlands

Abstract

Playas undergo dynamic environmental changes throughout the growing season, resulting in the need for a persistent seed bank for plants to respond to these changes. Therefore, we investigated seasonal germination patterns of species found in seed banks of playa wetlands. We used the seedling-emergence technique to determine recruitment patterns from seed banks of eight playas. In the greenhouse, seed-bank samples were subjected to two treatments, drawdown or flooded, over a 210-day duration divided into seven 30-day time periods. In both treatments, seedling emergence differed among time periods and species but was similar among playas. Approximately 52% of drawdown seedlings and 44% of seedlings occuring in the flooded treatment germinated in the first 30 days. Plants occuring in playa seed banks had variable germination strategies. Three patterns for common (>5% occurrence) species were identified in the drawdown treatment: (1) early germinators (those species that germinated rapidly after exposure to treatments with low germination during the remainder of time periods), (2) late germinators (those that germinate after specific environmental conditions have existed for some time), and (3) continous germinators (those with even germination rates throughout submersion). Two patterns were found for common species in the flooded treatment: (1) early germinators and (2) continuous germinators. Germination throughout the period of suitable environmental conditions was the dominant strategy for persistence in the unpredictable playa environment. With only a few exceptions, species persisting in seed banks of playas do not show germination for all available seeds upon creation of suitable environmental conditions but rather use viable dormant seeds as a hedge against the unpredictable environment.