Germination,survival, and growth of grass and forb seedlings: Effects of soil moisture variability

Seed germination and seedling growth, survivorship, and final biomass and their responses to watering interval were studied in two grass and six forb species to assess germination and seedling growth responses to increased soil moisture variability as might occur with future increases in precipitation variability. Seeds were planted in prairie soil and watered at 1, 2, 4, or 7 d intervals (I). Seed germination peaked at I = 4 d whereas leaf growth in grasses and forbs, and final biomass in grasses peaked at I = 7 d, suggesting that growth and biomass were favored at greater soil moisture variability than seed germination. Biomass responses to I were stronger than the germination responses, suggesting that soil moisture variability more strongly influenced post germination growth. Individual species responses to I fell into three groups; those with responses to I for: (1) seed germination and seedling survival, (2) biomass, or (3) both germination and biomass production. These species groups may be more useful than life form (i.e., grass/forb) for understanding seed germination and seedling dynamics in grasslands during periods of soil moisture variability. Seed germination and early growth may assume more importance in grassland plant community dynamics under more variable precipitation patterns.