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

Authors: Fay, Philip; FORBES, MEGAN - NATURAL RESOURCES RES INS

Submitted to: Acta Oecologica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2009
Publication Date: 7/6/2009
Citation: Fay, P.A., Forbes, M.J. 2009. Germination, survival, and growth of grass and forb seedlings: effects of soil moisture variability. Acta Oecologica. 35:679-684.

Interpretive Summary: The establishment, maintenance, and change through time in plant populations in the field depends in part on the successful germination of seeds and growth of seedlings. Seeds and seedlings are highly sensitive to variability in growth conditions, to which they are inevitably exposed. One of the primary sources of variability is from wetting and drying of soil in reponse to episodic precipitation events. Since periods of drying between such events may increase under future climatic regimes, responses in seeds and seedlings may play an increasingly important role in plant community change. The potential responses of seeds and seedlings to varying periods of soil drying were studied by growing seeds of eight widespread and abundant grass and forb species under watering regimes that caused varying degrees of soil drying. Seedling biomass production proved more tolerant of longer dry periods than seed germination, and the species formed several groups according to whether they were responsive to soil moisture drying in germination, biomass, or both. Different species will be favored under different soil moisture regimes, and seed germination and seedling growth may assume more importance in plant community dynamics in grasslands if precipitation patterns become more variable.

Technical Abstract: Seed germination and seedling growth, survivorship, and final biomass and their responses to varying numbers of days between watering were studied in two grass and six forb species native to the U.S. Central Plains grasslands. Our object was to assess the potential role of germination and seedling growth in plant community dynamics in grassland communities experiencing increased soil moisture variability as might occur with future increases in precipitation variability. Seeds were planted in prairie soil and watered to saturation at 1, 2, 4, or 7 day intervals (I). The I treatments caused significant differences in soil moisture variability, seed germination, and seedling growth and biomass. Seed germination peaked at I = 4 d while leaf growth in grasses and forbs, and final biomass in grasses peaked at I = 7 d, suggesting that growth and biomass in these life-form classes were favored at greater soil moisture variability than seed germination. Also, biomass responses to I were stronger than the germination responses, suggesting that soil moisture variability more strongly influences post germination growth. Grass and forb seedling survival from germination to harvest was unaffected by I. Individual species responses to I fell in three groups that fell across life-forms; those with strong responses to I for 1) seed germination and seedling survival, 2) biomass, or 3) both germination and biomass production. The responsiveness to I in these groups was greater than the responsiveness to I when the species were grouped by life-form, indicating that these species groups may be more useful 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.