title: Climatic variation and seed persistence: freeze-thaw cycles lower survival via the joint action of abiotic stress and fungal pathogens.
abstract: Global climate change is altering thermal cycles in soils during late winter, a transition that may directly threaten seed survival via abiotic stress, facilitate infection by soil-borne pathogens, or both. Using field-collected soil and seeds of the perennial bunchgrass Elymus canadensis, we tested the hypothesis that soil freeze-thaw events limit survival within the soil through direct effects on seed persistence and amplification of soil pathogen attack using a factorial experiment that manipulated freeze-thaw cycles (constant freeze vs. freeze-thaw) and fungicide addition. Freeze-thaw treatment resulted in lower seedling emergence and delayed emergence time relative to constant-freeze controls. Fungicide-treated soils had greater emergence relative to untreated soils; the lowest seedling emergence was observed in no-fungicide, freeze-thaw-treated soils (<1 %). The strong effects of thermal variability and fungi on seeds were mitigated through interactions at the seed-soil interface, as subsequent experiments showed that fungicide and freeze-thaw treatments alone do not influence dormancy. Our work demonstrates that changes in freeze-thaw events directly limit seedling emergence, delay seedling phenology, and provide opportunities for fungal pathogens to limit seed persistence. As recruitment from seeds is a key determinant of plant population dynamics, these results suggest that climatic variation may generate unique consequences for populations under changing climate regimes.
authors.affiliation: Department of Zoology, University of Wisconsin, Madison, WI, 53706, USA. bconnolly2@wisc.edu.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Connolly
authors.affiliation: Department of Zoology, University of Wisconsin, Madison, WI, 53706, USA.
authors.forename: John L
authors.initials: JL
authors.lastname: Orrock
mesh_terms: D002980:Climate; D057231:Climate Change; D005615:Freezing; D005658:Fungi / Q000502:physiology*; D006109:Poaceae / Q000254:growth & development* / Q000382:microbiology; D011157:Population Dynamics; D012621:Seasons; D036226:Seedlings / Q000254:growth & development / Q000382:microbiology; D012639:Seeds / Q000382:microbiology / Q000502:physiology*; D012988:Soil Microbiology
keywords: Climate change; Elymus canadensis; Emergence; Phenology; Soil pathogens