title: Interactive effects of water, light and heat stress on photosynthesis in Fremont cottonwood.
abstract: Fremont cottonwood seedlings are vulnerable to water stress from rapid water-table decline during river recession in spring. Water stress is usually cited as the reason for reduced establishment, but interactions of water stress with microclimate extremes are more likely the causes of mortality. We assessed photosynthetic responses of Fremont cottonwood seedlings to water, light and heat stresses, which commonly co-occur in habitats where seedlings establish. Under moderate temperature and light conditions, water stress did not affect photosynthetic function. However, stomatal closure during water stress predisposed Fremont cottonwood leaves to light and heat stress, resulting in greatly reduced photosynthesis beginning at 31 °C versus at 41 °C for well-watered plants. Ontogenetic shifts in leaf orientation from horizontal to vertical, which occur as seedlings mature, reduce heat and light stress, especially during water stress. When compared with naturally occurring microclimate extremes, seedling stress responses suggest that reduced assimilation and photoprotection are common for Fremont cottonwood seedlings on exposed point bars where they establish. These reductions in photosynthesis likely have negative impacts on growth and may predispose young (<90-day-old) seedlings to early mortality during rapid water-table declines. Interactions with heat and light stress are more important in these effects than water stress alone.
authors: Department of Land, Air and Water Resources, University of California, Davis, Davis, CA 95616-8627, USA.
authors: Emily S
authors: ES
authors: Tozzi
authors: Hsien Ming
authors: HM
authors: Easlon
authors: James H
authors: JH
authors: Richards
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D002734:Chlorophyll / Q000378:metabolism; D003681:Dehydration; D005453:Fluorescence; D006358:Hot Temperature; D008027:Light; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D032107:Populus / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D012621:Seasons; D036226:Seedlings / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide
keywords: Populus fremontii; chlorophyll fluorescence; leaf orientation; microclimate; photoprotection; photorespiration