title: Solar furnaces or swamp coolers: costs and benefits of water use by solar-tracking flowers of the alpine snow buttercup, Ranunculus adoneus.
abstract: Solar tracking or heliotropism simultaneously raises organ temperature and light interception. For leaves and flowers carbon gain is maximized at the expense of water loss. In this study I explore how costs and benefits associated with water use by solar-tracking flowers of the alpine snow buttercup, Ranunculus adoneus change with ambient temperature. First, I test whether heliotropism increases the water cost of reproduction in the snow buttercup under extant alpine conditions. I then explore whether water use for evaporative cooling in solar-tracking flowers reduces the risk of over-heating as temperatures increase. Solar tracking, by elevating floral temperature and irradiance causes a 29% increase in water uptake by flowers. Gas exchange measurements suggest that the extra water taken up by solar-tracking flowers is released through transpiration. Transpirational cooling in turn allows solar-tracking flowers to gain advantages of enhanced light interception and warmth while reducing the risk of over-heating. Transpiration reduces excess temperature in solar-tracking flowers, but at a water cost. Results show that even in cool alpine habitats, flower heliotropism has water costs to balance its reproductive advantages. Plants with solar-tracking flowers may tolerate hotter conditions if soil moisture is plentiful, but not under drought.
authors.affiliation: Division of Biological Sciences, University of Missouri, Columbia, MO 65211-7400, USA. galenc@missouri.edu
authors.forename: Candace
authors.initials: C
authors.lastname: Galen
mesh_terms: D025461:Feedback, Physiological; D035264:Flowers / Q000502:physiology*; D018524:Phototropism / Q000502:physiology*; D018526:Plant Transpiration / Q000502:physiology*; D031947:Ranunculus / Q000502:physiology*; D013696:Temperature; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water