title: Circadian patterns of xylem sap properties and their covariation with plant hydraulic traits in hybrid aspen.
abstract: Physiological processes taking place in plants are subject to diverse circadian patterns but some of them are poorly documented in natural conditions. The daily dynamics of physico-chemical properties of xylem sap and their covariation with tree hydraulic traits were investigated in hybrid aspen (Populus tremula L.×P. tremuloides Michx) in field conditions in order to clarify which environmental drivers govern the daily variation in these parameters. K+concentration ([K+]), electrical conductivity (σsap), osmolality (Osm) and pH of the xylem sap, as well as branch hydraulic traits, were measured in the field over 24-h cycles. All studied xylem sap properties and hydraulic characteristics including whole-branch (Kwb), leaf blade (Klb) and petiole hydraulic conductances (KP) showed clear daily dynamics. Air temperature (TA) and photosynthetic photon flux density (PPFD), but also water vapour pressure deficit (VPD) and relative humidity (RH), had significant impacts on KwbKlb, KP, [K+] and σsap. Osm varied only with light intensity, while KBvaried depending on atmospheric evaporative demand expressed as TA, VPD or RH. Xylem sap pH depended inversely on soil water potential (ΨS) and during daylight also on VPD. Although soil water content was close to saturation during the study period, ΨSinfluenced also [K+] and σsap. The present study presents evidence of coupling between circadian patterns of xylem sap properties and plant hydraulic conductance providing adequate water supply to foliage under environmental conditions characterised by diurnal variation.
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia. Electronic address: annika.meitern@ut.ee.
authors.forename: Annika
authors.initials: A
authors.lastname: Meitern
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia.
authors.forename: Eele
authors.initials: E
authors.lastname: Õunapuu-Pikas
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia.
authors.forename: Arne
authors.initials: A
authors.lastname: Sellin
mesh_terms: D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D018526:Plant Transpiration / Q000235:genetics / Q000502:physiology*; D032107:Populus / Q000378:metabolism* / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D052584:Xylem / Q000378:metabolism / Q000502:physiology*
chemical_list: D011188:Potassium
keywords: Atmospheric evaporative demand; Circadian patterns; Hydraulic conductance; Osmolality; Potassium ions; pH