Meitern Annika, Õunapuu-Pikas Eele, Sellin Arne
Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia.
Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005 Tartu, Estonia.
J Plant Physiol. 2017 Jun;213:148-156. doi: 10.1016/j.jplph.2017.03.012. Epub 2017 Mar 22.
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 (σ), 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 (K), leaf blade (K) and petiole hydraulic conductances (K) showed clear daily dynamics. Air temperature (T) and photosynthetic photon flux density (PPFD), but also water vapour pressure deficit (VPD) and relative humidity (RH), had significant impacts on KK, K, [K] and σ. Osm varied only with light intensity, while K varied depending on atmospheric evaporative demand expressed as T, VPD or RH. Xylem sap pH depended inversely on soil water potential (Ψ) and during daylight also on VPD. Although soil water content was close to saturation during the study period, Ψ influenced also [K] and σ. 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.
