Effect of increased air temperature and vapour pressure deficit on water relations, gas exchange, and stem increment in saplings of Norway spruce ().
Gristin Rohula-Okunev, Priit Kupper, Arvo Tullus, Mai Kukum��gi, Marili Sell, Ivika Ostonen
Author Information
Gristin Rohula-Okunev: Institute of Ecology and Earth Sciences, University of Tartu, Tartu 50409, Estonia.
Priit Kupper: Institute of Ecology and Earth Sciences, University of Tartu, Tartu 50409, Estonia.
Arvo Tullus: Institute of Ecology and Earth Sciences, University of Tartu, Tartu 50409, Estonia.
Mai Kukum��gi: Institute of Ecology and Earth Sciences, University of Tartu, Tartu 50409, Estonia; and Institute of Forestry and Engineering, Estonian University of Life Sciences, F. R. Kreutzwaldi 1, Tartu 51006, Estonia.
Marili Sell: Institute of Ecology and Earth Sciences, University of Tartu, Tartu 50409, Estonia.
Ivika Ostonen: Institute of Ecology and Earth Sciences, University of Tartu, Tartu 50409, Estonia.
Whilst temperature (T ) increase on tree function has been well studied, the associated effect of vapour pressure deficit (VPD) is less clear. We investigated the impact of increasing T and VPD on canopy transpiration rate (E ), shoot gas exchange, and stem growth in Norway spruce (Picea abies ) saplings grown in organic and mineral soils in climate chambers with three treatment conditions for 12weeks: (1) 'ambient' (VPD���0.5kPa); (2) 'highT' treatment (+3��C relative to ambient; VPD���0.6kPa); and (3) 'highT/lowRH' treatment (+3��C and -7% RH relative to ambient; VPD���0.8kPa). The stem diameter increment, assimilation rate (A ), and E were highest, and the needle-to-fine root biomass ratio was smallest in 'highT/lowRH' treatment (P A of trees grown in organic soil was higher (P <0.05) in 'highT/lowRH' treatment compared to ambient conditions, but no significant difference was found in mineral soil. Our findings indicate that the effect of a 3-��C temperature increase on spruce was marginal under well-watered conditions, and moderate VPD increase instead improved the tree's functioning. Thus, aside from temperature, the impact of the RH as a primary driver of the VPD should be considered when predicting spruce response to global warming.
