Stem cycle analyses help decipher the nonlinear response of trees to concurrent warming and drought
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RESEARCH PAPER
Stem cycle analyses help decipher the nonlinear response of trees to concurrent warming and drought Lorena Balducci 1
&
Annie Deslauriers 1 & Sergio Rossi 1 & Alessio Giovannelli 2
Received: 5 April 2019 / Accepted: 25 July 2019 # INRA and Springer-Verlag France SAS, part of Springer Nature 2019
Abstract & Key message High-resolution analysis of stem radius variation can quantify the impact of warming and drought on stem water balance and stem growth in black spruce [Picea mariana (Mill.) B.S.P.)]. Drought affected plant water status and stem growth. However, warming affects the components of the circadian stem cycle differently if the impacts occur in the daytime or nighttime. The interactive effect of abiotic stresses had less impact on the circadian stem cycle than when the stresses occurred independently. & Context Warming and recent droughts in boreal regions reflect the multiple dimensions of climate change. How these climaterelated stresses will affect the stem growth of trees remains to be described. Plant water relations can detect the dynamics of stem depletion and replenishment under conditions of climate-forced stress. & Aims This study aimed to verify the impacts of a combination of asynchronous warming (nighttime versus daytime warming) and drought on stem water balance and stem growth in black spruce [Picea mariana (Mill.) B.S.P.)]. & Methods We investigated the water status and variations in stem radius of black spruce saplings growing in a controlled environment from May through August. We grew four-year-old saplings in warmer conditions either during the day (DW) or night (NW) at temperatures ca. 6 °C warmer than the ambient air temperature (CT). We then simulated a one-month drought in June. Automatic point dendrometers provided a high-resolution analysis of variations in stem radius, and we also monitored leaf water potentials and volumetric soil water content during the entire experimental period. & Results We detected significant reductions in stem radius variation under water deficit conditions. In the daytime warming scenario, we observed a significant increase in the duration of contraction and a decrease in expansion of the stems. The amplitude of this contraction and expansion was reduced under the nighttime warming conditions. The main effect of warming was to enhance drought stress by accelerating soil water depletion. Changes in predawn water potential drove the duration of stem circadian cycles under conditions of daytime warming, whereas irreversible growth dynamics drove these cycles under nighttime warming conditions due to the midday water potential. The interaction of night/daytime asynchronous warming and drought reduced the amplitude rather than the duration of stem contraction and expansion. Handling Editor: Erwin Dreyer Contribution of the co-authors A.D., A.G., and S.R. planned the research. L.B. performed measurements and analyzed the data with advices from A.G., S.R, and A.D. L.B wrote the manuscript with the contribution of all authors. This article is
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