Low resistance but high resilience to drought of flushing Norway spruce seedlings

Abstract

Spring drought episodes are becoming more frequent and intensive in European temperate forests. To study tree resilience to spring drought, Norway spruce seedlings were exposed to three levels of drought stress (well-watered (W), moderately stressed (M), and severely stressed (S)) for 42 days and then fully irrigated for 14 days. Drought strongly reduced gas exchange parameters for both M and S seedlings. After 42 days, stomatal conductance was lower by 83% and 97% in M and S, respectively, than in W seedlings. Respiration prevailed over photosynthesis in S seedlings at the end of the drought period. Drought mostly reduced longitudinal growth, especially in shoots and needles. Xylem growth reduction was caused mainly by lower number of newly produced tracheids, not by changes in their size. Norway spruce seedlings showed good resilience to spring drought, as the observed physiological parameters started to recover after rewatering and seedlings started to sprout and form new tracheids. In M seedlings, all physiological traits recovered to the level of W seedlings during the 14-day irrigation period but the recovery took longer in S seedlings. Shoots and needles did not regrow in length but leaf mass per area increased during the recovery phase. To conclude, Norway spruce seedlings showed good resilience to spring single-drought-event, but time necessary to full recovery from stress could make seedlings more vulnerable to recurrent drought events.

Stem notching decreases stem hydraulic conductance but does not influence drought impacts and post‐drought recovery in Scots pine and Norway spruce

“…Therefore, based on the inability to reliably predict stomatal conductance from RWC or Ψ p levels, we conclude that g sw recovery in both pine and spruce is limited by certain non‐hydraulic factors (see Brodribb & Cochard, 2009). More rapid and complete restoration of leaf water status compared to gas exchange was also found in other studies on Pinaceae species (see, e.g., Hájíčková et al, 2021; Rehschuh et al, 2020). We propose that the analysis of the dependence of stomatal dynamics on not only Ψ leaf but also on other main parameters of leaf water status (Ψ p and RWC) is necessary to be performed to understand whether post‐drought g sw recovery is actually limited by the recovery of leaf hydraulic supply or by non‐hydraulic factors (Brodribb & Cochard, 2009).…”

Damage caused by an exceptionally warm and dry early summer on newly planted Norway spruce container seedlings in Nordic boreal forests

“…The reduced growth was partly caused by dry leader shoots, but it can also be caused by reduced photosynthesis (Helenius et al 2005b) and/or earlier growth cessation (Matisons et al 2021). Hájíčková et al (2021) studied the resistance of four-year-old Norway spruce seedlings to drought stress during flushing. They observed that the shoot growth reduced more under severe drought stress, whereas moderate stress affected root growth more.…”

Abscisic Acid and Cytokinins Are Not Involved in the Regulation of Stomatal Conductance of Scots Pine Saplings during Post-Drought Recovery

“…At the same time, recovery of stomatal conductance is often delayed compared to other physiological traits [ 2 ]. Delayed or incomplete recovery of gas exchange after water stress relief is often observed in various conifers [ 11 , 12 , 13 , 14 ]. High drought sensitivity of stomatal conductance and delayed and/or insufficient recovery of stomatal conductance together cause plants to experience a prolonged period of diminished gas exchange and assimilation, thus deteriorating plant carbon balance.…”