Sprouts of shoot-clipped oak (Quercus alba and Q. robur) germinants show morphological and photosynthetic acclimation to contrasting light environments

Abstract

Sprouting by woody plants can increase species resilience to disturbance and foster regeneration during periods with little recruitment from seed. Though sprouting often plays a critical role in oak forest regeneration, there is little information available on sprouting capacity and sprout physiology at the seedling stage, particularly for new germinants. This study compared sprouting capacity and sprout photosynthesis of shoot-clipped germinants of two temperate oaks established in contrasting light environments. We studied the North American Quercus alba and the European Q. robur, both are in the section Quercus and appear to share similar biological and ecological requirements. Sprouting capacity for both species was enhanced under high light availability (29% more sprouts per plant), a response not previously noted for oak germinants. Seedling sprouts acclimated to high light with a 34% decrease in leaf area ratio, a 56% increase in leaf mass per area, and a 49% increase in the light-saturated maximum photosynthetic rate. Though both species appeared similarly adapted to shoot loss, a greater sprouting capacity (29% more sprouts per plant) and plant-level net photosynthesis (73% higher) was observed for Q. robur, regardless of light environment. As naturally regenerated oak seedlings in forest understories often experience disturbance or stress resulting in shoot loss or die-back, our results highlight the importance of the light environment during early plant development. Our comparison of temperate oaks from different continents should facilitate exchange of successful stand regeneration practices within the range of temperate oak forests.

Increasing temperature and vapour pressure deficit lead to hydraulic damages in the absence of soil drought

“…The light roofs of the climate chambers were adjusted in height so that light intensity at canopy height was in all chambers ~390 µmol m −2 s −1 . At this light intensity, all three species are at, or approach their light saturation point (Čater & Kobler, 2017 ; Pena‐Rojas et al, 2004 ; Petersson et al, 2020 ; Staudt et al, 2003 ). All plants were regularly (i.e., every 2–3 days) watered by hand to ensure complete soil hydration, and soil volumetric water content (VWC) was manually measured bi‐weekly to ensure no soil drought occurred (Supporting Information: Figure S2 ).…”

Influence of canopy openness, ungulate exclosure, and low‐intensity fire for improved oak regeneration in temperate Europe

“…trees following fire in central Europe was notably high and almost unaffected by fire intensity. A recent greenhouse experiment revealed that seedlings of Q. robur responded similarly to the fire adapted North American white oak (Q. alba L.) when they experienced shoot destruction typically sustained during fire (Petersson, Löf, Jensen, Chastain, & Gardiner, 2019).…”

“…trees following fire in central Europe was notably high and almost unaffected by fire intensity. A recent greenhouse experiment revealed that seedlings of Q. robur responded similarly to the fire adapted North American white oak ( Q. alba L.) when they experienced shoot destruction typically sustained during fire (Petersson, Löf, Jensen, Chastain, & Gardiner, ). Together, these findings suggest that European temperate oak species ( Q. robur and Q. petraea) may respond to fire in a similar fashion as their North American congeners.…”