Anatomical acclimation of mature leaves to increased irradiance in sycamore maple (Acer pseudoplatanus L.)

Abstract

Trees regenerating in the understory respond to increased availability of light caused by gap formation by undergoing a range of morphological and physiological adjustments. These adjustments include the production of thick, sun-type leaves containing thicker mesophyll and longer palisade cells than in shade-type leaves. We asked whether in the shade-regenerating tree Acer pseudoplatanus, the increase in leaf thickness and expansion of leaf tissues are possible also in leaves that are already fully formed, a response reported so far only for a handful of species. We acclimated potted seedlings to eight levels (from 1 to 100%) of solar irradiance and, in late summer, transferred a subset of them to full sunlight. Within 30 days, the pre-shaded leaves increased leaf mass per area and became thicker mostly due to the elongation of palisade cells, except for the most shaded individuals which suffered irreversible photo-oxidative damage. This anatomical acclimation was accompanied by a transient decline in photosynthetic efficiency of PSII (Fv/FM), the magnitude of which was related to the degree of pre-shading. The Fv/FM recovered substantially within the re-acclimation period. However, leaves of transferred plants were shed earlier in the fall, indicating that the acclimation was not fully effective. These results show that A. pseudoplatanus is one of the few known species in which mature leaves may re-acclimate anatomically to increased irradiance. This may be an important mechanism enhancing utilization of gaps created during the growing season.

Partial root‐zone drying irrigation improves intrinsic water‐use efficiency and maintains high photosynthesis by uncoupling stomatal and mesophyll conductance in cotton leaves

“…Previous studies have confirmed anatomical adjustments in mature leaves of several species as an acclimation response to changes in environmental conditions (Albaladejo et al, 2017; Li et al, 2022; Wyka et al, 2008, 2022; Zhang et al, 2017). Accordingly, modifications in some morphoanatomical traits, including LMA, LD, T leaf , upper epidermis thickness, sponge tissue thickness, leaf vein diameter and chloroplast ultrastructure in mature leaves have been observed under conditions of drought stress (Cao et al, 2015; Li et al, 2022; Meng et al, 2014; Nadal et al, 2020).…”

“…The enhancement of g m under PRD conditions was mainly driven by changes in S c /S, S c /S m , ΔL cyt,1 and ΔD chl Previous studies have confirmed anatomical adjustments in mature leaves of several species as an acclimation response to changes in environmental conditions (Albaladejo et al, 2017;Li et al, 2022;Wyka et al, 2008Wyka et al, , 2022Zhang et al, 2017). Accordingly, modifications in some morphoanatomical traits, including LMA, LD, T leaf , upper epidermis thickness, sponge tissue thickness, leaf vein diameter and chloroplast ultrastructure in mature leaves have been observed under conditions of drought stress (Cao et al, 2015;Li et al, 2022;Meng et al, 2014;Nadal et al, 2020) Nevertheless, since T leaf was not influenced by PRD conditions, in our study, we are led to suggest that the higher leaf density was the main factor that contributed to the larger LMA that was observed under PRD conditions.…”