Vertical gradients in photosynthetic physiology diverge at the latitudinal range extremes of white spruce

Abstract

Light availability drives vertical canopy gradients in photosynthetic functioning and carbon (C) balance, yet patterns of variability in these gradients remain unclear. We measured light availability, photosynthetic CO2 and light response curves, foliar C, nitrogen (N) and pigment concentrations, and the photochemical reflectance index (PRI) on upper and lower canopy needles of white spruce trees (Picea glauca) at the northern and southern extremes of the species' range. We combined our photosynthetic data with previously published respiratory data to compare and contrast canopy C balance between latitudinal extremes. We found steep canopy gradients in irradiance, photosynthesis, and leaf traits at the southern range limit, but clear convergence across canopy positions at the northern range limit. Thus, unlike many tree species from tropical to mid-latitude forests, high latitude trees do not require vertical gradients of metabolic activity to optimize photosynthetic C gain. Consequently, accounting for self-shading is less critical for predicting gross primary productivity at northern relative to southern latitudes.Northern trees also had a significantly smaller net positive C balance than southern trees suggesting that, regardless of canopy position, low photosynthetic rates coupled with high respiratory costs may ultimately constrain the northern range limit of this widely distributed boreal species.SHORT TITLE: Variation in photosynthetic canopy gradients of white spruce at the species' range limits.

Indication of Light Stress in Ficus elastica Using Hyperspectral Imaging

“…In addition, the results of the study confirm the need for remote spectral monitoring of vegetation, taking into account its light history, which was previously pointed out by other authors [38][39][40][41].…”

Temperature responses of leaf respiration in light and darkness are similar and modulated by leaf development

“…Furthermore, our study showed that the Kok method underestimates R L and overestimates the inhibition of respiration by light, which is in line with recent studies (Fang et al ., 2022; Sun et al ., 2023). The mean apparent inhibition of respiration (1‐ R L kok / R Dk ) of our two tree species was 0.39, which is comparable to the reported apparent inhibition rate of trees, for example Eucalyptus saligna (0.4; Ayub et al ., 2011), Eucalyptus globulus (0.31; Crous et al ., 2017), and Picea glauca (0.2; Schmiege et al ., 2023), herbs, for example Triticum aestivum (0.29; Griffin & Turnbull, 2013). However, the actual inhibition (1‐ R L Kok‐iterCc / R Dk ) was only 0.19 in tree leaves.…”

Contrasting photoprotective responses of forest trees revealed using PRI light responses sampled with airborne imaging spectrometry

“…Like many spectral vegetation indices, PRI is also strongly influenced by illumination and canopy structure (Barton & North, 2001; Gitelson et al ., 2017). Canopy regions varying in light exposure have contrasting PRI‐light responses reflecting their recent light histories associated with canopy position but also their instantaneous light environments (Gamon et al ., 2005; Gamon & Berry, 2012; Atherton et al ., 2017; Schmiege et al ., 2022). Adjacent trees of different height and contrasting hydraulic conductance and stomatal conductance exhibit different PRI‐light responses, indicating more photosynthetic downregulation in taller trees (Gamon & Bond, 2013).…”