Conifer needles live a very long time. Over their lifespan of four, five or even 10 years, they inevitably encounter very different light conditions. In the beginning, they grow in the open, under bright sun, but as the tree matures and grows, the needles become more shaded within the tree’s developing canopy. However, once a leaf is mature, it can’t easily change its shape to adjust to different light conditions. So how do conifer needles survive the switch from sunny to shady conditions over their lifespan?

A new paper, published in Annals of Botany, addresses this question by testing whether young needles already have characteristics that prepare them for the shade.  

“To test this hypothesis, we measured photosynthetic light responses at both the shoot and needle levels in four evergreen coniferous species native to northern Japan (Picea glehnii [Sakhalin spruce], Picea jezoensis [Ezo spruce], Abies sachalinensis [Sakhalin fir], and Taxus cuspidata [Japanese yew]), each with distinct shade tolerance, and needle configuration,” write Kitao and colleagues. 

Notably, in three of the four conifer species studied, the developing needles had shade characteristics, even when growing in full sunlight. These characteristics might have developed from mutual shading or conservative leaf anatomy.

The researchers found that shade-tolerant species generally have shoots with sparsely attached needles and that shade-grown seedlings have less densely packed needles than those growing in the full-sun. The low-density needle configuration may help increase light reception within the canopy.

“Needle packing within shoots reduced the light intensity reaching needle surfaces,” write Kitao and colleagues. As a result “shoot-level light acclimation may be regulated by needle configuration, consistent with species-specific shade tolerance.”

And so, it appears that conifers anticipate the change in their needle environment from sunny to shade, with needles pre-adapted to shade conditions.

READ THE ARTICLE: Kitao, M., Yazaki, K., Sugai, T., Harayama, H., Agathokleous, E., and Tanaka, R.(2026) Densely packed needles along the shoots of evergreen conifers exhibit shade-acclimated photosynthetic characteristics even under full sunlight. Annals of Botany. Available at: https://doi.org/10.1093/aob/mcag030.

Cover image: Picea jezoensis (Ezo spruce) by Alexander Yakovlev / iNaturalist CC BY-NC