Data from: Structural controls on photosynthetic capacity through juvenile-to-adult transition and needle aging in Mediterranean pines

1. Needle photosynthetic potentials strongly vary among primary (juvenile)
and secondary (adult) needles (heteroblasty) in Pinus species, but there
is limited understanding of the underlying structural, diffusional and
chemical controls. 2. We studied differences in needle photosynthetic
characteristics among current-year juvenile and adult needles and among
different-aged adult needles in Mediterranean pines Pinus halepensis
Mill., P. pinea L. and P. nigra J. F. Arnold subsp. salzmannii (Dunal)
Franco, hypothesizing that needle anatomical modifications upon
juvenile-to-adult transition lead to reduced photosynthetic capacity due
to greater limitation of photosynthesis by mesophyll conductance and due
to an increase in the share of support tissues at the expense of
photosynthetic tissues. We also hypothesized that such alterations occur
with needle aging, but to a lower degree. 3. Photosynthetic capacity per
dry mass was 2.4-2.7-fold higher in juvenile needles, and this was
associated with 3.4-3.7-fold greater mesophyll diffusion conductance, and
2-2.5-fold greater maximum carboxylase activity of Rubisco (Vcmax) and
2.2-3-fold greater capacity for photosynthetic electron transport (Jmax).
The latter differences were driven by modifications in mesophyll volume
fraction and changes in the share of nitrogen between structural and
photosynthetic functions. Analogous changes in photosynthetic
characteristics occurred with needle aging, but their extent was less. 4.
These results indicate that conifer foliage photosynthetic machinery
undergoes a profound change from a fast return strategy in juveniles to
slow return stress-resistant strategy in adults and that this strategy
shift is driven by modifications in foliage biomass investments in support
and photosynthetic functions as well as by varying mesophyll diffusional
controls on photosynthesis. Changes in needle morphophysiotype during tree
and needle aging need consideration in predicting changes in tree
photosynthetic potentials through tree ontogeny and during and among
growing seasons.