Study design
To investigate inter-annual responses to natural variation in ambient
solar radiation and species-level variation, pollen samples were
collected during dehiscence season of 2013 (collection date: May 14th)
and 2014 (May 26th) from the same Pinus nigra J.F. Arnold,
P. pinaster Aiton, P. sylvestris L. and P. uncinataRamond ex DC. (Table 1) trees in both years in Geneva Botanical Garden
and Conservatory (N 46.2253, E 6.1465). The number of trees varied per
species, depending on availability. Five fully sun-exposed branches were
sampled on each tree, on the south facing side during or immediately
after dehiscence. Pollen cones were placed in an individual paper bag,
which again were placed within a plastic zip lock bag to minimize
contamination and stored at room temperature in sealed plastic boxes.
An ambient solar-radiation exclusion experiment was set up on April 28th
2014 in order to investigate variations in p- coumaric acid at the
flower level, ten freestanding/sun-exposed Pinus sylvestris trees
6–8 metres in height were selected from the Arboretum and Botanical
Garden of Milde in Bergen, Norway (N 60.2557, E 5.2706). Two south
facing branches with a distance of one to two metres between on each
tree were used, one randomly allocated to the shade treatment and
covered with a shade cloth fabric with 90% shade intensity, the other
marked and left without any shade cloth under ambient solar radiation.
Similar to a study by Fraser et al. (2011), which used the natural
shading of forest canopy to screen out solar radiation, the shade cloths
in our experiment screen out a proportion of total incoming solar
radiation. Pollen was collected on May 28th 2014, when one to three male
pollen cones from one branch tip were placed in an individual paper bag,
which again was placed within a plastic zip lock bag to minimize
contamination and stored at room temperature in sealed plastic boxes.