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.