Inter-annual and inter-specific variability in response to
natural variation in ambient solar radiation
There was a substantial difference in p CA concentrations in
pollen grains from the same individual tree samples in 2013 and 2014,
and between Pinus spp. (Table 2 and Fig. 2 a). On average, pollen
from 2014 contained 31% more p CA than pollen from the same trees
in 2013. The 95% credible interval of the differences between the two
years means did not cross zero, providing strong statistical support
that p CA abundance was different between the years for the
individuals of all species tested (Pinus nigra, P. pinaster, P.
sylvestris and P. uncinata ) (Fig. 2 b).
The measured solar radiation shows variation between the two collection
years, particularly during the pollen development period, but not during
the preceding growing season (Fig. 1). The total amount of solar
radiation during the month (28 days) before pollen collection in May
2013 was 5214 W/m2 compared to 6401
W/m2 in 2014 and two months before was 9429
W/m2 in 2013 and 12191 W/m2 in 2014.
Across both years, there was strong and consistent species-level
variation, which can be partially accounted for by pollen size (Fig. 2
c, d). However, differences between species remained even after
correcting for pollen size corrections, and Pinus pinaster still
showed higher p CA ratios compared with the other species (Fig. 2
c, d).