3. Results
3.1. Radiation level
Maxima noon values of instantaneous UV-B radiation and
PAR recorded outside the tree canopy for a sunny and a cloudy
day during the winter season were 1.64 and 0.28Wm−2, and
1163 and 248molm−2 s−1, respectively. Radiation measurements
revealed that under cloudy and sunny conditions, the
superficial-inner lemons received significantly less radiation than
the outer surface. In both sunny and cloudy days, the penetration
of UV-B radiation was significantly lower than the PAR one.
For a sunny day we recorded reduction values of 67% for PAR
and 76% for UV-B, respectively. Although under cloudy conditions,
the difference between outer and inner measurements was
lower than under sunny ones, the lowest UV-B penetration was
recorded during a cloudy day. Interestingly at low elevation angles
(morning and afternoon), the relative proportion of UV-B was
slightly higher for both studied position of the canopy (data not
shown).