H. Kinnunen et al., UV-absorbing compounds and waxes of Scots pine needles during a third growing season of supplemental UV-B, ENVIR POLLU, 112(2), 2001, pp. 215-220
Methanol-extractable UV-absorbing compounds, wax tube distribution and the
chloroform-soluble waxes of the needles of mature Scots pines were studied
in a UV-B field experiment in Oulu (65 degreesN). Throughout the experiment
, UV-B lamp banks were placed over the same selected branch and each year n
eedle samples were taken from the same branch. In the third exposure year,
needle samples were taken twice a month from 3-day-old needles (18 June) to
fully developed needles (13 August). On 28 September, the previous year's
needles (c + 1, c + 2) were also collected. There was a significant negativ
e correlation between the amount of waxes and UV-absorbing compounds. A hig
h amount of UV-absorbing compounds was observed early and late in the seaso
n when the amount of waxes was low and epicuticular waxes were undeveloped
(youngest needles) or already eroded (c + 2 needles). The amount of UV-abso
rbing compounds (A(310)/cm(2) and A(320)/cm(2)) was significantly (30-day-o
ld needles) or slightly (all the other needle ages) higher in the ambient n
eedles compared to the needles under supplemental UV-B. This possibly indic
ated the already inhibited pigment synthesis in the UV-B-treated needles du
ring the third year of supplemental UV-B. This observation could mean that
the protective mechanisms may not be effective under accumulated UV-B dose.
(C) 2001 Elsevier Science Ltd. All rights reserved.