Lj. Tranvik et S. Bertilsson, Contrasting effects of solar UV radiation on dissolved organic sources forbacterial growth, ECOL LETT, 4(5), 2001, pp. 458-463
The photochemical transformation of dissolved organic matter (DOM) in lakes
and oceans has been shown to either reduce or enhance bacterial utilizatio
n. We compared the effects of UV radiation on the bacterial use of DOM in a
wide range of lakes. Although complex DOM was converted in all irradiated
samples into carboxylic acids that are readily utilized by bacteria, irradi
ation in several lakes resulted in a decreased ability of DOM to support ba
cterial growth. The effect of irradiation on the ability of DOM to promote
bacterial growth was a positive function of the terrestrial humic matter, a
nd a negative function of indigenous algal production. We suggest that the
net effect of irradiation is a result of counteracting but concurrent proce
sses rendering DOM either labile or recalcitrant. Humic DOM is predominantl
y transformed into forms of increased lability, whereas photochemical trans
formation into compounds of decreased bacterial substrate quality dominates
in algal-derived DOM. Hence, solar-induced photochemical reactions interac
t with microbial degraders in different ways, depending on the origin and n
ature of the organic matter, affecting the transfer of energy within aquati
c food webs, as well as the degradation and preservation of detrital organi
c matter, in different directions.