## 3 Results and Discussions
### Effects of Phyto-Derivatives Treatments  
Preliminary tests on biofilms grown on agarised BG11 medium were carried out to compare the effects of lavender and liquorice extracts on the vitality of phototrophs. As shown in Figure 4, among the yield values of the controls there were no significant differences (\(p>0.05\)); however, those of all the treated biofilms were significantly lower than the controls (\(p<0.001\)). The immediate reduction in yield of the controls and, to some extent, in the treatments, may be due to the partial submergence of the biofilm by addition of the treatment solution, which may have reduced gas exchange to the cell [43]. However, even after removal of this effect from the treatment yields (i.e., F\({}_{\text{v}}\)/F\({}_{\text{m}}\) treated biofilm--F\({}_{\text{v}}\)/F\({}_{\text{m}}\) control), there was still a 50% (LAV), 30% (LIQ10) and 60%  
Figure 4: Changes over time of photosynthetic yield (F\({}_{\text{v}}\)/F\({}_{\text{m}}\)) of cultured biofilms treated at days 0 and 5 with diverse phyto-derivatives, (**a**) control (CTRL), (**b**) lavender essential oil (_Lavandula angustifolia_ Mill.) (LAV), (**c**) liquorice alcoholic leaf extract (_Glycyrhiza glaba_ L.) (LIQ) at 10% and (**d**) 30%. After each treatment measurements were made immediately, then at 5, 30 and 90 min, 1 and 5 days (10 days in total). (LIQ30) reduction in F\({}_{\text{v}}\)/F\({}_{\text{m}}\). There was a significant reduction in yields of the lavender and both the liquorice treated biofilms after five minutes (\(p<0.001\)) and it remained so for the full 10 days. Therefore, it seems yield is susceptible to the two plant extracts, although the mode of action is not easy to determine. The minimal fluorescence (F\({}_{\text{o}}\)) values either remained relatively unchanged (LAV) or decreased (LIQ), actually indicating no photodamage [44], while a larger decrease in F\({}_{\text{m}}\) was observed that could represent enhanced nonradiative energy loss (heat dissipation) that may act in photo-protection or -repair [45]. In all treatments, yield did recover to some extent, rapidly within the first day, then slower until day five: Recovery from the maximum reduction was 20% for both treatments of LAV, 10% and 6% for LIQ10, 22% and 25% for LIQ30. This recovery is not thought to be a result of new growth; as observations of the biofilms did not indicate this, more likely, it was the occurrence of cellular repair of the photosynthetic apparatus. Yield responded similarly to the second treatment (day 5)--an initial decrease, followed by a slow partial recovery. This time the recovery resulted in yield values that were not significantly different to the initial (day 5) value (\(p>0.05\)). However, yields did remain significantly lower than the original levels (day 0) during the experiment (\(p<0.01\)). In a study of the recovery of structure and function of freshwater biofilms after being treated with short pulses of herbicide (Diuron) or bactericide (Triclosan), it was established that short biocide pulses can efficiently cause transient effects on biofilms, while longer pulses would result in more persistent effects with chronic ones that could be lethal to the biofilm [46]. In the scenario here using phytoextracts, given their volatile nature, they may behave in a similar manner to the through-flow pulse method and more frequent applications would be needed to determine if there is a chronic effect on biofilm status. A second test has been carried out inside well plates containing a piece of biofilm (250 mg each) evaluating the effect of two applications of LAV, LIQ and a mixed solution of both (LIQLAV) on photosynthetic and heterotrophic microorganisms. As shown in Figure 5 there were no significant differences between the yields before treatments and those of the control biofilms (\(p>0.05\)). The effects of the phyto-derivatives on the photosynthetic yield were comparable to the synthetic BENZ (\(p>0.05\)) and resulted in significant lowering of yield (\(p<0.01\)-\(0.001\)).