THE ROLE OF DROUGHT IN THE IMPACT OF CLIMATIC-CHANGE ON THE MICROBIOTA OF PEATLAND STREAMS

1. Simulation of climate change (summer drought) stimulated autotrophy in a stream draining a Welsh peatland. Biofilm autotrophic biomass (c hlorophyll) increased by 145% and was correlated with an increased ove rall metabolic activity (r = 0.75, P < 0.05). Bacterial population den sities were not significantly affected. 2. The increased autotrophy wa s probably related to a decrease in the organic:inorganic ratio of nut rients released from the wetland to the stream. 3. Bacterial reserves of poly-beta-hydroxyalkanoate (PHA) fell by 51%. Increased nitrate con centrations were inversely correlated with autotrophic diversity (r = -0.88, P < 0.001). 4. The increased autotrophic biomass represents an increased nutrient supply for the higher trophic levels which could pr omote higher productivity within the stream ecosystem as a whole. 5. T he simulation also caused a cooler (11%, P < 0.01) streamflow from the drought-impacted wetland, which could mitigate against any adverse te mperature-dependent effects of future climatic change.