Preconditioning of leaves by solar radiation and anoxia affects microbial colonisation and rate of leaf mass loss in an intermittent stream


Correspondence: Daniela Dieter, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Müggelseedamm 310, 12587 Berlin, Germany.



  1. Seasonal flow intermittence in streams often coincides with early leaf abscission of riparian vegetation due to water stress. When accumulated on dry stream beds or in remaining pools, leaves are exposed to solar radiation or fermentation processes, respectively. However, very little information exists on how these preconditioning processes could affect leaf decomposition when stream flow has recovered.
  2. We simulated natural preconditioning of leaves by irradiation with UV-VIS fluorescent lamps and incubation under anoxic conditions. Mass loss rates of preconditioned leaf litter from deciduous trees (Alnus glutinosa, Fraxinus excelsior, Populus tremula and Quercus petreae) were quantified in a temporary stream during base flow conditions. Coarse and fine mesh litter bags were used to study the effect of benthic macroinvertebrates and microorganisms on leaf mass loss.
  3. Preconditioning reduced the concentration of macronutrients such as P, K and Mg and increased the relative cellulose content of the leaves. Preconditioning changed the fungal community structure (analysed by DGGE) depending on leaf species and sampling date. Preconditioning in anoxic conditions also suppressed fungal decomposer biomass (measured as ergosterol) by 42% resulting in 33% lower mass loss rates in fine mesh bags. In contrast, mass loss rates were not affected by preconditioning when macroinvertebrate decomposers had access to the leaf litter.
  4. In streams exhibiting seasonal flow intermittence, preconditioning will influence organic carbon dynamics towards lower rates of microbially mediated turnover and towards poorer quality of downstream-transported material.