-Plant litter breakdown, an important process for energy and matter flows in freshwater ecosystems, has been extensively studied except in the karst (and calcite depositing) habitats. The aim of this paper was to answer three questions regarding the breakdown of leaf litter in calcite depositing environment: (i) Does leaf decomposition hinder calcite deposition and vice versa?; (ii) What role do other environmental factors play?; and (iii) How long does leaf litter persist in these habitats? Leaves of beech (Fagus sylvatica) and butterbur (Petasites hybridus) were exposed for 8 weeks in 8 microhabitats: 2 calcite deposition rates r 2 flow velocities r 2 seasons. A linear model was better at predicting leaf litter persistence but only for the period after the extreme loss of leaf mass occurring during the initial leaching of highly hydrosoluble compounds in the first week (11.6% of beech and 54.2% of butterbur regardless of the studied environmental factors). Higher flow velocity and calcite deposition rates stimulated the breakdown of both leaf species. During summer, breakdown was accelerated for butterbur leaves only. Since breakdown rates of both litter types were faster at high calcite depositing sites, it can be concluded that the breakdown process is not hindered by calcite deposition in general. The amount of deposited calcite per gram of leaf litter increased linearly over time (after the first week of exposure) on both leaf species. More calcite was deposited on the fast-decomposing butterbur leaves than on beech leaves.
Considerable amount of riparian leaf litter is annually supplied to the cascade Plitvice Lakes and trapped on tufa barriers where it decays together with aquatic macrophytes. These barriers are the sites of heavy calcite precipitation that can widely differ in terms of current velocity. We conducted a leafbag experiment at sites differing in flow velocity and tufa deposition rate. Decomposition of Petasites spp. and Fagus sylvatica was higher under high current (0.80 m/s) and high tufa deposition areas than in low current (< 0.20 m/s) and low tufa deposition areas (k = 0.085 vs. 0.021 for Petasites spp. and 0.009 vs. 0.002 for Fagus sylvatica). We concluded that although tufa deposition could interfere with decomposition by obstructing physical abrasion and also restricting microbial conditioning, thin calcite crusts developed on the surface of the leaves made them more fragile and thus accelerated their decomposition. High current velocity probably magnified this effect by supporting higher tufa deposition and coarser type of tufa fabrics. IntroductionLeaf litter processing in aquatic ecosystems involves a sequence of processes, from the dissolution of labile organic compounds (leaching), microbial conditioning to mechanical fragmentation by macroinvertebrates (WEBSTER and BENFIELD, 1986) and physical abrasion BOULTON and BOON (1991), especially by current velocity. The rate of litter breakdown is determined by intrinsic differences among leaves, a number of environmental variables, and the feeding activity of detrivores (e.g., ALLAN, 1995;DANGLES and CHAUVET, 2003; FER-REIRA et al., 2006;LEROY and MARKS, 2006;CARTER and MARKS, 2007).Several studies investigated the breakdown of leaf litter in karst systems where tufa precipitates (CASAS and GESSNER 1999;VIVAS and CASAS, 2002;CASAS et al., 2006;CARTER and MARKS, 2007). These studies reported contradictory results: CARTER and MARKS (2007) reported significantly faster breakdown at the tufa site than at the site without tufa precipitation, while CASAS and GESSNER (1999) found tufa precipitation to impair decomposition.
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