Heterogeneity in leaf litter decomposition in a temporary Mediterranean stream during flow fragmentation

Abstract

In temporary Mediterranean streams, flow fragmentation during summer droughts originates an ephemeral mosaic of terrestrial and aquatic habitat types. The heterogeneity of habitat types implies a particular ecosystem functioning in temporary streams that is still poorly understood. We assessed the initial phases of leaf litter decomposition in selected habitat types: running waters, isolated pools and moist and dry streambed sediments. We used coarse-mesh litter bags containing Populus nigra leaves to examine decomposition rates, microbial biomass, macroinvertebrate abundance and dissolved organic carbon (DOC) release rates in each habitat type over an 11-day period in late summer. We detected faster decomposition rates in aquatic (running waters and isolated pools) than in terrestrial habitats (moist and dry streambed sediments). Under aquatic conditions, decomposition was characterized by intense leaching and early microbial colonization, which swiftly started to decompose litter. Microbial colonization in isolated pools was primarily dominated by bacteria, whereas in running waters fungal biomass predominated. Under terrestrial conditions, leaves were most often affected by abiotic processes that resulted in small mass losses. We found a substantial decrease in DOC release rates in both aquatic habitats within the first days of the study, whereas DOC release rates remained relatively stable in the moist and dry sediments. This suggests that leaves play different roles as a DOC source during and after flow fragmentation. Overall, our results revealed that leaf decomposition is heterogeneous during flow fragmentation, which has implications related to DOC utilization that should be considered in future regional carbon budgets.

Key role of streambed moisture and flash storms for microbial resistance and resilience to long‐term drought

“…maximised with time since dry, due to the reduced labile OM sources in dried sediments. Experiments on the effect of drought on leaf litter decomposition have shown a clear reduction in the decay rate(Abril, Muñoz, & Menéndez, 2016) and significant effects were already detected even after 7 days of emersion(Mora-Gómez, Duarte, Cássio, Pascoal, & Romaní, 2018). In accord with our expectations, this was accompanied by the response of the extracellular enzymes which, although being not sharp, evidenced the reduced activity in the long-term drought, especially for hemicellulose degradation (XYL activity).…”

Dynamic stream network intermittence explains emergent dissolved organic carbon chemostasis in headwaters

“…Streamflow intermittence varies across headwaters (e.g., Godsey & Kirchner, ; Jensen, McGuire, & Prince, ) and reach‐scale patterns of stream drying have been linked to variation in carbon cycling and transport (e.g., Acuña, Giorgi, Muñoz, Sabater, & Sabater, ; Shumilova et al, ). DOC sources and transformation rates vary within intermittent reaches through wetting and drying (Acuña et al, , Acuña et al, ; Datry, Corti, Claret, & Philippe, ; Dieter et al, ; Abril, Muñoz, & Menéndez, ; Harjung, Sabater, & Butturini, ), and legacies of drying can impact C cycling through the accumulation of organic matter and drying impacts on biotic communities (von Schiller et al, ). Although most work on the legacies of drying on biota have focused on macroinvertebrates (Leigh et al, ), metabolism studies have shown that gross primary productivity is also depressed following drying in intermittent reaches compared with years when stream drying does not occur (Acuña et al, ).…”

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter

“…For example, in the arid zone, where IRES are usually characterized by open canopy (Steward, Schiller, Tockner, Marshall, & Bunn, ), aridity and percentage of riparian vegetation best explained the variance in sediment leachates. Inputs of riparian vegetation litter onto the dry riverbeds and its subsequent decomposition, can represent an additional input of nutrients to sediments in the arid zone areas (Abril et al, ), where soils generally contain less carbon and nitrogen compared to the continental zone (Table S1 and Delgado‐Baquerizo et al, ). Changes in land‐use (particularly, in the percentage of pasture cover at the global scale as well as within individual climate zones except continental) were correlated with the amount of leached substances from leaves, potentially through modifying the composition of plant material accumulated in beds of IRES.…”

“…This variable is expected to be intensified in the future (Milly & Dunne, 2016) and will most likely lead to fluctuations in moisture conditions in dry riverbeds. Low moisture level reduces litter decomposition and C consumption, thereby promoting the release of DOM upon rewetting (Abril et al, 2016;Aerts, 1997;Bruder et al, 2011;Gessner, 1991) and hence increasing the probability of negative consequences for stream ecosystems such as blackwater events leading to hypoxia (Hladyz et al, 2011). (Abril et al, 2016), where soils generally contain less carbon and nitrogen compared to the continental zone (Table S1 and Delgado- Baquerizo et al, 2013).…”

“…During the dry phase, a diversity of substrates (leaf litter, epilithic biofilms, wood, animal carcasses, sediments) accumulate on the dry riverbed (Datry et al, 2018) . Absence of water reduces decomposition rates of substrates (for particulate organic matter, OM), while sunlight and intense desiccation alter their physico-chemical properties, a process known as preconditioning (Abril, Muñoz, & Menéndez, 2016;Bruder, Chauvet, & Gessner, 2011;del Campo & Gómez, 2016;Dieter et al, 2011;Taylor & Bärlocher, 1996). When surface water returns after drying events, accumulated organic and inorganic substrates are rewetted and can be transported downstream (Corti & Datry, 2012;Obermann, Froebrich, Perrin, & Tournoud, 2007;Rosado, Morais, & Tockner, 2015).…”