Leaf litter breakdown budgets in streams of various trophic status: effects of dissolved inorganic nutrients on microorganisms and invertebrates

Abstract

1. We investigated the effect of trophic status on the organic matter budget in freshwater ecosystems. During leaf litter breakdown, the relative contribution of the functional groups and the quantity/quality of organic matter available to higher trophic levels are expected to be modified by the anthropogenic release of nutrients. 2. Carbon budgets were established during the breakdown of alder leaves enclosed in coarse mesh bags and submerged in six streams: two oligotrophic, one mesotrophic, two eutrophic and one hypertrophic streams. Nitrate concentrations were 4.5-6.7 mg L )1 and the trophic status of each stream was defined by the soluble reactive phosphorus concentration ranging from 3.4 (oligotrophic) to 89 lg L )1 (hypertrophic). An ammonium gradient paralleled the phosphate gradient with mean concentrations ranging from 1.4 to 560 lg L )1 NH 4 -N. The corresponding unionised ammonia concentrations ranged from 0.08 to 19 lg L )1 NH 3 -N over the six streams. 3. The dominant shredder taxa were different in the oligo-, meso-and eutrophic streams. No shredders were observed in the hypertrophic stream. These changes may be accounted for by the gradual increase in the concentration of ammonia over the six streams. The shredder biomass dramatically decreased in eu-and hypertrophic streams compared with oligo-and mesotrophic. 4. Fungal biomass increased threefold from the most oligotrophic to the less eutrophic stream and decreased in the most eutrophic and the hypertrophic. Bacterial biomass increased twofold from the most oligotrophic to the hypertrophic stream. Along the trophic gradient, the microbial CO 2 production followed that of microbial biomass whereas the microbial fine particulate organic matter and net dissolved organic carbon (DOC) did not consistently vary. These results indicate that the microorganisms utilised the substrate and the DOC differently in streams of various trophic statuses. 5. In streams receiving various anthropogenic inputs, the relative contribution of the functional groups to leaf mass loss varied extensively as a result of stimulation and the deleterious effects of dissolved inorganic compounds. The quality/quantity of the organic matter produced by microorganisms slightly varied, as they use DOC from

Contributions of fungi to carbon flow and nutrient cycling from standing dead Typha angustifolia leaf litter in a temperate freshwater marsh

“…Such data help clarify the functional role of microbial assemblages (bacteria and fungi) and consumers (e.g., invertebrates) in organic matter processing (Hieber and Gessner 2002) and could provide unique insights into the potential effects of eutrophication on detrital carbon and nutrient flow pathways in ecosystems (Baldy et al 2007;Suberkropp et al 2010). Data collected in the present study allows the construction of a partial budget to assess the contribution of fungal decomposers to overall leaf carbon loss in T. angustifolia.…”

Comparison of Fungal Activities on Wood and Leaf Litter in Unaltered and Nutrient-Enriched Headwater Streams

“…4H). These estimates of fungal importance in litter decomposition do not include fungus-mediated losses of plant carbon as dissolved organic carbon and fine particulate organic carbon, which can be comparable to losses of plant C due to respiration (3). A considerable portion of allochthonous litter input may be also lost from a stream reach due to downstream transport and other breakdown factors, such as abiotic leaching, mechanical fragmentation, and invertebrate feeding.…”

Thresholds in macroinvertebrate biodiversity and stoichiometry across water-quality gradients in Central Plains (USA) streams

“…Nutrients can stimulate bacterial and fungal growth, which can increase detrital food quality (Meyer and Johnson 1983, Arsuffi and Suberkropp 1989, Stelzer et al 2003. Baldy et al (2007) found that microbial biomass and CO 2 production on leaf litter increased along a dissolved P gradient and then reached a plateau between 0.02 and 0.04 mg/L soluble reactive P (SRP). Rosemond et al (2002) also found that the half-saturation constant for litter decay across 16 tropical stream sites with differing SRP concentrations was between 0.007 and 0.013 mg/L SRP.…”