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Data from: Leaf litter breakdown along an elevational gradient in Australian alpine streams

Citation

Werry, Lloyd et al. (2022), Data from: Leaf litter breakdown along an elevational gradient in Australian alpine streams, Dryad, Dataset, https://doi.org/10.5061/dryad.tdz08kq2n

Abstract

These data were generated to investigate the rate of leaf litter breakdown and how temperature and other factors such as microbial and and invertebrate activities were influenced over elevational and temporal gradients. Breakdown of allochthonous organic matter is a central step in nutrient cycling in stream ecosystems. There is concern that increased temperatures from climate change will alter the breakdown rate of organic matter with important consequences for ecosystem functioning of alpine streams. Dried leaves of Snow Gum (Eucalyptus pauciflora) and cotton strips were deployed in coarse (6mm) and fine (50µm) mesh size bags along an 820 m elevation gradient. Loss of mass in leaf litter and cotton tensile strength per day (k per day), fungal biomass measured as ergosterol concentration, invertebrate colonization of leaf litter and benthic organic matter (mass and composition) were determined. Both microbial and macroinvertebrate activities were equally important in leaf litter breakdown with the abundance of shredder invertebrate taxa. The overall leaf litter breakdown rate and loss of tensile strength in cotton strips (both k per day) were greater during warmer deployment periods and at lower elevations with significant positive relationships between mean water temperature and leaf breakdown and loss of tensile strength rate, but no differences between sites, after accounting for the effects of temperature. Despite considerably lower amounts of benthic organic matter in streams above the tree line relative to those below, shredders were present in coarse mesh bags at all sites. Ergosterol concentration was greater on leaves in coarse mesh bags than in fine mesh bags, implying differences in the microbial communities. The importance of water temperatures on the rate of leaf litter breakdown suggests potential effects of climate change-induced temperature increases on ecological processes in such streams.

Methods

1) Leaf litter breakdown: dried leaves of Snow Gum (Eucalyptus pauciflora) were weighed and placed in streams in coarse (6mm) and fine (50µm) mesh size bags along an 820m elevation gradient. Final dry mass of leaves were taken to evaluate loss of mass and rate (k) of percentage mass loss calculated over the period of exposure.

2) Loss of cotton tensile strength: Sterile cotton strips (3x10cm) were placed in different mesh-sized bags with leaves with known tensile strength. Final tensile stength was obtained after exposure in streams and rate of tensile loss was calculated (k per day). Tensile strength was determined using a tensiometer (an Instron 4500 Uni Testing System).

3) Ergosterol  levels: Fungal biomass on leaves exposed in the streams were measured as ergosterol concentrations. Ergosterol was extracted from leaf samples for 30 minutes in 10ml of alkaline methanol at 80 degrees celcius. The ergosterol was then purified by solid phase extraction (Sep-Pak Vac RC tC18 500mg sorbent, Waters) after cooling. Separation of ergosterol was done on a high-performance liquid chromatograph (Agilent Technologies, 1200 Series, Waldbronn, Germany) and measured with an ultraviolet detector (wavelength of 282nm). Using a standard calibration curve prepared with the chemical standard (Fluka, purity at 97%), ergosterol concentrations were determined and normalised to dry mass of the leaves.

4) Invertebrate colonization of leaf litter were made from bag types 

5) Water quality measurements were measured in situ at each site during sampling episodes

Usage Notes

Please refer to ReadMe file.

Funding

Australian Research Council, Award: DP180102016