DOI: 10.5061/dryad.280gb5mnv
title: Clockwise and counterclockwise hysteresis in the S. purpurea micro ecosystem

description: Incremental increases in a driver variable, such as nutrients or detritus,
 can trigger abrupt shifts in aquatic ecosystems that may exhibit
 hysteretic dynamics and a slow return to the initial state. A model system
 for understanding these dynamics is the microbial assemblage that inhabits
 the cup-shaped leaves of the pitcher plant Sarracenia purpurea. With
 enrichment of organic matter, this system flips within three days from an
 oxygen-rich state to an oxygen-poor state. In a replicated greenhouse
 experiment, we enriched pitcher-plant leaves at different rates with
 bovine serum albumin (BSA), a molecular substitute for detritus. Changes
 in dissolved oxygen (DO) and undigested BSA concentration were monitored
 during enrichment and recovery phases. With increasing enrichment rates,
 the dynamics ranged from clockwise hysteresis (low), to environmental
 tracking (medium), to novel counter-clockwise hysteresis (high). These
 experiments demonstrate that detrital enrichment rate can modulate a
 diversity of hysteretic responses within a single aquatic ecosystem, and
 suggest different management strategies may be needed to mitigate the
 effects of high versus low rates of detrital enrichment.
description: Replicate <em>S. purpurea </em>pitchers were enriched
 with 5.0 (high concentration) or 0.5 (low concentration) mg of bovine
 serum albumi (BSA) per mL of pitcher fluid in 2015 and 2.0 mg/mL
 (intermediate concentration) in 2016. For each experiment, a set of
 control pitchers received no organic matter. These controls were used
 to determine when oxygen levels in experimental pitchers had recovered.
 Experimental pitchers were loaded with organic matter (between 9:00 am and
 9:45 am) following pitcher-fluid sampling and DO measurement for the first
 four days of the experiment.  We measured DO twice a
 day each day from day 20 to day 28, and once on Days 30, 31, 33, and 35.
 DO was measured using a D-166MT-1S microelectrode (Lazar Research
 Laboratories). The microelectrode was calibrated prior to each sampling
 event according to the manufacturer’s instructions. A single
 microelectrode was used to take readings from each pitcher and was rinsed
 twice with reverse osmosis water between readings. The order of readings
 from different replicates was randomized so that changes in temperature
 and sunlight over the sampling period were not confounding factors. During
 readings, the microelectrode was placed 2.5 cm below the surface of the
 pitcher fluid and swirled so that the more oxygen-rich pitcher fluid at
 the top of the pitcher was mixed and readings reflected average DO. Due to
 the sensitivity of the microelectrode, readings were taken as soon as the
 reader settled on a value for more than 10 s.  Pitcher
 fluid was sampled following each DO measurement for spectrophotometric
 analysis using a Bradford assay. Using sterile pipette tips, a 300
 µL aliquot was taken from 2.5 cm below the surface of each pitcher and
 placed in a sterile 1-mL microfuge tube. Sample tubes were immediately
 transported to the lab where they were centrifuged at 13,000 xg for two
 minutes. The supernatant containing soluble BSA was removed, placed in a
 sterile 1-mL microfuge tube, and stored at -80°C until analyzed.
 The data were analyzed using the following R scripts:
 HYS_vFinal_removedreplicates, hysteresis_functions.R,
 reviewer3figure.R
description: This dataset was collected in two separate years (2015 and 2016).
 High and low concentration treatment data were collected in 2015 and
 interediate treatment data were collected in 2016.