Field testing a 13C labeling method in an East African ant-plant

Mizell, Gabriella 1 ; Kim, Thomas1; Sullivan, Benjamin1; Palmer, Todd2; Pringle, Elizabeth1

Published Sep 18, 2023 on Dryad. https://doi.org/10.5061/dryad.h9w0vt4q4

Data files

Sep 18, 2023 version files 1.63 MB

Abstract

Tree carbon allocation is a dynamic process that depends on the tree's environment, but we know relatively little about how biotic interactions influece these dynamics. In central Kenya, the loss of vertebrate herbivores and the savanna's invasion by the ant Pheidole megacephala are disrupting mutualisms between the founational tree Acacia drepanolobium and its native ant defenders. Here we piloted a ¹³Carbon (C) pulse-labeling mathod to investigate the influece of these biotic interactions on C allocation strategies by adult trees in situ. Trees withstood experimental conditions and took up sufficient labeled ¹³CO₂for ¹³C to be detected in various C sinks, including ant mutualists. The ¹³C in ants collected shortly after labeling suggested that trees exposed to herbivores allocated relatively more newly assimilated C to native ant defenders. Our results demonstrate the viability of the pulse-labeling method and suggest the C allocation to ant partners depends on the biotic context of the tree, but further investigation with replication is needed to characterize such differences in relation to invasion and herbivore loss.

GENERAL INFORMATION

Title of Dataset: Field testing a 13C labeling method in an East African ant-plant
Author Information
A. Principal Investigator Contact Information
Name: Elizabeth Pringle
Institution: University of Nevada, Reno
Address: 1664 N Virginia St. ms 0314 Reno, NV 89557
Email: epringle@unr.edu
B. Associate or Co-investigator Contact Information
Name: Gabriella Mizell
Institution: University of Nevada, Reno
Address: 1664 N Virginia St. ms 0314 Reno, NV 89557
Email: gmizell@nevada.unr.edu
Date of data collection (single date, range, approximate date): 2020-03-07 - 2020-09-09
Geographic location of data collection: 0.003036 N, 36.96572 E. Ol Pejeta Conservancy, Laikipia, Kenya
Information about funding sources that supported the collection of the data:
U.S National Science Foundation to Elizabeth Pringle (NSF DEB-1935498)

DATA & FILE OVERVIEW

File List:
- Licor Data.zip - contains 8 csvs of environmental variables measured in the labeling tent. There is one csv per labeling event.
  isotope.time.csv - data for solid samples analyzed for 13C, including tree tissue and ants.
- CO2_efflux_calcs.csv - data for gas samples analyzed for 13C, including branch and soil respiration, and atmospheric gas samples
- 13C_stem_investment.xlsx - contains stem 13C data and calculations for scaling stem samples to whole tree stem 13C
- 13C_ant_investment.xlsx - contains ant 13C data and calculations for scaling ant samples to whole ant colony 13C
Relationship between files, if important: In licor Data folder: Files that begin with the same 3 letters are labeling events for the same tree. There are 2 labeling events per tree.
Additional related data collected that was not included in the current data package: NA
Are there multiple versions of the dataset? No

METHODOLOGICAL INFORMATION

Description of methods used for collection/generation of data:
See article in Plant Ecology: Carbon allocation in an East African ant-acacia: field-testing a 13C-labeling method for evaluating biotic impacts on the carbon cycle.
Methods for processing the data:
The data in the Licor data folder came directly from the LI-8100 gas analyzer - all data processing is documented in the associated R script.
The raw data we received from UC Davis Stable Isotope Facility included the delta 13C values. This file was widened to include a new column for each experimental treatment. Columns that were not used in our analyses (e.g., total C and total N in each sample) were removed.
Instrument- or software-specific information needed to interpret the data:
R version 4.1.1 (2021-08-10) with RStudio interface
Necessary packages: plyr, dplyr, tidyverse, ggplot2, ggbreak, gg.gap, ggpubr, glmmTMB, DHARMa, MuMIn, magrittr, car, lmtest, emmeans, multcompView, FSA
People involved with sample collection, processing, analysis and/or submission:
Gabriella Mizell, Elizabeth Pringle, John Lemboi, John Mosiany

DATA-SPECIFIC INFORMATION FOR: Licor_data.zip

Each csv in the zipped file contains the same information

Number of variables: 8
Number of cases/rows: MUE_L2_1: 14568, MUE_L2_2: 11230, MUO_L1_1: 18069, MUO L1_2: 17825, MIE_L1_1: 20794,
MIE_L1_2: 2976, MIO_L3_1: 17329, MIO_L3_2: 13134
Variable List:
- Date - the date and time the reading occurred
- CO2 - the CO2 level (ppm) inside the tent
- Tbench - the temperature (Celsius) of the IRGA - it need to be at least 50C before it was ready to record CO2 data.
- V1 - Photosynthetically active radiation (PAR), measured in micro moles per meter squared per second
- V2 - relative humidity (%)
- V3 - Temperature (Celsius)
- Hour - The hour of the day the measurement was taken
- DOY - the day of the year the measurement was taken

DATA-SPECIFIC INFORMATION FOR: isotope.time.csv

Number of variables: 13
Number of cases/rows: 141
Variable List:
- sample.id - a unique code for each sample used as a descriptive name for isotope analysis.
- tree - the tree that the sample came from
- time.hours - the timepoint at which the sample was collected, in hours
- delta.13C - the proportion of 13C to 12C in each sample, expressed in delta notation
- time.days - the timepoint at which the sample was collected, in days
- treatment - the labeling treatment of the tree from which the sample comes from. Either control or label
- meta.material - the broadest classification of the material of the sample. Either tree or ants
- material - the type of sample. Ants, thorns, stems, new.stems, or leaves
- sub.material - additional material classification
- ant.treatment - the invasion status of the tree from which the sample comes from. Either control or invaded
- herbivore.treatment - whether or not herbivores were present or excluded from the tree from which the sample comes from
- ant.species - the species name of the ant samples. C.mimosae, P.megacephala, or T.penzigi
- notes - if there was any additional information about the sample that was not captured by the other columns. This only applied to leaf data. first.event means the leaf sample was collected after the first labeling event, while second.event means the leaf sample was collected after the second labeling event.
Missing data codes:
na - data is not necessary for a column for a sample

DATA-SPECIFIC INFORMATION FOR: CO2_efflux_calcs.csv

Number of variables: 11
Number of cases/rows: 46
Variable List:
- tree - the tree from which the sample came from
- sample.type - the type of gas sample that was collected. Either branch, soil, or atmospheric
- treatment - the labeling treatment of the tree from which the sample was collected. Either control or label
- time - the timepoint that the sample was collected at, in hours.
- 10 - the CO2 concentrtation at 10 minutes, in ppm
- 20 - the CO2 concentration at 20 minutes, in ppm
- 30 - the CO2 concentration at 30 minutes, in ppm
- delta.13C.30min - the proportion of 13C to 12C in each sample at 30 minutes, expressed in delta notation
- intercept - the intercept calculated after fitting a linear model through the three timepoints (10, 20, 30) for each sample
- r2 - the fit of the linear model for each sample, using r2
- CO2.efflux - the calculated efflux value, using the delta.13C.30min + the intercept multiplied by 1/the CO2 concentration of the sample.
Missing data codes:
na - data not necessary for a column for a sample

DATA-SPECIFIC INFORMATION FOR: 13C_ant_investment.xlsx

Number of variables: 16
Number of cases/rows: 8
Variable List:
- treatment- whether the sample comes from a control tree or labeled tree
- sample - the name of the sample
- labeling treatment - whether the tree that the sample comes from was labeled with 13CO2 or unlabeled (control)
- ant treatment - whether the tree that the sample came from was at the uninvited site or invaded site
- herbivore treatment - whether the tree that the sample came from was exposed to herbivores or not
- at-% 13C - the atom % 13C of the sample
- prop13C - the proportion of the sample that is 13C relative to 12C
- total C_ug - the total amount of C in the sample in micrograms
- ug 13C in sample - the amount of micrograms in the sample
- sample weight_g - the weight of the sample in grams
- estimated ant biomass_g - the estimated total ant biomass of the labeled tree based on allometry
- ug 13C in ants per tree - the total amount of 13C in the ant colony in micrograms
- g 13C in ants per tree - the total amount of 13C in the ant colony in grams
- difference_control_label - the difference in g of 13C in the ants on the tree between the control tree and labeled tree. Only trees in the label labeling treatment contain a value because this column (difference_control_label) shows the difference between g 13C in ants per tree in the labeled tree and paired control, which is located one row below each labeled tree.
- 13C_uptake_g - the amount of g of 13C that the labeled tree took up. This only applies to trees in the label labeling treatment, as 13CO2 was not added to control trees.
- percent_newC_to_ants - the percentage of the added 13C that is in ants on the labeled tree. This only applies trees in the label labeling treatment, as 13CO2 was not added to control trees.

DATA-SPECIFIC INFORMATION FOR: 13C_stem_investment.xlsx

Number of variables: 17
Number of cases/rows: 6
Variable List:
- treatment- whether the sample comes from a control tree or labeled tree
- sample - the name of the sample
- labeling treatment - whether the tree that the sample comes from was labeled with 13CO2 or unlabeled (control)
- ant treatment - whether the tree that the sample came from was at the uninvited site or invaded site
- herbivore treatment - whether the tree that the sample came from was exposed to herbivores or not
- at-% 13C - the atom % 13C of the sample
- prop13C - the proportion of the sample that is 13C relative to 12C
- totalC_ug - the total amount of C in the sample in micrograms
- ug_13C_in_sample - the amount of 13C in micrograms in the sample
- g_13C_in_sample - the amount of 13C in grams in the sample
- sample weight_g - the weight of the sample in grams
- 13C_prop_sample - the proportion of 13C to sample weight in the sample
- estimated_stem_biomass_g - the estimated total stem biomass of the labeled tree based on allometry
- g_13C_stem - the total amount of 13C in the stem of the whole tree
- difference_control_label - the difference in g of 13C in the ants on the tree between the control tree and labeled tree. Only trees in the label labeling treatment contain a value because the it is the difference between g_13C_stem in the labeled tree and paired control, which is located one row below each labeled tree.
- 13C_uptake_g - the amount of g of 13C that the labeled tree took up. This only applies to trees in the label labeling treatment, as 13CO2 was not added to control trees.
- percent_newC_to_stem - the percentage of the added 13C that is in stem on the labeled tree. This only applies trees in the label labeling treatment, as 13CO2 was not added to control trees.