Delta-15N values for leaf and soil samples from a mesocosm experiment looking at dung beetle presence and the movement of dung-derived nitrogen (DDN)

We deployed 18 mesocosms into each of the ecosystem types (logged forest and oil palm) in mid-May 2016, to give the soil one month to recover from the disturbance. We constructed mesocosms from black plastic containers, 40 cm diameter and 25 cm high after removing the base. We dug mesocosms 20 cm into the ground leaving 5cm above the surface. We arranged them in a 6 x 3 grid with a minimum of 3 m between each mesocosm to minimise interaction between the soil nutrient cycling in each mesocosm. As proximity of the seedlings to mature trees may increase competition for nitrogen and other nutrients we recorded the distance of each mesocosm to the nearest mature tree (any species with diameter at breast height > 30 cm) for inclusion in our analyses. We randomly selected 12 of the mesocosms, to receive 15N-labelled dung patties weighing 300 ± SD 2.27 g in logged forest and 410 ± SD 2.04 g in oil palm. We populated six randomly selected mesocoms from within those 12 treated with dung with a standardised dung beetle communities (Fig. 1, Table S2). The remaining six mesocosms were left as soil only controls. We covered each mesocosm with a fine nylon mesh secured with a rubber belt to prevent beetles leaving or colonising the mesocosms, and to standardise any microclimatic effects between treatments. However, after 48 hours we opened the dung beetle treatments for a 24 hours period to allow the beetles to emigrate rather than forcing them to artificially stay in the same pat (cf. Roslin 2000; Slade et al. 2017), and then re-covered the mesocosms with netting. We sampled soil seven times from logged forest over the course of the experiment. Any remaining surface dung was removed prior to soil sampling, and replaced thereafter, in order to reduce the possibility of contamination. If a soil core was unsuccessful (most likely due to beetle channels) a second core was taken directly beside. On each sample day, a core of 10cm depth was taken and split into vertical horizons 0- 2cm, 2-5 cm and 5-10cm. We sampled leaves eight times over the eight-month duration of the experiment, with high frequency during the first month, aimed to capture the initial assimilation of DDN into the plants. We collected one leaf from the Dipterocarpaceae or palm seedlings for each sample event. For dipterocarp seedlings we alternated collection of the terminal leaf from top and bottom (leaving the topmost, newest leaf) between consecutive sample days, and for palm seedlings we sampled the two penultimate leaflets from alternating sides of the mid-stem, from the youngest fully formed frond. As assimilated 15N did not plateau in logged forest during the 8-month timeframe of the experiment, we took a sample after 21 months in order to determine whether all DDN had been turned over in the plant biomass after this time. The leaf and soil samples were dried at 60°C for a minimum of 48 hours. We then ground samples to a fine powder using a ball mill (Retsch UK Ltd., Hope, UK). We weighed ground samples into 6 x 4 mm ultraclean tin capsules (Elemental Microanalysis Ltd., Okehampton, UK) using an ultra-microbalance with readability 1 μg (Mettler-Toledo, Greifensee, Switzerland) to provide sufficient elemental carbon and nitrogen for analysis by continuous flow isotope ratio mass spectrometry (SERCON, Crewe, UK). Isotope ratios are expressed in per mil (‰) relative to international reference standards (Rstandard), which are Atmospheric Nitrogen and Vienna PeeDee Belemnite (VPDB) for nitrogen and carbon, respectively. The delta value describes the isotopic composition of each sample, which signifies a measurement of difference relative to laboratory standards. The calculation of δ values is given by: δHX = [(RSAMPLE /RSTANDARD −1)]*1000

Authors

• Kemp, Victoria — Queen Mary University of London
• Bernard, Henry — Universiti Malaysia Sabah
• Kratina, Pavel — Queen Mary University of London
• Grey, Jonathan — Lancaster University
• Slade, Eleanor — National University of Sinagpore, University of Oxford

Keywords

• dung beetles
• nitrogen
• forest
• function
• mineralisation
• oil palm
• agriculture
• 15N
• stable isotope
• SAFE project
• HTMF

Funders

• NERC (NE/K016148/1)

Permits

• Research — Sabah Biodiversity Centre (SABC) (JKM/MBS.1000-2/2 (374) )
• Research — Sabah Biodiversity Centre (SABC) (JKM/MBS.1000-2/2 JLD.4 (41))
• Research — Sabah Biodiversity Centre (SABC) (JKM.1000-2/2 JLD.5 (153))

Worksheets

Files

• 3_Kemp_15N_mesocosms_data.xlsx

Taxa

0 GBIF taxa, 0 sequence-derived taxa.