DOI: 10.5061/dryad.x3ffbg7ws
title: Necromass mass loss and microbial abundance for necromass interactions study

description: Soil organic matter (SOM) is increasingly recognized as a key component of
 terrestrial carbon cycling, yet the relative contribution of microbial
 necromass—and especially fungal necromass—remains poorly understood. We
 produced fungal necromass of different biochemical quality (low vs. high
 melanin content) from Hyaloscypha bicolor and decomposed it in forest
 topsoil to study (i) how microbial decomposer and predator communities
 differ between soil and necromass, (ii) whether necromass-associated
 communities are subsets of bulk soil communities or contain additional
 “unseen” colonizers, and (iii) if microbial predators (protists,
 nematodes) exert top-down control on the necromass decomposers and
 necromass decomposition rates. Over two sampling times (4 and 12 weeks),
 necromass consistently exhibited rapid early mass loss, followed by
 reduced decay, and more strongly stabilized mass in high melanin residues.
 Quantitative PCR revealed substantially higher bacterial and fungal
 abundances in necromass relative to soil, especially for low melanin
 necromass. Metabarcoding showed distinct decomposer communities in
 necromass as compared to soil, with half or more of the observed necromass
 taxa absent in bulk soils at the site level. Necromass also supported
 differentiated predator communities, including a high nematode richness at
 early decay stages and a predominance of protist bacterivores. Structural
 equation modeling indicated that predator community composition influenced
 both bacterial and fungal abundance, and marginally significantly affected
 necromass decomposition rates. We conclude that fungal necromass acts as a
 microbial “hotspot” enriched in specialized decomposers and predators, and
 that predator–decomposer interactions can potentially regulate necromass
 decay. Our findings highlight the need to integrate top-down control and
 colonization processes into models of fungal necromass turnover and its
 ultimate contribution to soil organic carbon.
description: We conducted the decomposition experiment in a mixed-age white
 pine (<em>Pinus strobus</em>) forest at the Cedar Creek
 Ecosystem Science Reserve (Cedar Creek; 45°25' N, 93°10' W) in
 eastern Minnesota, USA. Cedar Creek is a 2300-ha site and National Science
 Foundation Long-Term Ecological Research site located on the Anoka Sand
 Plain, which is characterized by excessively drained soils containing up
 to 90% sand. In early August 2020, we buried mycobags containing either
 low- or high-melanin necromass within the top 5 cm of mineral soil in
 twelve plots, placing two mycobags of each necromass type per plot (48
 bags in total). We retrieved them after one and three months (i.e., 4 and
 12 weeks) on September 3 and November 5, 2020, respectively. These times
 were chosen based on previous necromass experiments, including at Cedar
 Creek, to capture the earlier and later stages of decomposition. Each
 retrieved bag was individually packaged, stored at 4°C, and promptly
 transported to the lab. One bag was lost during the course of the
 experiment and thus excluded from all analyses. In the lab, the remaining
 necromass was transferred to sterile 2 ml plastic tubes using a clean
 spatula. It was then freeze-dried for 3 days at -50degrees C, under
 vacuum. The final dry weight (mg) of necromass for each sample was then
 measured using an analytical microbalance and mass remaining was
 calculated as percentage of initial dry weight added to each
 bag.
description: # Necromass mass loss and microbial abundance for necromass interactions
 study
 [https://doi.org/10.5061/dryad.x3ffbg7ws](https://doi.org/10.5061/dryad.x3ffbg7ws) ## Description of the data and file structure We conducted the decomposition experiment in a mixed-age white pine (*Pinus strobus*) forest at the Cedar Creek Ecosystem Science Reserve (Cedar Creek; 45°25' N, 93°10' W) in eastern Minnesota, USA. Cedar Creek is a 2300-ha site and National Science Foundation Long-Term Ecological Research site located on the Anoka Sand Plain, which is characterized by excessively drained soils containing up to 90% sand. In early August 2020, we buried mycobags containing either low- or high-melanin necromass within the top 5 cm of mineral soil in twelve plots, placing two mycobags of each necromass type per plot (48 bags in total). We retrieved them after one and three months (i.e., 4 and 12 weeks) on September 3 and November 5, 2020, respectively. These times were chosen based on previous necromass experiments, including at Cedar Creek, to capture the earlier and later stages of decomposition (Cantoran et al., 2023). Each retrieved bag was individually packaged, stored at 4°C, and promptly transported to the lab. One bag was lost during the course of the experiment and thus excluded from all analyses. At each necromass sampling time, we also collected three soil cores (0–5 cm) from each plot, carefully removing any organic horizon. The cores were taken at least 50 cm from the buried mycobags to avoid local necromass effects. We pooled the three cores per plot into a single composite sample *in situ* (n = 24 total per sampling time), stored them at 4°C, and processed them within days of harvest. In the laboratory, necromass from each mycobag was carefully extracted with sterile pipette tips, transferred to sterilized 2 mL tubes, and stored at –20°C before freeze-drying. Soil samples were passed through a 2 mm mesh sieve, placed in 15 mL centrifuge tubes, and stored at –20°C prior to freeze-drying. ### Files and variables #### File: Data\_mass\_remaining.xlsx **Description:** Mass loss from fungal necromass. ##### Variables * Sample_ID (individual sample replicate) * Plot (plot replicate of mycobag or soil sample at site, n = 12) * Habitat (whether the sample was from low melanin necromass or high melanin necromass) * Incubation (whether sample came from 4 week harvest or 12 week harvest) * Necromass* *mass remaining (percentage of necromass mass remaining)  #### File: Data\_bacterial\_fungal\_abundances.xlsx **Description:** bacterial and fungal gene copy abundances on fungal necromass. ##### Variables * Sample_ID (individual sample replicate) * Plot (plot replicate of mycobag or soil sample at site, n = 12) * Habitat (whether the sample was from soil, low melanin necromass or high melanin necromass) * Incubation (whether sample came from 4 week harvest or 12 week harvest) * Bacterial abundance (log 16s gene copies/g dry mass) * Fungal abundance (log ITS gene copies/g dry mass) * Fungal to Bacterial Ratio (log ITS gene copies/g dry mass / log 16s gene copies/g dry mass) **Access information** Other publicly accessible locations of the data: * N/A Data was derived from the following sources: * N/A