Harvard Forest

Data Archive

HF449

Effects of Long-Term Soil Warming on Ecosystem Function at Harvard Forest 2019

Related Publications

Data

• hf449-01: ecosystem functionality measurements (preview)

Overview

• Lead: Kristen DeAngelis
• Investigators: Luiz Domeignoz-Horta
• Contact: Information Manager
• Start date: 2019
• End date: 2019
• Status: completed
• Location: Prospect Hill Tract (Harvard Forest)
• Latitude: +42.54 degrees
• Longitude: -72.18 degrees
• Elevation: 365 meter
• Datum: WGS84
• Taxa:
• Release date: 2024
• Language: English
• EML file: knb-lter-hfr.449.1
• DOI: digital object identifier
• EDI: data package
• DataONE: data package
• Related links:
• Carbon Cycle Dynamics in Soil Warming Experiments at Harvard Forest 2019
• Study type: short-term measurement
• Research topic: forest-atmosphere exchange; large experiments and permanent plot studies; soil carbon and nitrogen dynamics
• LTER core area: organic matter movement
• Keywords: climate change, microbes, soil carbon, soil nitrogen, soil warming
• Abstract:

  Across biomes, soil biodiversity promotes ecosystem functions. However, whether this relationship will be maintained within ecosystems under climate change is uncertain. Here, using two long-term soil warming experiments, we investigated how warming affects the relationship between ecosystem functions and bacterial diversity across seasons, soil horizons, and warming duration. Soils were sampled from these warming experiments located at the Harvard Forest Long-Term Ecological Research (LTER) site, where soils had been heated +5°C above ambient for 13 or 28 years at the time of sampling. We assessed seven measurements representative of different ecosystem functions and nutrient pools. We also surveyed bacterial community diversity. We found that ecosystem function was significantly affected by season, with autumn samples having a higher intercept than summer samples in our model, suggesting a higher overall baseline of ecosystem function in the fall. The effect of warming on bacterial diversity was similarly affected by season, where warming in the summer was associated with decreased bacterial evenness in the organic horizon. Despite the decreased bacterial evenness in the warmed plots, we found that the relationship between ecosystem function and bacterial diversity was unaffected by warming or warming duration. Our findings highlight that season is a consistent driver of ecosystem function as well as a modulator of climate change effects on bacterial community evenness.

• Methods:

  Experimental design and soil sampling

  Soil samples were collected from two long-term warming soil experiments located at the Harvard Forest in Petersham, MA (42°30′30′′N, 72°12′28′′W), as described in Domeignoz-Horta et al. (2023). The Prospect Hill Soil Warming Study was established in 1991 (Melillo et al. (2002)), and the Soil Warming x Nitrogen Addition (SWaN) Study was established in 2006 (Contosta et al. (2011)). Warmed plots are heated continuously +5 °C above ambient using buried resistance cables placed 10 cm below the soil surface and spaced 20 cm apart. Soil samples were collected in 2019 on July 15th and October 19th, from Prospect Hill and SWaN, which had been warmed for 28 and 13 years, respectively, at the time of sampling. The experiments are located adjacent to one another and have the same dominant plant overstory (Acer rubrum, Betula lenta, Betula papyrifera, Fagus grandifolia, Quercus velutina, Quercus rubra) and soil type (coarse-loamy incepitsols). The temperature ranges from a mean low of 3.3 °C to mean high of 13.1 °C and mean annual precipitation, including snow, is 1107 mm distributed evenly across seasons. Both Prospect Hill and SWaN organic and mineral soils are acidic, with the organic horizon having pHs between 3.8 and 4.2 and the mineral soils having pHs between 3.9 and 4.4 (Pold et al. (2017), Anthony et al. (2020), Pec et al. (2021)). The organic horizon in the control, unheated plots has a depth of approximately 5 cm, and the organic horizon in the heated +5°C plots has a depth of approximately 2-3 cm (Pold et al. (2017)). Duplicate cores were taken from each plot to 10 cm depth using a 5.7 cm diameter tulip bulb corer. Cores were separated into the organic and mineral horizons, duplicate soil cores were pooled by depth increment, roots and rocks were removed, and then the soil was sieved less than 2 mm. After sieving, samples were kept at ambient temperature, and within 4 hours of collection, samples were taken back to the lab for further analyses. The full sampling design was two sites (Prospect Hill, SWaN) x two treatments (control, heated) x two seasons (summer, fall) x two sampling depths (organic horizon, mineral soil) x five replicate plots for a total of 78 samples (one sample from the SWaN experiment had a mineral horizon that was beyond the reach of the corer for the July sampling and this same plot was subsequently not sampled in October). Due to issues with sequencing library preparation, the final dataset had 69 samples.

  Ecosystem functionality measurements

  To assess ecosystem functionality, we utilized five soil properties or functions that were measured as a part of Domeignoz-Horta et al. (2023), including microbial biomass carbon, respiration, and the potential activities of four enzymes: phenol oxidase and peroxidase, β-glucosidase (BG), and N-acetyl-glucosaminidase (NAG). Additionally, we measured total soil organic carbon and total nitrogen. Altogether, there were seven different soil functions or properties measured for this study.

  To measure total soil organic C and N and soil water content, soils were weighed into pre-weighed aluminum tins and dried in a 65°C oven until they reached a constant mass the same day the samples were brought back to the lab. Constant mass was verified by weighing the soils multiple times throughout the drying process. The drying temperature was selected so soils could be utilized for a separate analysis that was performed in Domeignoz-Horta et al. (2023) but not included in this study. After the soils achieved a constant mass, the tins were weighed again. The dry soil weight was subtracted from the wet soil weight, then divided by the dry soil weight to calculate water content. For total C and N, the dried soils were ground to a fine powder using a mortar and pestle. The soil was then weighed and packaged in duplicate into tins, which were run on a Perkin Elmer 2400 Series II CHN Elemental Analyzer with acetanilide as a standard at the University of New Hampshire Water Quality Analysis Lab. Total C and total N or duplicates were averaged.

  Within three days of sampling, microbial biomass carbon was measured. Soils were stored at 15°C in the intervening time between sample collection and MBC measurement. The three day storage was to allow for similar treatment as samples used in carbon use efficiency calculations for Domeignoz-Horta et al. (2023). Four replicate soil samples were each split into two subsamples, with one group serving as a control and one group which was fumigated with chloroform vapors under vacuum pressure for 24 hours. Dissolved organic carbon (DOC) was then extracted from both the unfumigated and fumigated samples using 15 mls of 0.05 M K2SO4 and quantified on a Shimadzu TOC analyzer. Microbial biomass carbon was determined by subtracting the DOC concentration in the unfumigated subsample from the fumigated subsample. Soils were stored at room temperature (20 °C) overnight before being aliquoted for soil respiration measurements. Soil respiration was measured on triplicate subsamples (0.15 or 0.3 g for the organic horizon or mineral soil, respectively) that were placed into Hungate tubes. Tubes were then sealed and incubated at 15 °C for 24 hours. A 30 ml headspace sample was then taken and injected into an infrared gas analyzer (Quantek 906) to measure CO2 concentrations.

  Prior to extracellular enzyme activity assays, soils were stored for no more than 4 days at 15°C after soil sample collection. Potential extracellular enzyme activity was measured using fluorescent substrates. Soil slurries were prepared with 1.25 g wet weight soil and 175 mls of 50 mM pH 4.7 sodium acetate in a Waring blender. For the BG and NAG assays, 200 μls of soil slurry was pipetted into black 96 well plates, and for the oxidative enzyme assay, 500 μls of soil slurry was pipetted into deep well plates. Plates were then placed in a 15°C incubator for 25 minutes to allow for temperature acclimation. This temperature reflects the average air temperature between the summer sampling and the fall sampling. After temperature acclimation, either 50 μls of 4000 μM 4-methylumbelliferyl β-D-glucopyranoside, or 50 μls of 2000 μM 4-methylumbelliferyl N-acetyl-glucosaminidase were added to each well. For assessing phenol oxidase and peroxidase activity, 500 μls of 25 mM L-DOPA + 0.03% H2O2 were added to each well. Each plate contained a standard curve as well as a slurry-only control. All plates were read on a SpectraMax M2 plate reader. BG and NAG plates were measured at 360/450 nm excitation/emission wavelengths after substrate addition. Oxidative enzyme plates were incubated for 4 hours after substrate addition, and then 100 μls were removed, transferred to a clear 96 well plate, and read at 460 nm. Since phenol oxidase and peroxidase both act on L-DOPA and 0.03% H2O2, any enzyme activity measured using these substrates was called oxidative enzyme activity. All enzyme activity was normalized for each sample by the sample’s microbial biomass carbon.

  Ecosystem multifunctionality calculations

  Multifunctionality was calculated for the organic horizons and mineral soil in R using the multifunc package (Byrnes et al. (2014)). We included microbial biomass carbon, soil respiration, total carbon, total nitrogen, N-acetyl glucosaminidase activity, β-glucosidase activity, and oxidative enzyme activity in the ecosystem multifunctionality index. Microbial biomass carbon, soil respiration, N-acetyl glucosaminidase activity, β-glucosidase activity, and oxidative enzyme activity were measured and described in Domeignoz-Horta et al. (2023) (HF431). These functions represent both process rates (respiration, potential enzyme activity) and nutrient pools (total C, total N, microbial biomass) (Garland et al. (2021)). The organic horizon and mineral soil layers were analyzed separately due to documented differences in soil parameters (Pold et al. (2014)) and microbiome properties (DeAngelis et al. (2015), Roy Chowdhury et al. (2021)). A multifunctionality index was calculated for each sample by taking the average of the z-score transformed ecosystem functions. While there are different ways of assessing diversity-multifunctionality relationships, we selected the averaging approach for ease of interpretation.

• Organization: Harvard Forest. 324 North Main Street, Petersham, MA 01366, USA. Phone (978) 724-3302. Fax (978) 724-3595.

• Project: The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. (ROR).

• Funding: National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210, DEB-1832110.

• Use: This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.

• License: Creative Commons Zero v1.0 Universal (CC0-1.0)

• Citation: DeAngelis K. 2024. Effects of Long-Term Soil Warming on Ecosystem Function at Harvard Forest 2019. Harvard Forest Data Archive: HF449 (v.1). Environmental Data Initiative: https://doi.org/10.6073/pasta/7b6ac989890568841673d24c749118c2.

Detailed Metadata

hf449-01: ecosystem functionality measurements

1. sample: sample ID
2. site: experimental site sampled
   • PH: Prospect Hill
   • SWaN: Soil Warming and Nitrogen Addition
3. warming_treatment: warming treatment of sample
   • Control: control
   • Heated: heated +5°C above ambient
4. horizon: soil type of sample
   • Mineral: mineral soils
   • Organic: organic horizon
5. experiment_duration: length of experiment at time of sampling in years (unit: dimensionless / missing value: NA)
6. plot: plot number that sample came from
7. timepoint: month of sampling
8. timepoint_days: day of year of sampling (unit: nominalDay / missing value: NA)
9. mg_soil_rep_1: amount of dried soil analyzed in replicate 1 (unit: milligram / missing value: NA)
10. ug_C_rep_1: micrograms of carbon in replicate 1 (unit: microgram / missing value: NA)
11. ug_N_rep_1: micrograms of nitrogen in replicate 1 (unit: microgram / missing value: NA)
12. mg_C_per_g_soil_rep_1: amount of carbon in replicate 1 divided by the amount of soil analyzed in replicate 1 (unit: milligramPerGram / missing value: NA)
13. mg_N_per_g_soil_rep_1: amount of nitrogen in replicate 1 divided by the amount of soil analyzed in replicate 1 (unit: milligramPerGram / missing value: NA)
14. C_N_ratio_rep_1: ratio of milligrams of carbon per gram soil in replicate 1 to milligrams of nitrogen per gram soil in replicate 1 (unit: dimensionless / missing value: NA)
15. mg_soil_rep_2: amount of dried soil analyzed in replicate 2 (unit: milligram / missing value: NA)
16. ug_C_rep_2: micrograms of carbon in replicate 2 (unit: microgram / missing value: NA)
17. ug_N_rep_2: micrograms of nitrogen in replicate 2 (unit: microgram / missing value: NA)
18. mg_C_per_g_soil_rep_2: amount of carbon in replicate 2 divided by the amount of soil analyzed in replicate 2 (unit: milligramPerGram / missing value: NA)
19. mg_N_per_g_soil_rep_2: amount of nitrogen in replicate 2 divided by the amount of soil analyzed in replicate 2 (unit: milligramPerGram / missing value: NA)
20. C_N_ratio_rep_2: ratio of milligrams of carbon per gram soil in replicate 2 to milligrams of nitrogen per gram soil in replicate 2 (unit: dimensionless / missing value: NA)
21. MBC_std: z-score transformed microbial biomass carbon (unit: dimensionless / missing value: NA)
22. BG_std: z-score transformed ?-glucosidase activity (unit: dimensionless / missing value: NA)
23. NAG_std: z-score transformed N-acetyl glucosaminidase activity (unit: dimensionless / missing value: NA)
24. OX_std: z-score transformed oxidative enzyme activity (unit: dimensionless / missing value: NA)
25. respiration_std: z-score transformed soil respiration (unit: dimensionless / missing value: NA)
26. avg_C_std: z-score transformed mean milligrams carbon per gram soil (unit: dimensionless / missing value: NA)
27. avg_N_std: z-score transformed mean milligrams nitrogen per gram soil (unit: dimensionless / missing value: NA)
28. mean_function: ecosystem multifunctionality index (unit: dimensionless / missing value: NA)