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Harvard Forest Data Archive
Root and Mycorrhizal Respiration at Harvard Forest Soil Warming Experiments 2007-2008Related Publications
- Lead: Andrew Burton, Jerry Melillo, Serita Frey
- Investigators: Sarah Butler, Carley Kratz
- Contact: Andrew Burton
- Start date: 2007
- End date: 2008
- Status: completed
- Location: Prospect Hill Tract (Harvard Forest), Slab City Tract (Harvard Forest)
- Latitude: +42.48 to +42.54
- Longitude: -72.18
- Elevation: 295 to 365 meter
- Release date: 2011
- EML file: knb-lter-hfr.171.8
- DOI: digital object identifier
- Related links:
- Barre Woods Soil Warming Experiment at Harvard Forest since 2001
- Prospect Hill Soil Warming Experiment at Harvard Forest since 1991
- Soil Warming Plus Nitrogen Addition Experiment at Harvard Forest since 2006
- Study type: long-term measurement
- Research topic: large experiments and permanent plot studies
- LTER core area: primary production
- Keywords: mycorrhizae, nitrogen, roots, soil respiration, soil temperature, soil warming
Soil heating typically causes large initial increases in soil respiration, with the enhancement lessening over time. This transient response is attributed to rapid decomposition of labile soil C compounds in the first years of heating, but the potential role of changes in root and mycorrhizal respiration is not well understood. To assess the degree to which root respiration adjusts to warmer soil temperature regimes, specific root respiration rates (nmol CO2/g/s) are being measured in three soil warming experiments at Harvard Forest. Soils in the experiments had been heated since 1991, 2003 and 2006. Respiration rates for fine roots (less than 1 mm) from control and heated plots were measured both at a common reference temperature of 18 deg C and at the ambient soil temperature of the measurement date for the control and heated (+ 5 deg C) treatments. Mycorrhizal respiration is being assessed through the use of hyphal ingrowth bags which allow determination both mycorrhizal hyphal biomass and respiration rate. Changes in mycorrhizal community composition are also being investigated.
Specific questions we will address include: Does rapid temperature acclimation occur in roots of large perennial woody plants? How do root biomass, root N concentration, and root respiration rates adjust to long-term changes in soil temperature and moisture and concomitant changes in N availability? How is mycorrhizal biomass and activity influenced by the effects of warmer soil temperatures on host C balance and soil N availability? How do the short- and long-term responses of roots and mycorrhizae to warming and associated changes in soil nutrient cycling affect soil CO2 efflux and C availability for aboveground NPP? Are the interrelationships between warmer soil temperature regimes and C fluxes to and from roots and mycorrhizae adequately described by current ecophysiological models?
This study utilized the control and heated plots of three soil warming experiments at Harvard Forest. The experiments use buried heating cables to warm the soil to a target of 5 deg C above ambient soil temperature. The warming experiments vary in age and size of treated area and include: a study with warming initiated in 1991 that utilizes 6 m x 6 m plots, with six replicates per treatment (Prospect Hill); a study with warming initiated in 2003 that uses large, 30 m x 30 m, unreplicated control and heated plots (Barre Woods); and an experiment with warming and nitrogen addition initiated in 2006, with 3 m x 3 m plots and six replicates per treatment (also at Prospect Hill). Specific root respiration rates per gram dry weight were determined at the ambient soil temperature of the control and heated plots on the measurement date and at a constant reference temperature of 18 deg C. Measurements at a constant reference temperature are considered to be one of the most reliable tests for the occurrence of partial acclimation in response to either seasonal changes in temperature or to warming treatments.
Respiration rates were measured using excised roots collected with 5 cm diameter x 10 cm deep soil cores periodically during the snow-free season from Septemer 2007 through May 2010. Samples of fine roots (less than 1 mm diameter) and larger diameter roots (1-3 mm, beginning in 2009) were hand sorted from the cores and brushed free of adhering soil and organic matter, with approximately 2 g fresh weight placed in a respiration cuvette attached to an infrared gas analyzer. Respiration was analyzed at a CO2 concentration of 1000 ppm which approximates the concentrations typically found near the soil surface in northern hardwood forests. The base of the aluminum root respiration cuvette was either inserted into a water bath to maintain the target measurement temperature for the sample. All samples were subsequently returned to the laboratory where sample dry weight was determined and samples were analyzed for N concentration using an elemental analyzer. On each sampling date, one sample was taken from each of the six control and six heated plots from the 1991 experiment. For the 2003 large plot experiment, root samples from six separate subplots within each large plot were measured. Sampling intensity for the 2006 experiment varied from two to six subplots per sample date.
The respiration of autotrophic mycorrhizal fungi is measured using hyphal in-growth bags beginning in 2010. These 75 cm3 cylindrical bags are made out of a fine pore nylon mesh, which excludes the growth of woody roots. The in-growth bags are filled with sand that has been sieved to 500 um grain size, acid washed and muffled to remove any organic and inorganic nutrients. The hyphal in-growth bags are autoclaved before they are buried in the soil to ensure sterility. The in-growth bags are buried 5 cm below the soil surface and incubate in the soil for approximately 3 months before being removed. Upon removal from the soil, the contents of the bag are poured into a 10 cm diameter PVC cap, which acts as a custom chamber for respiration measurements with an infra-red gas analyzer. The CO2 flux from each hyphal in-growth bag is measured at the bag temperature for 10 minutes. Twelve of these hyphal in-growth bags were installed in heated plots and 12 in control plots in the 1991 experiment at Prospect Hill (two per plot). One bag per each of twelve subplots per treatment is used in the 2003 Barre Woods experiment.
The biomass of mycorrhizal fungi also is quantified using the hyphal in-growth bags. Filter floatation and phosopholipid fatty acid analysis are used to estimate the fungal biomass in each in-growth bag. The phospholipid fatty acid analysis is carried out using the sand from the hyphal in-growth bags to quantify the amount of fungal biomass. In the filter floatation method the sand contents of the bag are washed into a 2 L beaker containing approximately 500 mL of tap water. Any hyphae remaining on the mesh in-growth bag are removed with tweezers. The mixture of sand and hyphae is stirred and then poured over a glass fiber filter under a vacuum. This procedure is repeated three times to remove any detectable amount of hyphae from the residual sand
Changes in the soil microbial community structure are evaluated using metagenomic and phospholipid fatty acid analysis. Phospholipd fatty acid analysis is carried out using fatty acid methyl ester markers for gram negative bacteria, gram positive bacteria, actinomycetes, arbuscular mycorrhizal fungi and other ectomycorrhizal and saprotrophic fungal groups. The metagenomic analysis is carried out using a targeted pyrosequencing approach. Pyrosequencing is a high-throughput method which will allow a large number of sequences to be acquired in a cost effective and timely manner. To examine the metagenome present in the soil, taxon specific primers are used to obtain bacterial, archaeal and eukaryotic rRNA sequences. Soil samples from each plot are pooled and an end-tagged label is ligated to the primer for each of the pooled samples, which are then be multiplexed for sequencing. The end-tagged labels permit each sequence to be matched to its corresponding sample during data analysis. Poor quality reads are filtered out of the data set and the remaining sequences are aligned to the sequences of known genomes with the aid of existing algorithms which are modified as necessary according to the complexity of the data set. The Joint Genome Institute (JGI) national user facility has a pyrosequencing platform that can provide sequences of sufficient length for a comparative analysis of the metagenome present in the soil. Metagenomic analyses is conducted on soils a composite sample consisting of ten soil cores with 1 cm diameter and 10 cm soil depth from each of the six heated and six control plots from the 1991 Prospect Hill experiment, and from six subplots per treatment at the 2003 Barre Woods experiment.
This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.
Burton A, Melillo J, Frey S. 2011. Root and Mycorrhizal Respiration at Harvard Forest Soil Warming Experiments 2007-2008. Harvard Forest Data Archive: HF171.
hf171-01: root respiration
- date: date
- year: year
- month: month
- day: day
- site: site
- PH: Prospect Hill Soil Warming Experiment
- BW: Barre Woods Soil Warming Experiment
- SW: Soil Warming Plus Nitrogen Addition Experiment
- treatment: treatment
- Control: non-warmed soil, no heating cable installation
- Heated: heated 5 deg C over control with resistance heating cables at 10 cm
- HeatplusN: nitrogen addition of 5 g N/m2/y as NH4NO3
- Nitrogen: nitrogen addition of 5 g N/m2/y as NH4NO3
- plot: subplot from which sample was taken
- temp.code: code for targeted measurement temperature
- Amb: ambient soil temperature at 5 cm for treatment on day of measurement
- Ref: standard reference temperature of 18 deg C
- root.diam: root diameter class
- less than 1: less than one mm
- 1 to 3: 1 to 3 mm
- root.resp: specific root respiration rate (unit: nanomolesPerGramPerSecond / missing value: NA)
- temp: actual temperature at which sample was measured (unit: celsius / missing value: NA)
- n.conc: root nitrogen concentration (unit: gramsPerKilogram / missing value: NA)