uid=HFR,o=lter,dc=ecoinformatics,dc=org all public read doi:10.6073/pasta/c9c607f39797fd87bd275dac95a8ab02 Edward Brzostek https://orcid.org/0000-0002-2964-0576 Adrien Finzi https://orcid.org/0000-0003-2220-4533 John Drake Researcher Allison Greco Researcher 2023 English

The exudation of carbon (C) by tree roots stimulates microbial activity and the production of extracellular enzymes in the rhizosphere. Here, we investigated whether the strength of rhizosphere processes differed between temperate forest trees that vary in soil organic matter (SOM) chemistry and associate with either ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi. We measured rates of microbial and extracellular enzyme activity, and nitrogen (N) availability in samples of rhizosphere and bulk soil influenced by four temperate forest tree species (i.e., to estimate a rhizosphere effect). The magnitude of the rhizosphere effects could not be easily characterized by mycorrhizal associations or SOM chemistry. Ash had the lowest rhizosphere effects and beech had the highest rhizosphere effects, representing one AM and one ECM species, respectively. Hemlock and sugar maple had equivalent rhizosphere effects on enzyme activity. However, the form of N produced in the rhizosphere varied with mycorrhizal association. Enhanced enzyme activity primarily increased amino acid availability in ECM rhizospheres and increased inorganic N availability in AM rhizospheres. These results show that the exudation of C by roots can enhance extracellular enzyme activity and soil-N cycling. This work suggests that global changes that alter belowground C allocation have the potential to impact the form and amount of N to support primary production in ECM and AM stands.

amino acids microbes mycorrhizae nitrogen rhizosphere soil water content LTER controlled vocabulary organic matter LTER core area Harvard Forest HFR LTER USA HFR default

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.

Creative Commons Zero v1.0 Universal https://spdx.org/licenses/CC0-1.0.html CC0-1.0 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf251 Prospect Hill Tract (Harvard Forest), Pisgah State Forest (NH). Coordinates based on WGS84 datum. -72.45 -72.18 +42.87 +42.50 2008 2010 genus Acer species saccharum sugar maple genus Fagus species grandifolia american beech genus Fraxinus species americana white ash genus Quercus species rubra red oak genus Tsuga species canadensis eastern hemlock complete Information Manager Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 hf-im@lists.fas.harvard.edu Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu

This research was conducted at two sites, the Harvard Forest and the Pisgah State Forest. The sites have similar land use history and stand age. Soils at both sites are inceptisols classified as Typic Dystrochrepts derived from glacial till overlying granite-schist-gneiss bedrock. Study plots dominated by one of five target tree species were identified at each site. Plots of sugar maple (Acer saccharum) and American beech (Fagus grandifolia) were located in Pisgah State Forest. Plots of eastern hemlock (Tsuga canadensis), red oak (Quercus rubra), and white ash (Fraxinus americana) were located in the Harvard Forest. These species differed in mycorrhizal association, with ash and sugar maple supporting AM fungi and hemlock and beech supporting ECM fungi. Further, hemlock and beech have recalcitrant leaf litter and SOM that is characterized by higher ratios of C-to-N and lower pH than sugar maple and ash. At each site we located six replicate, 8-m radius, monodominant plots within larger mixed hardwood/conifer stands where the target tree species constituted 100 % of standing basal area in the inner 5-m core and 80 % in the entire 8-m radius plot.

Soil samples were collected in May, June, and August of 2010 from each of the six replicate plots for each species. We chose the May, June and August time-points because they span the majority of the growing season and are coincident with major phenological events, including leaf out, peak leaf area index, and the start of the seasonal decline in C uptake at the Harvard Forest, respectively. At each sampling point, we collected the top 15 cm of mineral soil using a 5-cm diameter soil bulk-density sampler from each plot. The samples were processed in the laboratory within 24 h of collection. We separated the mineral soil horizons into rhizosphere and bulk soil fractions. Fine roots were removed from each sample. Soil adhering to fine roots was operationally classified as rhizosphere soil.The remaining soil was defined as the bulk soil fraction. After separation, the bulk soil fraction was then sieved through a 2-mm mesh.

The 2 M KCl extractable pool size of amino acids was determined for every soil sample across the three sampling dates. Eight grams of each mineral soil fraction were extracted in 30 mL of 2 M KCl. The concentration of amino acids for all extracts was quantified using the o-phthaldialdehyde and b-mercaptoethanol (OPAME) method. Concentrations of amino acid N were determined by comparing the fluorescence of the samples relative to a standard curve composed of glycine.

We assayed proteolysis following a method modified from Watanabe and Hayano (1995) and Lipson et al. (1999) for every soil fraction and sample date. Initial and incubated subsamples (2–3 g) received 10 ml of a 0.5 mM sodium acetate buffer (pH 5.0) with a small volume of toluene (400 μL) added to inhibit microbial uptake. After the reagent addition, the initial samples were immediately terminated and the incubated subsamples were incubated at 23°C for 4 h. Enzyme activity in all the initial and incubated subsamples was terminated through the addition of 3 mL of a trichloroacetic acid solution. Proteolytic rates for each soil were calculated from the difference between amino acid concentrations in the incubated and initial subsamples of each soil assayed using the OPAME method. For every soil fraction at each sample date, we also assayed the potential activities of the chitinolytic enzyme, n-acetyl-glucosaminidase (NAG) and acid phosphatase and the lignolytic enzymes, phenol oxidase and peroxidase. All the assays were run using a 1 g subsample of each soil homogenized in a pH 5.0 sodium acetate buffer at 23°C. NAG and acid phosphatase activities were determined using a fluorometric microplate assay, while phenol oxidase and peroxidase activities were determined using a colorimetric microplate assay.

Subsamples of fresh soils (5-10g) were weighed and then dried in an oven at 60°C for 48 hours to determine soil moisture content.

Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu https://ror.org/059cpzx98 pointOfContact 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. National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210. hf251-01-soil-moisture.csv soil moisture hf251-01-soil-moisture.csv 1964 d0b46ca1b6ccb50d257f68c89d915011 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p25/hf251/hf251-01-soil-moisture.csv species tree species ACSA sugar maple FAGR American beech FRAM white ash TSCA eastern hemlock NA missing value horizon soil horizon B mineral soil (bulk) O organic horizon NA missing value site site site NA missing value year year of measurement YYYY 1 year NA missing value may.avg soil moisture content measured in May, average of 6 plots (%) dimensionless 0.00000001 real NA missing value may.se standard error on soil moisture content average of 6 plots, measured in May (%) dimensionless 0.000000001 real NA missing value june.avg soil moisture content measured in June, average of 6 plots (%) dimensionless 0.00000001 real NA missing value june.se standard error on soil moisture content average of 6 plots, measured in June (%) dimensionless 0.000000001 real NA missing value august.avg soil moisture content measured in August, average of 6 plots (%) dimensionless 0.00000001 real NA missing value august.se standard error on soil moisture content average of 6 plots, measured in August (%) dimensionless 0.000000001 real NA missing value 18 hf251-02-enzyme-activity.csv enzyme activity hf251-02-enzyme-activity.csv 23331 a1e1d333dfaf5114fdf4049f79eb0061 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p25/hf251/hf251-02-enzyme-activity.csv year year of sampling YYYY 1 year NA missing value month month of sampling month of sampling NA missing value site site site NA missing value species tree species ASCA sugar maple FAGR American beech FRAM white ash TSCA eastern hemlock QURU red oak NA missing value plot plot number plot number NA missing value soil soil B mineral soil (bulk) O organic horizon R mineral soil (rhizosphere) NA missing value proteolysis proteolysis, the rate of protein depolymerization into free amino acids (converted to μg amino-acid-N/g dry soil/per hour) microgramPerGramPerHour 0.000000001 real NA missing value aa extractable amino acid concentration microgramsPerGram 0.000000001 real NA missing value nag b-N-acetylglucosaminidase activity micromolePerGramPerHour 0.000000001 real NA missing value ap acid phosphatase activity micromolePerGramPerHour 0.000000001 real NA missing value phenox phenol oxidase activity micromolePerGramPerHour 0.000000001 real NA missing value perox peroxidase activity micromolePerGramPerHour 0.000000001 real NA missing value 234 soil short-term measurement https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf180