DOI: 10.5061/dryad.2280gb64q
title: Carbon and nitrogen dynamics in subsoils after 20 years of added precipitation in a Mediterranean grassland

description: Precipitation is a major driver of ecosystem change and the
 physicochemical characteristics of soil. Under different climate change
 scenarios, increased drought frequency and changing precipitation are
 predicted to impact Mediterranean ecosystems, including in Northern
 California. Studies based on two major climate models examined the impact
 of increased precipitation in parts of California, where the additional
 precipitation occurred during winter or spring months. It was found that
 altering precipitation seasonality has significant impacts on plant
 community dynamics, microbial and fungal dynamics, and abiotic soil
 processes. Subsoils are large carbon reservoirs. However, most studies
 investigating precipitation effects on soil organic matter (SOM) primarily
 focus on near-surface soils. Recent studies indicated different responses
 to environmental perturbation in surface (&lt;30 cm) versus deep soils
 (&gt;30 cm) due to important differences in physicochemical
 characteristics. Here, we present soil data at depth (~300 cm) from a
 20-year precipitation manipulation experiment. We determined changes in
 total elemental concentration and stable isotope composition of soil C, N,
 δ13C, and δ15N for ambient control vs. additional precipitation in the
 winter and spring months. The addition of winter precipitation resulted in
 the largest cumulative C stock (0–300 cm); however, there were no
 statistically significant changes in carbon stock throughout the depth
 profile. However, there was evidence for vertical translocation of carbon
 to deep soil layers, specifically of plant-derived carbon, with both
 winter and spring precipitation additions. The precipitation addition in
 winter also resulted in the highest subsoil carbon stock compared to the
 control (ambient) and spring treatments. Overall, added winter
 precipitation led to the best conditions for carbon accumulation since the
 added precipitation coincides with lower temperatures and improved growing
 conditions at our field site. This study highlights the importance of the
 timing of precipitation events, especially with regard to deep carbon
 stocks (&gt;1 m).
description: # Carbon and nitrogen dynamics in subsoils after 20 years of added
 precipitation in a Mediterranean grassland There are 4 xlsx files
 associated with this dataset: * Sample_Metadata_Precipitation_Expt.xlsx
 gives associated metadata with each sample ID. This metadata includes the
 location where it was sampled, the replicate, the depth, and so on. -
 FTIR_elemental_data_merged.csv gives all the isotopic, elemental, and FTIR
 data associated with each sample ID. NAs refer to missing or lacking data.
 This data sheet partially represents data that comes out of the Stable
 Isotope Ecosystem Laboratory at UC Merced, with metadata attached for each
 sample. The measurements included in this datasheet (C% and N%) make it
 possible to calculate carbon stocks, an important bulk density-corrected
 factor, for each site. Measurements of stable isotopes δ13CC andδ15NN were
 also important markers of decomposition and turnover for the sites we were
 analyzing. This isotopic and elemental base has been merged with DRIFTS
 data (Diffuse Reflectance Fourier Transformed Spectroscopy). This data
 gives information on the presence of certain key function groups present
 in organic matter. Columns in this dataset with the int\_ prefix refer to
 integrated peak areas for spectral ranges of interest (these are defined
 in the associated publication). We then calculated proportions of our peak
 areas of interest, which are the columns that have \_prop suffixes. -
 mean_cstock_300cm.csv reports the mean carbon stock and standard error for
 each 10cm interval for each treatment (control, spring, winter) -
 mean_BD_WC_pH.csv reports the mean and standard error for each physical
 and chemical parameter for each 10cm interval. These parameters include
 bulk density, water content, and pH in H2O and CaCl2. #### Description of
 the data and file structure The information included in
 Sample_Metadata_Precipitation_Expt is largely descriptive. This
 information is largely redundant and is also included in the files with
 elemental/isotopic data. The sample ID column in this file refers to the
 unique 3-digit code I assigned every sample I collected. The field site
 column refers to the site at which the sample was collected. The replicate
 column refers to the numbered replicate it was at that particular field
 site. The date collected column refers to the calendar date the sample was
 collected on. The depth column refers to the depth at which the sample was
 collected in cm. The raw data for the elemental and isotopic analyses are
 included in FITR_elemental_data_merged. The identifier column in this
 dataset refers to the unique identifier assigned by the Stable Isotope lab
 at UC Merced. The Sample ID refers to the unique 3-digit code assigned to
 each sample. The amount column refers to the mass of sample in mg that was
 weighed and combusted for the elemental analysis. The Area 28 column is
 the area under the curve for the N2 peak, and is used to compute the
 d15N_corrected within the isotope lab software. The Area 44 column is the
 curve for the CO2 peak, and is used to compute the d13C_corrected within
 the isotope lab software. The d13C_corrected is the stable isotope value
 in per mil. The d15N corrected is the stable isotope value in per mil. The
 N_wt_percent value is the N content of the sample reported as percent (%).
 The C_wt_percent value is the C content of the sample reported as percent
 (%). The C/N is the C: N ratio computed based on the N and C weight
 percents. The C_stock is the computed C stock value with a coarse fraction
 correction, and reported as g/cm^2. The C_stock_CF column is the computed
 C stock value without a coarse fraction correction, reported as g/cm^2.
 The rest of the columns in this data are from
 Sample_Metadata_Precipitation_Exp, and are described in the above
 paragraph. The mean_cstock_300cm file includes data to compute C stocks.
 The treatment column in this file refers to field water addition treatment
 (Control, Winter, Spring). Bulk density refers to the bulk density
 (reported as g/cm^3) collected. The coarse fraction refers to the
 lab-measured coarse fraction (reported as a fraction, unitless). The
 C_stock is the mean computed C stock value and reported as g/cm^2 for each
 10cm depth interval. All missing data represented as NA. The mean_BD_WC_pH
 file is the mean data for three key physical and chemical parameters for
 soils at this site. Namely, Bulk Density (reported as g/cm^3), Water
 Content (reported as g/g), and pH in both H2O and CaCl2. This sheet
 reports mean values for each of these characteristics for each treatment.