Stable C isotope data of southern mixed-grass prairie vegetation from Oklahoma, United States

Stable carbon isotopic data (δ13C) of 41 individual plant species was collected from long-term grazed and ungrazed pastures in Oklahoma, USA. These data can serve as a library of stable carbon isotope values for Southern mixed-grass prairie species. Seventeen warm-season (C4) and twenty-four cool-season (C3) plants were identified and collected from the United States Department of Agriculture (USDA) Southern Plains Experimental Range (SPER). Plant samples were dried at 55°C, and ground finely. The δ13C isotopic compositions were determined using a Europa Scientific automated nitrogen carbon analyzer (ANCA/NT) with a Solid/Liquid Preparation Module (Dumas combustion sample preparation system) coupled to a Europa 20–20 Stable isotope analyzer continuous flow isotope ratio mass spectrometer (Sercon Ltd, formerly Europa Scientific Ltd., Crewe, England). These data can be used as end members in isotopic mixing models or in paleoecology to correlate soil ages with plant species composition. Data from plant species provides information about soil organic carbon sequestration and possible long-term climate change.


a b s t r a c t
Stable carbon isotopic data ( δ 13 C) of 41 individual plant species was collected from long-term grazed and ungrazed pastures in Oklahoma, USA. These data can serve as a library of stable carbon isotope values for Southern mixed-grass prairie species. Seventeen warm-season (C 4 ) and twenty-four cool-season (C 3 ) plants were identified and collected from the United States Department of Agriculture (USDA) Southern Plains Experimental Range (SPER). Plant samples were dried at 55 °C, and ground finely. The δ 13 C isotopic compositions were determined using a Europa Scientific automated nitrogen carbon analyzer (ANCA/NT) with a Solid/Liquid Preparation Module (Dumas combustion sample preparation system) coupled to a Europa 20-20 Stable isotope analyzer continuous flow isotope ratio mass spectrometer (Sercon Ltd, formerly Europa Scientific Ltd., Crewe, England). These data can be used as end members in isotopic mixing models or in paleoecology to correlate soil ages with plant species composition. Data from plant species provides information about soil organic carbon sequestration and possible long-term climate change.
© 2020 Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license. ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Table   Subject Agricultural and Biological Sciences Specific subject area Soil Science Type of data

Value of the Data
• Stable carbon isotopes ( δ 13 C) are used across a wide variety of disciplines of agricultural, ecological, physiological sciences to infer biological, climate, and soil processes, but are expensive and time-consuming to obtain. • Researchers in geography, paleoecology, and soil science could use these individual plant species to complement their own work. • Data from individual plant species provides information about soil organic carbon sequestration and possible long-term climate change. • These data can be used as end members in isotopic mixing models or in paleoecology to correlate soil ages with plant species composition.

Data Description
This article contains summarized delta 13 C ( δ 13 C) of C 4 and C 3 plant species from the Southern Plains Experimental Range, Oklahoma, United States ( Table 1 ). Forty one individual plant species were collected in 2007 and 2008 from long-term grazed and ungrazed pastures comprising seventeen warm-season (C 4 ) and twenty-four cool-season (C 3 ) plants. Plant samples were Table 1 Delta 13 C ( δ 13 C) of C 4 and C 3 species from the Southern Plains Experimental Range.

Experimental Design, Materials and Methods
Field sampling and design for these data are described in detail in Follett et al. [2] . This study was conducted on the United States Department of Agriculture (USDA) Southern Plains Experimental Range (SPER), 2 km north of Ft. Supply, Harper County, OK (99 °23' W, 36 °27' N; elevation 610-640 m). The SPER includes 1,746 ha of native sandhill rangeland (Berg, 1994) that in 1936 was "observed to be in extremely poor condition as a result of severe drought, intense heat, and close grazing." Current use is for rangeland and pasture research conducted by the United States Department of Agriculture, Agricultural Research Service, Southern Plains Range Research Station, near Woodward, OK. The SPER was established following the historical drought of the 1930's. In 1941, experimental pastures, ranging from 20 to 80 ha in size and associated exclosures, varying from 0.4 to 4 ha, were fenced and long-term grazing studies began. Between 1940 and 1961, a stocking rate study compared light, moderate, and heavy grazing rates on replicated pastures and determined sustainable grazing levels for this southern plain mixed prairie. Since 1961, the moderately grazed pastures and non-grazed exclosures within grazed pastures have been maintained at these same levels [1] . Improved pastures were planted  to optimize grazing forages with specific plant species. These included both native (switchgrass and sand bluestem) and non-native (weeping lovegrass and caucasian bluestem) species that varied in aboveground productivity.
Individual plant species were collected in long-term grazed and ungrazed pastures and identified to determine plant species composition and isotopic signature. The plants were collected in 2007 and 2008 during the growing season and represent the diversity of species found in the pastures. Forty-one individual plant species were collected, including seventeen warm-season (C 4 ) and twenty-four cool-season (C 3 ) plants. Plant samples were oven dried at 55 °C, and ground finely to pass through a 0.2 mm sieve for C, N and isotope analysis.
The δ 13 C isotopic composition was determined using a Europa Scientific automated nitrogen carbon analyzer (ANCA/NT) with a Solid/Liquid Preparation Module (Dumas combustion sample preparation system) coupled to a Europa 20-20 Stable isotope analyzer continuous flow isotope ratio mass spectrometer (Sercon Ltd, formerly Europa Scientific Ltd., Crewe, England). Data are expressed as δ 13 C relative to the international standard Pee Dee Belemnite.
The δ 13 C was calculated using the equation where R sample is the ratio of δ 13 C/ δ 12 C in the soil and R standard is the ratio of δ 13 C/ δ 12 C international Pee Dee Belemnite (PDB).
Samples were run in duplicate and averages of δ 13 C are presented in Table 1 .

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.