• Aeroponic growth experiments of Buckwheat (Fagopyrum esculentum)

subjected to 15N labeled ammonium nitrate mixed with SeaCom (no

nitrogen) liquid fertilizer compared to control of standard fertilizer.

• Hand held or lab bench spectroscopy instruments

Analytical Spectral Devices Field Spec Pro (ASD) field portable

spectrometer (350-2500 nanometers (nm) / 28,571 to 4,000 cm-1)

Agilent Technologies Exoscan field portable Fourier transform infrared

(FTIR) spectrometer (4000-650 cm-1)

Nicolet 6700 lab FTIR spectrometer (Optimized for 4500 to 500 cm-1)

The highly variable natural abundances in most stable isotopes in contrast

to their standard elemental concentrations make their analysis particularly

useful in many applications, particularly in chemical fingerprinting and the

identification of source signatures. Usually, to obtain accurate nitrogen

stable isotope data for a given portion of organic matter in the laboratory,

isotope-ratio mass spectrometry (IRMS) is the analytical tool of choice.

IRMS is very high in precision; however, sample run times and instrument

calibrations are time consuming, costly and represent data from a single

location on the Earth’s surface at a particular time and performed only in

laboratory conditions. Alternatively, field based Fourier-Transform

infrared spectroscopy (FTIR) based spectroscopy can be performed

rapidly, at a lower cost, and provide geospatially robust data. Isotopic

shifts within the infrared spectrum have traditionally been measured using

lab based FTIR spectroscopy. Three major methods are employed here:

a traditional approach of isotope measurement using IRMS, FTIR

spectroscopy, and a nontraditional computational approach, all of

which aim to quantify isotopic downshifts within the spectra of several

plant pigments. This will provide researchers with faster and cheaper

measurements that could cover broader areas and eventually be translated

to use with airborne or space-based instruments in order to provide

biogeochemical understanding at larger spatial scales not possible by

current instrumentation and techniques.

ABSTRACT

BACKGROUND

Validate the spectral downshifts that have been

observed experimentally through computational

modeling and IRMS measurements.

OBJECTIVE

Spectral absorption feature shifts due to heavier isotope uptake of labeled

plants (black) versus the control (red).

A 19 cm-1 down shift in the SWIR of the ASD 1st derivative data

A 7 cm-1 down shift in the Exoscan data

A 102 cm-1 down shift in the Nicolet data

(Overlaid with library spectra of the Chlorophyll b molecule)

Chlorophyll molecule – Modeling at Rivanna

Modeling isotope-induced frequency downshifts using molecular modeling

software and ultra-high performance computing capabilities at UVA’s

Rivanna cluster.

EXPERIMENTAL RESULTS CURRENT RESEARCHValidation of isotope-induced frequency shifts

though molecular modeling at Rivanna

Fertilizer sources identification with isotopes helps to

• Understand nutrient loads and origins, as anthropogenic

impacts are often hard to quantify in the environment.

• Isotope analysis when linked with water samples in nearby

streams and rivers enable researches to better differentiate

agricultural fields that have been applied with organic fertilizers

• Better identify nonpoint source polluters in waterways.

• Development of future remote sensors to provide

biogeochemical understanding at larger spatial scales.

• Areas of high anthropogenic nitrogen loading could be mapped

and efforts taken to mitigate the adverse environmental effects.

REFERENCESElmore, A. J., & Craine, J. (2011). Spectroscopic analysis of canopy nitrogen and nitrogen isotopes in

manages pastures and hay land. IEEE Transactions on Geoscience and Remote Sensing , 49 (7), 2491-

2498.

Kleinebecker, T., Schmidt, S., Fritz, C., Smolders, A., & Holzel, N. (2009). Prediction of c13C and c15N

in plant tissues with near-infrared reflectance spectroscopy. New Phytologist , 184 (7), 732-739.

Shearer, G., & Kohl, D. (1986). N2 fixation in field settings: Estimation based on 15N natural

abundance . Austrian Journal of Plant Physiology , 13, 699-756.

Wang, L., Okin, G. S., & Macko, S. A. (2010). Remote Sensing of Nitrogen and Carbon Isotope

Compositions in Terrestrial Ecosystems. In J. B. West, G. J. Bowen, T. E. Dawson, & K. P. Tu,

Isoscapes: Understanding movement, pattern, and process on Earth through isotope mapping (pp. 51-

70). New York: Springer.

Wang, L., Okin, G., Wang, J., Epstein, H., & Macko, S. (2007). Predicting lean and canopy 15N

compositions from reflectance spectra. Geophysical Research Letters , 34, L02401.

Yun, S.-I., Ro, H.-M., Choi, W.-J., & Chang, S. X. (2006). Interactive effects of N fertilizer source and

timing of fertilization leave specific N isotopic signatures in Chinese cabbage and soil. . Soil Biology

and Biochemistry , 38 (7), 1682-1689.

HOW:

Concentrations of the different isotope abundances, reported as ratios of

the different forms of the element can be used to explain many

biogeochemical processes. In plant matter, the stable isotope ratio of

nitrogen can used to understand the nitrogen cycle. Nitrogen (N) fertilizer

sources can be identified in plant matter and the surrounding soils as

organic manure based fertilizers are more enriched in 15N versus Haber

process inorganic urea fertilizers (Yun et al. 2006). Also, in areas with high

levels of nitrogen availability and increased rates of nitrogen leaching there

is 15N enrichment (Shearer & Kohl, 1986). Most researchers still rely

heavily on the IRMS for stable isotope analysis but some are investigating

alternative methods such as using handheld spectrometers for

measurements to be performed in a non-destructive manner and capable in

the field environment (Wang et al. 2010). There is a general consensus

among the stable isotope community that a larger spatial scale, including

regional analysis of isotope concentrations would be beneficial.

Spectroscopic analysis and remote sensing capabilities for stable isotopes

is currently being suggested and the possibility researched (Elmore &

Craine, 2011; Kleinebecker et al. 2009 and Wang et al. 2007). Stable

isotopes inherently have different masses that cause them to behave

distinctly within the electromagnetic continuum. Specifically they generate

isotope effects in their bonds with other elements where a bond with a

heavier isotope will vibrate at a different spectral band (Hoefs, 2009).

Declan McCarthy, Sonja Long, Stephen A. Macko

Department of Environmental Sciences, University of Virginia

Remote Sensing Techniques for Nitrogen Stable Isotope Analysis in Plant Matter

MATERIAL AND METHODS