Weed Science (2010) 58, 359-368

David R. Gealy and Albert J. Fischer (2010)
¹³C Discrimination: A stable isotope method to quantify root interactions between C₃ rice (Oryza sativa) and C₄ barnyardgrass (Echinochloa crus-galli) in flooded fields
Weed Science 58 (3), 359-368
Abstract: Assessing belowground plant competition is complex because it is very difficult to separate weed and crop roots from each other by physical methods. Alternative techniques for separating crop and weed roots from each other are needed. This article introduces a stable isotope method that can quantify the amounts of roots of rice and barnyardgrass intermixed in flooded field soils. It relies on the biological principle that rice, a C₃ (photosynthetic pathway) species, discriminates more effectively than barnyardgrass, a C₄ species, against a relatively rare isotopic form (¹³C) of CO₂. This results in different ¹³C : ¹²C isotope ratios (expressed as delta¹³C) in root tissues of the two species. delta¹³C values for monoculture barnyardgrass and rice grown in a standard flood-irrigated system were highly stable over 4 crop-years, averaging -13.12 ± 0.80 (SD) and -28.5 ± 0.11 (SD)‰, respectively, based on analysis by an isotope ratio mass spectrometer. Standard concentration curves relating measured delta¹³C values to set proportions of rice : barnyardgrass root biomass were described by linear regressions, typically with r2 values of 0.96 or greater. Quantities of intermixed rice and barnyardgrass roots sampled 0 to 5 cm deep from soil between rice rows were estimated by extrapolation from standard curves based on delta¹³C values. About 50% more barnyardgrass root tissue was detected in plots of Lemont long-grain rice than in weed-suppressive PI 312777 indica rice, demonstrating the feasibility of using this stable carbon isotope method in flooded rice systems.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): David R. Gealy, Albert J. Fischer

Research topic(s) for pests/diseases/weeds:
environment - cropping system/rotation
molecular biology - genes

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Echinochloa crus-galli (weed)	Rice (Oryza)