Publicação on-line; 46 ref.; 3 tables; 2 illus.; Summary (En)

ABSTRACT
Background: Weedy rice (Oryza sativa L.) is the main weed of rice crop.
The high genetic variability of weedy rice contributes to the high
phenotypic diversity between biotypes and different responses to
environmental stress.
Objective: The present study aimed to evaluate the response of
imidazolinone-susceptible and -resistant weedy rice populations to
increased atmospheric [CO2].
Methods: The experiment was arranged in a complete randomized
design with six replications. The treatments included two [CO2]
concentration (700 and 400 μmol mol-1) and three treatments: resistant
genotype (IMI-resistant) treated with imazethapyr; resistant genotype
without imazethapyr, and a susceptible genotype without imazethapyr.
Results: The IMI-resistant and –susceptible weedy rice responded
similarly to [CO2] enrichment. Enhanced [CO2] increased competitive
ability of the weedy rice populations tested, by means of increased plant
height. Weedy rice seed production also increased with enhanced [CO2]
by means of increased photosynthesis rate and reduced transpiration
(increased water use efficiency). Increased seed production also means
increased weed persistence as it increases the soil seedbank size. The
application of imazethapyr on IMI-resistant weedy rice did not alter its
response to [CO2]; conversely, increased [CO2] did not change the
resistance level of weedy rice to imazethapyr. High [CO2] increased
spikelet sterility, but this beneficial effect was negated by the overall
increase in production of filled grains.
Conclusions: Enhanced [CO2] concentrations increases weedy rice
growth, photosynthesis rates, seed production and spikelet sterility;
the imidazolinone application does not affect the response of weedy rice to
enhanced [CO2] affects weedy rice response to imidazolinone herbicide

Keywords:
climate change
ecology
weed biology