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Suppression of native wild rice germination by exotic para grass

Wurm, Penelope A., Bellairs, Sean M. and Kernich, Beckie J. (2006). Suppression of native wild rice germination by exotic para grass. In: 15th Australian Weeds Conference: Managing Weeds in a Changing Climate, Adelaide, 24-28 September 2006.

Document type: Conference Paper
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IRMA ID 80805078xPUB1
Author Wurm, Penelope A.
Bellairs, Sean M.
Kernich, Beckie J.
Title Suppression of native wild rice germination by exotic para grass
Conference Name 15th Australian Weeds Conference: Managing Weeds in a Changing Climate
Conference Location Adelaide
Conference Dates 24-28 September 2006
Conference Publication Title 15th Australian Weeds Conference proceedings: Managing weeds in a changing climae
Place of Publication Meredith, SA
Publisher Weeds Management Society of South Australia
Publication Year 2006
ISBN 0 646 46344 6   (check CDU catalogue open catalogue search in new window)
Start Page 823
End Page 826
Total Pages 4
Field of Research 0607 - Plant Biology
0502 - Environmental Science and Management
HERDC Category E1 - Conference Publication (DEST)
Abstract Wild rice (Oryza meridionalis Ng) underpins vertebrate food chains on the monsoonal floodplains. This native annual grass is displaced by the introduced pasture, para grass (Brachiaria mutica (Forssk.) Nguyen). This study investigates whether the mechanism for this displacement is through effects on the germination of wild rice seed. Wild rice has a seed dormancy mechanism that prevents seeds germinating when they are first dispersed into the moist floodplain soil at the end of the annual wet season.The presence of para grass may prevent or change environmental cues that would otherwise break dormancy and stimulate germination of wild rice. Initially we found that, under wild rice cover, some 76% of seeds had germinated, 17% had died and 5% remained ungerminated after two wet seasons. When wild rice seeds were sown into a well established para grass cover, almost no seed germinated, a large proportion remained alive but ungerminated, and a greater proportion died than under wild rice cover. We then investigated how para grass may prevent germination of wild rice, by (a) determining dormancy breaking cues for wild rice seeds and (b) comparing floodplain seed bed conditions under para grass and wild rice cover. In the laboratory, breaking of dormancy was dependent on the seeds being exposed to high temperatures. In the field, para grass produced much higher above ground biomass than wild rice, and modified the seedbed. Temperatures were lower at the soil surface under para-grass cover than under wild rice cover. This study showed wild rice has a dormancy mechanism, which prevents germination under significant canopy and litter cover . Thus, a weed species (para grass) can modify habitat conditions so that dormancy breaking and germination in a native species (wild rice) is prevented. Managers may need to deal with habitat modification by weeds, as well as direct competition with natives, when dealing with environmental weeds.
Keyword Oryza meridionalis
Brachiaria mutica
Seed dormancy
Seeedbed conditions
Monsoonal floodplain
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