NITROGEN FIXING SYMBIONTS: LEGUME SURVIVAL AND COEXISTENCE UNDER DROUGHT IN CALIFORNIA GRASSLANDS
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Date
2022-05
Authors
Kataoka, Natalie Catherine
Journal Title
Journal ISSN
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Publisher
University of Oregon
Abstract
For the past 200 years, non-native species have been anthropogenically introduced in
California grasslands, reducing native species abundance and diversity. Trifolium hirtum is a
non-native legume commonly used for cattle fodder and cover cropping because of its ability
to fix nitrogen via bacterial symbionts. T. hirtum currently coexists with California native
legume Trifolium willdenovii in established communities, however, T. hirtum has the
potential to outcompete T. willdenovii under increased environmental stress, such as that
caused by climate change. Considering how symbiotic rhizobia contribute to these Trifolium
species’ ability to coexist or compete with other species, as well as how climate change alters
these interactions, is essential for understanding potential impacts on native biodiversity and
the response of important forage species to changing climate conditions.
I tested 1) how rhizobial symbionts contributed to the survival and growth of a native and
non-native legume species. 2) How drought influences the competitive relationships of the
two legumes. And 3) how each species responded under interspecific and intraspecific
competition. For both non-native T. hirtum and native T. willdenovii, I measured rhizobia
nodule mass, seeded background count, weed species counts, and weighed the aboveground
biomass of individuals grown under drought and ambient precipitation treatments. On
average, there were no differences in the mass of nodules by species, however there was an
observed a negative correlation between the biomass and nodule mass of uninoculated
background T. willdenovii. Drought positively impacted the biomass of background T. hirtum
individuals, however drought treatments negatively affected focal T. hirtum biomass
compared to ambient precipitation. Drought had no significant effect on focal T. willdenovii
biomass.
Description
21 pages