Browsing by Subject "Legume"
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Item Consequences of elevated temperature on prairie plants: legumes, nitrogen, and phenology.(2012-05) Whittington, Heather ReneeBecause prairies are often nitrogen (N) limited, prairie legumes can have significant impacts on the nitrogen (N) dynamics of these communities because of their ability to add fixed N to their surroundings through symbiotic biological N2-fixation and their N-rich tissues that can stimulate net nitrogen mineralization. Predicted increases in temperature have the potential to alter legume traits and functioning, which can feedback to affect ecosystem dynamics. The goal of this dissertation was to examine the effect of elevated temperature on the growth, phenology, and N nutrition of four prairie legumes: Amorpha canescens, Dalea purpurea, Lespedeza capitata, and Lupinus perennis, using both a growth chamber experiment and a manipulative field warming experiment. In the growth chamber experiment, seedlings of Lespedeza exhibited higher biomass and shoot N content at 28°C than 25°C, while Lupinus seedlings displayed decreased nodulation and lower shoot N concentration at the higher temperature. In the field warming study, Dalea and Lupinus displayed higher biomass under warming and all species exhibited lower shoot N concentrations under warming. Neither N2-fixation nor net N mineralization were affected by warming. Warming accelerated flowering for several species, including Amorpha and Dalea, and accelerated spring green-up, as evidenced by higher normalized difference vegetation index (NDVI) values in warmed communities in May. These results indicate that prairie legumes are responsive to increases in temperature in a species-specific manner and that warming may alter N-cycling by changing legume abundance and tissue N chemistry. Additionally, significant interannual variation in many variables and in their responses to warming emphasizes the need for long term studies to better understand and predict potential consequences of elevated temperature on plants and their ecosystems.Item Crop Sequence Effects of Pulse Crops and Agronomic Research on Lupine(Minnesota Agricultural Experiment Station, 1984) Robinson, R.G.; Rabas, D.L.; Smith, L.J.Item Limits to range expansion in the native annual legume Chamaecrista fasciculata.(2011-08) Stanton-Geddes, John LouisSpecies range limits are determined by historical (e.g., range expansion), ecological (e.g., biotic interactions) and genetic (e.g, gene flow) processes, but comprehensively understanding the relative role of these processes in limiting any single species‟ range has been elusive. This research is timely for understanding species‟ responses to climate change. The goal of this research was to examine the processes that limit the range of the native annual legume Chamaecrista fasciculata, by integrating ecological-genetic field studies and population genetic laboratory studies. In Chapter 1, I investigate the extent to which C. fasciculata is in demographic range edge equilibrium at its western and northern range edges, and the effect of biotic interactions at these range edges. I find that C. fasciculata fitness is reduced to zero when planted beyond the western and northern range limits, indicating it is in equilibrium with its range. Neighbors increase early-season survival, but decrease seedpod production. The goal of Chapter 2 was to examine if the mutualism between C. fasciculata and its associated rhizobia was disrupted beyond the range edge, potentially limiting range expansion. The results demonstrate that compatible rhizobia are nearly absent beyond both range edges, which may limit range expansion. In Chapter 3, I ask how the habitat where C. fasciculata establishes may change with range shifts. I conclude that habitat type influences C. fasciculata fitness, but the outcome depends on both the substrate and competitive environments. Finally, in Chapter 4, I use population genetic methods to gain insight into the history of range expansion, population structure and gene flow. Population genetics indicate that the edge populations have reduced genetic diversity compared to the southernmost interior population, and are highly differentiated from each other. However, there is little evidence for contemporary gene flow between populations at the scale investigated. Overall, this work suggests that ecological-genetic or metapopulation dynamics are likely to be involved in setting the northern and western range limits. Further, it highlights the value of integrated approaches to studying species‟ range limits.Item Terminal differentiation of symbiotic rhizobia in certain legume species and its implications for legume-rhizobia coevolution.(2010-08) Oono, RyokoThe symbiotic association between legume plants (Fabaceae) and nitrogen-fixing rhizobia is a classic system of cooperation, but with largely unexplored differences among species in life history traits. Rhizobia transform physiologically and morphologically into nitrogen-fixing bacteroids inside host nodules. The transformation is terminal (bacteroids are swollen and apparently nonreproductive) in some legume host species but not others, regardless of rhizobial genotype. The phylogenetic distribution of this host trait in the Papilionoideae subfamily of legumes suggests that the common ancestor of the papilionoids did not host terminally differentiated bacteroids and there appear to have been at least five independent origins of hosts imposing terminal differentiation on bacteroids. To consider possible advantages of this host trait, I compared the symbiotic efficiency of terminally and non-terminally differentiated bacteroids of a single rhizobial strain with dual-host capabilities. In the two available dual-host cases, I found greater fixation efficiency (N2 fixation per CO2 respiration) as well as plant return (host biomass) on investment per nodule mass in the hosts with terminal bacteroid differentiation than in those without. This suggests that host traits leading to terminal bacteroid differentiation may have been derived multiple times because of increased net symbiotic benefits to the host. Lastly, I tested whether legumes hosting terminally differentiated bacteroids impose sanctions, i.e. reduce benefits to the undifferentiated reproductive clonemates of less-mutualistic bacteroids in the same nodule. Host sanctions could maintain the evolutionary stability of the symbiosis despite "cheaters" - less-mutualistic rhizobia that potentially benefit from the fixation by other rhizobia sharing the same individual plant host. Legume roots were split so that half of each nodulated root system was exposed to nitrogen-free atmosphere (Ar:O2) to simulate cheating and the other half was in normal air (N2:O2). Rhizobial fitness (rhizobia per nodule) was compared between the two halves. A clear host sanctions effect in peas and alfalfa demonstrated that terminal differentiation of bacteroids does not compromise a legume host's ability to sanction. Differences in rhizobial life history suggest various rhizobial symbiotic traits for cooperation and cheating, perhaps leading to different mechanisms in different legume host species that maintain stability of the mutualism.