Browsing by Subject "Endophytes"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Community ecology of New Guinea rainforest trees: Carbon storage, dynamics, and fungal endosymbionts(2015-08) Vincent, JohnThis dissertation examines the community ecology of trees and fungal endophytes in the lowland rainforests of New Guinea. Forest inventory and soil nutrient data from a large permanent plot in addition to a chronosequence of regenerating forest were used to quantify carbon stocks and forest dynamics. These data were coupled with intensive sampling of foliar fungal endophytes at three sites to investigate local and regional variation in community composition of endosymbionts associated with a diverse sample of rainforest trees. The Wanang 50 ha forest dynamics plot is located in mature lowland wet rainforest in the Middle Ramu area of the Madang province in Northern Papua New Guinea. Established in 2009, the Wanang plot is the first spatially explicit, large-scale, long-term forest plot in Oceania aimed at studying forest dynamics and biodiversity through time. Chapter 1 investigated carbon storage in the Wanang forest dynamics plot and spatial and demographic variation in biomass. During the first census, every stem >=1 cm in diameter at breast height (1.3 m above ground) was tagged, measured, and mapped to the nearest 10 cm. A subsequent species identification survey was carried out to associate every stem with a species or morphospecies concept. The first census at Wanang recorded a total 253,350 individual trees comprising 581 taxa, including 531 species and 50 morphospecies in 253 genera and 85 families. Our estimate of biomass averaged 222.3 Mg per hectare (95% CI: 211.3-232.7). This finding agrees closely with two previous estimates derived from a distributed network of small forest plots, suggesting this figure is a reasonable approximation of aboveground biomass in lowland forests in New Guinea. We found that there was significantly more carbon held in small trees than is typically assumed for lowland rainforest and that there is substantial fine-scale spatial variation in forest carbon (range: 161.5-324.43 Mg/ha). New Guinea forests have substantially lower biomass than tropical rainforests on average (global average: 373.7 Mg/ha), possibly driven by frequent natural disturbance. Chapter 2 explored the extent to which species composition and basal area in Wanang forest is associated with topography and soil nutrients. Additionally, the reputation that New Guinea rainforests are unusually dynamic was tested for the first time by comparing mortality rates and indicators of forest regeneration stage to other tropical rainforests. Soil nutrients and topography account for 29% of variation in tree species composition but only 4% of variation in basal area among 20 m by 20 m quadrats at Wanang. Basal area and gap phase character was significantly different than that observed at a comparable forest dynamics plot at Barro Colorado Island, Panama. Comparison of basal area in the mature forest of the Wanang plot to an adjacent regenerating forest chronosequence produced an estimate that 6% of the Wanang plot was naturally disturbed in the past decade. Disturbance at Wanang, in addition to tree falls, includes frequent small land slumps that result in catastrophic mortality of trees in portions of forest up to approximately one hectare. Mortality rate was also higher in Wanang than has been reported for any other lowland rainforest. These results lend quantitative support to the notion that New Guinea lowland rainforests are exceptionally dynamic. This dynamic character likely plays a role in the lower than average biomass and low density of large trees at Wanang described in chapter 1. A large forest plot, such as Wanang, offers the opportunity for biodiversity discovery and studies of species interactions otherwise not possible. Chapter 3 focused on the relative importance of host specificity and dispersal limitation in structuring community composition of fungal endophytes in rainforest trees. Fungi were isolated from a diverse sample of eleven tree species representing five genera in the lowland rainforests of Papua New Guinea. Collections resulted in the culturing and sequencing of 2,079 fungal endophytes from three sites. Sequences of the internal transcribed spacer (ITS) region, a common fungal ribosomal barcode, were clustered into molecular operational taxonomics units (MOTUs) at 95% similarity. A total of 670 endophytes were collected from a single site in 2010, comprising 61 MOTUs. A slightly modified collection method carried out at three sites in 2011 resulted in isolation of 1,409 endophytes belonging to 191 MOTUs. Composition of endophytes varied by host species and genus both within individual sites and in aggregate. Spatial proximity of host trees did not correlate with similarity of endophyte composition within species, genera, or trees (i.e. regardless of taxonomy). The endophyte community both within sites and regionally was comprised of few abundant host generalist and many rare taxa. Regional turnover of fungal endophyte taxa was low, illustrated by sites separated by hundreds of kilometers having high similarity in endophyte community composition. These findings are consistent with the hypothesis that host specificity plays a larger role than dispersal limitation in structuring fungal endophyte communities. The findings of these three chapters provide a novel perspective of forest ecology in New Guinea that capitalized on the strengths of the long-term, large-scale plot setup of the Wanang forest dynamics plot. Additional plot censuses, focused studies of seed dispersal, and more intensive sampling of foliar endophytes will further elucidate the patterns described in this dissertation.Item The effects of endophytic Fusarium verticillioides on the interactions of maize and its fungal pathogen Ustilago maydis.(2010-08) Lee, KeunsubDiverse microbial organisms, including mycorrhizal fungi, endophytes and pathogens inhabit plants, interact with each other, and affect their fitness. Although theoretical studies suggest that the outcomes of multispecies interactions are often different from those of pairwise interactions, most empirical studies have focused on pairwise plant-pathogen interactions. Using endophytic isolates of Fusarium verticillioides (Sacc.) Nirenberg, the corn smut pathogen, Ustilago maydis DC (Corda) and maize, our studies suggest that endophytes could play important ecological roles for host defense and their impact needs to be appreciated when studying plant interactions with other organisms occurring in the same host. First, our results suggest that F. verticillioides likely interacts with U. maydis directly to reduce the host damage by pathogen infections, which we define here as 'aggressiveness.' Since the endophyte alone did not have detectable effects on plant growth, we inferred that F. verticillioides indirectly improves plant growth in the presence of the pathogen, U. maydis . Secondly, we found that U. maydis aggressiveness is constrained by the genetic association between traits governing aggressiveness and fitness, i.e., trade-off, and the endophyte, F. verticillioides enforces limits to U. maydis aggressiveness. Pathogen fitness decreases as the level of aggressiveness increases. Surprisingly, endophyte co-inoculation with the pathogen resulted in increased pathogen fitness, likely because the biotrophic pathogen, U. maydis depends on plant resources for its reproduction and plants in the endophyte co-inoculation treatments grow better than do plants in the pathogen only inoculation treatments. Lastly, we found strain-specific effects of the endophyte on the ecological and fitness outcomes of maize- U. maydis interactions. The endophyte strain which produced least amount of fusaric acid had least impact on U. maydis aggressiveness, suggesting that the secreted secondary compound of the endophyte may play antagonistic role against the pathogen. Together, these results suggest that F. verticillioides endophytes play important defensive roles for host plants and that the evolution of plant-pathogen interactions is responsive to the microbial environment in which they occur.Item Fungal communities of soybean cyst nematode-infested fields under corn and soybean monoculture and crop rotation(2019-12) Strom, NoahUnderstanding how continuous monoculture impacts fungal communities of corn and soybean is essential for developing agricultural practices that minimize yield losses and protect plants from disease. In continuous crop monoculture, negative plant-soil feedbacks involving a build-up of detrimental fungi are thought to be involved in yield declines. However, positive plant-soil feedbacks involving a build-up of microbial antagonists to specific plant pathogens may also occur over long-term monoculture. Changes in soil properties and depletion of key nutrients may also negatively impact yields under crop monoculture. In my dissertation, I investigate soil and root-associated fungal communities under long-term corn-soybean monoculture and crop rotation. I focus on relationships between the mycobiota in different agroecosystem compartments (bulk soil, rhizosphere, rhizoplane, and root endosphere) and on shifts in fungal communities in relation to soil properties, pathogen density, and yield. In chapters 1 and 2, I explore fungal communities in bulk soils, rhizosphere soils, and root endospheres of corn and soybean using a high throughput amplicon sequencing approach and ask whether variation in communities is related to continuous monoculture, soil properties, or the density of a major soybean pathogen, the soybean cyst nematode (Heterodera glycines, SCN). Long-term monoculture of both crops resulted in dramatically different soil and root-associated mycobiota compared to annual crop rotation. Nematophagous fungi increased in abundance and diversity over continuous soybean monoculture, while arbuscular mycorrhizal fungi (AMF) increased in abundance and diversity over continuous corn monoculture. In chapter 1, positive relationships between soil P and Mortierellales, an order containing phosphate-solubilizing fungi, and negative relationships between soil P and AMF suggest biological causes for the observed shifts in available soil P under continuous soybean and corn monoculture. However, structural equation modeling did not show that changes in soil P had a direct effect on yield in either crop and identified soil N and crop host-specific pathogens (fungal pathogens of corn and the SCN) as the most important factors in monoculture yield decline. In chapter 2, I found evidence of selective filtering and enrichment of nematophagous taxa in soybean root-associated compartments due to the "rhizosphere effect" and overlap between fungal communities in soybean roots and SCN cysts, suggesting that the soybean root promotes the growth of fungi that ultimately colonize the SCN cysts. In chapter 3, I used a culture-based approach to characterize the root endophytic mycobiota of corn and soybean and investigated the potential for soybean and corn root endophytes to produce substances that are toxic to the SCN. This project resulted in the first reported isolation of the nematode biocontrol fungus Hirsutella rhossiliensis from a soybean root and showed that the diversity of soybean fungal endophyte communities was correlated with the density of the SCN. Several corn and soybean endophytes produced nematicidal metabolites, in vitro. These projects open the door to future research investigating the utilization of fungi for improved P uptake by plants and the use of root endophytes in the biocontrol of the SCN.Item Measuring warfare in wood: linking competition among wood-degrading fungi of northern forests to its ecological consequences(2014-08) Song, ZeweiCompetition between distinctive groups of fungi determines the pattern of wood decomposition in forests, but the outcome of these battles may shift in a changing climate. With more than 70% of Earth's biotic carbon stored in woody tissues, understanding the processes that unlock this carbon and release the greenhouse gas CO2 is critical. For my thesis research, I am addressing several key questions about how fungi colonize and dominate wood on the forest floor. Quantitative PCR was developed to measure biomass of specific fungi from a community in Chapter one. This technique was coupled with ergosterol, dilute alkali solubility, pH and carbon component analysis to measure biotic and abiotic dynamic during wood decomposition. With these comprehensive tools, factors that may influence fungal competition and decomposition outcomes were studied in the following chapters. In Chapter two, wood type was shown not to influence the competition between a brown rot fungus and a white rot fungus. It is contrary to the observations on wood preferences in nature, but reflected different foraging strategies by fungi. This led to the study of Chapter three on priority effect. By increasing the inoculum potential either inside or outside wood substrate, I have shown evidence that a weak competitor fungus can outcompete its more aggressive opponents, thus achieving co-existence. Another two factors, temperature and endophytes, along with priority effect were studied in Chapter four. Endophytes showed a much larger effect in influencing wood decomposition than temperature, mostly through antagonisms against soil fungi. Studies on these factors reveals potential for a more comprehensive model for wood decomposition. Emphasis on the role of microbial components, especially the often neglected endophytic communities, is possible to explain the variability in wood decomposition that can not be explained by abiotic factors, alone.