Honors Projects for Tropical Plant and Soil Sciences
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ItemBiochar Increasing Internal Tolerance to Manganese Toxicity in a Manganese-Rich Acid Soil(University of Hawaii at Manoa, 2014)Manganese (Mn) toxicity is a serious constraint on crop productivity in prime agricultural land in central Oahu. Liming alleviates Mn toxicity by raising soil pH and supplying calcium (Ca), reducing plant available Mn. Biochar shows promise as a sustainable alternative to lime in remediating Mn toxicity. We implemented a series of soybean greenhouse experiments to test the potential of five biochars with differing physico-chemical properties to remediate Mn toxicity. Additionally, to compare the effects of calcium nutrition and pH, we conducted another experiment with 4 increasing rates of two different Ca sources, lime (CaCO3) and a neutral Ca salt (CaSO4). Our results showed that pH increase was effective in alleviating Mn toxicity from the soil; however, Ca nutrition independent of pH also contributed to alleviation. Biochar treatments maintained soybean growth similar to the limed control, despite having toxic levels of Mn in tissue and soil, suggesting alleviation by increasing plant Mn tolerance. A second planting in the same biochar treatments resulted in Mn toxicity in almost all biochars, suggesting that biochars’ alleviating properties lack persistence in the soil, except for the anaerobic digest biochar, which continued to detoxify Mn. A follow-up bioassay grow- out was conducted, which gave results suggesting that alleviation from anaerobic digest biochar was from biochar-derived compounds absorbed into the plant. We propose that alleviation of Mn toxicity from biochar involves Mn tolerance through organic chelates, specifically phenolic compounds. Increasing internal tolerance with biochar can have implications not only in agriculture, but also in phytoremediation of heavy metals.
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ItemHawaii's Chocolate Bug: Investigating Drosophila melanogaster as an inoculant for small-scale cacao fermentation(University of Hawaii at Manoa, 2012-05-12)Currently, Hawai'i cacao production is performed on a small scale. Fermentation is an essential step when developing the flavor of the chocolate. Much of the fermented cacao that is being produced in Hawai'i does not maintain the quality that is required to generate a premium product. Small-scale cacao producers in Hawaii are challenged by low quality, low ambient temperature fermentation due to small batch size. Hawai'i producers are not currently using any form of controlled microbial inoculant. It is also highly desirable to process cacao more quickly and produce more reliable results. In this experiment, fruit flies (Drosophila melanogaster) were cultured in the lab and applied to small-scale ferments to assess the viability of applying fruit flies as an inoculant in order to improve small-scale cacao fermentation. Five treatments were applied to cacao beans. Treatments consisted of two populations of whole flies shaken in distilled water, two populations ground in distilled water, and a hand/ambient air inoculation. Dried bean samples were assessed with a dry bean cut test and total aerobic bacteria populations and total yeast populations with Petrifilm™ plates. In general, population 2, whole fly dilutions, had the highest average colony count of anaerobic bacteria per cm2, and hand/ambient inoculation had the highest average colony count of yeast/mold per cm2. Population 2 also performed the most effectively in a cut bean test, with only 20% undesirable beans. These results indicate the further investigation of inoculants for small-scale cacao fermentation is necessary.