Antropogenic And Natural Pyrogenic Carbon In Tropical Environments: From The Rhizosphere To The Landscape

Despite an increasing body of literature, the interactions of pyrogenic carbon (PyC) in the environment are not as well understood as other forms of C. This dissertation focused on generating knowledge of the interactions of (PyC) in tropical terrestrial ecosystems. Main areas of concentration include 1. Investigations into the mechanisms driving increased biological nitrogen fixation (BNF) in common bean (Phaseolus vulgaris) following the additions of anthropogenic PyC to agricultural soil, 2. Evaluating the differing ability of pyrolyzed and non-pyrolyzed crop residues to protect introduced strains of rhizobium against soil water deficit, and 3. Tracing the movement of natural PyC through the landscape and waterways following land-use change from forested ecosystems to intensive agricultural lands. Biological N fixation and nodule biomass increased by up to twenty-fold and thirty six-fold, respectively, following additions of anthropogenic PyC. This change was linked to greater plant-P uptake (r2=0.22; P0.05). Improved P nutrition likely resulted from 360% greater mycorrhizal colonization with biochar additions. When microbial inoculants were introduced to soil using pyrolyzed and non-pyrolyzed biomass, DNA fingerprinting of the root nodules indicated that nodule occupancy was dominated by native rhizobium and not the introduced strain. However, measured nodule occupancy (1-38%) of the introduced CIAT899 rhizobial strain by beans was significantly greater than expected values based on application rates (2-7%), irrespective of carrier. When natural terrestrial PyC was traced in stream water catchments following land-use change, up to 60% losses of the initial PyC stocks occured in the first 10 years after conversion from forest from mineralization and/or erosion. However, PyC was not preferentially eroded relative to total C or non-PyC C. This was true even when scaled to the entire river watershed where PyC concentrations in the headwaters and outlet into Lake Victoria were 3.8 and 3.5% of total C, respectivley . Pyrogenic C enrichment was found with depth in the soil profile from 5% of OC in the topsoil (0-0.15 m) to 23% of OC at 1-2 m