Thesis

Effects of litter removal and addition on the nutrient mineralization dynamics in tropical savannas of Mato Grosso, Brazil.

The tropical savanna of Brazil (cerrado) is extremely species diverse and it encompasses many different physiological features. These physiological differences are influenced by rainfall and nutrient availability in the soil. Plant litter decomposition recycles nutrients from plants to soil and in turn, affects nutrient availability and plant growth. However, the rate at which these nutrients become available to the soil, and how mineralization is affected by litter inputs, are poorly understood. Thus, a field experiment was conducted to assess how litter inputs and reductions affect nitrogen (N) and phosphorus (P) availability. It was hypothesized that N and P mineralization would be significantly influenced by manipulation of the surface litter and that there would be a positive correlation between soil moisture and nutrient mineralization. Results showed that litter inputs or reductions did not significantly affect net mineralization, extractable soil organic carbon (SOC), P, and N, and total mineralization. There were significant differences between sites and over time for net N and SOC mineralization, extractable SOC, N, and P, and total mineralization. There were also site versus time interactions found for net N and SOC mineralization and extractable N and SOC due to the transition between wet to dry seasons within the duration of the experiment. Four variable step-wise regressions (air temperature, relative humidity, soil moisture, and precipitation) helped explain the abiotic factors that contribute to the variance in P, N, and SOC mineralization and extractable P, N, SOC at each site. Our results indicate that a short term manipulative experiment (six months) was not an adequate amount of time to alter nutrient availability in response to litter manipulation. Extending this study could produce significant results and help explain the effects of land use changes on nutrient output in these highly manipulated tropical forests.

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