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University of Helsinki (2020)

Soil respiration around termite mounds in African semi-arid savanna

Manninen, Petra

Titre : Soil respiration around termite mounds in African semi-arid savanna

Auteur : Manninen, Petra

Université de soutenance : University of Helsinki,

Grade : Master’s thesis / Master’s Programme in Geography 2020

Soils are important stocks of carbon and the soil-atmosphere CO2 flux is the second largest carbon flux between ecosystems and the atmosphere. Soil respiration is in previous studies considered to be mostly controlled by soil moisture and temperature, but also the activity of soil macrofauna. In African semi-arid savannas these parameters are controlled by seasonality. Mound-building termites are abundant in these savannas and in addition to the carbon cycle, they affect soil properties when building mounds and foraging outside them. Gas exchange and heat transfer in mounds is a complex phenomenon that varies depending on mound architecture and environment variables. Mound ventilation brings the CO2 generated in termite and their nest metabolism outside the mounds. CO2 emissions of termites, especially outside their mounds, should be studied to clarify their impact on the savanna soil respiration. In attempt to understand soil respiration around termite mounds, soil respiration rates was measured from surrounding area of six mounds of fungus-growing termite species Macrotermes michaelseni and Macrotermes subhyalinus using closed static chamber method in Tsavo ecosystem, southern Kenya. Measurements were made during the three assumed rainy seasons, in November 2016, April 2017, and December 2017. Research focused whether CO2 emissions come from the soil or from termites. The effect of prevailing wind was also studied to understand the role of mound ventilation better. Soil moisture, soil temperature, and the amount of rainfall were also measured and their effect on respiration was studied. The results show that a single reason for the changes in soil respiration rates around termite mounds is difficult to find. Most of the variation between measurement sites and measurement periods were due to changes in soil moisture. Prevailing wind direction was also found to be possible reason for changes in soil respiration rates. Soil respiration rates were higher near the mounds, so termite activity or changes in soil properties caused by them are assumed to be a contributing factor. Due to limited amount of data, many of the uncertainties on the subject should be further researched.


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