Doctor of Philosophy in Agriculture
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Item Effects of Exotic Tree’s Growth Morphology and Litter Substrate Quality on the Adjacent Native Grasses(KeMU, 2022-10) Gichuki, Philip MwangiLight irradiance, water and litter substrate quality are major plant nutritional factors that control above and below ground plant resources. The study sought to find out the effects of exotic tree’s growth morphology and litter substrate quality on the adjacent native grasses. Specific objectives were; to determine the effect of the adjacent tree canopy structure and the above ground processes that affect the delivery of resources to the adjacent native pasture, to analyze the adjacent tree roots structure and their below ground effects on the adjacent native pasture and to analyze the adjacent tree litter quality and below ground processes that affect the delivery of resources to the adjacent native pasture. Three native grass study sites adjacent to Eucalyptus, Cypress and Acacia were marked for the study. There was an additional site with no tree nearby that acted as control. Their crown, roots and litter substrate quality were studied. This was done from a distance of 1m to a distance of 60m away from the tree stand. Crown structure such as the diameter, breast height, total height, foliage transparency, die backs, position, exposure and density were analyzed. Canopy light radiation was determined by measuring photosynthetic active radiation and stomata conductance of the adjacent native grass. Roots growing structure such as branching density, diameter of fine roots, length, and depth were studied. Other roots characteristics such as exudates, fungal biomass, Ecto-mycorrhizal and Arbuscular mycorrhizal association were examined. Litter substrate quality such as phyto-chemicals, microbial biomass, Lignin, Lignin N ratio, Lignin P Ratio, Tannins, Polyphenols, Cellulose, C:N ratio, C:P ratio, mineralization rate, duff and bulk densities were deliberated. Litter bag experiment was carried out to determine litter mass loss and mineralization rate. The experiment had two Seasonal Treatments, four vegetation treatment types and seven different distance treatments. Data collection involved measurements of photosynthetic active radiation, stomatal conductance, quantifying N and P in the sample, analysis of microbial biomass, Ectomycorrhizal, Arbuscular mycorrhizal, fungal biomass, leaf chemistry and root exudates. Data was summarized using excel package and then analyzed using Statistical Package for Social Sciences (SPSS) for window version 22. All the hypotheses were tested at α=0.05 and regression analysis made. The study results did not find much difference in the two exotic trees compared to Acacia in terms of changes in soil pH. The rate of decomposition and litter chemistry of the two exotic trees were different compared to Acacia. Likewise, the performance of adjacent pasture in terms of species composition, richness and cover also varied greatly. This was due to differentiated light quality in terms of Photosynthetic Active Radiation, soil porosity and competition for available Nitrogen. In addition, Competition for the available moisture is another considerable factor. Dense roots network was found to affect adjacent grass soil moisture in their root zone. Microbial biomass N, C and P was found to influence the rate of decomposition and release of nutrients to the soil. The study concludes that some of the valued exotic trees have potential of influencing negatively the adjacent crops/grasses if associated risks and benefits have not been studied well. The study recommends that any establishment of tree adjacent to crops or grasses, should consider tree species space requirement, potential spread of roots and contextual dependency relationship between N input pool and changes in soil properties