Soil organic carbon characteristics under different vegetation types in Otago, New Zealand

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dc.contributor.advisor Schwendenmann, L en
dc.contributor.advisor Vogeler, I en
dc.contributor.advisor Lear, G en
dc.contributor.author Li, Xiaoqing en
dc.date.accessioned 2019-02-28T22:44:35Z en
dc.date.issued 2019 en
dc.identifier.uri http://hdl.handle.net/2292/45655 en
dc.description.abstract The importance of maintaining and increasing soil organic carbon in terrestrial ecosystems has been widely acknowledged both for mitigating greenhouse gas emissions and for providing food security. Grasslands play an important role in the global carbon cycle as they store around 34% of the global terrestrial carbon. Most of the grassland carbon is stored in the soil. In recent decades, afforestation and woody plant encroachment of grasslands has been observed worldwide. Land cover change from herbaceous to woody vegetation has been found to affect carbon storage and chemistry. This thesis aims to quantify changes in physical and chemical soil organic carbon characteristics at the micro and macro scale to improve the understanding of soil carbon cycling following land cover change in Otago, New Zealand. I used established analytical and statistical methods and refined analytical techniques to address the research objectives. I found that soil texture (e.g. sand content), soil carbon stocks, mean weight diameter and the proportion of the macroaggregate heavy fraction were significantly different between the tussock grass dominated catchment and the pine forest catchment, however, SOC saturation deficit was similar. Inherent soil characteristics in this complex landscape may have masked the effect of recent vegetation change on soil aggregation, and soil fraction associated carbon. Besides, I found no significant differences in soil phytolith assemblage, soil phytoliths, and phytolith occluded carbon (PhytOC) storage between tussock grassland and pine forest. This suggests that phytoliths derived from past (grassland) vegetation masked the contribution of phytoliths from the contemporary woody vegetation. Further, I analyzed lipids (n-alkane and n-fatty acids) in plant and soil samples to separate plant growth forms, to trace the source of soil carbon, and to verify if lipid biomarkers can be used to assess the vegetation history of 'secondary grasslands'. Combining n-alkane and n-fatty acids provided a more robust approach to identifying and separating plant growth forms and helped to trace the origin of soil carbon. Soil CO2 efflux, an indicator of soil carbon loss, was variable across topographic (elevation and aspect) gradients. The differences in soil characteristics below and above the historic tree line (1150 m) may be related to the past woody vegetation cover. This thesis provides empirical data to improve soil carbon models and following a standardisation of extraction methods and further ecosystem studies, I envisage PhytOC and n-fatty acids to be useful indicators to elucidate the effects of land cover change on soil organic carbon. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA99265138614102091 en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.rights.uri http://creativecommons.org/licenses/by-nc-sa/3.0/nz/ en
dc.title Soil organic carbon characteristics under different vegetation types in Otago, New Zealand en
dc.type Thesis en
thesis.degree.discipline Environmental Science en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Doctoral en
thesis.degree.name PhD en
dc.rights.holder Copyright: The author en
dc.rights.accessrights http://purl.org/eprint/accessRights/OpenAccess en
pubs.elements-id 764298 en
pubs.record-created-at-source-date 2019-03-01 en


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